Rhodoferax
| Rhodoferax | |
|---|---|
| Scientific classification | |
| Domain: | Bacteria |
| Phylum: | Proteobacteria |
| Class: | Betaproteobacteria |
| Order: | Burkholderiales |
| Family: | Comamonadaceae |
| Genus: | Rhodoferax |
| Species | |
Rhodoferax is a genus of Betaproteobacteria belonging to the purple nonsulfur bacteria, a polyphyletic group of phototrophic bacteria. Originally, Rhodoferax species were included in the Rhodocyclus genus as the Rhodocyclus gelatinous-like group. The Rhodoferax genus was first proposed in 1991 to accommodate the taxonomic and phylogenetic discrepancies arising from its inclusion in the Rhodocyclus genus.Rhodoferax currently comprises three described species: R. fermentans, R. antarcticus, and R. ferrireducens. The most recent addition, R. ferrireducens, lacks the typical phototrophic character common to the other Rhodoferax species. This difference has led researchers to propose the creation of a new genus, Albidoferax, to accommodate this divergent species.
Rhodoferax species are Gram-negative rods, ranging in diameter from 0.5 to 0.9 µm with a single polar flagellum. The first two species described for the genus, R. fermentans and R. antarcticus, are facultative photoheterotrophs that can grow anaerobically when exposed to light and aerobically under dark conditions at atmospheric levels of oxygen.R. ferrireducens is a nonphototrophic facultative anaerobe capable of reducing Fe(III) at temperatures as low as 4 °C. All Rhodoferax species possess ubiquinone and derivatives with eight unit isoprenoid side chains. Dominant fatty acids in Rhodoferax cells are palmitoleic acid (16:1) and palmitic acid (16:0), as well as 3-OH octanoic acid (8:0). Major carotenoids found in the phototrophic species are spheroidene, OH-spheroidene, and spirilloxanthin.
As of 2013, two genomes have been sequenced from the genus Rhodoferax. Sequencing of the R. ferrireducens T118 genome was carried out by the Joint Genome Institute, and assembly was completed in 2005. The R. ferrireducens genome contains a 4.71 Mbp chromosome with 59.9% GC content and a 257-kbp plasmid with 54.4% GC content. It has 4,169 protein-coding genes, six rRNA genes, and 44 tRNA genes on the chromosome, as well as 75 pseudogenes. The plasmid contains 248 protein coding genes, one tRNA gene, and 2 pseudogenes. Examination of the R. ferrireducens genome indicates that though it cannot grow autotrophically, several genes associated with CO2 fixation are present. The genome contains the gene for the ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) large subunit, while the small subunit is missing. Other Calvin-cycle enzymes are present, but the phosphoketolase and sedoheptulose-bisphosphatase genes are missing. The genome also contains several genes suggesting R. ferrireducens may have some ability to resist exposure to metalloids and heavy metals. These genes include a putative arsenite efflux pump and an arsenate reductase, as well as genes similar to those found in organisms capable of tolerating copper, chromium, cadmium, zinc, and cobalt. Despite its psychrotolerance, the genome appears to lack any known major cold-shock proteins.
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