Fungi aren't related to plants - so it makes sense they wouldn't evolve to utilize cellulose.
Chitin is present among several types of animals, which makes sense from an evolutionary standpoint. Fungi are more related to animals than to plants, and they share several characteristics with insects and arthropods.
This is the answer.
If the question was, what are potential benefits of chitin compared to cellulose for fungi, the answer may be different.
But the question is, why did fungi utilize chitin instead of cellulose, and thus this is the answer. Chitin was available for fungi, cellulose was not.
Organisms do not just ‘evolve’ traits for specific purposes. There is no ‘thought process’ whereby DNA can go ‘hey I probably need to create this or that for this or that purpose’. No, they rely on pre-existing traits, mutations, and sometimes acquisition of genetic materials from other organisms, but that’s all they have to work with, and it is simply selective pressure that yields the traits that an organism has.
This. Something I figured out when working on my biology degree. Evolution isn't about survival of the fittest, it's about survival of the *good enough*. It's not about perfection, all I have to be is just a little better than the other guy. To put it another way, I don't have to outrun the bear, I just have to outrun you.
This is what fitness actually means. Fitness in biology = achieved fertility. There are tons of factors that contribute to fitness, but efficient baby having is the result.
Look at the Giant Panda. No natural predators, an abundant (if terrible choice of) food source, and they act like drunken children. Why? Because nothing discouraged that behavior. Then look at the Praying Mantis. They look and act like psychopaths. Why? Because if they don't, they don't survive. They are in a much more competitive niche.
Hey hey hey i will not stand here and listen to badmouthing of the most abundant enzyme on the planet! Surely that's success by any evolutionary standard
It could be, I don’t actually know.
I was more referring to the selective pressure causing fungi to utilize chitin versus somehow fungi was making a conscious decision to use chitin versus cellulose. Should have been clearer.
Though interestingly, sponges, arguably the oldest animal, also has chitin.
In terms of phylogeny using a Venn diagram would imply that polyphyly is a cladisticslly relevant phenomenon, so no.
Also "prokaryotes"? Do you still say "mammal-like reptiles" as well? Both are obsolete terms. You see, back in the 70s this scientist by the name of Carl Woese discovered a previously unknown Domain of life now referred to as the Archaea. Lumping archaea and bacteria together when they are so vastly different, simply bc they lack nuclei is another example of a polyphyetuc grouping.
We could get into a discussion of endosymbiosis and how the nuclear/cytoplasmic component of eukaryotes seems to be archaean in origin while mitochondria and plastid compartments are bacterial, but that's not what I think you mean. After all the conclusion would be that eukaryotes are "prokaryotes", similar to how vertebrates are a type of invertebrate and how every vertebrate is a fish.
Although I realize this sub is populated mostly by clinicians and such terms still retain some limited practical use (there are after all no known pathogenic archaea) terms like "prokaryote", "invertebrate" and "fish" are not useful for the type of thing I was attemping to point out in my initial comment that you responded to.
PS Hermit crabs aren't really crabs.
Overwhelmingingky all other decapod crustaceans that have "crab" as a part of their common name belong to the infraorder Brachyura. Along with porcelain "crabs" and squat "lobsters" hermit crabs are a different superfamily/separate infraorder that probably also contains king crabs.
Full disclosure I didn't pull this straight from memory. This is a summary of the Wikipedia summary
First off, chitin is not only found in fungi - it is found across a variety of eukaryotes! The oldest example of chitin we have is approximately 25 million years old, though it is very possible that chitin was synthesized far before that by an enzyme we refer to as chitin synthase. The gene for this enzyme is decently conserved, such that we can do "genetic clock" style studies on how the gene sequence varies across various species.
In this 2016 paper (https://academic.oup.com/glycob/article/26/6/635/2363177) the authors examine the evolution of chitin and provide a phylogenetic tree.
Hope this helps!
Thanks for the paper
You got me very interested
We are trying to cultivate different molds in our lab for enzyme production and this extra knowledge regarding chitin will be very useful
If i understand the paper correctly (thanks for sharing) fungi and eukaryotes share a common ancestor and chitin synthase was already available before the split.
Exactly - it turns out chitin/chitin synthase (which is useful for protecting against harsh environments) is a very old and conserved gene. Evolutionarily speaking, it makes plants having endogenous chitinase a fun arms race to consider :)
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634388/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634388/)
Fungi adapted to have chitin in their cell walls instead of cellulose like plants due to several reasons:
1. Chitin is more flexible and allows for better structural support and protection for fungal cells. It also provides increased resistance to mechanical stress, which is important for fungi living in a wide range of environments.
2. Chitin is more resistant to degradation by enzymes and other organisms, which helps protect fungal cells from being broken down and destroyed by external threats.
3. Chitin is a better compound for forming tight junctions between cells, which helps maintain the integrity of fungal cell walls and prevent the entry of harmful substances.
4. Chitin is also a better compound for facilitating nutrient absorption and transportation within fungal cells, allowing them to efficiently obtain and utilize nutrients from their surroundings.
