Evolution

Shape-Shifting Cyanobacteria

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Science  08 Apr 2011:
Vol. 332, Issue 6026, pp. 150
DOI: 10.1126/science.332.6026.150-d
CREDIT: BETTINA SCHIRRMEISTER

Two-and-a-half billion years ago, cyanobacteria may have caused the first mass extinction on Earth by inventing oxygenic photosynthesis. During their slow evolution, these prokaryotes donated their light-harvesting organelles to plants, developed a nitrogen-harvesting mechanism, and, not least, adopted many multicellular morphotypes. Few cyanobacteria have been sequenced, however, and as a result, their evolutionary history and phylogeny are largely unknown. Schirrmeister et al. used multiple phylogenetic analyses on the limited number of 16S rDNA cyanobacterial sequences available to compare the resulting trees with established morphologically derived clades and to the scant fossil record. They obtained a monophyletic tree with Gloeobacter being the nearest outgroup and Chlamydia as the closest eubacterium. Rates of evolution among the cyanobacteria may be slow, but they organized into multicellular forms that displayed some functional specialization several times—and well before eukaryotes undertook this major transition. Since then, cyanobacteria appear merely to have evolved into three major clades, which have shifted between multicellular and unicellular morphotypes. Most modern lineages appear to have multicellular common ancestors, including the important marine genera Synechococcus and Prochlorococcus.

BMC Evol. Biol. 11, 45 (2011).

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