by MerryWhen you're outnumbered five or ten to one, strategy counts. Bacteria and archaea are master strategists, thriving despite the omnipresent hordes of phage. For some time, it has been known that prokaryotic cells have ploys for blocking phage adsorption,

http://schaechter.asmblog.org/schaechter/2008/02/getting-crispr.html

CRISPR--a widespread system that provides acquired resistance against phages in bacteria and archaea. Sorek R (2008) Nat Rev Microbiol.
A putative RNA-interference-based immune system in prokaryotes: computational analysis of the predicted enzymatic machinery, functional analogies with eukaryotic RNAi, and hypothetical mechanisms of action. Makarova KS (2006) Biol Direct.
CRISPR provides acquired resistance against viruses in prokaryotes. Barrangou R (2007) Science.
February 21, 2008