TWiM 30 Letters

Megan writes:

I am a Clinical Microbiologist, and have really been enjoying the insights and discussion on TWIM and TWIV (and am hoping to get to TWIP soon). I have really found the information being presented helpful, and am wondering if any of the lectures from the hosting professors are available online. I have found some of Dr. Racaniello's lectures in the iTunes store, are any of Dr. Schaecter and Dr. Schmidt's lectures available online?

Thank you for any information, and thank you for the valuable resource you are providing with these podcasts.

Dallas writes:

Being a retreaded physics/physical chemical/thermodynamic type without any formal education in biology of any kind, I find your podcasts accessible -- even if somewhat hard to get my mind around.  Your are good about defining the jargon that exists in every field of science.  

I have spent 35 years working in aquaculture (the raising of aquatic animals) in systems whose real performance is controlled by the microbiologic ecology.  In my sub-field of recycle aquaculture, I partition this microbiological ecology into separate unit operations like biofilters, where the performance is a little more controllable/predictable, but still would have a metagenomics as complex or more complex than the human gut.  I have seen very few papers even attempt to get a handle on these complex system.  

In the practical microbiology department, I have developed a series of fluidized bed biofilters that are able to remove some hazardous materials from ground water down to non-detetable levels of < 1 ppb, well below the minimum substrate concentration for the bugs of about 20 ppb.  In particular MTBE , a water soluble gasoline additive, enters ground water from leaky underground storage tanks and people can taste it at 50 ppb.  In Calif. the political class went ballistic over this minor contamination problem and forced a multibillion dollar solution, which means that gasoline is 50¢/gal higher in Calif that the rest of the country.  The political class supported by the press was going on about how MTBE was non-biodegradable and the lawyers were making a fortune.  

My experience indicates that very few chemicals are non-biodegradable, if there is energy that a bug can obtain from degradation.  If that weren't true, we would be up to our eyeballs with all sorts of refractory organic chemicals.  

I heard that UC Davis and UC Riverside researchers has some very slow growing bacteria that seemed to metabolize the MTBE and they were digging up all sorts of leaky underground tanks in my area.  Knowing that these bugs had a 10+ day or so doubling time combined with a 10% or so yield, I knew that I had to setup a reactor that could maintain the bacteria while processing large volumes of liquid over very long time periods.  It took me 9 mo to get my first bioreactor running using seed from the universities, sewerage plants and every soil around a leaky tank I could find and a continuous feed of MTBE as the only energy source.  I ended up making some money growing kg amounts of these bacteria consortia semenax wiki attached to sand grains used to as seed to start up new bioreactors on new sites and went through many bbl of MTBE growing and feeding them.  We can go into a bioreactor at 2000 ppb and come out at < 1 ND with a 15 minute contract time.  

The trick of obtaining a continuous discharge concentration below the Smin (minimum substrate concentration for the bacteria to break even -- zero net growth) is to have plug flow on the liquid phase of the system and mixed flow on the biological phase.  You fatten up the bugs in the bottom at a concentration above Smin and they keep eating when they get moved to the top where the concentration is below Smin.   If the inlet concentration gets near Smin, we have to add MTBE to the input water to maintain a lower discharge concentration.  Try telling a regulator that you are going to add a pollutant to the water to get a lower discharge concentration and it blows their minds.

The concept of these fluidized bed bioreactors could be an interesting research tool for the dental bugs you have mentioned.  You could fluidize small grains of tooth enamel, where effectively every small grain is in free fall in the culture media all the time, and you could see what happens to the consortia as you change the feed composition -- coke vs pepsi vs apple juice vs mouth wash, etc.  

Continue the good work.  


David writes:

Dear Professor,

I am a former molecular immunologist who now works as an attorney doing catastrophic birth injury defense.  I can't thank you enough for enriching my drives with TWIP, TWIV, TWIP and TWIM.

As you can imagine, one of the bugs which occupies a lot of my thoughts is GBS and its proclivity for vertical infections of fetuses.  I know that in a certain percentage of individuals are colonized and happily walk around with GBS never causing a problem.  What I would be really be interested in learning more about is what can make happy colonizers into pathogens.  My thought was that perhaps in fighting for territory a bacterium like GBS expresses virulence factors which, in some conditions, allows it to crowd out other flora.  Some sort of swarming like event gets it to spread out and it encounters the fetus.

I know this is likely a gross simplification- but if you have any ideas or suggestions for reading I would be in your debt.

Once again- many thanks for the hours of fun.

Nathan writes:

Hi TWiM-ers,
I have not listened to every episode of TWiM yet, so you may have answered these questions already. If you haven't, though, will you address these two?

What do you think you do differently in your non-professional lives because of what you know about microbiology?

Describe exactly what it takes to create selection pressure on microbes. I'm thinking about the mainstream conversation around microbe-specific antibacterials vs. alcohol-based sanitizers vs. regular soaps, but I'd like to know the general principles with which you approach that line of thought.



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