Guffanti A A, Hicks D B
Department of Biochemistry, Mount Sinai School of Medicine, City University of New York, NY 10029.
J Gen Microbiol. 1991 Oct;137(10):2375-9. doi: 10.1099/00221287-137-10-2375.
Alkaliphilic Bacillus species that grow at pH 10.5 must cope with a low protonmotive force (-50 mV) due to a reversed transmembrane pH gradient at least 2 pH units more acid inside. Here we demonstrate that strictly alkaliphilic B. firmus RAB and two strains of B. alcalophilus (ATCC 27467 and DSM 485) grow exponentially in batch cultures with a doubling time of less than 1 h in 100 mM buffered medium, while the actual medium pH remains above 10.2. The ATCC strain continued to grow rapidly for at least 7 h, but the growth rate of the DSM strain declined dramatically after 3 h. However, both the B. alcalophilus strains, B. firmus RAB and facultatively alkaliphilic B. firmus OF4 were readily maintained for at least 24 h between pH 10.4 and 10.6 in a chemostat where nutrients were constantly replenished. A critical nutrient may be limiting in batch cultures of the DSM strain of B. alcalophilus. The facultative alkaliphile grew equally well in batch cultures at an initial pH of 7.5 or 10.5. Its molar growth yield (23 mg dry wt mmol-1) on malate (Ymal) was the same at the two pH values and was comparable to Ymal for B. subtilis grown at neutral pH. B. firmus RAB and B. alcalophilus ATCC 27467 grown at pH 10.5 also showed Ymal values at least as high as the neutralphile, indicating efficient use of the energy source even at low protonmotive force. Moreover, the phosphorylation potential of B. firmus OF4 grown at pH 7.5 (45.2 kJ mol-1) or pH 10.5 (46 kJ mol-1) was in a conventional range for bacteria.
在pH 10.5环境下生长的嗜碱芽孢杆菌属细菌，由于跨膜pH梯度逆转，细胞内酸性至少高出2个pH单位，必须应对低质子动力（-50 mV）的情况。在此，我们证明，严格嗜碱的坚强芽孢杆菌RAB以及两株嗜碱芽孢杆菌（ATCC 27467和DSM 485）在100 mM缓冲培养基的分批培养中呈指数生长，倍增时间小于1小时，而实际培养基pH保持在10.2以上。ATCC菌株至少能快速生长7小时，但DSM菌株的生长速率在3小时后急剧下降。然而，嗜碱芽孢杆菌的两个菌株、坚强芽孢杆菌RAB以及兼性嗜碱的坚强芽孢杆菌OF4在恒化器中，在pH 10.4至10.6之间，营养物质不断补充的情况下，都能轻松维持至少24小时的生长。在嗜碱芽孢杆菌DSM菌株的分批培养中，一种关键营养物质可能受到限制。这种兼性嗜碱菌在初始pH为7.5或10.5的分批培养中生长情况相同。其在苹果酸上的摩尔生长产率（23 mg干重 mmol-1）（Ymal）在两个pH值下相同，与在中性pH下生长的枯草芽孢杆菌的Ymal相当。在pH 10.5下生长的坚强芽孢杆菌RAB和嗜碱芽孢杆菌ATCC 27467的Ymal值也至少与中性菌一样高，表明即使在低质子动力下，它们也能高效利用能源。此外，在pH 7.5（45.2 kJ mol-1）或pH 10.5（46 kJ mol-1）下生长的坚强芽孢杆菌OF4的磷酸化电位处于细菌的常规范围内。
