Insights into the carbonic anhydrases and autotrophic carbon dioxide fixation pathways of high CO tolerant Rhodovulum viride JA756.

Biofixation of CO is being extensively investigated to solve the global warming problem. Purple non-sulfur bacteria are fast growers that consume CO and produce beneficial biomass. Better the growth at higher CO levels, more efficient are the strains for biofixation. Nine among fifty strains that were analyzed at elevated CO levels responded with better growth. Considering its enhanced growth at high CO and metabolic versatility, Rhodovulum viride strain JA756 was chosen to make further studies. Strain JA756 tolerates up to 50% (v/v) CO with its optimum between 20-40% (v/v), yielding a biomass of 3.4 g. L. The pattern of specific enzyme activity of carbonic anhydrase corresponded well with that of its growth. To gain insights into the genomic composition and genes related to carbonic anhydrases and CO fixation, draft genome sequencing of JA756 was carried out which revealed the presence of two non-homologous genes encoding for β and γ carbonic anhydrases, both of which are assumed to be implicated in maintaining intracellular inorganic carbon concentration at equilibrium. Most of the genes involved in the Calvin pathway, reductive tricarboxylic acid pathway, 3-hydroxypropionate bicycle and C pathways were found in the draft genome. While the experimental determinations of active roles of two of these pathways are still underway, the expression of key genes of Calvin and C pathway suggest their functional role in the organism. Owing to its metabolic versatility, JA756 can be advantageous for biological CO assimilation facilities located by the coastline, inland and also at wide ranges of CO concentrations.