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