Culturing Techniques for Algae Growth

Hello all, hope you are doing good. In the previous video lecture on algal growth, we have spoken about the isolation of algae from various water and soil sources. In today's video lecture, we will be looking into the next aspect of growing algae that is the media and methods for culturing algae. Now a culture medium is a very important factor when we look into the algal growth because it is the culture medium which is going to provide all the essential nutrients for the algae to grow. Design of the culture medium is very very important for a successful growth of algae. So the medium is comprising of various components. These include carbon sources, nitrogen sources and other elements which are added in smaller quantities such as minerals, trace elements, vitamins and growth factors. Amongst these, carbon and nitrogen have to be provided in the maximum quantity because that is what the algae utilizes the most. That too... carbon need not be provided in the medium because we know algae are autotrophic which means they are able to fix their own carbon from in the form of carbon dioxide from the atmosphere and convert it into an organic form. The atmospheric air can be sterilized and provided to the algae for growth or we can even provide carbon dioxide enriched air so that more amount of carbon dioxide is available for photosynthesis. The nitrogen can be provided in the medium in an organic form or inorganic form based on which algal strain we are planning to grow. The other components that are included in the medium are minerals which comprise of phosphorus, sulfur, potassium, magnesium, iron, manganese, sodium, calcium. These are some of the minerals that are added into the medium which are required as part of various processes, enzymes, biomolecules for the algal growth. Apart from these, we also have certain elements or minerals which are provided in minor quantities or minute quantities of micrograms, nanograms or picograms even per litre. These include the trace elements such as boron, copper, molybdenum, zinc, cobalt which are provided in very small quantities that is why they are called as trace elements. All of these components are required for growth of an algae, good growth of an algae. We also have vitamins and growth factors which can be added as supplements in the medium so that they are enhancing the growth of algae. These two are added in very small quantities due to which vitamins, growth factors and trace elements are considered as micronutrients of an algal medium. Though algae are autotrophic, there are a few strains and species of algae such as chlorella and sendesmus which can be grown heterotrophically as well which means We can add an organic carbon source inside the medium and the algae is capable of absorbing it for its own nutrition. So there are only a few strains of algae which can be grown heterotrophically. For all the other algae we have to provide carbon in the form of carbon dioxide in the air that is being supplied into the culture vessel. Though there are many many media that have been devised for algae there is no one single medium which can be accepted by all. This is because every algal cell structure, morphology is very different from the other due to which we need to design a medium as per our requirements. Before we get into the designing of a medium and what are the factors involved in that, you need to know about stock solution. So most of the algae are grown in media which comprise of one or the other stock solution. Stock solution here is just a mixture of macronutrients. trace elements and vitamins in a concentrated form. So these concentrated stock solutions are then diluted whenever we are preparing a medium in whatever concentration is required. There are different types of mineral stock solutions that are present. So before we get into the algal growth media, I just wanted to let you know what is the meaning of a stock solution. It is a concentrated solution comprising of all the different components or all the different nutrients. Now before we talk about the specific media which are used for algae growth. What we need to know is that there are several factors which are determining the growth of algae and which are very important when we look into designing of a medium for algae. The first factor which is important to be looked into is the light source. Now we know that algae are photosynthetic in nature so light is what drives this photosynthetic reaction and due to this the intensity of light The spectral quality of light, the photoperiod for which the light should be provided to the algae is important or is necessary to be considered when we are designing a medium. The light intensity plays an important role. But again, the requirement varies with respect to the culture vessel, what is the depth of the vessel, what is the density of the algal culture. We know that at higher depths and when the cell concentration is very high, the light intensity has to be increased so that it can penetrate through the culture. For example, if we take a small conical flask, a light intensity of 1000 lux is suitable. But if we go for much larger volumes like bioreactors or if we are looking for larger tanks. we may have to increase the light intensity to 5000 or even 10,000 lux so that it can penetrate the depth of that culture vessel. So based on the culture vessel's depth and the type of culture that we are going to grow in there, that density of the algal culture, the intensity of the light will vary. The light that we are providing can be provided using a natural source that is the solar light, sun's light, sun's radiations or we can provide the light with the help of fluorescent tubes. Then again we have to make sure that there should not be too much of light intensity because that can result in photoinhibition. So even if it is direct sunlight or if we keep the container, the culture vessel close to the artificial light, the intensity should not be too much such that it triggers photoinhibition or causes overheating. So these need to be avoided whether we are using natural or artificial illumination. Now the fluorescent tubes if being used, We need to use the tubes which are