Bacterial immune system probed

Bacteria have a clever gene-based immune system that helps them fend off attack, researchers have found.

Writing in Nature, Quebec-based scientist Josiane Garneau, from Laval University, has shown that when Streptococci and other bugs come under attack from bacteria-hijacking viruses called bacteriophages or even trnamissible pieces of DNA termed plasmids, they add a piece of the genetic code from the invader to a special region of their own DNA.

The molecular equivalent of a DNA trophy cabinet, this microbial library consists of many short chunks of genetic material garnered from previously-encountered attackers. It's been termed the CRISPR region, short for clustered regularly interspersed short palindromic repeats.

This region, Garneau and her colleagues have discovered, serves as an immune memory for the bacterium. If the same bacteriophage turns up again, its DNA sequence is compared with the version lodged in the CRISPR region. If there's a match then a set of cellular scissors, directed by one of a family of genes called cas, chops up the invader's genome before it can do any damage. Understanding how this system operates could hold the key to "vaccinating" biotechnologically significant bacteria such as those used in the cheese and dairy industry to make the bugs less vulnerable to bacteriophage attack.