hi my name is dr alice lee and today's lecture 14 will discuss what microorganisms require chemically in order to grow as you can see from this figure of the periodic table there are a handful of essential chemical elements required for growth we will learn what these chemicals are used for in the cell and where microbes can get these chemicals for growth if you were observant on the first slide could you list all the major chemical requirements for microbial growth if you want you can pause the video and take a moment to brainstorm the answer write them all down okay got it well hopefully you came up with a list with some of these items carbon hydrogen nitrogen sulfur phosphorus etc they're all key elements we'll talk about them in a bit there are also various micronutrients needed in smaller amounts trace elements and vitamins or growth factors molecular oxygen there's a certain concentration that may or may not be required and the micronutrients such as organic growth factors are usually special vitamins or other factors like amino acids plenty of water as most microbes obtain almost all their nutrients in solution from the surrounding aqueous environment how about physical requirements can you list these well temperature ph and osmotic pressure we'll talk more about the physical requirements in the next lecture so we're going to start off with the chemical requirements today so all cells consist of what i call the chinops or which stands for carbon hydrogen nitrogen oxygen phosphorus and sulfur these elements are what we call macronutrient elements meaning that they're required in large amounts by the cell the key macronutrients are carbon and nitrogen all cells need carbon about half of the dry weight of a typical bacterial cell is made up of carbon it is the major element in all macromolecules oxygen and hydrogen are also required and they're usually attached to carbon nitrogen is about 13 by dry weight of the cell nitrogen is a key element in proteins nucleic acids and other cell parts phosphorus is needed for synthesis of nucleic acids and phospholipids and is usually acquired in organic or inorganic phosphate form and phosphorus is also found in the high energy bonds of atp sulfur is needed in the amino acid cysteine of methionine and also in vitamins like thiamine and biotin sulfur originates from inorganic sources in nature such as sulfate and sulfide oxygen is an important element in organic compounds in macromolecules molecular oxygen or o2 requirements vary between different species of microbes other important elements are all metals that are used as cofactors and enzymes and often to stabilize membranes in cell structure mineral ions are necessary in most microbes elements such as iron potassium sodium they play an important role in enzymes and macromolecules so where do these microbes get their macronutrients such as carbon well the majority of bacteria are what we call heterotrophs they rely on other organisms to form the organic compounds such as carbohydrates like glucose that they then use as carbon sources heterotrophs get most of their carbon from the source of their energy organic materials such as proteins carbohydrates and lipids this usually supplies their hydrogen and oxygen requirement therefore carbon also in this form serves to supply their energy source the autotrophs are able to assimilate inorganic carbon dioxide as a carbon source usually by reducing it in which case we mean by adding hydrogen atoms to make complex cell constituents made of carbon hydrogen and oxygen these organic compounds can then be used by the heterotrophs autotrophs can be classified as photoautotrophs or phototrophs which use light for us for photosynthesis whereas chemo auto troves or chemolithotrophs gain energy by oxidizing inorganic substances such as iron and ammonia both of these types of autotrophs carry out the autotrophic process of carbon fixation nitrogen as we had mentioned is about 13 of the dry weight of the cell it's very important and needed for protein synthesis it's used primarily to form the amino group of amino acids of proteins dna and rna these nucleic acids their synthesis requires nitrogen think nitrogenous bases right most microbes can get it from decomposing protein-containing material such as organic cellular material then they re-incorporate the amino acids into new proteins some use sources like ammonia ammonium ions some get nitrogen from nitrates that are in solution already and some photosynthetic cyanobacteria can use nitrogen gas to get their nitrogen through nitrogen fixation processes sulfur is used in amino acids such as cysteine and methionine these are sulfur-containing amino acids and sulfur is also needed in several vitamins such as thymine biotin and lipoic acid sulfur is usually obtained from either sulfur containing amino acids which are organic sources or from sulfate oxidized or sulfide reduced sources these are inorganic sources phosphorus is needed for nucleic acids and phospholipids of cell membranes and also in atp phosphorus is usually supplied to a cell in the form of inorganic phosphate microbes require several metals for growth typically in very small amounts and these are referred to as trace elements for example iron copper molybdenum zinc boron cobalt and manganese since they're required in such small amounts microgram or microgram quantities we call them micronutrients chief among them is iron which plays a key role in cellular respiration by serving as a redox center or they may function as cofactors in enzymes involved in electron transport reactions although sometimes these elements are added to the lab medium they can be naturally present in tap water and other media components unlike trace metals or trace elements grow factors are typically organic compounds they are required in only small amounts so again a type of micronutrient and they're only required by certain organisms many microorganisms can satisfy their own requirements for growth factors through biosynthetic processes meaning that they make their own but some require one or more preformed already