Rhodovulum sulfidophilum is a gram-negative purple nonsulfur bacteria. The cells are rod-shaped, and range in size from 0.6 to 0.9 μm wide and 0.9 to 2.0 μm long, and have a polar flagella. These cells reproduce asexually by binary fission. This bacterium can grow anaerobically (photoautotrophic or photoheterotrophic) when light is present, or aerobically (chemoheterotrophic) under dark conditions. It contains the photosynthetic pigments bacteriochlorophyll a and of carotenoids.
There is interest in R. sulfidophilum for its applications in producing artificial spider silk and biocompounds, waste remediation and for its use in aquaculture.
Taxonomy
Rhodovulum sulfidophilum was first reported by Hansen and Veldkamp in 1973, and given the name Rhodopseudomonas sulfidophila. The bacterium was later reclassified to the Rhodovulum genus in 1994 by Hiraishi and Ueda, as all marine Rhodobacter and Rhodopseudomonas species were transferred to the genus Rhodovulum due to marine Rhodobacter species being able to be differentiated phenotypically from the freshwater species. The Rhodovulum genus have been described with additional properties of G+C content of the DNA that ranges from 66.3 to 66.6 mol% in type strain DSM 1374.
Genome
A genome draft for R. sulfidophilum DSM 1374 was published in 2013, and was predicted to have a chromosome with 3983 genes that code for protein, and two circular plasmids with 93 and 84 genes respectively. The first complete genome was published for strain DSM 2351, revealing a circular chromosome and three circular plasmids of differing DNA base-pair size. Additionally, draft genomes of the AB14, AB26 and AB30 strains were published, and when compared showed diversity between the different strains of R. sulfidophilum. These draft genomes also revealed that they contained genes confirmed to be involved in cellular processes, such as carbon dioxide fixation and sulfur oxidation. Strain AB26 was discovered to have a unique 100 kb plasmid sequence homologous to plasmid 3 that contain genes related to metal metabolism and transport (e.g. manganese, nickel and zinc transport proteins). A later study that analyzed isolates of R. sulfidophilum found that AB26 reserved around 16% of its entire 4,380,746 base pair genome to transport and also had 20 response regulators, and 22 histidine kinases. Another study that genetically characterized R. sulfidophilum discovered that the bacterium contained one copy of pucA and pucB (α- and β- genes) each within the puc operon. In addition, it was found that there were no Integration Host Factor (IHF) and Fumerate and Nitrate Reductase (FNR) regulation protein binding sites in this bacterial species like with Rhodobacter sphaeroides. It was speculated that the lack of binding sites for these proteins are indicative of why the puc operon is expressed when oxygen is present. It was also discovered that while the mRNA sequences between R. sphaeroides and R. sulfidophilum were homologous, a regulatory region exhibited an exchange of TGT to CGT in R. sulfidophilum. Studying the genome of R. sulfidophilum is of particular interest for better understanding relevant metabolic pathways.
When analysing evolution and horizontal gene transfer of Proteobacteria photosynthetic gene clusters, it was shown that R. sulfidophilum shares regions of genetic similarity to a group of other species that range from Roseibacterium elongatum to Dineoroseobacter shibae.
Metabolism
Rhodovulum sulfidophilum is metabolically versatile and can adapt to various environmental conditions by using various metabolic pathways under anaerobic conditions. Primary sources of energy for R. sulfidophilum consist of light, organic compounds and inorganic sulfur compounds.
When provided with a light source and nitrogen, using either malate as a carbon source or sulfide as an electron source, it can undergo photosynthesis to produce ATP. Rhodovulum sulfidophilum is capable of oxidizing sulfide or thiosulfate to yield sulfates in the ecosystem without accumulating intermediates and have an unusual tri-heme cytochrome subunit bound to the reaction center, therefore allowing for photolithoautotrophic growth. Oxidation of thiosulfate is done by the SoxAX protein, which is a heterodimeric c-type cytochrome. Additionally, unlike other nonsulfur purple bacteria, R. sulfidophilum is able to synthesize its peripheral antenna complex under dark aerobic conditions. Rhodovulum sulfidophilum can utilize a wide variety of organic compunds, and grows both photoorganotrophically and heterotrophically.