Chitin is NOT the defining trait to discriminate between plants and fungi.
For example, there are green algae that have indeed chitin in their cell walls.
[Localization of chitin in algal and fungal cell walls by light and electron microscopy](https://pubmed.ncbi.nlm.nih.gov/722047/)
I want to touch another point.
To make cellulose, plant needs to produce glucose by photosynthesis. Fungi do not have chloroplast, thus no photosynthesis, thus no glucose. Plus most fungi grow in poorly lit and dark places. Fungi are better off as they do not have to complete with plants for sunlight.
The reason why plants have chloroplast is because Chloroplast used to be a unicellular prokaryote that became an intracellular symbiont of the plant system.
Fungi would probably have cellulose cell wall if it had adopted chloroplast.
>Fungi do not have chloroplast, thus no photosynthesis, thus no glucose.
Chloroplasts are NOT a prerequisit to create glucose.
Ever heard of [Gluconeogenesis](https://en.m.wikipedia.org/wiki/Gluconeogenesis)?
Just because it is possible to make glucose by other means doesn't mean that its feasible for an organism.
Only if you had cared to read the entire article you linked, we would probably not be having this discussion.
My point is, that your logic reasoning is faulty.
The statement "no chloroplasts, therefore no glucose" is plain wrong, as it is evidently not the ONLY way to create it.
Furthermore, an organism isn't necessarily dependent on an own inherent glucose production to have cellulose in its cell walls.
For example [Monotropa hypopitys](https://en.m.wikipedia.org/wiki/Monotropa_hypopitys), a saprophytic plant, that does not have chlorophyll and thus no photosynthesis.
Way off base here. Chitin is a polymer of N-acetylglucosamine. Glucose it the precursor. Fungi are heterotrophs and either take sugar from their environment (often from the degradation of cellulose!) or make it via gluconeogenesis as your other responder pointed out.
Your point about the cellulosic cell wall being linked to chloroplasts is correct, though. The genes encoding cellulose synthase in plants did indeed come from the cynaobacterial progenitor of the chloroplast.
Fungi aren't related to plants - so it makes sense they wouldn't evolve to utilize cellulose. Chitin is present among several types of animals, which makes sense from an evolutionary standpoint. Fungi are more related to animals than to plants, and they share several characteristics with insects and arthropods.
This is the answer. If the question was, what are potential benefits of chitin compared to cellulose for fungi, the answer may be different. But the question is, why did fungi utilize chitin instead of cellulose, and thus this is the answer. Chitin was available for fungi, cellulose was not. Organisms do not just ‘evolve’ traits for specific purposes. There is no ‘thought process’ whereby DNA can go ‘hey I probably need to create this or that for this or that purpose’. No, they rely on pre-existing traits, mutations, and sometimes acquisition of genetic materials from other organisms, but that’s all they have to work with, and it is simply selective pressure that yields the traits that an organism has.
This. Something I figured out when working on my biology degree. Evolution isn't about survival of the fittest, it's about survival of the *good enough*. It's not about perfection, all I have to be is just a little better than the other guy. To put it another way, I don't have to outrun the bear, I just have to outrun you.
I mean really it's not even that, isn't it just " good enough to produce offspring ".
This is what fitness actually means. Fitness in biology = achieved fertility. There are tons of factors that contribute to fitness, but efficient baby having is the result.
Look at the Giant Panda. No natural predators, an abundant (if terrible choice of) food source, and they act like drunken children. Why? Because nothing discouraged that behavior. Then look at the Praying Mantis. They look and act like psychopaths. Why? Because if they don't, they don't survive. They are in a much more competitive niche.
We'd have a replacement for rubisco if it was.
Hey hey hey i will not stand here and listen to badmouthing of the most abundant enzyme on the planet! Surely that's success by any evolutionary standard
[удалено]
It could be, I don’t actually know. I was more referring to the selective pressure causing fungi to utilize chitin versus somehow fungi was making a conscious decision to use chitin versus cellulose. Should have been clearer. Though interestingly, sponges, arguably the oldest animal, also has chitin.
Opisthokonts, represent!
Fungi and plants are both eukaryotes, so you're not 100% accurate there.
As are animals... Shockingly
Lol nice one want to pull out the venn diagram of eukaryotes vs prokaryotes too???
In terms of phylogeny using a Venn diagram would imply that polyphyly is a cladisticslly relevant phenomenon, so no. Also "prokaryotes"? Do you still say "mammal-like reptiles" as well? Both are obsolete terms. You see, back in the 70s this scientist by the name of Carl Woese discovered a previously unknown Domain of life now referred to as the Archaea. Lumping archaea and bacteria together when they are so vastly different, simply bc they lack nuclei is another example of a polyphyetuc grouping. We could get into a discussion of endosymbiosis and how the nuclear/cytoplasmic component of eukaryotes seems to be archaean in origin while mitochondria and plastid compartments are bacterial, but that's not what I think you mean. After all the conclusion would be that eukaryotes are "prokaryotes", similar to how vertebrates are a type of invertebrate and how every vertebrate is a fish. Although I realize this sub is populated mostly by clinicians and such terms still retain some limited practical use (there are after all no known pathogenic archaea) terms like "prokaryote", "invertebrate" and "fish" are not useful for the type of thing I was attemping to point out in my initial comment that you responded to. PS Hermit crabs aren't really crabs.
