Production of indole and hydrogen sulfide by the oxygen-tolerant mutant strain Clostridium sp. Aeroto-AUH-JLC108 contributes to form a hypoxic microenvironment

In this study, the oxygen-tolerant mutant strain Clostridium sp. Aeroto-AUH-JLC108 was found to produce indole when grown aerobically. The tnaA gene coding for tryptophanase responsible for the production of indole was cloned. The tnaA gene from Aeroto-AUH-JLC108 is 1677 bp and has one point mutation (C36G) compared to the original anaerobic strain AUH-JLC108. Phylogenetic analyses based on the amino acid sequence showed significant homology to that of TnaA from Flavonifractor . Furthermore, we found that the tnaA gene also exhibited cysteine desulfhydrase activity. The production of hydrogen sulfide (H 2 S) was accompanied by decrease in the amount of the dissolved oxygen in the culture medium. Similarly, the amount of indole produced by strain Aeroto-AUH-JLC108 obviously decreased the oxidation–reduction potential (ORP) in BHI liquid medium. The results demonstrated that production of indole and H 2 S helped to form a hypoxic microenvironment for strain Aeroto-AUH-JLC108 when grown aerobically.