More on the shocking life of yeasts

(Brief Update: Hello Ontario! Did I attract the attention of a Toronto homebrewing club or something? Anyway – welcome!)

I am amazed at how much depravity I uncover as I explore the mystery that is
Saccharomyces cerevisiae.

I’ve previously discussed how the filthy little beasts have drunken orgies and exchange sexually transmitted diseases with each other. Now I find out the inebriated little jerks are peeing in my beer, possibly to try to give me cancer!

No, seriously. Given enough “Free Amino Nitrogen”, for example in the form of the pirate’s favorite amino acid, like tiny little single-celled bladders, the yeast will start excreting extra nitrogen in the form of Urea all over whatever they’re growing in.

Of course, the whole time they’ve also been excreting ethanol. It turns out, under certain conditions urea (more formally known as “carbamide” nowadays) and ethanol will combine like drunken evil “Wonder Twins” to form Ethyl Carbamate.

Front Cover of the bookI ran into this as I was reading through my shiny new Wine Microbiology book, which has two pages on this yeast pee byproduct. An article linked to from recently reminded me of it and prompted this post.

To be honest, this seems a lot like the acrylamide media circus (compare the two links…) that popped up back in 2002. In both of these cases, we’re talking about a substance that occurs as a natural result of the preparation process rather than some new industrial chemical, and in both cases the processes in question have been around probably since prehistory. And in both cases, the real situation seems to boil down to something like “pay attention to your preparation technique, and if you try to live entirely on a diet of overcooked French fries and dessert wines, you might be at an increased risk for cancer.” QED. Or perhaps DUH.

Other than not trying to live on a French McDonald’s® diet, there are some things you can do when you brew to limit ethyl carbamate formation. Put very simply: don’t overfertilize your grapes because that can directly lead to unnecessarily high levels of nitrogen available in your wine, and don’t leave your bottles of brew in hot conditions for long, because ethyl carbamate forms faster in hot conditions.

There, problem solved. A more detailed “ethyl carbamate preventative action manual” may be found here. Meanwhile, I’m pretty sure our favorite drunken little micro-hedonists are too busy partying and making our wines and beers to be plotting our cancerous dooms.


After my previous post, there are bound to be a few wiseguys/wisegals with dirty minds who couldn’t resist chuckling and wondering “yeah, well if yeast have sex, they must get STDs too, right? Ha ha!”

Yeah, well, very funny.

Of course they do.

In fact, that bottle of hefeweizen you may have consumed at one time or another was almost certainly full of Yeast Herpes!.

Alert readers will be wondering how I can have said “there don’t seem to be any viruses of yeast” in the last post and now be telling you you’ve been eating and drinking yeast-herpes all your life.

Here’s the deal: Generally when we think of viruses we’re thinking of little protein-wrapped packages of genetic material floating around freely, which can ultimately attach to and infect some cell, forcing the cell to make more copies of the virus which are released one way or another to continue the cycle.

Fungi, including yeasts, don’t seem to have any viruses that infect their cells from outside. They do, however, have “virus-like particles”, which seem like they were probably once more traditional types of virus, whose populations have lost whatever genes were necessary to be released from and infect into yeast cells. Without this ability, there’s only one good way for the virus to spread from an infected cell to an uninfected one: sex.

It would seem that there is so much yeast-sex going on that it ends up being a much more efficient way for the viral particles to spread. As a result, despite the fact that only the cell fusion of yeast-sex can spread the particles, there are very few known yeast strains that don’t carry double-stranded RNA virus particles (“L-A”, “L-BC”, “M1“, “M2“, and possibly some others), and there don’t seem to be any known yeast strains that aren’t infected with yeast-herpes.

It’s not actually “herpes” of course, but just like herpes, it is a retrovirus, which is actually merged into the yeast’s own DNA strands, and which is then transcribed into RNA to make virus particles.  These in turn get converted back to DNA by reverse transcriptase and integrated into the infected cell’s genome. The review I found whence I got all of this information[1] mentions three versions of these “retrotransposons designated “Ty1”, “Ty2”, and “Ty3”. (I assume that’s “Transposon, yeast”.).

