If you’re a keen biologist and you’ve heard the term sporulation being used again and again, you may not know what it actually refers to – or how it works. You can probably guess from its name that it involves spores, but there’s a lot more to it than that.
In our helpful guide below, we’ll define sporulation, as well as have a detailed look at the processes it undertakes with different types of organism. Read on!
What Is Sporulation?
To put it simply, sporulation is the emergence and creation of spores from vegetative cells when the environmental conditions are not favorable.
In this sense, you can understand it as an adaptation to the conditions, with it allowing the organism to survive conditions that it is not normally equipped for – such as a lack of nutrition, or extreme levels of temperature.
Spores are structures with multiple layers, and are often temporarily inactive. The spores come from vegetative cells, which are cells that are actively growing, which is quite different.
The spore itself can then help to keep the organism’s genetic content safe during the unfavorable conditions.
Spores contain other important pieces, such as enzymes and certain acids, that will help it to grow properly when they are back in good environmental conditions.
Overall, it is during the bad conditions that some of the vegetaive cells alter in distinct ways, which create the spores, something which they would not typically produce in normal conditions.
Types Of Spores
A variety of organisms produces spores: algae, bacteria, fungi, plants, and protozoa. We’ll be going into the process of sporulation in a few of them later on. The spores vary by organism.
Spores also come in many different types. Some are asexual spores, such as exogenous ones, while others (such as zygotes) are sexual. On the other hand, some are classified as “endospores”, which are created within the organism.
Bactria do this. Their contrast is “exospores”, which you can probably guess the definition of – they grow outside the cell. Other contrasts in spore types are megaspores and microspores.
On top of all those types, you can also get “vegetative spores”.
Sporulation In Different Organisms
It’s not time to look at the process of sporulation across different types of organism, and how it varies with each one.
Sporulation Process In Amoeba
Amoeba are single cell protozoa that can alter their shape. They generally reproduce asexually, using a variety of different methods, such as regeneration and multiple fission (which is where their nucleus is divided, as well as their cell body).
Another method is through sporulation and encystment, which is what we’ll be covering.
Like other types of protozoa, amoeba will protect themselves from harsh environmental conditions by creating a cyst wall, in a process which is known as encystment. Some bacteria have even been known to survive themselves by entering the cyst.
The process of encystment begins with the withdrawal of their pseudopodia, which is an impermanent protrusion on their surface that helps them eat and move. After that, they form a protective and hard layer, before finally entering dormancy.
Scientists can study the encystment process without creating the unfavorable conditions, instead using a non-nutrient medium (such as an agar) to provoke the amoeba.
Once they have done that, they have been able to study how it reacts. Under their experiments, scientists have noted how the mobility rate of the amoeba changes and how its cells start to shrink.
On top of that, the body can change its shape into something more akin to a sphere.
On top of all that, scientists have also found that cyclic AMP (cyclic adenosine monophosphate) helps to perform vital roles in the encystation, as it always does with many biological processes.
In this instance, taurine (or other type) amines are connected to certain receptors that are on the membrane of the amoeba, which then activate adenylate cyclase there, which helps kick the encystation sequence into action.
The changes don’t stop here, though, as countless other molecular and chemical alterations occur during the process of encystment. For example, there is a notable loss of proteins, as well as DNA and RNA, though some amoeba have learned to make their own RNA.
On top of this, the form of metabolism alters during encystment. While the amoeba uses aerobic (with air) metabolism before, it changes to anaerobic (without air) metabolism , before the full dormancy at the finish point.
In addition to those, their phosphorylated compounds begin to have a rapid turnover. Finally, scientists also noticed that the amoeba begins to incorporate glucose compounds into a polysaccharide, which are carbohydrates.
Sporulation occurs in many different amoebas, even the more social ones. For example, sporulation occurs with dictyostelium discoideum, which is a type of amoeba that dwells in soils.
When sporulation occurs in amoeba such as these, the result is a unique mass group of spores that are held with the help of a tapering stalk.
Amoeba have a response to being starved, which is that all their cells come and join together, creating a whole cluster that becomes a “migratory slug”. This slug has over 100,000 cells in it, which is impressive and large.
Once they have formed, the tip of the mass has some cells on its tip that help bring the slug upright and create a cellulose tube. The slug has to move to a location with conditions that are favorable for its growth and health if it is to transform.
When cells are entering into that cellulose tube, they all add to its overall strength, because they undergo the process of vacuolization – which is where vacuole structures are formed.
The prestalk cells on the tip that helps to put the slug upright then climb and enter into the stalk too, followed by the prespore (exactly as it sounds, the part that will become part of the spore).
The stalk is eventually finished and this prespore encloses and becomes dormant spores. These are made safe and protected by a coating made of protein.