emitting light either in the blue range or in the red light spectrum because these are the most active portions for the photosynthetic reaction. And even the duration, not just the intensity, even the duration of artificial illumination should be checked. It should be a minimum of 18 hours of light per day though there are certain phytoplanktons which can even develop under constant illumination. But for many of the algae, we need to check the illumination. illumination should not be excessive or it should not be provided for a long period of time. The next factor which has a major role to play when we are designing a medium is the pH of the culture medium. Now the pH generally should be neutral to slightly acidic for freshwater algae and that means it is between 7 to 9 with the optimum range being between 8.2 to 8.7. For marine algae the pH should be alkaline so the a pH should be increased it can go up to seven I mean up to nine so based on which type of algal species we are trying to grow. The maintenance of pH is usually done by aerating the culture so if it is a high density algal culture we can even add carbon dioxide which allows to correct the pH so that we can adjust the pH with the help of that carbon dioxide itself. So the pH variation will occur during the growth of the organism we need to buffer it or we need to check the change in pH so that the organism can grow well. The third factor is the aeration and mixing of the medium. Now mixing is a very important parameter, one for preventing the sedimentation of the algae and two for ensuring that all the organism cells are equally exposed to the light and nutrients. There is uniform distribution of the nutrients. There is no thermal stratification which means there is no division of temperature between the upper layers and the lower layers of the culture vessel. And mixing is also helping us to improve the gas exchange between the culture medium and air. So there has to be mixing in an algal culture so that all of these points are checked and all of these points can be taken care of. The mixing can be done with the help of a mechanical stirrer or a mechanical aerating mechanism. Or it can be done in especially in outdoor cultures, it can be done with the help of paddle wheels and jet pumps. This is usually seen in the case of... ponds and however it has to be noted that not all algal species can tolerate vigorous mixing. So there are certain algae which are very sensitive or delicate and for them the mixing has to be very gentle to avoid breakage or damage to the cells. So it has to be made sure that the air that is being that is containing the carbon source for photosynthesis the air that is containing carbon dioxide is present in the atmosphere and we know that it is present only at a percentage of 0.03 percent. So, this air even if we bubble the air, the atmospheric air or carbon dioxide enriched air through the medium, that bubbling of the air also is helping in mixing of the medium. So, that is the meaning of aerating the medium. When we are aerating the medium, that also helps in mixing of the medium. The bubbles help in mixing of the medium and help in uniform distribution of all the components of the medium. The next factor that is important is the temperature. So the optimal temperature for phytoplankton cultures is usually between 20 and 24 degree Celsius. Again this can vary with the composition of the culture medium with the strain of the algae that we are going to use the species of algae also. Most commonly the cultured species of algae tolerate temperatures between 16 and 27 and lower than that will slow down their growth and higher than say even 35 degree Celsius becomes lethal for a number of species. If it is required the algal cultures can be cooled by flow of cold water over the surface of the culture vessel or even by if it is in a closed room it can be even controlled the temperature can be controlled by using refrigerated air conditioning units. So based on how where we are growing the algae the temperature can be controlled so that it is within the range for that is required for the algae. The last factor which is important for the growth of algae is salinity. Now marine phytoplanktons are tolerant to changes in salinity but then again usually it has been seen that salinity is between 20 to 24 gram per liters is found to be optimal. So most species usually grow at a salinity that is slightly lower than that of their native habitat. So we need to see where we are, where we have taken the algae from, isolated the algae from, what is the salinity in that environment and then slightly lower salinity if we maintain in the lab then the algae will grow well. So these are some of the factors that can or that have to be considered while we are trying to grow the algae. Now in some cases for example in the case of diatoms we will even need to add or make sure there is a continuous source of silica in the medium because silica gets incorporated into the outer shell or the frustule of the diatom. So based on which type of algae we are growing and which type of algae is being considered, the type of medium will definitely differ. Now these are some of the common media that can be used for the growth of algae. One thing to remember is that algae can be grown either in a completely synthetic medium as shown over here, a synthetic medium is one wherein all the components are known to us. So it can be grown in a complete synthetic media or algae also grow very well in media based on natural water. So if we take a natural water either fresh water or marine water and enrich it with mineral supplements or with stock solutions we have seen that algae grow well. Algae are known to grow well even in liquid wastes such as effluents from factories or effluents from fermentation industries, wastewater treatment plant effluents or all of these effluents are also known to harness algal growth. So algae can either be grown in totally synthetic media or in media that is supplemented with minerals such as water supplemented with minerals or in liquid effluent wastes. Now the minerals that are provided I have told you are provided in the form of a stock solution. This stock solution is comprised of important