If anyone stares at you when you yell “Yeast herpes! NOOOOO!!!!” and run screaming from the room next time someone offers you a beer, feel free to point them to this post for an explanation.

POSTSCRIPT: My previous post made it sound like yeast cells were normally haploid. The review paper I’m citing in this post makes an interesting assertion though: it states that in the wild, yeast cells are usually diploid, and haploid cells normally only show up as a result of environmental stresses. This is somewhat at odds with, for example, a more recent Genetics textbook[2] that I have in my possession, which explicitly describes that once the two haploid mating cells merge to form a diploid cell, it “promptly undergoes meiosis to produce four haploid ascospores”. This may perhaps be a case of a difference between growth in laboratory conditions versus normal environmental conditions. Perhaps in the natural environment which has not been carefully formulated to specifically promote yeast growth, diploid yeast cells persist until particular conditions induce meiosis. Hopefully the spiffy new book I have on order will show up one of these days and will hopefully have some discussion of the topic.

[1] Wickner RB: “Yeast virology.” FASEB J. 1989 Sep;3(11):2257-65.
[2] Snustad DP, Simmons MJ: “Principles of Genetics (3rd Edition)”; 2003; John Wiley & Sons, Hoboken NJ [ISBN: 0471441805], pp 42-43

Hot a on α action!

I’m busily house-hunting, but here’s a short science post anyway (even if for some reason I don’t appear to be showing up on the main “Just Science 2008” feed…)

Yeast have sex.

Of course, it’s a bit different from the way we multicellular organisms handle the process. For one thing, instead of “male” and “female”, they have “a” and “?”. No, I don’t know who came up with this bizarre naming scheme and yes, I also think whoever came up with it ought to be slapped, or at least forced to explain him- or herself in public.

Like humans, yeast cells have multiple chromosomes. Unlike humans, yeast are normally haploid (humans are diploid). [UPDATE: The review paper I cite in the next post suggests this statement may not be quite so clear-cut.]

Yeast spend most of their time reproducing asexually by “budding” – they make a copy of each of their chromosomes, then shove them all into a little “bud” of cell wall material along with enough enzymes to get started, and the bud then detaches and starts its life as a an independent cell. A clone of its parent cell, but independent anyway.

Yeast can also reproduce sexually, however. Both “a” and “?” cells excrete very tiny proteins referred to as “mating factors” – one type for “a” and one type for “?”. These factors inhibit DNA copying and budding in cells of the opposite “sex”, and instead helps trigger a process whereby cells of opposite “sexes” literally merge to form a single diploid cell. In athe same process of similar to meiosis by which reproductive cells of animals are made, this diploid cell can then make copies of each chromosome (giving a total of four copies of each chromosome – two copies of one parent cell’s chromosomes and two of the other). The parent cell then splits itself into four spores, each containing one more or less randomly-chosen copy of each chromosome. This little trick allows yeasts to reshuffle chromosomes around the population, helping to find and maintain the most advantageous combination of versions of each gene in the cell for the environment in which the population is living.

A practical side-effect of this is that you can effectively breed yeasts, by combining cultures with different characteristics. Hypothetically, many of the yeasts from each culture will end up “mating” with yeasts from the other culture, and if you have a good way of selecting cells that have the combined traits of both strains that you want you can easily make your own new naturally-recombinant strain.

This also seems to relate to why there don’t seem to be any viruses of yeasts…but I’ll save that for another post.

Grossly Oversimplified Science: Obtaining Pure Yeast Cultures

Various yeasts of the genus Saccharomyces (particularly the “Baker’s Yeast” Saccharomyces cerevisiae) represent quite possibly the most important bit of intentional microbiology that we have. We eat and drink the little critters and their byproducts in more or less every human culture that I know of, and are now getting more seriously into burning them, too.

As I’ve mentioned before, gluttony is my second most favorite deadly sin, so bread and booze microbiology is naturally of interest to me. It seemed worthwhile to look into developing my own yeast (and bacteria…but that’s for another post) stocks to brew, vint, and bake with, so I did some poking around. I dug out my copy of Rog Leistad’s “Yeast Culturing for the Homebrewer”, Peter Duncan and Bryan Acton’s “Progressive Winemaking”, a number of internet sources, and finally some scientific papers. I know, I’m a nerd.

