RESUMO
Nitrogen fixation is catalysed by some photosynthetic bacteria. This paper presents a phylogenetic comparison of a nitrogen fixation gene (nifH) with the aim of elucidating the processes underlying the evolutionary history of Rhodopseudomonas palustris. In the NifH phylogeny, strains of Rps. palustris were placed in close association with Rhodobacter spp. and other phototrophic purple non-sulfur bacteria belonging to the alpha-Proteobacteria, separated from its close relatives Bradyrhizobium japonicum and the phototrophic rhizobia (Bradyrhizobium spp. IRBG 2, IRBG 228, IRBG 230 and BTAi 1) as deduced from the 16S rRNA phylogeny. The close association of the strains of Rps. palustris with those of Rhodobacter and Rhodovulum, as well as Rhodospirillum rubrum, was supported by the mol% G+C of their nifH gene and by the signature sequences found in the sequence alignment. In contrast, comparison of a number of informational and operational genes common to Rps. palustris CGA009, B. japonicum USDA 110 and Rhodobacter sphaeroides 2.4.1 suggested that the genome of Rps. palustris is more related to that of B. japonicum than to the Rba. sphaeroides genome. These results strongly suggest that the nifH of Rps. palustris is highly related to those of the phototrophic purple non-sulfur bacteria included in this study, and might have come from an ancestral gene common to these phototrophic species through lateral gene transfer. Although this finding complicates the use of nifH to infer the phylogenetic relationships among the phototrophic bacteria in molecular diversity studies, it establishes a framework to resolve the origins and diversification of nitrogen fixation among the phototrophic bacteria in the alpha-Proteobacteria.
Assuntos
Evolução Molecular , Transferência Genética Horizontal , Oxirredutases/genética , Filogenia , Rodopseudomonas/genética , Alphaproteobacteria/genética , Sequência de Aminoácidos , DNA Ribossômico/análise , Genes Bacterianos , Dados de Sequência Molecular , Fixação de Nitrogênio/genética , Oxirredutases/química , RNA Ribossômico 16S/genética , Rodopseudomonas/enzimologia , Alinhamento de Sequência , Análise de Sequência de DNARESUMO
Partial sequences of farnesyl diphosphate (FPP) synthase genes derived from the Rhodobacter-Rhodovulum group and from the Rhodopseudomonas palustris-Bradyrhizobium japonicum group of the alpha-Proteobacteria were subjected to phylogenetic analysis to investigate the relationships of phototrophic and non-phototrophic bacteria in the alpha-Proteobacteria . The four Rhodovulum species formed a monophyletic group within the Rhodobacter cluster, and Agrobacterium ferrugineum IAM 12616(T) intermingled with the Rhodobacter species. This topology is in good agreement with the 16S rRNA phylogeny, although the FPP synthase gene was more divergent than the 16S rRNA. On the other hand, strains of the phototrophic Rps. palustris formed a cluster far from that of the non-phototrophic Bradyrhizobium japonicum strains. Moreover, Rps. palustris strains were differentiated from the nodule-forming B. japonicum, Mezorhizobium loti MAFF 303099 and Sinorhizobium sp. NGR 234 in the FPP synthase phylogeny. This relationship does not agree with the 16S rRNA phylogeny, wherein Rps. palustris was more closely related to B. japonicum than to strains of the Rhodobacter-Rhodovulum group. These results suggest that the FPP synthase gene of Rps. palustris diverged from that of B. japonicum.
Assuntos
Alquil e Aril Transferases/genética , Alphaproteobacteria/enzimologia , Alphaproteobacteria/genética , Evolução Molecular , Filogenia , Alphaproteobacteria/classificação , Geraniltranstransferase , Dados de Sequência Molecular , RNA Bacteriano/genética , RNA Ribossômico 16S/genética , Análise de Sequência de DNARESUMO
Farnesyl diphosphate (FPP) synthase is essential not only for phototrophic bacteria in carotenoid biosynthesis, but also for non-phototrophic bacteria in the biosynthesis of physiologically important compounds. The gene encoding FPP synthase was assessed as a molecular marker to investigate the intermingled relationship between the phototropic and non-phototropic bacteria in the alpha-Proteobacteria based on 16S rRNA analysis. The FPP synthase amino acid sequences from three phototropic bacteria, Rhodobacter sphaeroides ATCC 11167(T), Rhodobacter capsulatus ATCC 11166(T) and Rhodovulum sulfidophilum W4(T), were determined and used in conjunction with sequences of other representative members of the alpha-, gamma- and epsilon-Proteobacteria and the low-G+C Gram-positive bacteria for phylogenetic analyses by the neighbour-joining and maximum-likelihood methods. The overall topology of the FPP synthase gene tree is consistent with that of the 16S rRNA tree, producing a distinct cluster of the three phototropic bacteria. A minor discordance between the two trees was observed in the cluster of the non-phototrophic Bradyrhizobiumjaponicum USDA 110 and Mesorhizobium loti MAFF 303099; the FPP synthase genes of these two rhizobial species are highly homologous as compared with their respective 16S rRNA. The results suggest that the FPP synthase and 16S rRNA genes have the same evolutionary pattern, evolving vertically from each common ancestral gene; the FPP synthase gene, therefore, could possibly be used for further study on the molecular systematics of photosynthetic bacteria.