minerals that are added in trace quantities. So because it is added in trace quantities what we do is we prepare the stock solution beforehand and then dilute it to a point and add it into the medium. As you can see here this is Bowles Basin Medium which is a freshwater algae medium that is used to grow a freshwater algae at a pH of 6.6 that is slightly acidic to neutral pH. This is choose medium which is also used for soil algae and freshwater algae. This is the trace element solution A5 trace element stock solution. As you can see it is made up of certain elements in very small quantities and only 1 ml of that is added into 1000 ml of this choose medium. We also have Bennex broth which is again a soil algae medium which is used to grow algae from the soil micro and macro algae. And then we have Walz medium. Walz medium is a marine water algal medium. Walz medium, you can see that if we are using seawater instead of distilled water to prepare this medium, then boron can be omitted. So the boron component can be avoided if we are using seawater. If we are using distilled water, the boron also has to be added. And to 1 liter of water, this 1 ml of nutrient solution is added. And after addition of nutrient solution, 100 microliters of vitamin solution is also added. This is the vitamin solution of which 100 microliters is added into 1 liter of the original medium. So this is again an example of a seawater medium. Apart from these there are many many more such as BG11 broad for cyanobacteria, pringsheem broad for cyanobacteria, we have Bristol's medium, Allen and Arnon's medium, ASM1 medium. There are several media which can be used for the growth of fresh water, marine water or soil algae. So this was about the culture media that have to be used. Now moving on to the culturing methods. So algal culturing can be done in close controlled lab conditions or even in less predictable outdoor tanks. This again is dependent on the person who is trying to grow the algae, their economic status, how much are they ready to put in or invest to grow the algae. Now the algae can be in indoor or outdoor conditions. Indoor conditions or indoor cultures allow control over illumination, temperature, the nutrient level, contamination levels can be checked in indoor cultures. It's much more easier when we are using it in indoor culture. Outdoor culture or an outdoor system is difficult to control all of these but then again it's important because it's economical and you can grow the algae for a longer period of time. Of course, there is no control over many of the parameters. It can also be the culturing method for algae can also be an open or a closed culture. Open cultures includes trays, ponds, tanks. This again can be indoor or outdoor, but it could be an open culturing system or a closed culturing system such as tubes, flasks, bags, etc. Algae can also be grown as axenic cultivation system or non-axenic. Axenic is where the algal culture is free of any foreign organism. it does not have any bacteria, no other algae grows over there, no fungal spores, nothing. This is very good but it is very expensive and difficult. In fact it is almost impractical when we are talking about a large scale or when we are talking about commercially maintaining an axenic culture for algae is impractical. Non-axenic is much cheaper, less laborious but definitely the quality is inconsistent because along with algae we could have other cells also. which can be found over there. So the culturing methods can be divided into three types based on their principle of growth. We have batch, continuous and semi-continuous mode of culturing. The batch cultures are very widely used because this is their advantages and these are the disadvantages. So they are very widely used because of their simplicity and their low cost and in a batch culturing system what we do essentially is it's a closed system. the volume is also limited and the resources are finite. So all the components that are required for the organism to grow that is the culture medium are added into a culture vessel. The vessel is inoculated with the algal population and then it is closed. The culture vessel is opened next only for harvesting. So this is a method wherein the algal cell density keeps increasing constantly until all the nutrients are exhausted. So when the nutrients are exhausted, we will harvest the culture and we will obtain the culture, I mean growth product from the algae, which will then be useful for us in various industries. Now this can be done either in Erlenmeyer flasks or we can do it in tanks, in any culture vessel it can be done because of its operational simplicity. So you just have to add everything and let the organism do its work. Another advantage is that if there is any defect in the system that can be remedied rapidly because for example if there is contamination in one of the vessels you can just stop the culturing in that vessel, empty the components and continue with culturing in the other vessel. So the remedy can be done immediately and the cost that is involved is low. But the major disadvantage is that there is low efficiency. It's not very efficient. You cannot predict the quality of the culture because the timing of harvest everything is depending on the culture medium. So we cannot depend on the efficient or we cannot depend on the quality of the product that comes out with every batch. It changes from one batch to the other. Also it is very laborious to harvest, clean, sterilize, refill and inoculate the medium between every batch. So every time harvesting is done we have to do the entire process of cleaning up and then only the next batch can be added. On the other hand or on the other end of the spectrum we have continuous culturing system. Continuous culturing systems are preferred or they are advantageous because of their very good efficiency. They are highly efficient. We know exactly what is the quality of the culture that is coming out. It is having consistent quality because the cultures here have been maintained at a steady state by regulated addition of fresh culture medium. and removal of an equal volume of spent medium. The cultures are being maintained at a steady state which means they