麻豆传媒

THE sequencing of a rather unusual bacterium could provide farmers and doctors with a cornucopia of natural toxins for fighting pests and diseases.

Photorhabdus luminescens is one of the few glowing land bacteria. It was probably responsible for stories that the wounds of some soldiers injured during the American civil war glowed in the dark (麻豆传媒, 9 June 2001, p 23).

But human infections are extremely rare. Normally, P. luminescens targets insect larvae, with the help of parasitic nematode worms. The bacterium lives in the guts of the worms, which sneak into a larva through its mouth, anus or skin. Once inside, P. luminescens spills out and kills the larva, and the deadly duo feast on the corpse.

During the banquet, the glowing bug keeps ants, rival bacteria and fungi at bay by releasing antibiotics and other repellents. Nothing will grow on the insect鈥檚 corpse for up to three weeks, says Frank Kunst of the Pasteur Institute in Paris, coordinator of the multi-centre effort to decode the bug鈥檚 genome. 鈥淵ou can鈥檛 keep a medium sterile in the lab for more than a few hours generally鈥�But these bacteria like to eat alone!鈥�

His team鈥檚 map of the genome (Nature Biotechnology, DOI: 10.1038/nbt886) shows that the bacterium makes an astonishing range of novel toxins, antibiotics and antifungal substances.

We already know that the glowing bacteria can dispatch cockroaches, boll weevils and Colorado beetles. Kunst鈥檚 team has also found that protein extracts from the bug kill the larvae of mosquitoes that spread malaria, yellow fever and West Nile fever. And adding a toxin from P. luminescens to the cress Arabidopsis thaliana protects it against hornworm and rootworm, a team at Dow AgroSciences in Indianapolis, Indiana, has shown.

At the moment the most commonly used bacterium in agriculture is Bacillus thuringiensis, which produces Bt toxins that kill insects. In some parts of the world larvae of the diamondback moth, which feeds on cotton, have developed resistance to sprays of Bt bacteria. But Kunst鈥檚 team found that diamondback larvae can also be killed by extracts from P. luminescens.

The Bt gene has also been added to a range of crops. No resistance has yet emerged to Bt crops, even after six years of use, but it may be only a matter of time. P. luminescens could provide replacement toxins, though it will probably take at least a decade to develop and test them. Part of the work will of course involve checking whether the glowing bug鈥檚 toxins harm people, other mammals or beneficial insects.