Chapter 15: Ecological Diversity of Bacteria

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Okay, so ready to dive in.

Today we're going microscopic,

microorganisms, but specifically, their ecological diversity.

How do these tiny life forms live, interact, carve out their existence?

Got a whole chapter on this and it gets pretty intricate.

Yeah, it's fascinating stuff.

You know, we often talk about microbes in terms of their metabolism, what they eat, how they get energy, but today is all about their ecological roles, where they live, their interactions, how they shape their environments.

It's a big piece of understanding these microbes along with their metabolic diversity and of course their evolutionary history, the phylogenetic side.

Right, so microbes metabolism hints at its ecological role, but it's not the whole story, right?

There's more to it than just what chemical reactions they can do.

Exactly, think about it.

Two bacteria, both breaking down sugars for energy.

One might have a flagellum, that whip -like tail, so it zips around finding food in open water.

The other, maybe it's sticky, clinging to surfaces in a nutrient poor area.

Same metabolism, but their morphology, their motility, that dictates their ecological niche.

It's not just what they can do, it's how and where they do it best.

Makes sense.

And this chapter points out something else interesting.

Sometimes microbes that are really far apart evolutionarily, they can end up with similar ecological roles and vice versa.

Evolution playing tricks, it seems.

Absolutely.

That family tree, the phylogeny, it doesn't always tell you everything about a microbes ecology.

You've got gene loss, where organisms ditch genes they don't need anymore.

Convergent evolution, where unrelated microbes find the same solutions to the same problems.

And then there's horizontal gene transfer, genes jumping between organisms.

It all makes things more complex, more interesting.

It reminds us that life finds a way, but not always in a straight line.

So we're unpacking this ecological diversity, all the twists and turns, as laid out in this chapter.

And I think a great place to start is with the phototrophic bacteria, the ones that figured out how to use light for energy.

Perfect place to begin.

And what's amazing is photosynthesis, it started with bacteria.

And the earliest versions, anoxygenic photosynthesis didn't even make oxygen.

No oxygen.

So what did they use instead of water?

The chapter mentions hydrogen gas, H2, ferrous iron, F2 plus oxida, even hydrogen sulfide, H2S.

Not exactly the stuff of life as we know it.

No, but it worked for a long time.

And these anoxygenic phototrophs, they're still around, thriving in environments where those electron donors are available.

But then along came oxygenic photosynthesis.

That was a game changer.

Using water, releasing oxygen, that's the cyanobacteria, their invention.

And it reshaped the planet, made way for oxygen -dependent life, like us.

Every breath we take, that's thanks to those ancient bacteria.

Wow, it's hard to wrap your head around that.

So both types, anoxygenic and oxygenic, how do they actually grab that light energy?

It's not just one pigment, right?

Yeah.

No, chlorophyll -like pigments are key, but they also use accessory pigments.

Think of it like having different solar panels catching different wavelengths of light, maximizes their energy harvest.

And then that energy goes to reaction centers, protein complexes in the membranes.

That's where light energy turns into chemical energy, ATP.

And there are two main types of these reaction centers, right?

The FES type and the Q type.

What's the difference, functionally?

It comes down to their components.

The FES type has iron sulfur clusters.

You find it in photosystem I of oxygenic phototrophs, also in green sulfur bacteria and heliobacteria, the anoxygenic types.

Then there's the Q type with kinones.

It's in photosystem II of oxygenic phototrophs and in the anoxygenic purple sulfur and purple non -sulfur bacteria.

They handle electrons differently during those light -dependent reactions.

And to make it all more efficient, they pack these pigments and reaction centers into internal membranes, more surface area to soak up the light.

Exactly.

So let's talk about some specific groups.

Let's And diverse.

The chapter talks about all sorts of shapes, single cells, spheres.

Those are in groups like crococales and fluorocapsules.

Then you've got filaments.

Those are oscillatoriales, nostocales, and stegomatales.

And diverse pigments too.

They have chlorophyll, a crucial for oxygenic photosynthesis, and then phycolelins.

These give them that bluish -green color often and help them capture light that chlorophyll misses, especially underwater.

And it's not just about sunlight to They're big players in nutrient cycles too.

Carbon dioxide, they fix that with the Calvin cycle, just like plants.

Exactly.

And many of them are nitrogen fixers too, taking atmospheric nitrogen into converting it to ammonia, something usable.

Some have special cells, heterocysts, where nitrogen fixation happens, no oxygen allowed, protects the nitrogenase enzyme.

Others separate it in time, fixing nitrogen at night when they're not photosynthesizing.

So they make the air we They're the base of the food web, and they're fertilizing the environment with nitrogen, multitasking at its finest.