are being maintained at a point on the growth curve where the growth rate and the total number of cells per ml is constant. So when it is being maintained in such a state whenever we are removing or whenever we are harvesting as I told you there is regulated addition of fresh culture medium and removal of an equal volume of culture. Whenever we are removing the equal volume of culture, whenever we are harvesting the cells, the product obtained or the algal biomass is at exactly the same condition or it is being harvested at the exact same point as it was harvested the previous day. So every time we harvest the products are having the same quality. That is why it is highly efficient and gives us consistent quality of the products. Now the fresh growth medium is stored in a large vessel and when the air is pumped into this vessel, into this vessel's air space, it pushes the medium into our culture vessel or the vessel where we are growing the algae. Once this pushes the medium over here, the culture vessel will increase now in the total volume of the culture and the air passed into the medium, this air is being passed into the medium with the help of a long glass tube so that the culture can be mixed and provide oxygen, carbon dioxide etc. Now when the fresh medium gets added, when this fresh medium falls into the culture vessel, level of the culture rises due to which the old medium and the old cells which are present here will flow out of the tube. This is the outflow tube and get collected in another chamber. This is the collecting chamber or the collecting receptacle. So from this collecting receptacle we can further take the culture the spent medium and the cells and harvest our product. Now the continuous culturing can be maintained with the help of two principles one is chemostat and the other one is turbidostat. A turbidostat is a continuous culturing system wherein the steady state is being maintained by a predetermined cell density. So the cell density has been set to a predetermined point. and this is measured by the extinction of light that is passing through the culture. The moment the light passing through the culture is now no more there or it is extinct or the photo cell that is attached over here is not able to detect the light it means that the culture has got filled with so many cells or the culture has now become so dense that fresh medium needs to be added and spent medium needs to be removed. So this point of the cell growth curve is already predetermined. So as soon as the light coming through this bulb is not being detected by the photocell it is understood that fresh medium needs to be added and spent medium needs to be removed. So this is the principle of turbidostat. It is adding or it is maintaining the continuous culture with the help of turbidity. The second one is the chemostat. In a chemostat again we are maintaining the cell culture or we are maintaining the growth rate at the same point in the growth curve with the help of a limiting nutrient. So a particular nutrient, a vital nutrient for example it could be nitrate. A limiting nutrient or a vital nutrient is provided in the medium in limiting volume or limiting concentration. So a very important, a very critical nutrient is provided in a minimal concentration. Why this is done is the moment that nutrient is getting over the moment that nutrient is finishing we add fresh medium so there is flow of fresh medium into the culture vessel and again the spent medium is being taken out so this rate at which the fresh medium is going to be added into the culture vessel of a chemostat is again pre-determined it has been determined when that particular limiting nutrient is going to get over and fresh medium needs to be provided so this again is a method of maintaining continuous culturing based on the concentration of a limiting nutrient hence it is called as chemostat. Turbidostat and chemostat are used for maintaining continuous culture of algae. Not only algae it is also used in the case of other organisms and the rate of flow of medium into the system is called as dilution rate. So when the number of cells in the culture vessel is constant over time and dilution rate will become equal to the rate of cell divisions because you remove the cells or the cells removed by outflow are replaced by equal number through cell division. That is how we are able to maintain the growth rate or we are able to maintain the total number of cells per ml. So this was about continuous culturing which is a highly preferred method but definitely expensive to maintain it in this continuous state or steady state. The third type of culturing system of algae is a semi-continuous method wherein there is fresh medium added to the culture vessel. and then it is closed. Once it has been closed and the organism is allowed to grow, maybe for a period of 24 hours or 48 hours, the procedure is remitted. There can be partial periodic harvesting. The thing to remember here is that only partially it is being harvested and this is followed immediately by addition of fresh nutrients so that original volume can be obtained. So there is only partial harvesting and the cultures are not harvested completely due to which the yield is definitely more than the batch method but the contaminants and metabolites tend to build up so that can lead to death of our organism as well that is one of the problems with semi continuous culturing but the advantage is that the yield is definitely better than batch culturing method the this is a comparative chart to show you what are the advantages and disadvantages of the three types of culturing methods of algae as I have told you some of them are efficient but they are expensive to maintain some others are very easy to maintain and very simple to operate but then they are least efficient. So these are this is just a comparative chart to show you the different culturing methods of algae. So in this class we have spoken about the media that are involved in the culturing of algae and the methods that are used for growing them. Based on this as we will see in the next few video lectures we will see how algae can be grown in large scale. I hope you all have understood this video. Thank you.

