Microbiology

A Tough Day Out for Nostoc

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Science  01 Mar 2002:
Vol. 295, Issue 5560, pp. 1605
DOI: 10.1126/science.295.5560.1605a

Cyanobacteria are ubiquitous but, being sessile, cannot escape the environmental onslaughts of sunlight, desiccation, and diurnal temperature fluctuation. Dvornyk et al. sampled Nostoc linckia from the opposing slopes of two canyons in Israel to look for genetic polymorphisms associated with the differential environmental stresses experienced by the cyanobacteria. The canyon walls are only 50 to 400 meters apart, but the south-facing slope receives six times as much solar radiation as the north-facing slope and thus offers an excellent opportunity to distinguish the relative mutational effects of contrasting UV doses. In the 60 strains analyzed, the authors found eight haplotypes of the kaiABC gene cluster, which regulates daily circadian rhythms in N. linckia, that differ by nucleotide sequence or in the copy number of genes. The multiple-copy haplotypes were found at the sampling sites exposed to the greatest environmental extremes. The kai multigene family is relatively large and evolutionarily recent, and the diversification may have evolved (in an adaptive manner) as a result of the site-specific environmental conditions, developing and changing in severity with time. — CA

Proc. Natl. Acad. Sci. U.S.A.99, 2082 (2002).

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