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Welcome back everyone to the Deep Dive.
We've got an interesting one today.
You know, we live in this world surrounded by, well, stuff.
Buildings, roads, all kinds of things, you know, the built environment, as they call it.
But have you ever stopped to think about, like, all the tiny life that's going on in and around all that stuff?
Yeah, it's pretty amazing when you start to, you know, really think about it.
It's not just about, like, avoiding germs or anything.
It's a whole, like, hidden world with huge implications.
Exactly.
And that's what we're into today, the microbiology of the built environment.
We've got a fantastic chapter to guide us, really covering everything from, well, how we mine metals to how we treat our water.
It even gets into things like how buildings that elves can be kind of like ecosystems for microbes.
Yeah, it's wild.
So our mission, basically, is to give you a clear path through all this.
It's a surprisingly broad field, you know, really important.
So buckle up.
We're starting off with something, well, pretty fundamental to how our world works, mineral recovery.
You know, they call microbes Earth's greatest chemists in the chapter, and that's not just hyperbole.
No kidding.
I mean, think about microbial leaching, like how we get metals from low -grade ores, like copper, for example.
Right.
About a quarter of all the copper produced globally uses this method.
A quarter.
That's mind -blowing.
Think about it.
These tiny organisms are really at the heart of our material economy.
Wow.
So how does it actually work, microscopic mining?
Well, imagine like piles of crushed up ore, often containing copper sulfide.
They circulate this weak sulfuric acid solution through it.
Okay.
So like dissolving the metal out.
Exactly.
And ferric iron, F3 plus SAC, that's kind of the key player here.
It naturally oxidizes the sulfide in the ore, releasing the copper.
Got it.
But how do the bacteria, you know, fit into all of this for us?
Well, that's where it gets really interesting.
Iron -oxidizing bacteria like acidithiobacillus ferroxidens and leptospirilum ferroxidens, they're amazing.
They take ferrous iron, F2 plus, that's a byproduct when the copper is released, and they convert it back into ferric iron.
So they're like regenerating the reactant, keeping the process going.
Exactly.
A self -sustaining system.
And what's fascinating,
you see different types of bacteria dominating at different temperatures.
Like in hotter zones, you get heat -loving archaea like sulfolobus taking over.
Wow.
It's like a little, you know, self -regulating chemical plant right there in the ore pile.
It really is.
And it's not just copper.
Microbial leaching is used for other metals too, like uranium, for instance.
Oh, okay.
So how does that work then?
Well, again, a ferroxidens plays a role.
It produces that crucial ferric iron, F3 plus erret, which then chemically oxidizes the insoluble U4 plus in the ore to a soluble U6 plus form.
Making it easier to extract.
Exactly.
And even gold, you know, in bioreactors, those are specially designed tanks, A, ferroxidens, and its relatives can be used to kind of liberate gold that's trapped in minerals like arsenopyrite.
Wow.
So these bacteria, they're not just good for getting the gold, they're also cleaning up the toxic stuff like arsenic and cyanide.
Yeah, pretty remarkable, right?
That's really impressive.
But I know there's flip side to this.
The chapter mentions acid mine drainage.
Yeah, that's a big problem.
It happens when pyrite iron sulfide isn't managed properly.
It gets exposed to air and water.
And then you have both natural chemical oxidation and bacterial oxidation happening.
And who are the culprits this time in terms of bacteria?
Actually, the same ones we were just talking about, acidithea bacillus ferroxidens and leptospirulum ferroxidens.
They speed up the oxidation of pyrite, producing sulfuric acid and ferrous iron, leading to incredibly low pH.
And I'm guessing that's where we get that classic mine drainage look, that rusty color in streams.
Exactly.
That's the ferrous iron reacting with oxygen, forming insoluble ferric hydroxide.
But it's not just about the color, obviously.
That acidic water, it's loaded with heavy metals, really bad for water quality and aquatic life.
There's even an archaea ferroplasma that thrives in those harsh conditions.
So it really drives home the point, right?
These microbes, they can have a huge impact, positive or negative, depending on the circumstances.
So we've seen microbes as miners, as polluters.
What about cleaning things up?
Bioremediation.
That's where things get really interesting.
Bioremediation, it's harnessing the power of microbes to clean up our messes.
Oil spills, for example.
Those are always so devastating to see.
Right.
But a lot of microorganisms can actually eat those hydrocarbons.
They aerobically oxidize them, breaking them down into CO2 and water.
They eat oil.
That's incredible.
It is.
And there are even specialist bacteria, like alkenovirax porcumensis, that produce these surfactant compounds to break the oil down into smaller droplets, making it easier for other microbes to get to it.
Like microbial dish soap.
Exactly.
Now anaerobic degradation can happen too without oxygen, but sometimes that leads to hydrogen sulfide, which can be corrosive.
Okay, so that's oil.
What about other stuff like heavy metals or even radioactive materials?
Bioremediation can tackle those too, though the strategy is different.
For inorganic pollutants, it's not always about breaking them down.
