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Occurrence of Hydrogenases in Cyanobacteria and Anoxygenic Photosynthetic Bacteria: Implications for the Phylogenetic Origin of Cyanobacterial and Algal Hydrogenases
Authors:Marcus Ludwig  Rüdiger Schulz-Friedrich  Jens Appel
Affiliation:1. Botanisches Institut, Christian-Albrechts-Universit?t, Am Botanischen Garten 1-9, D-24118, Kiel, Germany
2. Institut für Biologie, Humboldt-Universit?t zu Berlin, Chausseestrasse 117, D-10115, Berlin, Germany
Abstract:Hydrogenases are important enzymes in the energy metabolism of microorganisms. Therefore, they are widespread in prokaryotes. We analyzed the occurrence of hydrogenases in cyanobacteria and deduced a FeFe-hydrogenase in three different heliobacterial strains. This allowed the first phylogenetic analysis of the hydrogenases of all five major groups of photosynthetic bacteria (heliobacteria, green nonsulfur bacteria, green sulfur bacteria, photosynthetic proteobacteria, and cyanobacteria). In the case of both hydrogenases found in cyanobacteria (uptake and bidirectional), the green nonsulfur bacterium Chloroflexus aurantiacus was found to be the closest ancestor. Apart from a close relation between the archaebacterial and the green sulfur bacterial sulfhydrogenase, we could not find any evidence for horizontal gene transfer. Therefore, it would be most parsimonious if a Chloroflexus-like bacterium was the ancestor of Chloroflexus aurantiacus and cyanobacteria. After having transmitted both hydrogenase genes vertically to the different cyanobacterial species, either no, one, or both enzymes were lost, thus producing the current distribution. Our data and the available data from the literature on the occurrence of cyanobacterial hydrogenases show that the cyanobacterial uptake hydrogenase is strictly linked to the occurrence of the nitrogenase. Nevertheless, we did identify a nitrogen-fixing Synechococcus strain without an uptake hydrogenase. Since we could not find genes of a FeFe-hydrogenase in any of the tested cyanobacteria, although strains performing anoxygenic photosynthesis were also included in the analysis, a cyanobacterial origin of the contemporary FeFe-hydrogenase of algal plastids seems unlikely. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users. [Reviewing Editor: Dr. Lauren Ancel Meyers]
Keywords:Heliobacteria   Chloroflexus   Oxygenic photosynthesis  Photosynthetic proteobacteria
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