Multicellular chemotrophs?

Question

What characteristics might define a group of multicellular chemosynthetic organisms (similar to that of bacteria living in earth's hot springs and deep sea vents, but relatively more complex, as mushrooms (a fungus with multiple cell fates) and lichens (a symbiosis between a fungus and an alga) are more complex than yeast)? For example, would they have to be sessile, or could they be motile? Vascular or nonvascular? Would their lifestyle necessitate a unique anatomy or mode of reproduction, or might they appear to be just another kind of plant or fungus?

Answer 1

Yeast is considered part of the fungus kingdom. Mushrooms are the "flowers" of fungi. So, you are basically asking if a species was more similar to a fungus than to a fungus, could it have characteristics of a fungus? Uh, maybe.
I'm not a biologist by any stretch of the imagination, but I think it is safe to say that complexity is roughly proportional to the size of a organism's genome (see chart in https://en.wikipedia.org/wiki/Genome_size).
I don't dispute that lichen - which are a symbiotic assembly of several different organisms - are more complex than any of its (two or three) component species, by definition.

Aside from those problems with your question, to answer what characteristics they'd have requires you to more clearly explain where they're getting their nutrients from - and what predators and competitors they have in their ecology. If you're familiar with the various life cycles and lifestyles of fungi, you no doubt know that they have all sorts of interesting characteristics.
They aren't motile because they don't need to be. As an organism increases in complexity, the value of the individual (the "investment" in that individual in terms of energy and time) increases (as far as its genes are concerned). Therefore, more complex behavior will be created only when and where it's needed.
Given the significant size limitations of diffusion, vascular structure will be necessary above a fairly small size. You'll note the overlap in genome size between plants and fungi in that Wikipedia chart and you can also compare the size and mass of a Giant Redwood with a Blue Whale. It's safe to say that the largest organisms in the world are plants, although exactly which plant is largest is being debated.

Size isn't necessarily the same as complexity, of course. I guess the best answer to your question is that it depends. If the chemicals flow from a steady fixed source, then a sessile lifestyle could work, if the flow varies (by season, or availability, or weather) then it may need to pack up and move to greener pastures.

Answer 2

If your creatures only live around hydrothermal vents and hot springs, they will have to be motile OR have a dispersal phase of their lifecycle (like spores or planktonic larvae drifting on the currents) because vents can be short-lived. They are also often widely spaced. See this article.

The lifetime of hydrothermal vents and their communities may be very short, a few decades, or very long depending on the rate of sea-floor spreading in the active region. Local communities of tubeworms, destroyed by fresh lava eruptions, can regrow within 2 to 3 years (Lutz and Haymon, 1994). Vents and vent fields are often separated by hundreds of kilometres and the question of how new vents are colonized is still being studied. Biologists at the Plymouth Marine Laboratory (UK) are studying larval DNA of vent animals to help trace their dispersal and relationships with populations elsewhere. American scientists have discovered species of animals normally only associated with vents, on whale carcasses on the deep-sea bed. They speculate that these carcasses provide ephemeral stepping-stones which allow animals to cross more easily between vents. However, recently it has been discovered that in some areas, such vents are very common and can be found at distances of only 20 miles or so apart. In these cases, spread from one vent to another would be relatively easy.

The main problem for your chemosynthetic organisms is that they are likely using chemical reactions which provide less energy than the oxygen producing/burning photosynthetic organisms. So they just do everything slower. If it takes a year for a photosynthetic plant to grow to maturity, it might take 3 or 4 years for a chemosynthetic one to reach the same size.

Answer 3

From Wikipedia:

Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environments. These molecules can be organic (chemoorganotrophs) or inorganic (chemolithotrophs).

So I am a chemotroph by virtue of the oxidation of cheese going on right now inside me.

I think that you mean chemolithotrophs: a multicellular organism with energy metabolism like that of a sulfur bacterium or something like that.

One could make a strong case that only prokaryotes do any energy metabolism. Eukaryotes have tamed commensal prokaryotes safely ensconced within their cells which do the work. Mitochondria are the degenerate prokaryotes inside my cells working on the cheese. Chloroplasts are the ones in plants that use solar energy to reduce carbon.

@Andrew nails it with his question: how is the proposed organism different? Clams and worms with commensal chemolithotrophs have prokaryotes which are not as degenerate as our mitochondria but at the end of the day it is a matter of degree.

Your organism would be either be totally bizarre (in which case make up whatever) or a eukaryotic cell with tame commensal prokaryotes of your choice depending on what kind of energy metabolism you want. If these are archons that are poisoned by oxygen then I could imagine a system for your multicellular beast which incorporates something like root nodules in nitrogen fixing plants. Within these root nodules are prokaryotes which do the nitrogen chemistry, and the plant gives them room and board and protects them from oxygen with oxygen-scavenging leghemoglobin.

Motile creatures mostly are chemoorganotrophs like me; chasing around food or wandering from plant to plant, eating other organisms. The rare exceptions are things like the aforementioned worms with commensal chemolithotrophs or organisms like jellyfish that contain photosynthetic commensals. Inorganic energy sources will not try to escape. Your organism could be sessile if the inorganic energy source were a constant - for example a steady flow of reduced iron from a hydrothermal vent. If your energy sources were spread out - maybe sulfur granules? - then it would benefit your organism to be able to wander around seeking them.

Answer 4

A good question. The funniest thing is that organisms you described actually lived on Earth at the very dawn of life. These organisms are said to be the "inventors" of photosynthesis, but you have to understand that they existed before photosynthesis.

Have a look: https://en.m.wikipedia.org/wiki/Microbial_mat

Answer 5

Multicellularity ultimately allows the delegation of tasks to different tissues. But that comes at a cost - Reproduction is far easier for bacteria than for us. It's not evident that we are winning the evolution race just because we are bigger with brains.

We have consciousness, and the internet, so we still think it is a good trade, though.

A multicellular chemosynthesizer (by definition, an organism that synthesizes complex carbon using chemical energy) needs to have access to that chemical energy. The chemical energy we commonly see on earth, is H2S. The electrons in H2S have more energy than the (H2O) electrons used in photosynthesis. Photosynthesis can get by with low energy electrons, because the sun (photo) provides the energy.

So, if you are limiting yourself to H2S, then I would think your organisms should be sessile, and associated with reducing environments. this means not a lot of O2, and that in turn means not a good chance for multicellularity, since oxygen is (almost universally used by multicellular organisms and) such a great electron acceptor for respiration. Anything that respires (i.e. most of life) and has learned to harness oxygen, is essentially harnessing fire (another use of oxygen) because oxygen is so reactive. It will take any electron you give it - even the low energy ones.

All of this is to say: it is unlikely to have a well developed chemosynthesizer that is multicellular, because oxygen is such a great basic ingredient for multicellularity, and H2S (which is the chemical energy that usually drives chemosynthesis) exists in reducing environments, precluding oxygen.

But sessile is a good bet.