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Using E. coli gene arrays to explore genome of the tsetse fly microbe Wigglesworthia glossinidia
By Bijal P. Trivedi

Scientists have used a gene chip carrying all the genes from the common gut bacterium E. coli to probe the unexplored genome of a related microbe, Wigglesworthia glossinidia.

The Wigglesworthia bacterium lives inside the blood-sucking African tsetse fly, which causes a deadly sleeping sickness in humans and a similar disease in cattle. The bacterium and the tsetse have a symbiotic relationship, each providing the other with essential metabolic compounds. Without Wigglesworthia, for instance, tsetse flies grow slowly and are unable to produce many eggs, affecting the insect's ability to reproduce. Researchers are targeting Wigglesworthia as a possible strategy for crippling the tsetse fly and hindering the spread of disease.

Researchers Leyla Akman and Serap Aksoy, both of Yale University School of Medicine in New Haven, Connecticut, used gene arrays containing all 4,290 protein-coding genes in the E. coli genome to detect similar and identical genes in Wigglesworthia. Genes that are unique to Wigglesworthia cannot be detected with these chips.

Because scientists have been unable to cultivate Wigglesworthia in the laboratory, Akman and Aksoy isolated the bacterium's DNA from the guts of tsetse flies. The researchers found that the Wigglesworthia genome is about 770 kb, one-sixth the size of the E. coli genome. In fact, it approaches the size the Mycoplasma genitalium genome—the smallest microbial genome reported to date.

The researchers identified 650 genes—accounting for about 85 percent of the Wigglesworthia genome—that were common to both microbes. Among these were the usual consort of genes associated with replicating and maintaining DNA, and producing RNA and proteins. As expected, a hefty portion of the bacterium's genome was made up of genes that produce transporter proteins, chaperones, and cofactors that allow the bacterium to exchange nutrients with the tsetse fly. The content of the genome also indicates that Wigglesworthia uses ammonia as its main source of nitrogen.

The authors conclude that using microarrays is a rapid and inexpensive approach for exploring the genomes of microbes that have not been sequenced. The study appears in the current issue of Proceedings of the National Academy of Sciences.

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Akman, L. & Aksoy, S. A novel application of gene arrays: Escherichia coli array provides insight into the biology of the obligate endosymbiont of tsetse flies. Proc Natl Acad Sci USA 98, 7546-7551 (June 19, 2001).

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