Lying Dangerously Dormant

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Science  11 Sep 2009:
Vol. 325, Issue 5946, pp. 1320
DOI: 10.1126/science.325_1320b

It was Louis Pasteur who first thought earthworms might play a part in aiding the persistence of anthrax in the soil. He did not follow up on this hunch, but observations on the sporadic occurrence of anthrax spores, coupled with the virus-infested nature of Bacillus anthracis and its close relatives, suggested to Schuch and Fischetti that this dangerous pathogen may do more in the soil than simply lie in wait, encased in a resistant coat. In a set of extensive analyses, B. anthracis was found to harbor not only its own distinctive virulence plasmids but also to act as host for several lysogenic bacteriophages.

Lysogeny was found to alter the capacity of the bacterium to sporulate, to form biofilm exopolysaccharide, to reproduce vegetatively, and to colonize earthworm guts. Phage-encoded sigma factors transcriptionally activated bacterial loci to switch on these phenotypes, enabling B. anthracis and its cousins to live in the soil in a variety of modes, and not just as dormant spores.

PLoS ONE 4, e6532 (2009).

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