Though the chapter does mention a downside.

Some can produce toxins, cause those harmful algal blooms.

Right.

It's important to remember that.

Their contributions are huge, but under certain conditions, some species can grow too quickly, release toxins.

That impacts animals, humans, water quality.

Even essential organisms can have downsides.

All right.

Let's move on to the purple sulfur bacteria.

They're anoxygenic, so no oxygen production.

They use hydrogen sulfide and they're part of the gamma proteobacteria.

What's cool about them is how they deal with the sulfur.

They oxidize it from hydrogen sulfide and they store it as granules.

You can actually see them inside or outside their cells.

If the hydrogen sulfide runs out, they can oxidize that stored sulfur further to sulfate.

They've got bacterial chlorophyll A or B to catch light and a Q -type photosystem.

And for carbon dioxide fixation, they use the Kelvin cycle.

And they're picky about where they live, right?

They need no oxygen, but sunlight and lots of hydrogen sulfide.

Muddy lake bottoms, salt marshes, sulfur springs.

And they get that purple color from carotenoids.

Exactly.

Those carotenoids, they do more than just color.

They're accessory pigments, expanding the range of light they capture.

And they're antioxidants, protecting them from damage.

They've carved out a specific niche where light and sulfur meet.

Now onto the purple non -sulfur bacteria.

A bit of a misnomer, they can handle small amounts of sulfide,

but the chapter really highlights their metabolic flexibility.

Absolutely.

They're alpha -proteobacteria and beta -proteobacteria, and they're often

photoheterotrophic, using light for a boost, but mainly getting carbon from organic compounds.

And they're not picky.

All sorts of compounds work.

Their color varies, too.

Different carotenoids at play.

So not tied to hydrogen sulfide like their sulfur cousins.

They have bacterial chlorophyll A or B, a Q -type photosystem.

And the chapter mentions they can even do fermentation or anaerobic respiration.

Right.

They're adaptable.

And a lot of them can fix nitrogen, too, adding to their ecological role.

The chapter also talks about the photosynthetic gene cluster.

All those genes for photosynthesis bunch together, regulated together.

And this cluster can even be transferred horizontally, spreading those photosynthetic abilities.

It shows how evolution can jumpstart adaptations.

Fascinating.

Now to another colorful group.

What?

The green sulfur bacteria.

They seem to prefer even more extreme environments.

They do.

These are anoxygenic phototrophs, part of the chlorobi phylum.

And they're stripped anaerobes.

Oxygen is toxic.

They use hydrogen sulfide or even elemental sulfur as electron donors.

And their carbon fixation pathway is unique.

The reverse citric acid cycle, it runs in reverse, shows how evolution finds different solutions.

And their pigments are different, too.

Bacteria chlorophylls, C, D, or E, those are in chlorosomes, special light harvesting structures.

And then bacteria chlorophyll is their FES -type reaction center.

Yeah.

Those chlorosomes are super efficient at capturing light, like concentrated antennas.

These bacteria often live deep down, low light, lots of hydrogen sulfide.

Their adaptations let them thrive where others wouldn't.

And some even consortia, partnerships with chemo organotrophic bacteria, a real web of interactions down there.

Then we have the green non -sulfur bacteria, also called filamentous anoxygenic phototrophs.

They belong to the chlorophyll C phylum.

And the chapter says they're happiest as photo heterotrophs, using simple organic carbon.

That's right.

They also have chlorosomes with bacterial chlorophyll C, like the green sulfur bacteria.

But their reaction center is the Q -type with bacterial chlorophyll A.

That mix of features is pretty unusual.

And unlike those strict anaerobes, many green non -sulfur bacteria can grow in the dark using aerobic respiration, gives them more flexibility when light is scarce.

We're seeing a whole range of light harvesting strategies here.

Now, onto the heliobacteria.

They seem to have a more limited repertoire.

They do.

These are anoxygenic phototrophs, part of the firmicutes.

They have an FES -type photosystem and a unique bacterial chlorophyll, bacterial chlorophyll G.

They're mainly photo heterotrophs, but picky about their organic compounds.

Interestingly, some can switch to chemotrophic growth in the dark, energy from chemicals, not light.

So not totally reliant on the sun adds to their adaptability.

And the chapter introduces two more groups more recently discovered.

The phototrophic acetobacteria and the phototrophic gematoma notetes.

They sound like frontiers of research.

They are.

The phototrophic acetobacteria, chlorocytobacterium thermophilum is a good example.

They like it hot, thermophilic, and they can tolerate some oxygen.

Unusual for anoxygenic phototrophs.

They've got chlorosomes with bacterial chlorophyll A and C and FES -type photosystem,

but they need organic carbon.

