Tuesday, December 05, 2006

Cousin May's Least Favorite Bacteria

Ogden Nash was a witty poet, but skipped some key biology. Termites may have found wood yummy, but without some endosymbiotic bacteria, wood wouldn't be more than garnish to them -- and the parlor floor would still support Cousin May.

It shouldn't be surprising that such bacteria might be a challenge to cultivate in a non-termite setting. Conversely, university facilities departments are not keen on keeping the native culture system in numbers! :-) Last week's Science has another paper showing off the digital PCR microfluidic chip I mentioned previously. They are again performing single cell PCR, except this time it is going for one cell per reaction chamber rather than one cell per set of chambers. That's because the goal now is not to count mRNAs, but to count bacteria positive for molecular markers. By performing multiplex PCR, they can count categories such as 'A not B', 'A and B', and 'B plus A'.

The particular A's and B's are degenerate primers targeting bacterial 16S ribosomal RNA and a key enzyme for some termite endosymbionts, FTHFS. The 16S rRNA primers have very broad specificity, whereas the FTHFS primers are specific to a subtype called 'clone H'. One more twist: reaction cells with amplifying both primer pairs were retrieved, further amplified, and sequenced. This enabled specific identification of the bacteria present in the positive wells, and in most cases the same 16S and FTHFS sequences were retrieved from wells amplifying both. This is some nifty linkage analysis!

In addition to all sorts of uses in microbiology, such chips might be interesting to apply to cancer samples. Tumors are complex evolving ecosystems, with both the tumors and some of their surrounding tissue undergoing a series of mutations. An interesting family of questions is what mutations happen in what order, and which mutations might be antagonistic. This device offers the opportunity to ask those sorts of questions, if you can design the appropriate PCR primer sets.

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