February 2015

Sometime last year, on his now-defunct tumblr feed, Recursive Muffin, Ethan Mitchell asked a question I thought the folks on This Week In Microbiology (which I’ve written about here and here) might be able to answer. I emailed them and they did so, at the end of episode 73. I thought the question and answer were interesting enough to transcribe here:

Question of the day: A strain of Flavobacterium (KI72) evolved the capacity to digest nylon, obviously in recent history. Fine and well. How long will it be until one of the cariogenic bacteria species evolves the ability to digest dental resin? After all, we are putting a lot of it on their dinner table.

Answered primarily by Michael Schmidt, who teaches microbiology to dental students at MUSC, with help by Michele Swanson and Vincent Racaniello. Keep in mind that this is a transcribed conversation, so informal, and that I don’t know how to spell some of these words:

Michael: This has already happened to some extent. In the United States we currently spend 5 billion dollars a year replacing resin-based composite fillings due to failure. The average lifespan of a resin-based filling that a dentist will put in today is around 6 years. And the recurrent decay usually compromises the restoration earlier in its lifespan, and that’s when the bacteria are effectively going after the “glue.” And they’re going—because it’s a polymerization and the microbes—if the restoration isn’t properly fixed and properly cured there’s enough carbon in there that they can get at before the polymerization is completely done, that they can actually get after it. And then afterwards, matrix metalloproteinases and cathepsins places the longevity ceiling at that 6 years, even at healthy and bacterial free restorations. And so these matrix metalloproteinases and cathepsins which are expressed specifically in dentin, they come in and they cause the restoration to fail.

Michele: But those are bacterial, Michael, or those are…

Michael: No, those are eukaryotic. The bacterial failure… places the longevity cap at around 6 years, so there’s currently a resin-based product in the market that’s from a Japanese company that puts chlorhexidine into some of these resin-based products in order to prevent microbial attack and to take out the… bacterial attack. So we’ve been looking at copper nano-particles to effectively prevent some of this decay, but what he is hypothesizing has already been happening in the US and it happens throughout the developed world, anyplace people are using resin-based fillings. The old silver fillings typically last 25-30 years without incident. Most people were concerned about the mercury issue but the amount of mercury in an amalgam based filling is insignificant in terms of health consequences if you look at the evidence-based literature. It really has no issue associated with the health of the individual.

Michele: And I don’t suppose there’s any data saying the half-life of the resin is decreasing? Which would be consistent with this idea that we’ve selected for bacteria, we’re enriching for bacteria, that can break it down more readily?

Michael: No, because the resins have gotten better. The polymerization agents and the curing times, so we don’t have a clean experiment to do it. The folks haven’t actually looked to see if resin-based dissolving bacteria… but that’s a question that I can ask my friends at the Forsyth Institute to see if they’ve hunted to see if there are any resin-eating bacteria out there. But it’s all about the polymerization because the polymer needs to be perfectly cured and any of you who’ve had a recent composite filling you remember the dentist putting on the dark glasses and giving you a pair of dark glasses and they put the magic light into your mouth to cure the filling. And typically they only put the UV lamp in there for 20-30 seconds and that’s what starts the curing process. And we’ve all made polyacrylamide gels and it’s a variation of polyacrylamide gels except we use… Temid and whats the inorganic… the inorganic salt. I haven’t made a gel in…

Vincent: I can’t remember either.

Michael: Because you just pull MP… not MPS…

Vincent: APS

Michael: APS. Ammonium persulfate and that’s what goes bad. The binary catalyst.

There was a rumor going around a couple of years ago that you could pee on a straw bale and it would turn into compost. The theory was nitrogen (in pee) plus carbon (in straw) equals compost. I liked the idea that pee could be useful, so I buried a straw bale in my yard to test it out, and wrote about it here.

18 months and many gallons of pee later, I dug it up–an incredibly stinky affair, but hey: science. The short story is that it didn’t work. At all. If anything I’d guess that whatever is in pee besides water has a preservative effect on the straw. There were a couple bugs and grubs, but really just a couple. There was no visible sign of any decay. My guess is that if I’d dumped water on that bale in the same quantity as the pee, it would have at least grown some mildew and broken down a little.

At this point, I have to assume the best place for pee is in the septic tank, as much as that pains my permaculture heart. I would love to be proven wrong about this, but don’t just tell me about a theory. Show me evidence.

Here’s mine. These images are of all the “decay” I could find after going through the entire stinky bale:


The bale, still buried. The level of the straw dropped about a foot over the course of 18 months and I topped it off, hoping that the drop meant decomposition, but it turned out it just compacted.


I found some kind of bug early on but never saw another of this kind.


And here are the 3 grubs I found.


Mostly it looked like this: Pee-soaked, compressed straw.


There was some discoloration like this.


Sal bug in a rare dry spot.


Not Back to School Camp is one of my very favorite things to do, and advisee group is one of my favorite things to do at NBTSC. At the recent Joshua Tree session, I led my 40-somethingth advisee group, and documented our getting to know each other:




















Last day of camp, 1/26/2015