Now a culture medium is a very important factor when we look into the algal growth because it is the culture medium which is going to provide all the essential nutrients for the algae to grow. Design of the culture medium is very very important for a successful growth of algae. So the medium is comprising of various components.

These include carbon sources, nitrogen sources and other elements which are added in smaller quantities such as minerals, trace elements, vitamins and growth factors. Amongst these, carbon and nitrogen have to be provided in the maximum quantity because that is what the algae utilizes the most. That too...

carbon need not be provided in the medium because we know algae are autotrophic which means they are able to fix their own carbon from in the form of carbon dioxide from the atmosphere and convert it into an organic form. The atmospheric air can be sterilized and provided to the algae for growth or we can even provide carbon dioxide enriched air so that more amount of carbon dioxide is available for photosynthesis. The nitrogen can be provided in the medium in an organic form or inorganic form based on which algal strain we are planning to grow.

The other components that are included in the medium are minerals which comprise of phosphorus, sulfur, potassium, magnesium, iron, manganese, sodium, calcium. These are some of the minerals that are added into the medium which are required as part of various processes, enzymes, biomolecules for the algal growth. Apart from these, we also have certain elements or minerals which are provided in minor quantities or minute quantities of micrograms, nanograms or picograms even per litre.

These include the trace elements such as boron, copper, molybdenum, zinc, cobalt which are provided in very small quantities that is why they are called as trace elements. All of these components are required for growth of an algae, good growth of an algae. We also have vitamins and growth factors which can be added as supplements in the medium so that they are enhancing the growth of algae.

These two are added in very small quantities due to which vitamins, growth factors and trace elements are considered as micronutrients of an algal medium. Though algae are autotrophic, there are a few strains and species of algae such as chlorella and sendesmus which can be grown heterotrophically as well which means We can add an organic carbon source inside the medium and the algae is capable of absorbing it for its own nutrition. So there are only a few strains of algae which can be grown heterotrophically.

For all the other algae we have to provide carbon in the form of carbon dioxide in the air that is being supplied into the culture vessel. Though there are many many media that have been devised for algae there is no one single medium which can be accepted by all. This is because every algal cell structure, morphology is very different from the other due to which we need to design a medium as per our requirements.

Before we get into the designing of a medium and what are the factors involved in that, you need to know about stock solution. So most of the algae are grown in media which comprise of one or the other stock solution. Stock solution here is just a mixture of macronutrients.

trace elements and vitamins in a concentrated form. So these concentrated stock solutions are then diluted whenever we are preparing a medium in whatever concentration is required. There are different types of mineral stock solutions that are present. So before we get into the algal growth media, I just wanted to let you know what is the meaning of a stock solution. It is a concentrated solution comprising of all the different components or all the different nutrients.

Now before we talk about the specific media which are used for algae growth. What we need to know is that there are several factors which are determining the growth of algae and which are very important when we look into designing of a medium for algae. The first factor which is important to be looked into is the light source. Now we know that algae are photosynthetic in nature so light is what drives this photosynthetic reaction and due to this the intensity of light The spectral quality of light, the photoperiod for which the light should be provided to the algae is important or is necessary to be considered when we are designing a medium. The light intensity plays an important role.

But again, the requirement varies with respect to the culture vessel, what is the depth of the vessel, what is the density of the algal culture. We know that at higher depths and when the cell concentration is very high, the light intensity has to be increased so that it can penetrate through the culture. For example, if we take a small conical flask, a light intensity of 1000 lux is suitable.

But if we go for much larger volumes like bioreactors or if we are looking for larger tanks. we may have to increase the light intensity to 5000 or even 10,000 lux so that it can penetrate the depth of that culture vessel. So based on the culture vessel's depth and the type of culture that we are going to grow in there, that density of the algal culture, the intensity of the light will vary.

The light that we are providing can be provided using a natural source that is the solar light, sun's light, sun's radiations or we can provide the light with the help of fluorescent tubes. Then again we have to make sure that there should not be too much of light intensity because that can result in photoinhibition. So even if it is direct sunlight or if we keep the container, the culture vessel close to the artificial light, the intensity should not be too much such that it triggers photoinhibition or causes overheating.

So these need to be avoided whether we are using natural or artificial illumination. Now the fluorescent tubes if being used, We need to use the tubes which are emitting light either in the blue range or in the red light spectrum because these are the most active portions for the photosynthetic reaction. And even the duration, not just the intensity, even the duration of artificial illumination should be checked. It should be a minimum of 18 hours of light per day though there are certain phytoplanktons which can even develop under constant illumination.

