Thiosulfate oxidation and mixotrophic growth of Methylobacterium oryzae

Thiosulfate oxidation and mixotrophic growth with succinate or methanol plus thiosulfate was examined in nutrient-limited mixotrophic condition for Methylobacterium oryzae CBMB20, which was recently characterized and reported as a novel species isolated from rice. Methylobacterium oryzae was able to utilize thiosulfate in the presence of sulfate. Thiosulfate oxidation increased the protein yield by 25% in mixotrophic medium containing 18.5 mmol-L-1 of sodium succinate and 20 mmol-L-1 of sodium thiosulfate on day 5. The respirometric study revealed that thiosulfate was the most preferable reduced inorganic sulfur source, followed by sulfur and sulfite. Thiosulfate was predominantly oxidized to sulfate and intermediate products of thiosulfate oxidation, such as tetrathionate, trithionate, polythionate, and sulfur, were not detected in spent medium. It indicated that bacterium use the non-S-4 intermediate sulfur oxidation pathway for thiosulfate oxidation. Thiosulfate oxidation enzymes, such as rhodanese and sulfite oxidase activities appeared to be constitutively expressed, but activity increased during growth on thiosulfate. No thiosulfate oxidase (tetrathionate synthase) activity was detected.