It's more about changing their form to make them less harmful, like uranium.
Okay, so how do they do that?
Well, some bacteria like shoanella, geobacter, and disulfovibrio can reduce soluble uranium, U6 plus A, to insoluble U4 plus A, which then precipitates out as urinonite a more stable form.
They do this while oxidizing organic matter or even hydrogen for energy.
So they're essentially locking the uranium away.
Exactly.
And scientists are working on ways to encourage this, like adding acetate to boost the bacterial activity.
That makes sense.
What about those really persistent organic pollutants?
I think the chapter called them xenobiotics.
How do they deal with those?
Xenobiotics are tough, for sure.
They're synthetic, not natural, so microbes haven't really evolved to break them down easily, but they've got some tricks.
For chlorinated compounds, there are both aerobic and anaerobic methods.
Like what kind of methods?
Well, aerobic degradation might involve enzymes called halogenases that can directly remove halogen atoms.
Or sometimes it's cometabolism where the pollutant is broken down unintentionally by enzymes meant for other things.
But a really important pathway is anaerobic reductive dechlorination.
Okay.
And what's that?
The chlorinated compounds, they act as electron acceptors.
The bacteria remove chlorine atoms one by one.
And are there any like star players in this process?
Oh, definitely.
Dehalococcoids and dehalogenomonas, they're fantastic at dechlorinating those really nasty solvents like PCE and TCE all the way down to ethene, the harmless gas.
Wow.
So we can actually use these bacteria to clean up those really tough contaminants.
Yes.
Using techniques like bio -stimulation, adding stuff to encourage the native microbes or bio -augmentation where we introduce these helpful bacteria directly.
That's incredible.
What about plastics?
I know that's a huge concern these days.
Plastics are tricky.
They're very resistant to breakdown, but there's been some really exciting research on Idonellus sacciensis.
Oh, what's special about that one?
It can actually attach to PET plastic and secrete enzymes, epithase and embutase, that break it down into monomers.
So they're basically like eating the plastic.
In a way, yes.
It's a slow process, but it shows that nature can sometimes find ways to deal with even our most recent inventions.
That's a hopeful sign.
So moving on from cleaning up waste, let's talk about something that's, well,
essential to all of us.
Water.
Wastewater and drinking water treatment.
Yeah, those are critical and microbiology is at the heart of it all.
Absolutely.
So wastewater treatment, what are the goals there?
Basically to reduce the organic and inorganic matter, prevent the spread of harmful microbes and get rid of toxins.
One key measure is BOD, biochemical oxygen demand.
What's that BOD?
Think of it as like how much food there is for microbes in the water.
A high BOD means lots of organic pollution.
Okay, that makes sense.
So how do we clean up all that wastewater?
It's a multi -stage process.
Primary treatment is mostly physical, removing large solids.
Secondary treatment, that's where the microbes come in.
Right, so what happens there?
Two common methods.
Activated sludge, where aerobic bacteria form these flocs, think like little clumps that really efficiently oxidize the organic carbon.
The other method uses crickling filters, beds of material that grow biofilms.
Biofilms, those are like those slimy layers of microbes, right?
Yeah, exactly.
As the water flows over them, the microbes in the biofilms break down the organic matter.
So that's secondary treatment.
Is that always enough?
Sometimes you need an extra step, tertiary treatment, to further refine the water.
Like removing phosphorus, either chemically or with special bacteria called PaOs, phosphorus -accumulating organisms.
So specific bacteria for a specific job.
Exactly.
And then there's nitrogen removal.
This usually involves two steps.
Nitrification, where bacteria convert ammonia to nitrate, and denitrification, where other bacteria convert nitrate into nitrogen gas.
And that nitrogen gas is just released into the air.
Yeah, it's harmless.
The chapter also mentions some more advanced methods, like nitrotation denitrification and the anomics process, which is anaerobic ammonia oxidation.
So they're always looking for more efficient ways to do this.
Absolutely.
And then there's aerobic granular sludge, where the microbes form these dense granules that can remove both nitrogen and phosphorus.
So what happens to all that sludge that gets removed?
It's processed further, often through anaerobic digestion.
More microbes come in, break down the organic matter without oxygen.
And that reduces the volume, right?
Right.
And it produces biogas, which we can use for energy.
And that anomics process, it can even be used to treat the nitrogen -rich brine from sludge digestion.
It's like a closed loop.
It is, in a way.
But there are new challenges.
The chapter mentions contaminants of emerging concern.
What are those?
Things like pharmaceuticals, personal care products, stuff that might not be completely removed by conventional treatment.
Even at low concentrations, they can be harmful.
Potentially, yes.
So that's a big area of research.
Now, let's switch gears to the water coming out of your tap,
drinking water.
Right.
So what's important there from a microbial standpoint?
The main goals are to remove pathogens, obviously.
But also anything that affects taste or odor, reduce nuisance metals, and decrease turbidity.
So how do we make sure the water is actually safe to drink?
It starts with sedimentation, letting the heavier stuff settle out.
Then coagulation and flocculation.