I have so far not found much of anything about isolating yeasts from scratch – virtually everything seems to assume that you will “buy” your yeast from somewhere else, and aside from scientific papers most assume that you’re only bothering to culture your own yeast to save money by stretching the sample you bought to brew several batches before buying more yeast from “the professionals” again. This annoys me.

Unfortunately, I’m still on the road and haven’t had time to directly embark on my culture project here. I’m also having a heck of a time tonight trying to come up with a way to make the process of isolating a pure culture sound interesting to anyone besides me. Here’s the extremely abbreviated version:

  • Take something that’s got (in this case) yeast in it (sourdough starter, unfiltered beer, whatever)
  • Make up some solidified yeast food: typically this is something like a mixture of sugar, predigested milk protein, and water, mixed with agar to solidify it, and with a small amount of acid added, since the acidity helps inhibit bacteria that might contaminate the yeast culture
  • Take a tiny bit of the original stuff-with-yeast-in-it, and smear it thinly over the top of the solid medium.
  • Cover the solid medium and put it somewhere warm for a while until you can see individual spots (“colonies”) of growth
  • (The idea is that if done right, at some point on the solid media the “smearing” will have spread out the yeast cells far enough that you can make out the mounds of offspring that an individual yeast cell has made. Each distinguishable round spot of growth is effectively made up of millions of clones of the original single cell that started the “colony”)

  • Take a bit of a single colony and put it in some sterile culture media.

If everything works correctly, this gives you a “pure” culture, isolated from any other kinds of cells that may have been in the original sample. In this example, this is hopefully a brewing or bread yeast culture that you can now use to make beer, wine, bread, or fuel ethanol (the latter assuming you have permission from the Bureau of Alcohol, Tobacco, and Firearms, since it requires distillation.)

Tomorrow: Fun facts about yeast cultures.

All this week: A topic important to secular and religious people alike

It’s not midnight here yet, I’m still on time!

Hello, “Just Science 2008” subscribers and everyone else. My life is insane at the moment but dagnabbit I’m going to do my best to get at least one post up on a scientific topic every day from today (Monday, February 4th) until Friday…

Today’s post is in the form of a gedanken experiment.

First, imagine the following:

  • Some “entities” existing somewhere
  • It doesn’t matter what “entities” you are imagining, whether they are products in a market setting, or data structures in a computer program, or topics of discussion on a news broadcast. All that matters is that there can be more than one of them.

  • A mechanism by which these “entities” are copied (and, optionally, also sometimes removed)
  • Products are manufactured or recalled, data structures can be copied or deleted, additional news anchors can be added to comment on a topic or conversely may shut up about them…

  • At least one mechanism by which changes can occur between or during copies
  • Product designs can be changed, a computer program may consult a “random number” generator and use it to make small changes in the data structure, scriptwriters may alter the news anchor’s teleprompter messages…

  • Some aspect of the “entities” that affects the rate at which they are copied (and/or, optionally, removed).
  • Demand by buyers in the market results in ramping-up of production, a computer program may perform some test or comparison of a data structure and use the result to determine how many copies of it to make (or whether or not to delete it), news topics that result in more people watching are repeated more often while those that people tune out from are dropped from the schedule…

What happens to this group of “entities” over time should be obvious. Taking the example of products in a market, producers introduce a variety of products (the group of “entities” in this example) and buyers examine their characteristics and, based on which ones they like, buy some of them. The producers observe which kinds of products are selling more and make more of those, while reducing or outright eliminating the production of those that aren’t selling well. Over time, a few of the kinds of products in this group which best fit the preferences of the buyers and the ability of the producers to make them. These products will dominate the market until the preferences of the buyers or the ability of the producers to produce them change [example: a shortage in the price of a particular material needed for a popular product].

You have most likely observed this process in the “news topic” context yourself, where it tends to happen much faster as “cheap and easy” news stories are happily picked up by news agencies to broadcast until people get sick of them and tune out.

This can all, hopefully, be understood as a purely logical outcome – a conclusion that universally and necessarily follows from the premises given. There should be nothing supernatural or even surprising here, is there?

So, now that you understand why and how evolution works (if you didn’t before), I can move on. (Incidentally, the part of the example above that describes a computerized system is actually referred to as a “genetic algorithm”.)

