Bacteria kill male bees by invading the mother's body

Many groups of bacteria are known as 'male killers' - they only kill male elements in the host species. A Cornell scientist has for the first time described how some male killing bacteria can remove male wasps.

The bacterium Arsenophonus nasoniae infects the wasps parasitic Nasonia vitripennis both male and female, but targets males, kills more than 70%, Patrick Ferree said, he is Cornell's postdoctoral researcher at birth. studying and molecular genetics.

Feree and Rochester University collaborator John Werren report this mechanism in the journal Current Biology on September 23.

Arsenophonus prevents the ability of males' eggs to develop normally into embryos by infecting mothers. Ferree said: 'Arsenophonus resides in the tissue around the developing egg in the mother's body, not inside the egg, they secrete an unknown substance to invade the egg and affect embryonic development. . The result of infection is that mother bees produce more females than males.

Unlike the previously described mechanisms that explain the unbalanced sex ratio in worms, Arsenophonus targets small cellular organs called the inner center of the growing body of males. The center acts to control cell division and participates in the process of dividing chromosomes into new cells.

On the left is the unfertilized normal Nasonia (male) embryo. The right image shows that the fertilized embryo is infected with bacteria that kill the male.The presence of bacteria causes the process of nuclear division to fail and ultimately the death of the male.

But why only males are vulnerable to Arsenophonus attacks? Male Nasonia grows from eggs fertilized by sperm. So the females are middle of the mother as well as the father's sperm. On the other hand, males develop from unfertilized eggs and therefore there is no neutrality from the father's sperm - Arsenophonus has evolved to destroy the egg-derived central, preventing embryonic development. male. Sperm-derived centrosomes in female embryos are not infected with Arsenophonus.

Ferree said: 'This is an example of an imbalance in the sex ratio that comes from the host's own reproductive structure. They attack and take advantage of gender differences - in this case the egg-derived centrosomes. "

'The ability to kill males is an advantage for these bacteria because they only pass through females - this helps females grow stronger and naturally spread more bacteria.'

This study is significant in understanding the interactions between pathogens and hosts, as well as the central formation of eggs derived from eggs. Ferree said: 'The egg-derived center has never been analyzed to understand the possible impact, I think the above-mentioned bacterium is the first to do this. The arthropods (insects) are diverse all over the world, so it's interesting to imagine how many bacterial reproductive mechanisms exist. '

The study (published in Current Biology [2008] 18: 1409--1414) was sponsored by the Ruth L. Kirschstein National Research Award and the National Institutes of Health.