Hydrogen sulfide oxidation under anoxic conditions by a nitrate-reducing, sulfide-oxidizing bacterium isolated from the Mae Um Long Luang hot spring, Thailand

•100% H2S was removed completely within 10 h by strain MAL 1HM19.•The end-products via H2S oxidation relied on the initial nitrate concentration.•Strain MAL 1HM19 is closely related to Paracoccus sp. (99.93% similarity).•soxB gene was detected in strain MAL 1HM19.•MAL 1HM19 tolerated high NaCl concentrations, pH 7.0-9.0 and temperatures 20-50 °C.

Biological removal of hydrogen sulfide (H2S) has been widely practiced across the world because it overcomes the drawbacks associated with physico-chemical processes. In this study, the role of a novel MAL 1HM19 strain of a nitrate-reducing, sulfide-oxidizing bacterium (NR-SOB) isolated from the Mae Um Long Luang hot spring (Thailand) was investigated in batch systems for H2S removal under different initial N-NO3− concentrations (60, 120 and 240 mg N-NO3−/L) at 35 °C. The strain MAL 1HM19 was capable of removing 100% of the gas-phase H2S within 10 h of incubation. In the liquid-phase, the final products depended on the initial N-NO3− concentration: at 120 and 240 mg N-NO3−/L, 15% and 18% SO42− formation was detected, while no SO42− was detected at an initial N-NO3− concentration of 60 mg N-NO3−/L. The identification of strain MAL 1HM19, based on the 16S rDNA nucleotide sequence, revealed it was closely related to Paracoccus sp. (99.93% similarity). The soxB gene was present in strain MAL 1HM19. In addition, strain MAL 1HM19 showed a good capacity to grow at several NaCl concentrations (0.03-7% w/v), at temperatures varying between 20 and 50 °C and within the pH range of 7.0-9.0.

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