But for many of the algae, we need to check the illumination. illumination should not be excessive or it should not be provided for a long period of time. The next factor which has a major role to play when we are designing a medium is the pH of the culture medium.

Now the pH generally should be neutral to slightly acidic for freshwater algae and that means it is between 7 to 9 with the optimum range being between 8.2 to 8.7. For marine algae the pH should be alkaline so the a pH should be increased it can go up to seven I mean up to nine so based on which type of algal species we are trying to grow. The maintenance of pH is usually done by aerating the culture so if it is a high density algal culture we can even add carbon dioxide which allows to correct the pH so that we can adjust the pH with the help of that carbon dioxide itself.

So the pH variation will occur during the growth of the organism we need to buffer it or we need to check the change in pH so that the organism can grow well. The third factor is the aeration and mixing of the medium. Now mixing is a very important parameter, one for preventing the sedimentation of the algae and two for ensuring that all the organism cells are equally exposed to the light and nutrients.

There is uniform distribution of the nutrients. There is no thermal stratification which means there is no division of temperature between the upper layers and the lower layers of the culture vessel. And mixing is also helping us to improve the gas exchange between the culture medium and air. So there has to be mixing in an algal culture so that all of these points are checked and all of these points can be taken care of. The mixing can be done with the help of a mechanical stirrer or a mechanical aerating mechanism.

Or it can be done in especially in outdoor cultures, it can be done with the help of paddle wheels and jet pumps. This is usually seen in the case of... ponds and however it has to be noted that not all algal species can tolerate vigorous mixing. So there are certain algae which are very sensitive or delicate and for them the mixing has to be very gentle to avoid breakage or damage to the cells. So it has to be made sure that the air that is being that is containing the carbon source for photosynthesis the air that is containing carbon dioxide is present in the atmosphere and we know that it is present only at a percentage of 0.03 percent.

So, this air even if we bubble the air, the atmospheric air or carbon dioxide enriched air through the medium, that bubbling of the air also is helping in mixing of the medium. So, that is the meaning of aerating the medium. When we are aerating the medium, that also helps in mixing of the medium. The bubbles help in mixing of the medium and help in uniform distribution of all the components of the medium.

The next factor that is important is the temperature. So the optimal temperature for phytoplankton cultures is usually between 20 and 24 degree Celsius. Again this can vary with the composition of the culture medium with the strain of the algae that we are going to use the species of algae also.

Most commonly the cultured species of algae tolerate temperatures between 16 and 27 and lower than that will slow down their growth and higher than say even 35 degree Celsius becomes lethal for a number of species. If it is required the algal cultures can be cooled by flow of cold water over the surface of the culture vessel or even by if it is in a closed room it can be even controlled the temperature can be controlled by using refrigerated air conditioning units. So based on how where we are growing the algae the temperature can be controlled so that it is within the range for that is required for the algae.

The last factor which is important for the growth of algae is salinity. Now marine phytoplanktons are tolerant to changes in salinity but then again usually it has been seen that salinity is between 20 to 24 gram per liters is found to be optimal. So most species usually grow at a salinity that is slightly lower than that of their native habitat. So we need to see where we are, where we have taken the algae from, isolated the algae from, what is the salinity in that environment and then slightly lower salinity if we maintain in the lab then the algae will grow well. So these are some of the factors that can or that have to be considered while we are trying to grow the algae.

Now in some cases for example in the case of diatoms we will even need to add or make sure there is a continuous source of silica in the medium because silica gets incorporated into the outer shell or the frustule of the diatom. So based on which type of algae we are growing and which type of algae is being considered, the type of medium will definitely differ. Now these are some of the common media that can be used for the growth of algae. One thing to remember is that algae can be grown either in a completely synthetic medium as shown over here, a synthetic medium is one wherein all the components are known to us.

So it can be grown in a complete synthetic media or algae also grow very well in media based on natural water. So if we take a natural water either fresh water or marine water and enrich it with mineral supplements or with stock solutions we have seen that algae grow well. Algae are known to grow well even in liquid wastes such as effluents from factories or effluents from fermentation industries, wastewater treatment plant effluents or all of these effluents are also known to harness algal growth.

So algae can either be grown in totally synthetic media or in media that is supplemented with minerals such as water supplemented with minerals or in liquid effluent wastes. Now the minerals that are provided I have told you are provided in the form of a stock solution. This stock solution is comprised of important minerals that are added in trace quantities. So because it is added in trace quantities what we do is we prepare the stock solution beforehand and then dilute it to a point and add it into the medium. As you can see here this is Bowles Basin Medium which is a freshwater algae medium that is used to grow a freshwater algae at a pH of 6.6 that is slightly acidic to neutral pH. This is choose medium which is also used for soil algae and freshwater algae.