Sporulation Process Of Fungi
Sporulation of fungi is a very important one to study out of all the organisms that can have the process occur to them, because they create a wide range of spores that vary in all kinds of different factors.
For example, they have lots of different shapes and features, as well as the fact they come in a wide variety of different sizes.
The spores can be produced in two different ways, and each have different methods of operating afterward.
The first way is that the spores can be created sexually, by using the process of meiosis, where the cells divide and the number of chromosomes in the gametes is lowered. Spores that are produced this way stay dormant to help with survival.
The other way is when spores are created asexually, and it’s these spores that are then used for dispersal. Mitosis is used to create these spores, which is a process where one cell divides into two identical other cells, known as daughter cells.
These spores are created in big numbers. The fact that they are all identical in their genetic build plays a big and helpful part, because it lets them help with reproduction when they are dispersed and land on the correct substrates.
Fungi spores have lots of different structures and sizes, and these all help them to be dispersed in the most effective manner.
When we talk about dispersion, we are referring to lots of different techniques: the wind may carry the spores, or perhaps some water will move them away too.
Sometimes they can even nestle in the fur of an animal, and that animal then moves them far away, where they can dislodge and settle again.
Types Of Fungi Spores
As we mentioned before, there is a whole wide range of different types of spores that comes from all different kinds of fungi.
We’re going to go through a few of the main types of fungi now, highlighting how they are all unique and the kind of spores that they help to create.
One key group of fungi is “Ascomycota”. These produces both asexual and sexual spores. The asexual spores are known as conidia, which are usually produced on the tip of a hyphae, and detahc when it has matured.
On the other hand, the sexual spores are named ascospores.
Another main group of fungi is “Basidiomycota”, which primarily create sexual spores. These are named similarly to the fungi that creates them, being scientifically named as basidiospores.
A third key group of fungi is known as “Zygomycota”, and these are like Ascomycota in the sense that they will produced spores that are both sexual and sexual. The sexual spores are known as zygospores, while the asexual spores are named sporangiospores.
It is worth noting a further interesting type of fungal spore known as the chlamydospore. These have a thick wall that helps to keep their interior contents safe from outside threats.
But how are they produced? Well, it’s all down to conditions that aren’t favorable. When that is the case, and the environment is doing the fungi no favors, then the chlamydospore spore develops from the hyphae.
Sporulation Process In Bacteria
Bacteria is another key organism with which sporulation can happen, and such a thing happens in all kinds of settings: water, soil, air, etc.
Many of the bacteria that are capable of creating spores exist in shapes that are similar to a rod, and are known more scientifically as “Gram-negative bacilli”. You may be wondering why they are referred to as “gram-negative”.
To put it very simply, it refers to the Gram staining method that is used to help identify and differentiate different types of bacteria. With these specific bacteria, they do not keep the crystal violet stain that is typically used in the Gram staining sequence.
When it comes to Gram-negative bacteria, some have been proven by scientists as being capable of creating spores. However, the number is very low.
This is because there are only a few species of them, and they are only found in a few different genus on top of that. However, a bacteria that has been recorded as being able to produce spores is the filamentous cocci.
The spores that they can form are known as endospores, which are tough and do not reproduce.
Types Of Spores
There are four different types of spore that can be produced by bacteria, and whatever type is made depends entirely on the type of bacteria that is involved in the process.
We have mentioned these just earlier, and they are created within the organism. They are the most common type of spore to be produced, and are most commonly produced by a variety of genus bacteria.
One of these is the bacillus genus, which are shaped like a rod. An example of a bacterium from this genus would be the bacillus anthracis. Another bacteria genus that creates endospores is clostridium.
An example bacterium of this genius would be clostridium botulinum, which is also rod-shaped, as well as being anaerobic.
The third type of most popular bacteria genus is sporosarcina, which has example bacterium such as sporosarcina ureae.
Endospores as a whole, especially when compared to other kinds, are the most defensive type, meaning that they can survive environmental conditions that are on the harsher side.
Why? They have a protective coat made up from many layers of proteins. On top of that, they have a high concentration of calcium, as well as high amounts of SASP and dipicolinic acid.
These are the opposite of endospores in a sense, because these spores are created outside the organism, rather than inside. When it comes to bacteria, exospores are only produced by members of Actinobacteria phylum.
However, this is one of the largest phyla of bacteria, so there’s plenty to choose from. When the spores are created, it’s done through budding with mycelium. Budding is the term given to a form of asexual reproduction.
These spores are hardy, able to endure unfavorable conditions of the environment, much better than other types of cell.
These are cells that are capable of grouping together when faced with difficult environmental conditions, allowing them to survive as a pack rather than perish individually.
