07 January, 2008

Still Alive

Been in a quasi-hibernation in this quasi-kaamos.

So I'm trying to reconcile 2 statements the professor of my Microbial Genetics course made in class last Thursday.

1) There are approximately 100 bacteria to every 1 cell in the human body.

2) It is estimated that only 1% of bacteria in any given sample of anything can be cultured and identified.

Each statement could be taken as true in its own context, at least if you ignore questions as to how such statements were formulated*, but together they don't make a lot of sense. Yes, there are ~3kg of bacteria in the human digestive tract alone (thinking of this ensures that I never feel lonely--I've always got a couple trillion close friends at hand). Nonetheless, if only 1% of the bacteria, even in a gut lumen sample, can be cultured and quantified, then how do we know how many were there to begin with? And as such, then how can we know what the ratio of bacterial cells to human cells is?

And as for the first statement, how does that work spatially? Bacteria range in size from 0.5-5.0 micrometers, and eukaryotic cells (e.g., human cells) are 10X as large. If these figures can be taken as directly proportional to volume and not just length, then there should be at most 10 bacteria to each human cell, and even then the total size and mass of those bacterial cells would be the same as the size and mass of the human. But if they are not directly proportional, then maybe it could work, although I still have a hard time imaging those volumes working out.

*Seriously though, how the hell did they get this figure? Did they take a whole healthy human and fractionate the entire body into its cellular components, then centrifuge everything and run it through flow cytometry to get the ratios? Or did they just take a liver biopsy and count that? But that would be inaccurate...

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