My purpose in starting with this is because it really and truly is fundamental to the topic that I expect to spend most of this week posting about, and which has been of vital importance to human culture and intellectual development for thousands of years. This most important subject involves such notable figures as Charles Darwin,St. Thomas Aquinas, Noted American Science-guy Benjamin Franklin, New England Puritan Cotton Mather and Quaker William Penn ,Hardcore Catholics like Pope John Paul II, Hardcore Athiests like PZ Myers, even famous religious figures like Jesus.

I refer, of course, to wine (and beer and other examples of ethanol production).

Okay, here’s the background: I just graduated with my B.S. in Microbiology, and I’ve got this whole “Hillbilly Biotech”/”Do-it-yourself”/”Practical Science” kind of thing going on in my interests. That being the case, I wondered what it would take to isolate, culture, and maintain my own yeast (and bacteria – more on that later) stocks from the environment rather than buying “canned” cultures – or at least play with the “canned” yeasts to create my own stocks. As I was poking around, though, I kept running into the same attitudes – namely that it’s “too hard” to do this, and although there are a number of people who advocate re-culturing canned commercial yeasts for a short time to save money, none of them think it’s feasible to do this for more than a couple of generations, at which point we are assured that you have to go buy it again or else “mutations” will inevitably appear and scary and mysterious “off-flavors” will result and the brewing police will come and throw you in jail for deviating from the archetype of whatever pre-defined style of wine or beer you’re trying to make. Or something like that. In any case, it’s because of this fear of “mutations” that I am starting out with this “evolution”-related post: in biological evolution, various forms of alterations in the genetic material are the “changes before or during copying” in the gedanken experiment above.

I didn’t buy it when people were telling me that it was “too hard” to learn how my computer works so that I could run Linux and should instead leave deciding what my computer should do to the “professionals”, and I’m not buying the same argument about commercial yeasts, either. If I felt that way, I might as well leave the rest of the complex technology of brewing to the “professionals” too, and consign myself to “Lite Beer” and “Thunderbird” for the rest of my life.

I’ve been spending much of the last few weeks perusing books, online articles, and scientific papers on subjects related to brewing in general and brewing yeasts in particular, and this should form the bulk of this week’s post topics, of not well beyond this week. Tomorrow I intend to start in on the actual process of culturing yeasts. Meanwhile, feel free to correct my no doubt horribly over-simplified explanation of evolutionary processes in the comments.

“Does beer and ice cream make gas?”

I get some odd Google searches hitting this site. Once in a while, however, I see one asking a question of vital importance and great usefulness to the general public. Today’s brief topic is this query: “Does beer and ice cream make gas?”.

I’m assuming the searcher did not mean gasoline. Biodiesel is all well and good, but who the heck would waste perfectly good beer and ice cream on such a thing? No, I assume the searcher wanted to know if eating these two fine foods together would expose one to the risk of increased flatulence.

Sad to say, the answer is most likely “yes”.

Flatulence gas (from humans, at least) is made up mostly of carbon dioxide and hydrogen gas[1], and for some people (but apparently not all!) methane. It’s worth noting that none of these components have any odor. All of the offensive smell comes from comparatively tiny amounts of sulfur-containing chemicals – most notably plain old Hydrogen Sulfide, and maybe a few molecules of indole-type compounds such as skatole which can make the origin of the stench obvious.

These main gases come from two sources – swallowed gases (air and carbonated beverages) and microbial fermentation. Obviously this is one place beer comes in – the carbonation adds to the amount of gas entering the digestive tract. Secondly, the beer probably contains some amount of remaining malt which some intestinal bacteria, like the yeast that made the beer in the first place, can break down and eat, possibly generating more carbon dioxide in the process. Beer also has small amounts of sulfur compounds in it which give it some of its flavors. It’s possible that some of this sulfur can end up as smelly by-products of microbial action as well.