They aren’t the most resistant to bad conditions though, but their waterproof cell wall helps. These types of cells are non-reproductive.
These are also known as resting cells. They are capable of enduring a wide variety of harsh conditions, such as high temperatures and UV lights being shone on them.
On top of that, they can survive dessication, which is the name given to when something is dried out thoroughly.
This certain type of spore is created inside the fruiting body of their parent bacteria. “Fruiting body” is the name given to structures with lots of cells where the spores are born.
The Sporulation Process
If a bacteria is put under unfavorable conditions, or is beginning to lack nutrition, it won’t actually immediately start the process of sporulation. Instead, the bacteria will try to relocate to a place with conditions that are more favorable for it.
It uses processes like chemotaxis to be able to get there, which allow it to travel. On top of that, it may simply just adapt to the new, harsh conditions. If that doesn’t work, they might even try to alter the way that they reproduce.
It is only after all the options have been exhausted that the bacteria will decide to perform sporulation.
It can only do this, however, if it has a functional Krebs cycle, which is to do with how they get their energy and aerobically respire. In addition, it also needs to have chromosome integrity.
If conditions are right, then the vegetative growth period can end. Inside the bacteria there is a phosphorelay system which monitors the conditions of the environment and then sends that information to the master regulator, which activates it.
That regulator, known as Spo0A, will help to monitor the expression of 121 genes that are used in the sporulation process. Once that’s done, sporulation can begin to take place across many stages.
The Spo0A master transcriptional regulator is activated, and then the replication of chromosomes begins. During this, each chromosome goes over to the opposite poles within the cell.
However, not all move. One of them stays in the mother cell, while all the other cells move and settle in the forespore – the precursor for the spore.
In the second stage, the cell has its “origin-proximal” regions attached to the opposite poles. On top of this, the chromosomes have their DNA stretch, which creates axial filaments.
These are groups of flagella which wrap themselves between the outer membrane and the cell wall, overall going around the body of the cell.
While the cell divides itself, about 3/10s of the earlier-mentioned proximal part gets covered, and becomes the forespore. The forespore contains chromosomes and is covered entirely by membrane.
The cortex of the peptidoglycan is synthesized. The peptidoglycan is a firm envelope that covers the cytoplasmic membrane of the bacteria.
The proteinaceous coat is then created. This is where the mature spore gets covered by two layers, including the outer coat of various proteins, and the cortex that has special peptidoglycan in it.
The mother cell of the bacteria then has lysis happen to it, which essentially means disintegration, breaking down. Some of the material that’s leftover from this lysis can then be used on the spore coat, making it bigger, better, and more protective.
Spores that are mature are put forth into the environment. They are extremely robust and can survive harsh environmental conditions such as radiation and high temperatures.
When the overall environment gets better, in terms of being compatible with the bacteria, then the spore can grow, while the bacterial organism returns to its former vegetative growth – having survived.
Sporulation Process In Yeast
We’ll be looking at “saccharomyces cerevisiae”, which is used for baking and brewing. Yeast is a type of fungus.
Just like bacteria, fungi attempt a variety of different adaptations and movements when they face environmental conditions that don’t work for them. Only when they’ve done these will they be provoked into sporulation.
For example, if the yeast is finding it difficult to get nitrogen, and the sources are low, then it might try to alter its morphology. It may also be the case that there is a lack of the nutrients that the yeast needs to survive and remain active and healthy.
That isn’t to say that the environment doesn’t have nutrients within it, they just may not be the ones that yeast thrives off.
If the yeast can’t adapt to the conditions, then it begins its creation of spores in a process called meiosis, which has many stages.
This first phase of the process sees the cell division sequences change, going from a mitotic cycle to an S phase of meiosis. While this is happening, recombination of the homolog happens, as does replication of DNA. On top of that, the RNA processing is altered.
During this second period, lots of different processes happen to the structures and functions of the cells. A haploid nuclei is created from the meiotic process, and then new cells come from that.
On top of that, the nucleus is fully removed from the cytoplasm, and the prosperous enlarge and swallow the nuclei. The space between the prospores and the nuclear membrane also sees organelles come to inhabit it, too.
In the final steps, a thick wall starts to emerge around all the spores, which helps to mature them too. The spores’ nucleus begins to see “chromatic compaction”, and a few of the organelles begin to regenerate.
On top of all those, the membrane of the prospore seals itself off and closes.
Once all that has been completed, then the yeast has successfully performed sporulation. This will help it to survive environmental conditions that it was not well suited to.
Sporulation is a fascinating process, allowing many different types of organisms to create spores and survive environmental conditions they struggle with. These organisms include bacteria, amoeba, and fungi – with yeast one of the types of fungi.
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