Hi, I'm Professor Joel Buldock, and welcome to my video on the Zygomycota, also known as the conjugating fungi. Now, the Zygomycota are just one of the five major phyla that make up the kingdom fungi. And actually, you might already know the most common member of this phylum.
It is the bread malt, also known as Rhizopus stolonifera, which will grow on the surface of bread, fruit, and vegetables. I brought home some strawberries. week and I left a few out on the counter for a few days and as usual you'll notice that or I decided to notice that some of these strawberries started to grow some white fuzzy stuff this is the Rhizopus fungi and it will so it what it does it actually feeds on the surface of these strawberries this is a before and after picture and I also did the same experiment using some bread so I let out I left a slice of white bread on the counter and over time it started growing these dark patches as well as this white sort of fuzzy stuff. These white fuzzy stuff are the fungi that I'm going to talk about in a few minutes. So in the next few slides I'm going to first introduce some general concepts that separate these fungi in the phylum of Zygomycota and then I'm going to go into the phases of the asexual reproduction followed by sexual reproduction.
Okay so let's begin. by giving some terms. Now most of the members that fall into this phylum of Zygomycota are going to be called sapropes. You might also hear the term saprophytic.
That means that they will live off decaying organic matter. So as you can see here this bread mold is considered a dead organic matter. These molds are going to grow on it and extract its nutrients. Very few of them are actually associated with any pathogenic infections with humans and animals. In fact, that common member, the Rhizopus stolonifera, it is considered an opportunistic human pathogen but rarely does cause any disease.
So for the most part, you don't have to worry about that mole growing on your bread. All members of the Zychomycota have coenacidic hyphae with haploid nuclei. So I'm showing you two pictures, one of coenacidic hyphae on the top and on the bottom, a septated hyphae.
So you can see that the top is a septated hyphae. What it means by being choeinocytic is that they do not have septum that separate their individual cells. So they'll have these long strands of hyphae with just various organelles and nuclei floating from one branch to the other. Also, their nuclei, as mentioned, are haploid.
That means that they only have one copy of every chromosome inside their nucleus. That differs from our chromosomes or our nucleus because our nucleus are diploid, meaning that we have two copies of every single chromosome. Now how do they reproduce? They can do that by two ways.
They can reproduce asexually as shown here or by sexual reproduction. So usually they reproduce asexually when they have tons of nutrients and the environmental conditions are good for them to grow. So they're going to reproduce by forming this very special hyphae called a sporangio 4. The sporangio 4 will form a sac-like structure called the sporangium and inside that sac will be hundreds of sporangio spores.
These sporangio spores are then are held up in the air so that in any air current that can go by when that sporangium ruptures those spores will be able to be carried through the wind current and land on other suitable growing environments. So that's what happens normally during good growth conditions. However when those conditions are not as favorable, so let's say they don't have enough nutrients, or the temperature is not in the right range for growth.
These two hyphae of two opposing mating strains will come together close enough so that they can fuse together and conjugate, hence the name conjugating fungi. And they're going to form a zygosporangia. So I'm showing you a picture of a zygosporangia. Here is sort of a thick-walled structure that forms between these two hyphae of opposing mating strains. and inside will be the zygospores.
Now, these zygosporangia are important to the species because they can withstand those less favorable conditions, allowing the fungi to go under dormancy until conditions do improve, until more nutrients come in their environment where they can undergo meiosis. Inside that zygosporangia, Form those haploid zygospores. Those zygospores can then germinate and form more fungi. Okay, so we'll go into that in one second.
Okay, so I want to first go step by step and talk to you about the asexual reproduction. So I'm bringing back a slice of bread here, and I'm showing you that there are these hyphae, we call them vegetative hyphae, that are buried inside the slice of bread. And they're going to secrete some enzymes that allow the starch to be broken up so it can absorb that glucose. It's going to take in the nutrients and make these aerial hyphae. which they will have the sporangium or rather the sporangio4 that will then grow the sporangiospores and i'm showing you the sporangium with the sporangiospores here in these dark circles and i'm peppering some of these little spores that became released okay so we're going to start with this zy uh this sporangiospore and we're going to follow it through its asexual reproduction So let's say the wind took the sporangiospore and it's landed on another slice of bread.
Now that slice of bread is going to have plenty of nutrients so that this sporangiospore can then begin to germinate and form a coenocytic hyphae as shown here. That coenocytic hyphae will continue to grow. It will branch. It will form specialized rhizoid hyphae.
These are the hyphae that bury inside the bread to acquire nutrients. It will also make a network of aerial hyphae. the sporangio 4 in which a sporangium that is filled with sporangiospores will then form. So again, this cycle can continue over and over again as long as growth conditions are suitable for it.
And so as the sporangio, I should say as the sporangium breaks apart, releases the sporangiospores, they can go off and land on other surfaces in which there are plenty of nutrients to grow. Okay, so I've already mentioned that sexual reproduction only occurs when environmental conditions are not as good for it. So we're going to say that that's what's happening here and there are going to be two opposing mating strains.
Now we don't call them male or female, we basically call them plus or minus and they have to be compatible. You can't have two plus strands, mating strands, or two minus mating strands. So I'm showing you here my plus strand and my minus strand. And I've boxed off two hyphae which are coming in close proximity from each other. So let's focus on these two hyphae of opposite mating strands.
So I've drawn them again here as a blue positive and a light pink minus strand. What happens when they come together, they're secreting out some enzymes or some chemicals that they sense each other and they're going to start forming what we call gametotangia. Now, these gametotangia are basically extensions of the hyphae, and in those gametotangia are going to be a copy of a haploid nucleus. Before I continue explaining the sexual reproduction process, I'd like to define a term, and that is plasmodomy. We're going to say that we're going to start out with the haploid donor cell nucleus.
That's the positive strand. Its haploid nucleus is going to penetrate the cytoplasm and join that of the negative recipient or negative strain. So that result is we're going to form a cell that has two haploid nuclei.
One nuclei from the plus strand and one from the minus strand. So the result will be a formation of a size, zygosporangium. The zygosporangium at this moment has two nuclei.
These two nuclei are going to fuse together. So that brings us to the next term, karyogamy. So in this case, a plus nucleus and a minus nucleus will fuse together and will give you a single nucleus that is now deployed.
So this will be the first time in which a fungal cell will have two copies of the chromosomes. Okay, so within that zygosporangium, these cells may stay dormant for a while. It will develop a thick wall that will have sort of like a knobby type texture. And over time, that diploid nucleus will undergo a couple rounds of meiosis to rearrange the parent chromosomes in which it acquired.
Eventually, that thick coat around the zygosporangium will melt away and it will form a zygospore. That zygospore will start to germinate a hyphae, a haploid coenocytic hyphae. And just as you've seen before, that hyphae can specialize to form a sporangiofor, which will grow a sporangium that will be complete with sporangiospores.
And so the whole cycle will start all over again, and these sporangiospores can then reproduce asexually as shown before. So this basically brings my video on the zygomycota to a conclusion. I want to introduce you to some terms that are associated with this phylum and also go through the asexual and sexual reproduction of the fungi in the zygomycota phylum. In this process, I've covered these terms that you see on the slide. Feel free to go back in the video to see where I've used these terms and you should be familiar with all of these words when you've completed my video.
Thank you and thanks for joining me.