Higher buffer concentrations showed greater ability to control pH (Fig. 1A), but not the growths of the HTN (Fig. 1B). pH rapidly dropped below the optimum pH range (4.5-8.5) for HNT [10] after 24 h incubation in the 26 mM buffered medium and 36 h incubation in the 52 mM buffered medium. Cultural time to reach maximum growth seemed to relate to the time where pH started to drop. The result suggested that suitable buffer (K2HPO4 and KH2PO4) concentration for HTN growth and sulfur oxidation activity is 52 mM in TMN medium.