I tend to assume that problems one might have with ice cream are mainly related to the lactose from the cream. Lactose is actually a combination of two kinds of “simple” sugar molecules linked together in pairs – glucose and galactose. Many unfortunate human beings are cursed with a lack of production of lactase, which is an enzyme that breaks lactose into its two simple sugars which can be easily absorbed and digested. Many bacteria which can live in the human intestine, on the other hand, make their own lactase. If the human eating the ice cream doesn’t make their own lactase so as to absorb and use up the simple sugars, it all gets down to the intestines where the intestinal bacteria can turn it into a major feast. Many bacteria generate a lot of carbon dioxide when eating these sugars, too, and this adds to the gases that build up in the intestine. This is similar to the issue with beans[2] and similarly ‘indigestible’ substances which can appear in food[3] – humans don’t use them up, so the bacteria get it all and make a huge amount of gas in the process of eating it.

Milk also has at least some sulfur in it[4], like just about any protein-containing food, but I’m not sure if it’s enough to add to the smell problem.

So, yes, beer and ice cream probably do make gas.

Incidentally, it seems as though methane production in humans only happens in some people. Methane is only produced by certain kinds of archaea, and not all humans have them growing in their intestines along with the regular bacteria. Don’t quote me on this, but I would tend to suspect that this would actually reduce the amount of gas that actually results in the end. Methanogens actually make the methane out of the other two major flatulence gases: carbon dioxide and hydrogen. I haven’t looked up the biochemistry, but I suspect the other byproduct is water. Since the pressure of a particular bubble of gas (and therefore its volume when your container is stretchable, like an intestine) is dependent on the number of actual molecules of any kind of gas in it, if you have methanogenic archaea in your intestines they should be taking a molecule of carbon dioxide plus more than one molecule of hydrogen gas, and producing just one molecule of methane out of it (plus some liquid water), so where you once had three or more molecules of gas you end up with just one. I’m sure somebody somewhere has done some kind of study on this, maybe I’ll go dig for it at some point. While I’m at it, perhaps I should look at patenting the use of archaeal “natural flora” as a probiotic?…

The picture at the head of this post, incidentally, came from this blog post of odd signs – apparently this one’s from an advertisement for some kind of backache treatment. Still, I couldn’t pass up putting it here…

[1] Furne JK, Levitt MD: “Factors influencing frequency of flatus emission by healthy subjects.” Digestive Diseases and Sciences, 1996; 41:8; pp 1631-1635
[2] Rockland LB, Gardiner BL, Pieczarka D: “Stimulation of Gas Production and Growth of Clostridium perfringens Type A (No. 3624) by Legumes.” Journal of Food Science; 1996; 34 (5); pp 411–414.
[3] Cummings JH, Macfarlane GT, Englyst HN: “Prebiotic digestion and fermentation” American Journal of Clinical Nutrition; 2001; 73(2); pp 415-420
[4] Ramsdell GA, Whittier GO: “Composition of Casein in Milk” Journal of Biological Chemistry; 1944; 154; pp 413-419

More Search Amusements. (p.s. I Ain’t Dead Yet.)

A bit longer of a delay between posts than I’d like, but here you go:

+ =?????

I am often amused (and regularly baffled) by the kinds of search queries that lead people to this blog.

I wrote a sloppy little script to parse the server’s access logs and figure out who’s searching for what, where. Since I added the ability to recognize Google Image Searches, it’s gotten even stranger.

I do get a lot of perfectly understandable hits – people looking for information about “heat-fixing slides”, expired jello, and looking for pictures of lactic-acid bacteria or whatnot. Some of them are pretty interesting questions…but first, some oddities.

At the top of my current wierd-o-meter: “carbonated leprechaun”…what??? What’s funnier is that this was a Google Image search – someone doesn’t just want information ABOUT carbonation of leprechauns, they want pictures. Now I can’t stop imagining a mash-up of “Darkman” and Leprechaun. Thanks a lot, whoever you are…”I needs me gold! ARGH! SUNLIGHT! [bubblebubblebubble…]”

Another recent one was just a search for the phrase “new england sucks”. As another Image search. Somebody not only doesn’t like New England, but they want pictures of “new england sucks”?…

Less risible but still kind of funny are searches influenced by unfamiliarity with the English language. I have no idea what the search for pictures related to “useful of DNA” was hoping to find. (Uses of DNA? How to “use” [work with] DNA? Diagrams of genetic processes?). I also see a number of searches just based on the name of the blog – people looking for information about furnishing “big rooms”. I have no idea what the search for “name of thing in room” was expected to turn up. This one’s another language issue, but even taking that into account I’m still baffled about this one. I wouldn’t expect to return any useful information for “Sache im Zimmer” (the original search was actually from a Spanish-speaking area, but No Entiendo Espanol, so I’ll use a German analogy instead.)

