Journal
APPLIED AND ENVIRONMENTAL MICROBIOLOGY
Volume 75, Issue 24, Pages 7649-7654Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/AEM.01639-09
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- Royal Society of New Zealand
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Caldalkalibacillus thermarum strain TA2.A1 grew in pH-controlled batch culture containing a fermentable growth substrate (i.e., sucrose) from pH 7.5 to 10.0 with no significant change in the specific growth rate, suggesting that this bacterium was a facultative alkaliphile. However, when strain TA2.A1 was grown on a nonfermentable carbon source, such as succinate or malate, no growth was observed until the external pH was >9.0, suggesting that this bacterium was an obligate alkaliphile. Succinate transport and sucrose transport by strain TA2.A1 showed pH profiles similar to that of growth on these carbon sources, and the molar growth yield on sucrose was higher at pH 9.5 than at pH 7.5, despite the increased energy demands on the cell for intracellular pH regulation. Succinate transport, succinate-dependent oxygen consumption, and succinate dehydrogenase and F1Fo-ATPase specific activities were all significantly lower in cultures of strain TA2.A1 grown at pH 7.5 than in those cultured at pH 9.5. No significant ATP synthesis via the F1Fo-ATP synthase was detected until the external pH was >8.5. On the basis of these results, we propose that nonfermentative thermoalkaliphilic growth is specialized to function at high pH values, but not at pH values near neutral pH.
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