from the environment and they must then be supplied in the media culture if you're growing them in the lab there are three main types of growth factors amino acids which are used for proteins purines and pyrimidines used for nucleic acids and vitamins which are often used as enzyme cofactors vitamins and most most vitamins function as these coenzymes also which are non-protein components of enzymes these growth factors collectively may be needed in varying concentrations ranging from none whatsoever to milligram quantities per liter the element oxygen is a universal component of cells and it's almost always provided in large amounts in water however prokaryotes display a wide range of responses to molecular oxygen or o2 for many microbes oxygen is an essential nutrient others cannot grow in its presence and may even be killed by it microbes can be grouped according to the relationship with oxygen oblique aerobes require oxygen for growth and they can grow at full oxygen tensions such as in the air it's about 21 oxygen these microbes use oxygen as a final electron receptor in aerobic respiration obligate anaerobes occasionally called aerophobes they do not need or use oxygen as a nutrient in fact oxygen is a toxic substance which either kills or inhibits their growth anoxic or oxygen-free environments are common in nature such as those found in mud marshes deep subsurface of the earth obligate anaerobic prokaryotes may live by processes like fermentation and anaerobic respiration bacterial photosynthesis or the novel process of methanogenesis that's only found in archaea facultative anaerobes sometimes called vacutative aerobes or just vacutative they're organisms that can switch between aerobic and anaerobic types of metabolism under anaerobic conditions where there's no oxygen they grow by fermentation or anaerobic respiration but in the presence of oxygen they can switch to an aerobic respiration a microaerophil requires oxygen to survive but it requires environments containing lower levels of oxygen than are present in the atmosphere therefore they need oxygen levels that are less than 20 concentration that that's the atmospheric oxygen concentration many microphiles microarrow files are also capnophiles as they require an elevated concentration of carbon dioxide too and finally aero tolerant and ropes they cannot use oxygen for growth but they tolerate it pretty well these bacteria use an exclusively anaerobic or fermentative type of metabolism whether or not there's oxygen present in their environment in the lab dioclycolate medium may be used to assess the oxygen requirements of a bacterium and they can be also used to assess and grow microbes under anaerobic conditions thioglycolate in the medium serves as a reducing agent to remove traces of oxygen by reducing it to water usually a redox indicator dye such as rizazarin is present in to signal oxic or oxygen containing regions the dye is pink when oxidized and colorless when reduced and thus gives you a visual assessment of the degree of penetration of oxygen into the medium the five tubes here show shown indicates five different five different oxygen classes of microbes that were inoculated into a thio glycolate medium the dots represent growth for example obligate air robes like micrococcus ludius will grow only where high concentrations of oxygen have diffused into the medium which would be at the top of the medium in this case there is more oxygen here since this is the space in the tube most exposed to any oxygen that's entering this tube this is not a seal tube it only has a loosely fitting cap as you can see for the other tubes oblique anaerobes like to grow on the bottom because they don't like oxygen so they prefer to grow where there is low to no oxygen facultative anaerobes such as e coli can either use oxygen or not but if oxygen is available they will use it because they get more energy that way so they'll grow at the top of the tube microarrow files like spirulium valuetans need a oxygen concentration slightly lower than the atmospheric concentration of about 20 percent so they like to grow slightly below the top of the tube aerial tolerant anaerobes like streptococcus who tolerate oxygen but don't need it to grow will grow throughout the tube most organisms are constantly exposed to molecular oxygen and for some like oblique aerobes it's become a requirement of life for many of them oxygen is not totally innocuous though and it's long been known to be toxic to many organisms including humans molecular oxygen is not toxic but oxygen can be converted to highly reactive toxogen toxic oxygen byproducts for example singlet oxygen is normal molecular oxygen that has been boosted into a higher energy state and is extremely reactive superoxide free radicals or super oxide anions they're called are formed in small amounts during normal respiration of microbes that use oxygen as the final electron acceptor these radicals are toxic to cellular components toxicity is generally caused by their great instability which leads them to steal electrons from neighboring molecules and this repeats itself peroxide anions are produced as part of hydrogen peroxide processes the hydroxyl radical is another intermediate form of oxygen probably the most reactive that's formed in the cytoplasm by ionizing radiation the peroxidation of lipids for example is a major consequence of exposure to some of these oxygen forms and the cell possesses therefore various enzymes including superoxide dismutase catalase and peroxidase as well as other cellular antioxidants which are able to scavenge many of these free oxygen radicals to repair peroxidized lipids for example or turn them into something less reactive like water the suggested reading is in chapter six for your tutorial text in this image here i'm actually holding a thigh glickly tube that doesn't look particularly interesting the thiogly broth medium is a complex medium we'll talk more about this later but it contains a small amount of argor making the medium viscous but still fluid and it also contains the thio glycolate reducing agent