What are those?
They add chemicals that make those tiny particles clump together, forming flocs that are easier to remove.
Then comes filtration, using sand, gravel, sometimes activated charcoal.
Okay, so that gets rid of all the particles.
Right.
And the final step is disinfection, usually with chlorine or UV radiation.
Chlorine, that's the most common, right?
It is.
It's very effective, kills a broad range of microbes, and leaves a residual amount that continues to disinfect as the water travels through the pipes.
But it can also form byproducts when it reacts with organic matter.
I've heard about those byproducts.
They can be harmful, right?
Some of them, potentially, yes.
UV radiation is an alternative.
Doesn't form byproducts, but it doesn't leave a residual disinfectant.
So chlorine is still important for keeping the water safe in the distribution system.
Exactly.
But, you know, microbes can still grow even in treated water.
They form biofilms inside the pipe.
Really?
Even after all that treatment?
Yes.
And those biofilms, they can sometimes harbor opportunistic pathogens, like mycobacterium, legionella, pseudomonas.
That's a bit unsettling.
It is.
And it's interesting, some of those biofilms can even protect pathogens from disinfectants.
Wow.
So even in our clean water, there's this whole hidden microbial world.
Exactly.
And it's not just in the water, it's in the air on surfaces everywhere.
Our indoor environments are full of microbes.
You mean, like, in our homes?
Yes.
The air, the dust, everything.
And it's heavily influenced by us, the occupants, and our pets.
So our homes have a unique microbial signature.
In a way, yes.
You can even tell if someone has pets based on the microbes in their house.
That's amazing.
What else affects the indoor microbiome?
Ventilation, humidity, the types of materials used in the building, and of course, cleaning products.
Antimicrobials can really change the microbial landscape.
So choosing the right cleaning products is important.
It can be, yes.
And, you know, even public spaces like subways, they have their own unique microbial communities.
And even within your home, things like toilets and shower heads can be sources of microbes.
It's really everywhere, isn't it?
It is.
And sometimes it causes problems like microbially -influenced corrosion.
MIC, right.
That sounds serious.
It is.
It's basically the acceleration of corrosion, especially in metals, because of microbes.
And it happens a lot in buried or submerged infrastructure, like pipelines.
So our infrastructure is at risk?
In some cases, yes.
Several groups of microbes are involved.
Sulfate -reducing bacteria, iron -reducing bacteria, iron -oxidizing bacteria, methanogens.
We hear a lot about sulfate -reducing bacteria.
What makes them so problematic in this context?
Well, they produce hydrogen sulfide, which is very corrosive.
And there's evidence that some can even directly take electrons from the metal surface, basically eating away at it.
Wow.
So they're not just producing a corrosive substance, they're directly attacking the metal.
Exactly.
And it's not just metals.
Microbes can also degrade stone and concrete.
Fungi, for instance, can produce acids that dissolve the minerals in stone.
Like on buildings and monuments?
Yes.
And a particularly damaging example is crown corrosion in concrete sewer pipes.
What happens there?
It involves a sulfur cycle.
Sulfate -reducing bacteria produce hydrogen sulfide, which wises to the top of the pipe.
There, sulfur -oxidizing bacteria convert it to sulfuric acid, which eats away at the concrete.
So it's a chain reaction that can lead to, like, pipe collapse.
Exactly.
It's a big problem.
It really is amazing and a bit scary how much influence these tiny organisms have on our world.
To wrap things up, let's revisit some key terms from the glossary.
Sure.
Starting with acid mine drainage.
We know it's that acidic, often reddish water that results from the oxidation of pyrite, mainly caused by microbes.
It's really bad for water quality and ecosystems.
Right.
And then there's bioremediation, the idea of using organisms, usually microbes, to clean up pollutants.
Yes, a very important concept.
Then we have BOD, biochemical oxygen demand, which is a measure of how much oxygen microids need to decompose organic matter in water.
Higher BOD means more pollution.
Makes sense.
And then there's microbial leaching, using microbes to extract metals from ores.
Like we talked about with copper, uranium, and gold, a surprisingly widespread technique.
And then there's MIC, microbially influenced corrosion, the acceleration of corrosion due to microbes, a threat to infrastructure.
Right.
And finally, xenobiotics, those synthetic compounds that are often difficult for microbes to break down because they're not natural.
That glossary really helps to tie everything together.
So clearly, microbes are so much more than just germs.
They're key players in our built environment from mining to water treatment to even shaping the indoor microbiome of our homes.
Absolutely.
And what's really fascinating is how all these seemingly separate areas are actually connected by the basic biology of these microbes and how they interact with our world.
It really makes you think, doesn't it?
What are the future challenges and opportunities that lie at this interface between microbes and our built world?
Could we harness these microbes to create even more sustainable and resilient systems?
Those are great questions to ponder.
And with that, I believe we've covered all the major points and examples from the chapter on the microbiology of the built environment.
I think so, too.
It's been a fascinating deep dive.
Thanks for joining us, everyone.
Thanks for having me.