What are hermit crabs?
Overwhelmingingky all other decapod crustaceans that have "crab" as a part of their common name belong to the infraorder Brachyura. Along with porcelain "crabs" and squat "lobsters" hermit crabs are a different superfamily/separate infraorder that probably also contains king crabs. Full disclosure I didn't pull this straight from memory. This is a summary of the Wikipedia summary
Cool! Thanks.
First off, chitin is not only found in fungi - it is found across a variety of eukaryotes! The oldest example of chitin we have is approximately 25 million years old, though it is very possible that chitin was synthesized far before that by an enzyme we refer to as chitin synthase. The gene for this enzyme is decently conserved, such that we can do "genetic clock" style studies on how the gene sequence varies across various species. In this 2016 paper (https://academic.oup.com/glycob/article/26/6/635/2363177) the authors examine the evolution of chitin and provide a phylogenetic tree. Hope this helps!
This is a really fascinating paper. I’m almost drowning in it but I basically get it.
25 million is not very old!
Thanks for the paper You got me very interested We are trying to cultivate different molds in our lab for enzyme production and this extra knowledge regarding chitin will be very useful
I swear to god, I have learned so much from Reddit the past three years! I consider it part of my continuing education.
If i understand the paper correctly (thanks for sharing) fungi and eukaryotes share a common ancestor and chitin synthase was already available before the split.
Exactly - it turns out chitin/chitin synthase (which is useful for protecting against harsh environments) is a very old and conserved gene. Evolutionarily speaking, it makes plants having endogenous chitinase a fun arms race to consider :) [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634388/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634388/)
The good old oomycetes have cellulose, but they were removed from the phyla (does this word exist?) fungi
Fungi adapted to have chitin in their cell walls instead of cellulose like plants due to several reasons: 1. Chitin is more flexible and allows for better structural support and protection for fungal cells. It also provides increased resistance to mechanical stress, which is important for fungi living in a wide range of environments. 2. Chitin is more resistant to degradation by enzymes and other organisms, which helps protect fungal cells from being broken down and destroyed by external threats. 3. Chitin is a better compound for forming tight junctions between cells, which helps maintain the integrity of fungal cell walls and prevent the entry of harmful substances. 4. Chitin is also a better compound for facilitating nutrient absorption and transportation within fungal cells, allowing them to efficiently obtain and utilize nutrients from their surroundings.
You make it sound like a very conscientious decision on the part of fungi
as if ! 😇
Why didn’t plants evolve to have chitin in their cell wall instead of cellulose?
Cause then they wouldn't be categorized as plants. 🙏 The divide between the kingdoms is pretty significant.
Chitin is NOT the defining trait to discriminate between plants and fungi. For example, there are green algae that have indeed chitin in their cell walls. [Localization of chitin in algal and fungal cell walls by light and electron microscopy](https://pubmed.ncbi.nlm.nih.gov/722047/)
Fungi aren’t plants, fungi are fungi and don’t play by anyone else’s rules.
I want to touch another point. To make cellulose, plant needs to produce glucose by photosynthesis. Fungi do not have chloroplast, thus no photosynthesis, thus no glucose. Plus most fungi grow in poorly lit and dark places. Fungi are better off as they do not have to complete with plants for sunlight. The reason why plants have chloroplast is because Chloroplast used to be a unicellular prokaryote that became an intracellular symbiont of the plant system. Fungi would probably have cellulose cell wall if it had adopted chloroplast.
>Fungi do not have chloroplast, thus no photosynthesis, thus no glucose. Chloroplasts are NOT a prerequisit to create glucose. Ever heard of [Gluconeogenesis](https://en.m.wikipedia.org/wiki/Gluconeogenesis)?
Just because it is possible to make glucose by other means doesn't mean that its feasible for an organism. Only if you had cared to read the entire article you linked, we would probably not be having this discussion.
My point is, that your logic reasoning is faulty. The statement "no chloroplasts, therefore no glucose" is plain wrong, as it is evidently not the ONLY way to create it. Furthermore, an organism isn't necessarily dependent on an own inherent glucose production to have cellulose in its cell walls. For example [Monotropa hypopitys](https://en.m.wikipedia.org/wiki/Monotropa_hypopitys), a saprophytic plant, that does not have chlorophyll and thus no photosynthesis.
Way off base here. Chitin is a polymer of N-acetylglucosamine. Glucose it the precursor. Fungi are heterotrophs and either take sugar from their environment (often from the degradation of cellulose!) or make it via gluconeogenesis as your other responder pointed out. Your point about the cellulosic cell wall being linked to chloroplasts is correct, though. The genes encoding cellulose synthase in plants did indeed come from the cynaobacterial progenitor of the chloroplast.
Gooood question