This is the trace element solution A5 trace element stock solution. As you can see it is made up of certain elements in very small quantities and only 1 ml of that is added into 1000 ml of this choose medium. We also have Bennex broth which is again a soil algae medium which is used to grow algae from the soil micro and macro algae. And then we have Walz medium. Walz medium is a marine water algal medium.

Walz medium, you can see that if we are using seawater instead of distilled water to prepare this medium, then boron can be omitted. So the boron component can be avoided if we are using seawater. If we are using distilled water, the boron also has to be added.

And to 1 liter of water, this 1 ml of nutrient solution is added. And after addition of nutrient solution, 100 microliters of vitamin solution is also added. This is the vitamin solution of which 100 microliters is added into 1 liter of the original medium. So this is again an example of a seawater medium. Apart from these there are many many more such as BG11 broad for cyanobacteria, pringsheem broad for cyanobacteria, we have Bristol's medium, Allen and Arnon's medium, ASM1 medium.

There are several media which can be used for the growth of fresh water, marine water or soil algae. So this was about the culture media that have to be used. Now moving on to the culturing methods. So algal culturing can be done in close controlled lab conditions or even in less predictable outdoor tanks.

This again is dependent on the person who is trying to grow the algae, their economic status, how much are they ready to put in or invest to grow the algae. Now the algae can be in indoor or outdoor conditions. Indoor conditions or indoor cultures allow control over illumination, temperature, the nutrient level, contamination levels can be checked in indoor cultures.

It's much more easier when we are using it in indoor culture. Outdoor culture or an outdoor system is difficult to control all of these but then again it's important because it's economical and you can grow the algae for a longer period of time. Of course, there is no control over many of the parameters. It can also be the culturing method for algae can also be an open or a closed culture.

Open cultures includes trays, ponds, tanks. This again can be indoor or outdoor, but it could be an open culturing system or a closed culturing system such as tubes, flasks, bags, etc. Algae can also be grown as axenic cultivation system or non-axenic. Axenic is where the algal culture is free of any foreign organism.

it does not have any bacteria, no other algae grows over there, no fungal spores, nothing. This is very good but it is very expensive and difficult. In fact it is almost impractical when we are talking about a large scale or when we are talking about commercially maintaining an axenic culture for algae is impractical. Non-axenic is much cheaper, less laborious but definitely the quality is inconsistent because along with algae we could have other cells also. which can be found over there.

So the culturing methods can be divided into three types based on their principle of growth. We have batch, continuous and semi-continuous mode of culturing. The batch cultures are very widely used because this is their advantages and these are the disadvantages.

So they are very widely used because of their simplicity and their low cost and in a batch culturing system what we do essentially is it's a closed system. the volume is also limited and the resources are finite. So all the components that are required for the organism to grow that is the culture medium are added into a culture vessel. The vessel is inoculated with the algal population and then it is closed.

The culture vessel is opened next only for harvesting. So this is a method wherein the algal cell density keeps increasing constantly until all the nutrients are exhausted. So when the nutrients are exhausted, we will harvest the culture and we will obtain the culture, I mean growth product from the algae, which will then be useful for us in various industries. Now this can be done either in Erlenmeyer flasks or we can do it in tanks, in any culture vessel it can be done because of its operational simplicity. So you just have to add everything and let the organism do its work.

Another advantage is that if there is any defect in the system that can be remedied rapidly because for example if there is contamination in one of the vessels you can just stop the culturing in that vessel, empty the components and continue with culturing in the other vessel. So the remedy can be done immediately and the cost that is involved is low. But the major disadvantage is that there is low efficiency. It's not very efficient.

You cannot predict the quality of the culture because the timing of harvest everything is depending on the culture medium. So we cannot depend on the efficient or we cannot depend on the quality of the product that comes out with every batch. It changes from one batch to the other. Also it is very laborious to harvest, clean, sterilize, refill and inoculate the medium between every batch.

So every time harvesting is done we have to do the entire process of cleaning up and then only the next batch can be added. On the other hand or on the other end of the spectrum we have continuous culturing system. Continuous culturing systems are preferred or they are advantageous because of their very good efficiency. They are highly efficient.

We know exactly what is the quality of the culture that is coming out. It is having consistent quality because the cultures here have been maintained at a steady state by regulated addition of fresh culture medium. and removal of an equal volume of spent medium.

