Evaluating the Sulfur Oxidation Capability of a Rhodopseudomonas palustris Strain by Gene and Enzyme Analyses for Potential Applications in Environmental Bioremediation

Sulfur-oxidizing bacteria are capable of oxidizing various sulfur compounds including sulfide and thiosulfate in the environment. Hydrogen sulfide (H2S), a product of anaerobic decomposition, is highly corrosive. With the typical smell of rotten eggs, the toxic gas H2S causes many harmful effects on the environment and human health. Sulfide:quinone oxidoreductase enzyme (SQR) produced by sulfur-oxidizing bacteria plays an important role in the sulfide oxidation process, contributing to minimizing sulfide toxicity in the environment. In this study, the presence of sqr gene and SQR enzyme in the photosynthetic purple bacterium Rhodopseudomonas palustris (R. palustris) isolated from domestic wastewater was determined by gene amplification (PCR) using specific primer pairs following by sequencing and denaturing SDS-PAGE method combined with sulfide oxidase assay that measures BaSO4 turbidity, respectively. The results showed that the sqr gene has 1254 bp in length, encoding for the SQR protein containing 417 amino acids with a molecular weight of 45.87 kDa and locating on the cell membrane. The enzyme operated optimally under the condition of pH 6.5 and temperature at 30 °C with sulfide oxidation activity recorded up to 20-21 U/ml. The study has initially shown the ability of the R. palustris bacterial strain to oxidize sulfide for further research using sulfur-oxidizing bacteria applied in environmental treatment.