Metabolic flexibility revealed in the genome of the cyst-forming α-1 proteobacterium Rhodospirillum centenum

<p>Abstract</p> <p>Background</p> <p><it>Rhodospirillum centenum </it>is a photosynthetic non-sulfur purple bacterium that favors growth in an anoxygenic, photosynthetic N₂-fixing environment. It is emerging as a genetically amenable model organism for molecular genetic analysis of cyst formation, photosynthesis, phototaxis, and cellular development. Here, we present an analysis of the genome of this bacterium.</p> <p>Results</p> <p><it>R. centenum </it>contains a singular circular chromosome of 4,355,548 base pairs in size harboring 4,105 genes. It has an intact Calvin cycle with two forms of Rubisco, as well as a gene encoding phosphoenolpyruvate carboxylase (PEPC) for mixotrophic CO₂fixation. This dual carbon-fixation system may be required for regulating internal carbon flux to facilitate bacterial nitrogen assimilation. Enzymatic reactions associated with arsenate and mercuric detoxification are rare or unique compared to other purple bacteria. Among numerous newly identified signal transduction proteins, of particular interest is a putative bacteriophytochrome that is phylogenetically distinct from a previously characterized <it>R. centenum </it>phytochrome, Ppr. Genes encoding proteins involved in chemotaxis as well as a sophisticated dual flagellar system have also been mapped.</p> <p>Conclusions</p> <p>Remarkable metabolic versatility and a superior capability for photoautotrophic carbon assimilation is evident in <it>R. centenum</it>.</p

The Complete Genome Sequence of Roseobacter denitrificans Reveals a Mixotrophic Rather than Photosynthetic Metabolism

Purple aerobic anoxygenic phototrophs (AAPs) are the only organisms known to capture light energy to enhance growth only in the presence of oxygen but do not produce oxygen. The highly adaptive AAPs compose more than 10% of the microbial community in some euphotic upper ocean waters and are potentially major contributors to the fixation of the greenhouse gas CO(2). We present the complete genomic sequence and feature analysis of the AAP Roseobacter denitrificans, which reveal clues to its physiology. The genome lacks genes that code for known photosynthetic carbon fixation pathways, and most notably missing are genes for the Calvin cycle enzymes ribulose bisphosphate carboxylase (RuBisCO) and phosphoribulokinase. Phylogenetic evidence implies that this absence could be due to a gene loss from a RuBisCO-containing α-proteobacterial ancestor. We describe the potential importance of mixotrophic rather than autotrophic CO(2) fixation pathways in these organisms and suggest that these pathways function to fix CO(2) for the formation of cellular components but do not permit autotrophic growth. While some genes that code for the redox-dependent regulation of photosynthetic machinery are present, many light sensors and transcriptional regulatory motifs found in purple photosynthetic bacteria are absent

RMeseeartcah Abrtoiclelic Flexibility Revealed in the Genome of the Cyst-forming α-1 Proteobacterium Rhodospirillum Centenum

Background: Rhodospirillum centenum is a photosynthetic non-sulfur purple bacterium that favors growth in an anoxygenic, photosynthetic N2-fixing environment. It is emerging as a genetically amenable model organism for molecular genetic analysis of cyst formation, photosynthesis, phototaxis, and cellular development. Here, we present an analysis of the genome of this bacterium. Results: R. centenum contains a singular circular chromosome of 4,355,548 base pairs in size harboring 4,105 genes. It has an intact Calvin cycle with two forms of Rubisco, as well as a gene encoding phosphoenolpyruvate carboxylase (PEPC) for mixotrophic CO2 fixation. This dual carbon-fixation system may be required for regulating internal carbon flux to facilitate bacterial nitrogen assimilation. Enzymatic reactions associated with arsenate and mercuric detoxification are rare or unique compared to other purple bacteria. Among numerous newly identified signal transduction proteins, of particular interest is a putative bacteriophytochrome that is phylogenetically distinct from a previously characterized R. centenum phytochrome, Ppr. Genes encoding proteins involved in chemotaxis as well as a sophisticated dual flagellar system have also been mapped. Conclusions: Remarkable metabolic versatility and a superior capability for photoautotrophic carbon assimilation is evident in R. centenum.This work was supported by the U.S. National Science Foundation Phototrophic Prokaryotes Sequencing Project, grant number 0412824, by a Grantin- Aid for Creative Scientific Research (No. 17GS0314) from the Japanese Society for Promotion of Science, and a Indiana University MetaCyt grant. W.D.S. is funded by the Japanese Society for Promotion of Science Postdoctoral Fellowship for Foreign Researchers (No. P07141)