Or from Sweden: “Aerobic Oxygen fraud”. Somebody’s figured out that we don’t actually need to breathe and that it’s all a ploy by the Oxygen Lobby to enslave us, I guess.

Maybe just because “chemicals” get mentioned here from time to time, I get the occasional hit from someone looking for illegal drug information (either technical or just news of drug busts or whatever). Note to “HILLBILLY METH” searcher: Hillbillies do moonshine. Meth comes from Rednecks. Jeez, doesn’t everyone have to do a semester of Rural Population Stereotype Taxonomy in college anymore?

There are some more relevant and interesting questions that show up here, too.

Oreo CookieI guess someone in southern California used an interesting analogy in their microbiology class, because I recently got a couple of searches from there looking for why the cell membrane is not like an Oreo® cookie. The answer: There’s no “creme” filling. No seriously – the membrane is two layers of the same kind of molecule stuck together. The phrase you’re looking for is “Phospholipid bilayer”. In a way, the molecules are a lot like detergents – they’ve got one end that “likes” water, and a long tail at the other end that doesn’t (much as oil doesn’t). Since the cell is surrounded by and full of water, you end up with one layer with all its hydrophilic ends touching the water outside the cell, and the other layer with its hydrophilic ends on the inside of the membrane touching the water inside the cell, and the hydrophobic ends of both layers all tangled up together in the middle – without anything between them. See? Not like an oreo cookie at all. Aside from this, cell membranes are also squishier and not chocolate flavored most of the time.

I’ll deal with “does beer and ice cream make gas” in another post later…

Give a man a fish, and you feed him for a day…

…but teach a man to fish, and he’ll sit in a boat and drink beer all day.

-== We interrupt this blog post to bring you this important announcement: Happy Birthday, Dad!==-

(His birthday was actually yesterday, but this week of school has been grinding me pretty hard and I’d forgotten all about it. He must be so proud – his son can handle a couple of semesters of biochemistry, complex microbial science, working with dangerous chemicals in a lab…but doesn’t seem to know how to use a simple calendar…I am filled with shame.)

We now return you to your regularly scheduled blog post:

This here critter is our resident fish. “He” is a classic specimen of real, old-fashioned, Honest-to-Aquaman Carassius auratus auratus – the Goldfish. And not one of those poor mutant freaks who can barely swim, either. No this here fish was rescued from the overcrowded “feeder goldfish” tank of a local Wal-Mart®. Handsome, ain’t he? I had a tough time getting even this good of a picture – every time I get near the tank he swims back and forth in front of me frantically, perhaps worshipping me as the magical fishfood god. He’s been here for about three years now, so I think he’s having a much longer life than most of them.

I’ve had no time to get into it, but part of the reason for having a fish is that I have a casual interest in aquaculture. That is, while I don’t currently have any intention of becoming a professional full-scale fish-farmer, the subject is interesting and, I think, very important in the near future. Once we figure out where we’re going to end up living next year and get settled in somewhere, I have considered trying to do the aquaculture equivalent of a backyard garden, though.

I think aquaculture is going to become extremely important in the relatively near future, as we run into the combination of overfishing of natural stocks, water shortages, contamination of natural waters with pollutants that build up in naturally-existing populations of fish, and the overall effects of climate change. I think understanding how to raise healthy and nutritious aquatic food without wasting water or causing environmental problems is going to be a useful set of knowledge to have. (There, see, not only do I love kittens and puppies and want to make the world a better place, but I’m also interested in Sustainable Environmental Practices™. While feeding the hungry. [Uphill. In the snow. With no shoes…]).

You may be wondering what interest an ex-professional-computer-nerd microbiologist would have in tending a pond full of eukaryotes. Well, aside from the obvious “Hey, I can have more than one interest, you know”, there actually is a lot of microbiological activity involved in the natural processes of the fishes’ homes. Plus, of course, the aforementioned beer doesn’t ferment and bottle itself, you know.

