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Mycoplasma pulmonis: The genome of a minimalist
By Birgit Hofmann-Reinert

Researchers have sequenced the genome of Mycoplasma pulmonis, a microscopic bacterium that causes respiratory and genital infections in mice and rats. With about 0.9 million base pairs, M. pulmonis possesses one of the smallest genomes of a free-living organism.

Mycoplasma pulmonis. The white bar equals 1mm.

Alain Blanchard, of the Institut de Biologie Végétale Moléculaire, in Bordeaux, France, led the study. The researchers identified 782 genes, the highest number among the four mycoplasma genomes sequenced to date. "The larger number of genes in M. pulmonis…can be mainly attributed to an increased number of membrane proteins," the researchers write in Nucleic Acids Research.

The smallest known bacterial genome is Mycoplasma genitalium with about 500 genes. It was sequenced in 1995 and later shown that about 350 of these genes were essential for life. Although the genome of M. pulmonis is the largest of the four sequenced mycoplasma genomes, the researchers were surprised to find that "several of the genes previously reported to be essential for a self-replicating minimal cell are missing in the M. pulmonis genome."

The M. pulmonis bacterium is a useful model for studying respiratory infections, including pneumonia caused by Mycoplasma pneumoniae in humans. Mycoplasmas are parasites of the mucous membranes in the respiratory, genital, or digestive tracts of animals and humans. They cause infection by excreting toxic byproducts that accumulate in the host's tissues.

The strain sequenced in the study was UAB CT.

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Chambaud, I. et al. The complete genome sequence of the murine respiratory pathogen Mycoplasma pulmonis. Nucleic Acids Res 29, 2145-2153 (May 15, 2001).

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