The genome sequence of the giant phototrophic gammaproteobacteriumThiospirillum jenensegives insight into its physiological properties and phylogenetic relationships

In a conserved culture of the purple sulfur bacteriumThiospirillum jenenseDSM216(T), cells of this species were easily recognized by cell morphology, large-size spirilla and visible flagellar tuft. TheTsp. jenensegenome is 3.22 Mb in size and has a GC content of 48.7 mol%. It was readily identified as a member of theChromatiaceaeby the complement of proteins in its genome. A whole genome comparison clearly placedTsp. jenensenearThiorhodovibrioandRhabdochromatiumspecies and somewhat more distant fromThiohalocapsaandHalochromatiumspecies. This relationship was also found with the sequences of the photosynthetic reaction center protein PufM. The genome sequence supported important properties of this bacterium: the presence of ribulose-bisphosphate carboxylase and enzymes of the Calvin cycle of autotrophic carbon dioxide fixation but the absence of carboxysomes, an incomplete tricarboxylic acid cycle and the lack of malate dehydrogenase, the presence of a sulfur oxidation pathway including adenylylsulfate reductase (aprAB) but absence of assimilatory sulfate reduction, the presence of hydrogenase (hoxHMFYUFE), nitrogenase and a photosynthetic gene cluster (pufBALMC). The FixNOP type of cytochrome oxidase was notably lacking, which may be the reason that renders the cells highly sensitive to oxygen. Two minor phototrophic contaminants were found using metagenomic binning: one was identified as a strain ofRhodopseudomonas palustrisand the second one has an average nucleotide identity of 82% to the nearest neighborRhodoferax antarcticus.It should be considered as a new species of this genus andRhodoferax jenenseis proposed as the name.

Automated summary

The purple sulfur bacterium Thiospirillum jenense DSM216(T) has a genome size of 3.22 Mb and belongs to the Chromatiaceae family. It possesses sulfur oxidation pathway and a photosynthetic gene cluster, but lacks parts of the tricarboxylic acid cycle and is highly sensitive to oxygen.