They're photo heterotrophs, light and food in a hot, sometimes oxygen -rich environment.

Specific needs for sure.

What about the phototrophic gematoma notetes?

Gematomonas phototrophica is the one to know there.

They're aerobic facultative photo heterotrophs.

So they mainly get energy from aerobic respiration using oxygen, but they've got the machinery for photophosphorylation too.

ATP from light.

It's a supplement, a boost when it's sunny, like a hybrid engine.

It's incredible.

All these ways bacteria have evolved to get energy.

Now, the chapter shifts gears, looks at ecological diversity based on specific metabolic traits, not just photosynthesis.

And a good place to start is the nitrogen fixers, the de -azotross.

Absolutely essential organisms.

They take nitrogen gas N2 and convert it to ammonia NH3.

Plants, other organisms, they need that form of nitrogen.

And the enzyme they use, nitrogenase, it's very sensitive to oxygen.

So they've come up with all sorts of ways to protect it.

And this ability, it's spread all over the bacterial world.

The chapter mentions free -living ones like azotobacter in the soil.

Symbiotic ones like mesorhizobium, they partner with legumes.

And even anaerobic ones like disulfovibrio in environments with no oxygen.

Exactly.

It's vital and it's evolved multiple times.

The chapter even mentions some diacetrophs use alternative nitrogenases with vanadium or iron instead of molybdenum.

It highlights their flexibility.

Next up in the nitrogen cycle, the nitrifying bacteria.

They take the ammonia from the nitrogen fixers and oxidize it.

First to nitrate, then to nitrate.

Right.

These are aerobic chemolithotrophs, meaning they get energy from oxidizing inorganic compounds, in this case, ammonia or nitrite.

They need oxygen.

Nitrosomonas is a classic example.

It does ammonia to nitrate.

And nitrobacter, that does nitrite to nitrate.

A lot of them have complex internal membranes, probably for those oxidation reactions.

And some, like nitrospera, can do both steps.

Then there are the denitrifiers.

They complete the cycle, taking nitrate and reducing it back to gaseous nitrogen forms.

Nitric oxide, nitrous oxide, denitrogen gas.

Yes.

And there's a lot of variety among them.

Metabolically, evolutionarily, they're usually facultative aerobes, can grow with or without oxygen.

And they're chemorganotrophs, using organic compounds as electron donors.

It's a crucial process, influencing how much nitrogen is available in different places.

The chapter then gets into sulfur metabolism.

Dissimilative sulfur and sulfate reducers.

What's the difference?

Both reduce sulfur compounds, but they use different starting materials.

Dissimilative sulfate reducers, like desulfovibrio, they take sulfate, SO42, and reduce it to hydrogen sulfide, H2S.

That's the rotten egg smell.

They use hydrogen gas or organic compounds as electron donors.

And what's really interesting is this ability is found all over the tree of life, five different phyla.

Evolved multiple times must be a good strategy.

Dissimilative sulfur reducers, like desulfuromonas, they reduce elemental sulfur and other oxidized forms to H2S, but not sulfate.

And on the flip side, you have the dissimilative sulfur oxidizers.

They get their energy from oxidizing those reduced sulfur compounds.

Right.

They use things like hydrogen sulfide, elemental sulfur, thiosulfate, and usually oxygen is their electron acceptor.

They live where those sulfur compounds and oxygen meet, like hydrothermal vents or the boundary between sediment and water.

The chapter mentions thiobacillus, saccharimacium, begiatoa, all with different adaptations.

And some can even use nitrate as an electron acceptor if oxygen is low.

Now to iron metabolism.

Dissimilative iron reducers.

These bacteria use ferric iron, FF3 plus sera, essentially rust, as their electron acceptor, like breathing metal.

That's a good way to put it.

Geobacter and shiwanella are well studied examples.

Geobacter is especially interesting.

It can fully oxidize acetate to carbon dioxide, and it uses these pily, like tiny wires, to transfer electrons to iron oxides outside the cell.

Shiwanella is more versatile.

It's a facultative aerob, so it can use oxygen if it's around.

And then we have the iron oxidizers.

They get their energy from oxidizing ferrous iron, F2 plus satyr.

Yes.

Aerobic iron oxidizers, like acetythiobacillus, which we also saw in sulfur oxidation, and gallinella, which makes those twisted stalks.

They tend to like acidic environments.

And there's anaerobic iron oxidation too, done by both chemotrophic and phototrophic bacteria.

It shows how interconnected these cycles are.

Last but not least in this metabolic section, the methanotrophs and methylotrophs.

They have a very specialized diet.

Single carbon compounds.

Exactly.

Methylotrophs grow on compounds without carbon bonds.

