Biology Department, University of Puerto Rico-Humacao, Humacao, PR 00791, USA.
FEMS Microbiol Ecol. 2010 Mar;71(3):341-50. doi: 10.1111/j.1574-6941.2009.00805.x. Epub 2009 Nov 3.
Although the implications of calcium carbonate (CaCO(3)) precipitation by microorganisms in natural environments are quite relevant, the physiology and genetics of this phenomenon are poorly understood. We have chosen Bacillus subtilis 168 as our model to study which physiological aspects are associated with CaCO(3) (calcite) formation during biofilm development when grown on precipitation medium. A B. subtilis eftA mutant named FBC5 impaired in calcite precipitation was used for comparative studies. Our results demonstrate that inactivation of etfA causes a decrease in the pH of the precipitation medium during biofilm development. Further analysis demonstrated that eftA extrudes an excess of 0.7 mol H(+) L(-1) with respect to B. subtilis 168 strain. Using media buffered at different pH values, we were able to control calcite formation. Because etfA encodes the alpha-subunit of a putative flavoprotein involved in fatty acid metabolism, we compared the intracellular levels of NADH among strains. Our physiological assay showed that FBC5 accumulated up to 32 times more NADH than the wild-type strain. We propose that the accumulation of NADH causes a deregulation in the generation of the proton motive force (DeltamicroH(+)) in FBC5 producing the acidification.
尽管微生物引起碳酸钙（CaCO（3））沉淀在自然环境中的意义重大，但人们对这一现象的生理学和遗传学仍知之甚少。我们选择枯草芽孢杆菌 168 作为模型，研究在沉淀培养基中生物膜发育过程中与 CaCO（3）（方解石）形成相关的生理方面。一个名为 FBC5 的枯草芽孢杆菌 eftA 突变体在方解石沉淀方面受到了损害，用于比较研究。我们的结果表明，ef tA 的失活导致生物膜发育过程中沉淀介质的 pH 值下降。进一步的分析表明，ef tA 相对于枯草芽孢杆菌 168 菌株向外排出超过 0.7 mol H（+）L（-1）。通过使用不同 pH 值缓冲的培养基，我们能够控制方解石的形成。由于 ef tA 编码一种参与脂肪酸代谢的假定黄素蛋白的α亚基，我们比较了不同菌株之间的细胞内 NADH 水平。我们的生理测定表明，FBC5 积累的 NADH 比野生型菌株多 32 倍。我们提出，NADH 的积累导致 FBC5 中质子动力势（DeltamicroH（+））的产生失调，从而导致酸化。
