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Tuesday, October 19, 2004 A Brief Profile of an Endosymbiont In reading about the giant Mimivirus which was recently sequenced, I came across a very strangely named bacterium named Wigglesworthia. Did some microbiologist have a sense of humor and decide to name a new genus after Dr. Evil's cat in Austin Powers? Alas, that isn't the case. I got my W's and B's mixed up as the cat's name is actually Mr. Bigglesworth. Wigglesworthia was discovered by Serap Aksoy in 1995 at Yale. The bacterium was named after Sir Vincent Brian Wigglesworth. In entomology circles, Wigglesworth was known as "the world's greatest insect physiologist" with a specialization in insect hormone action (invertebrate endocrinology). So why is a microscopic bug named after a guy who specialized in macroscopic ones? Well, it turns out that Wigglesworthia was originally isolated from the gut of the tsetse fly--medically important because it is the vector for sleeping sickness--one of the insects meticulously described by Wigglesworth. As a gut bacterium, it isn't all that surprising that from genome analysis we see that Wigglesworthia is related to the Enterobacteria which includes the laboratory workhorse and human gut bacterium E. coli. Wigglesworthia, however, has lost a lot of its genes while co-evolving and becoming more dependent on the tsetse fly. In fact, it has one of the smallest bacterial genomes sequenced: less than 770 kb or one-sixth of that of E. coli. The bacteria live inside specialized cells of a U-shaped gut organ called the mycetome. Wigglesworthia isn't completely getting a free ride though--the fly requires the bacteria for survival. One reason for the tsetse fly's dependence on Wigglesworthia is nutrition. Genomic studies have revealed bacterial genes that encode pathways for vitamin biosynthesis. This also has an interesting impact on fertility. In tsetse flies that do not carry the endosymbiont, fertility is dramatically reduced. Fertility can be restored if the flies are given a B vitamin supplement. How does this work? The young actually inherit the mother's endosymbiont. Scientists speculate that Wigglesworthia may infect the larvae through the mother's milk. Since the tsetse fly is a major carrier for sleeping sickness, Wigglesworthia might be a key tool to help control insect populations. [posted by S. Y. Affolee on 10:57 AM : ]
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