Methane, methanol, methylated amines.

Methanotrophs are a subset.

They specialize in methane.

The chapter talks about aerobic methanotrophs, like methylomonas and methylacinus.

They use methane monoxygenase, an enzyme that needs oxygen to break down methane.

There are two types, based on their carbon assimilation pathways in their internal membranes.

And some methanotrophs even form symbioses with eukaryotes, like muscles and tube worms, in methane -rich areas.

Those symbioses are really important in those environments.

It lets the eukaryotes access the energy in methane.

And the chapter mentions that anaerobic methane oxidation happens too, though we're still figuring out the details.

And then there are the aerobic facultative methylotrophs, like hyphomicrobium.

They can use other methylated compounds, but not methane itself.

So from light to nitrogen, sulfur, iron, even methane.

The metabolic diversity is amazing, and it drives so many essential processes on earth.

Now the chapter looks at bacteria with shapes, structures, or lifestyles.

Starting with the microbial predators.

Sounds a bit scary.

It's a fascinating part of the microbial world.

Bacteria that prey on other bacteria.

Bidelovibrio is a great example.

Tiny, very motile, attacks gram -negative bacteria.

It gets into the periplasm, the space between the membranes grows and divides, and bursts the host cell.

Like a tiny vampire.

And then there's Myxococcus, a social predator.

How does that work with bacteria?

Myxobacteria are very cooperative.

They glide, they communicate with signals, when they find prey, they swarm, secrete enzymes to break it down, everyone eats, and it gets even more interesting.

When nutrients are low, they aggregate, farm fruiting bodies.

Those contain spores called myxospores.

It's a complex life cycle, predation, and survival structures.

Very unusual for single -celled organisms.

Incredible.

From lone attackers to organized packs.

Next, the spirocheses.

They have a very distinctive shape.

That's very distinctive.

Gram -negative, long, slender, coiled into a helix.

And their motility is unique.

They have endoflagella, flagella -like structures inside the periplasm, running the length of the cell.

When those rotate, the whole cell spins, moves like a corkscrew.

They're found in lots of places, water and in animals.

Unfortunately, the chapter mentions some famous pathogens are spirochetes,

trypanema pallidum, that causes syphilis, and Borrelia burgdorferi, the Lyme disease agent.

Yeah, their shape and motility probably help them move through thick fluids, penetrate tissues, which can be bad news for the host.

Now for the budding and prostichotistect bacteria.

They have unusual ways of reproducing, or those interesting extensions.

Budding is asexual reproduction.

A new cell grows as a bud from the parent cell, then detaches.

Hyphomicrobium, we talked about it before, it buds.

Prostachy are extensions of the cytoplasm, they're enclosed by the cell wall, and they increase the surface area.

Stalks are different, they're not living, they extend from the cell.

Colobacter is the classic example.

It attaches to surfaces with its stalk.

And it has a life cycle with two forms, a stalked cell and a modehull swarmer cell.

Then there are these sheaths bacteria.

They grow inside a tube -like structure.

Must be good protection in tough environments.

It is.

Bacteria like spherotilis and leptothrix, they grow in these sheaths, made of polysaccharides, or proteins.

Protection from predators, toxins, helps them stay put in flowing water.

When they want to spread, they release swarmer cells that can move and start new sheaths.

Some sheathed bacteria can oxidize iron or manganese, but it's not always for energy, it might be for sheath building, or detoxification.

And finally, the magnetic microbes.

This sounds like science fiction.

It does, but it's real.

They have magnetosomes inside their cells.

Those are little crystals of magnetic minerals, like magnetite or grisite, enclosed in membranes, arranged in chains, like tiny compasses.

They use it for magnetotaxis, orienting and moving along magnetic field lines.

So what's the advantage of having a built -in compass?

Probably helps them find the right oxygen levels.

In many aquatic sediments, oxygen is high at the top, low at the bottom.

These microbes often like a narrow zone in between.

By sensing the magnetic field, they can swim up or down to find that zone.

Amazing.

Tiny organisms, internal navigation systems.

This deep dive has really shown how diverse microbial ecological strategies are.

It really has.

From light harvesting to those different metabolisms, unique structures and lifestyles, microbes have evolved to thrive in almost every environment on earth, no matter how extreme.

And all those strategies, they're not just interesting little quirks.

They drive the big cycles, the biogeochemical cycles that make life possible.

They're the engineers shaping and maintaining our planet.

Exactly.

So as you go about your day, think about all those microbial interactions happening around you.

The air, the soil, the water, all shaped by these diverse communities.

It really makes you appreciate the complexity of life.

And maybe you'll even be inspired to learn more about some of these microbes or the processes they drive.