The cultures are being maintained at a steady state which means they are being maintained at a point on the growth curve where the growth rate and the total number of cells per ml is constant. So when it is being maintained in such a state whenever we are removing or whenever we are harvesting as I told you there is regulated addition of fresh culture medium and removal of an equal volume of culture. Whenever we are removing the equal volume of culture, whenever we are harvesting the cells, the product obtained or the algal biomass is at exactly the same condition or it is being harvested at the exact same point as it was harvested the previous day. So every time we harvest the products are having the same quality.

That is why it is highly efficient and gives us consistent quality of the products. Now the fresh growth medium is stored in a large vessel and when the air is pumped into this vessel, into this vessel's air space, it pushes the medium into our culture vessel or the vessel where we are growing the algae. Once this pushes the medium over here, the culture vessel will increase now in the total volume of the culture and the air passed into the medium, this air is being passed into the medium with the help of a long glass tube so that the culture can be mixed and provide oxygen, carbon dioxide etc.

Now when the fresh medium gets added, when this fresh medium falls into the culture vessel, level of the culture rises due to which the old medium and the old cells which are present here will flow out of the tube. This is the outflow tube and get collected in another chamber. This is the collecting chamber or the collecting receptacle. So from this collecting receptacle we can further take the culture the spent medium and the cells and harvest our product.

Now the continuous culturing can be maintained with the help of two principles one is chemostat and the other one is turbidostat. A turbidostat is a continuous culturing system wherein the steady state is being maintained by a predetermined cell density. So the cell density has been set to a predetermined point.

and this is measured by the extinction of light that is passing through the culture. The moment the light passing through the culture is now no more there or it is extinct or the photo cell that is attached over here is not able to detect the light it means that the culture has got filled with so many cells or the culture has now become so dense that fresh medium needs to be added and spent medium needs to be removed. So this point of the cell growth curve is already predetermined.

So as soon as the light coming through this bulb is not being detected by the photocell it is understood that fresh medium needs to be added and spent medium needs to be removed. So this is the principle of turbidostat. It is adding or it is maintaining the continuous culture with the help of turbidity. The second one is the chemostat. In a chemostat again we are maintaining the cell culture or we are maintaining the growth rate at the same point in the growth curve with the help of a limiting nutrient.

So a particular nutrient, a vital nutrient for example it could be nitrate. A limiting nutrient or a vital nutrient is provided in the medium in limiting volume or limiting concentration. So a very important, a very critical nutrient is provided in a minimal concentration.

Why this is done is the moment that nutrient is getting over the moment that nutrient is finishing we add fresh medium so there is flow of fresh medium into the culture vessel and again the spent medium is being taken out so this rate at which the fresh medium is going to be added into the culture vessel of a chemostat is again pre-determined it has been determined when that particular limiting nutrient is going to get over and fresh medium needs to be provided so this again is a method of maintaining continuous culturing based on the concentration of a limiting nutrient hence it is called as chemostat. Turbidostat and chemostat are used for maintaining continuous culture of algae. Not only algae it is also used in the case of other organisms and the rate of flow of medium into the system is called as dilution rate. So when the number of cells in the culture vessel is constant over time and dilution rate will become equal to the rate of cell divisions because you remove the cells or the cells removed by outflow are replaced by equal number through cell division. That is how we are able to maintain the growth rate or we are able to maintain the total number of cells per ml.

So this was about continuous culturing which is a highly preferred method but definitely expensive to maintain it in this continuous state or steady state. The third type of culturing system of algae is a semi-continuous method wherein there is fresh medium added to the culture vessel. and then it is closed.

Once it has been closed and the organism is allowed to grow, maybe for a period of 24 hours or 48 hours, the procedure is remitted. There can be partial periodic harvesting. The thing to remember here is that only partially it is being harvested and this is followed immediately by addition of fresh nutrients so that original volume can be obtained.

So there is only partial harvesting and the cultures are not harvested completely due to which the yield is definitely more than the batch method but the contaminants and metabolites tend to build up so that can lead to death of our organism as well that is one of the problems with semi continuous culturing but the advantage is that the yield is definitely better than batch culturing method the this is a comparative chart to show you what are the advantages and disadvantages of the three types of culturing methods of algae as I have told you some of them are efficient but they are expensive to maintain some others are very easy to maintain and very simple to operate but then they are least efficient. So these are this is just a comparative chart to show you the different culturing methods of algae. So in this class we have spoken about the media that are involved in the culturing of algae and the methods that are used for growing them.

Based on this as we will see in the next few video lectures we will see how algae can be grown in large scale. I hope you all have understood this video. Thank you.

Transcript for:Culturing Techniques for Algae Growth

Transcript for:
Culturing Techniques for Algae Growth