Toxic truths

A soil bacterium produces a lethal toxin which kills insects as they chew their way into a plant

Published: Monday 15 July 1996

OF LATE, Bacillus thuriengiensis, a soil bacterium, has become a microbiologist's hot property, owing to its ability to make a protein toxin (13t) which selectively kills an insect consuming this protein. The sensitivity of these insects which include mosquitoes, beetles, butterfly- larvae and aphids, depends upon the genotypes of the insect and the bacteria. Efforts of many research laboratories, both in Denmark and abroad, have revealed the factors governing the biology of bacterial virulence and its interaction with the insect and also about the gene encoding for Bt toxin (Danish Environment, No 4).

Since these insects pose a serious threat to agricultural productivity, scientists have been working towards developing a cost-effective and environment-friendly method for the control of insect pests. Pesticide formulations based on Bt cells or spores (dormant cells) for biological control of insects feeding on crop plants offers an alternative to more expensive and hazardous chemical pesticides.

In Denmark, scientists working at the National Environment Research Institute and the Royal Agricultural University have shown the efficacy of these biopesticides in controlling white -butterfly- larvae infestation in cabbage fields. Another way of using Bt toxin is by inserting it in the plant itself and making a pest-resistant, transgenic (having genetic material from an unrelated species) crop plant.

The bacterial toxin gene, when made to produce the protein inside the plant cell, will work in the same way as it does under natural conditions. Moreover, by making genetically wise alterations in the structure of the gene, the time and site of toxin expression in the crop plant can be regulated. Cotton, corn and potato are three major crops anticipated to hit the market as Bt transgenics in the near future.

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