Since one of my interests in this context is water conservation, my main interest is in figuring out how to maintain a healthy “closed” system. In an aquaculture context, a “closed” system is one that you don’t normally add substantial amounts of water to. (An example of an “open” system might include raising fish in pens floating in a natural lake, or having a constant stream of fresh ground or river water pumping through your tanks). This poses certain problems, since you have to feed the fish, and this adds an ever-increasing load of potentially uneaten fishfood and especially of eaten fishfood – that is, fish wastes.

Fishfood being digested by either fish or bacteria ends up adding ammonia to the water, which is poisonous to the fish (and crawdads and whatever else is in there). Also excreted is carbon dioxide, which makes the water more acidic, and unused food also dumps sulfur and phosphorous into the system.

If you’ve ever had a fishtank, you may know about the ammonia. Certain kinds of Oxygen-using bacteria can actually get some of their biochemical energy from turning reduced nitrogen into oxidized nitrogen, ultimately turning the ammonia (NH3) into much less poisonous nitrate (NO3). These bacteria tend to colonize the tank’s filter, where they do their thing using the oxygen in the water that flows through. Even nitrate is dangerous if it builds up too much, though. In an aquarium, they usually recommend just taking out some of the tank’s water and replacing it with fresh water every week or two to get rid of the build-up. I’d show you pictures of the bacteria, but I still can’t afford a decent microscope. (sniffle.)

Anyway, I want to build a denitrification column one of these days. There are bacteria that can “breathe” nitrate in place of oxygen, and in the process they can reduce the nitrate back down to plain old harmless nitrogen gas, which just bubbles out of the water. If you build a long, tall tube full of something like gravel that bacteria can grow on, and then pump the water through it slowly, oxygen-breathing bacteria near the bottom of the tube rapidly use up the oxygen in the water, leaving the nitrate. With no oxygen further up the tube, bacteria that can breathe the nitrate instead can grow like crazy, and exhale the extra nitrogen out of the system.

That’s one way of avoiding the need to use up as much fresh water as you’d need if you relied only on replacing the water to get rid of the nitrate.

I’ll save the sulfur and phosphorous parts for another day. Meanwhile, I think the next podcast or two will deal with MRSA, since it’s been in the news so much lately. I normally find the neglected non-medical microbiology more interesting, but the biochemistry and genetics involved with Methicillin Resistant Staphylococcus Aureus (not to mention S. aureus itself) is pretty interesting, and I find the media discussions of it unsatisfying.

Stay tuned…

#1 on Google!

Over on’s The World’s Fair, the author has started an amusing meme.

It goes like this: the challenge is to find 5 sets of search terms for which your own blog or site is the #1 hit on a Google search. Note that it is acceptable to quote specific phrases but of course it’s more impressive if you don’t. Here are 8 that (as I type this) for which this blog is the #1 hit (links go to the blog address that is the hit):

There was at least one other which I’m having trouble remembering at the moment. Perhaps I’ll update later if I remember what it was.

Microbial Fuel Cell netcast…

It’s only my first attempt at anything like this, so constructive comments are welcome…

(Hopefully you can see the embedded audio player here…)For those of you just tuning in, this is a 90-second explanation of Why Microbial Fuel Cells work. A longer (though still simple) explanation can be found at a slightly older post here.[Update: this was featured in the November 6, 2007 broadcast! Hooray, I can now claim to be an international “radio personality”!]Presuming hosting this file doesn’t kill my bandwidth, I’ll leave it up here. BelowAbove, you should see an embedded flash player (assuming you have Macromedia® Flash® player installed) which you should be able to click on to start the audio. I’ll also place a direct download link below. It should be noted that like everything else on this blog (unless otherwise specified), this audio is also available under the Creative Commons non-commercial/attribution/share-alike license, so as long as you have no problem with the terms of that license you are welcome to copy, redistribute, put up on bittorrent, host a public performance, turn into an interpretative dance art project, or whatever else you might want to do with it so long as you give me credit for it, don’t use it for commercial purposes, and distribute any derivative works of it under the same terms.

You can download the audio directly from here – right-click on the link and select “save link as…”. Ogg Vorbis format available on request…