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March 26, 2009 — Certain bacteria have
learned to manipulate the proportion of females and males in insect
populations. Now Uppsala University researchers have mapped the entire
genome of a bacterium that infects a close relative of the fruit fly.
The findings, published in PNAS, reveal extremely high
frequencies of gene exchange within this group of bacteria. In the
future it is hoped that it will be possible to use sex-manipulating
bacteria as environmentally friendly pesticides against harmful insects.
Bacteria belonging to the Wolbachia group are adapted to
invertebrate animals such as insects, spiders, scorpions, and worms.
These bacteria spread via the female's eggs from one generation to the
next and manipulate the sex quotas among the infected animals so that
more females are produced in the population. Mechanically speaking, the
bacteria convert genetic males into females or kill male embryos that
are then eaten by their sisters or make females lay unfertilized eggs
that all become females. However, what happens most commonly is that
the males cannot reproduce with non-infected females. This gives the
infected females a great advantage, and the infection spreads rapidly
among the population.
The studies of the whole genome have shown that these bacteria carry
genes that are common among higher organisms, but rare among other
bacteria. The scientists believe that the bacteria have stolen these
genes from the genome in the host cell and that they now use them to
manipulate the sex quotas among the insects.
"With the help of viruses, these bacteria exchange genes with each
other, which leads to a rapid dissemination of genes that are thought
to be important for sex manipulation," says Lisa Klasson, one of the
researchers behind the study.
The researchers have shown that the genomes of these bacteria are
evolutionary mosaics, with DNA pieces from many closely related
bacteria. The effect is that each gene has its own evolutionary history
and that the potential for variation is infinite.
"It's fascinating that bacteria, with only 1,000 genes, can control
complicated developmental processes and behaviors in insects," says Siv
By mapping how the genes in these bacteria change over time and
figuring out the mechanisms behind sex manipulation, scientists will be
able to lay a foundation for finding new pesticides for insects, based
on nature's own principles.
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