MICROBIOLOGY: Low Water Pressure

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Science  23 Aug 2002:
Vol. 297, Issue 5585, pp. 1239a
DOI: 10.1126/science.297.5585.1239a

A particularly fearsome combination of an insect-predatory nematode and its enterobacterial partner (Photorhabdus) has been the subject of intense study. The partners' intertwined life cycles result in a molecular complexity (and a large bacterial genome of 5.5 Mb) of considerable commercial interest because of the range of toxins and antibiotics produced. Photorhabdus lives in the gut of the nematode, and when the nematode penetrates a caterpillar, the bacteria are regurgitated. The bacteria express several toxins that immobilize the caterpillars and destroy them from the inside out. The predatory partner replicates within the nutrient broth of the insect's carcass, with the offspring taking up a new generation of bacteria as they feed.

Daborn et al. have used a large toxin gene (makes caterpillars floppy) from Photorhabdus to endow Escherichia coli with the ability to evade a caterpillar's immune responses and to produce a loss of turgor. The toxin has little similarity to known proteins, except for a BH3 domain also found in pro-apoptotic proteins. This region of the genome is also associated with a shift in GC content, which suggests it may have been acquired laterally from another bacterium as a “pathogenicity island.” — CA

Proc. Natl. Acad. Sci. U.S.A. 99, 10742 (2002).

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