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Genome sequence of Pasteurella multocida
By Bijal P. Trivedi

With the genome of Pasteurella multocida (Pm) in hand, researchers hope to identify proteins that enable the bacterium to cause a range of human and animal diseases, including cholera in birds, hemorrhagic septicemia in cattle, and atrophic rhinitis in swine. The bacterium causes infections in humans through dog and cat bites. Using the genome sequence, researchers have identified two Pm proteins also found in the bacterium that causes whooping cough. These proteins are components of whooping cough vaccine and may prove useful for preventing infections caused by Pm.

Artist's rendition of an exploding Pasteurella multocida, showing a single circular chromosome and microarray analysis. P. multocida was extensively studied by Louis Pasteur for development of attenuated bacterial vaccines more than a century ago.

Barbara May, of the University of Minnesota, and colleagues analyzed the sequence of Pm—which contains 2,257,487 units of DNA—with gene finder programs. The researchers report in the current issue of Proceedings of the National Academy of Sciences that the genome contains 2,014 protein-coding genes.

Two intriguing Pm genes resemble the filamentous hemagglutinin (fha) genes found in the whooping cough bacterium, Bordella pertussis. The fha proteins help the pertussis bacterium grab onto the host cell, and the Pm versions of these proteins may play similar roles, making them promising vaccine targets.

The other striking feature of this genome is that 2.5 percent of the genes produce proteins that are involved in transport of iron into the cell or its processing. Iron is an essential nutrient for nearly all organisms because of its presence in the electron transport chain—a production line for energy molecules called ATP.

May and her team used microarrays to study how gene expression changes when the bacterium is deprived of iron. About 174 genes showed a two-fold change in gene expression; 53 percent showed a decrease in activity and 47 percent showed an increase. About 16 genes showing higher activity at low iron levels are thought, based on comparison with other organisms, to be iron transporter proteins.

Several families of gene-transporter proteins in Pm are also found in Yersinia pestis, the bacterium that caused the black plague that swept through medieval Europe in the 1300s.

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May, B.J. et al. Complete genomic sequence of Pasteurella multocida, Pm70. Proc Natl Acad Sci USA 98, 3460-3465 (March 13, 2001).

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