Sucrose transport by the alkaliphilic, thermophilic Bacillus sp. strain TA2.A1 is dependent on a sodium gradient

An alkaliphilic Bacillus designated strain TA2.A1, isolated from a thermal spring in Te Aroha, New Zealand, grew optimally at pH 9.2 and 70°C. Sodium chloride (>5 mM) was an obligate requirement for the growth of strain TA2.A1 on sucrose, and growth on sucrose was inhibited by monensin, an ionophore that collapses the sodium gradient (ΔpNa+) across the cell membrane. Sucrose transport by strain TA2.A1 was sodium dependent and was inhibited by monensin. The Kt for sucrose tran-sport was 33 μM and the Eadie–Hofstee plot was linear, suggesting one high-affinity uptake system for sucrose. The affinity for sodium was low (0.5 mM), and the Hill plot had a slope of 1.6, suggesting that sodium binding was noncooperative and that the sucrose transporter had more than one binding site for sodium. Based on these results, Bacillus strain TA2.A1 uses a sodium gradient for sucrose uptake, in addition to the sodium-dependent glutamate uptake system reported previously.