Abstract
Besides amino acid decarboxylation, the ADP biosynthetic pathway was reported to enhance survival under extremely acidic conditions in Escherichia coli (Sun et al., J. Bacteriol. 193∶ 3072–3077, 2011). E. coli has two pathways for ATP synthesis from ADP: glycolysis and oxidative phosphorylation. We found in this study that the deletion of the F1Fo-ATPase, which catalyzes the synthesis of ATP from ADP and inorganic phosphate using the electro-chemical gradient of protons generated by respiration in E. coli, decreased the survival at pH 2.5. A mutant deficient in hemA encoding the glutamyl tRNA reductase, which synthesizes glutamate 1-semialdehyde also showed the decreased survival of E. coli at pH 2.5. Glutamate 1-semialdehyde is a precursor of heme synthesis that is an essential component of the respiratory chain. The ATP content decreased rapidly at pH 2.5 in these mutants as compared with that of their parent strain. The internal pH was lowered by the deletion of these genes at pH 2.5. These results suggest that respiration and the F1Fo-ATPase are still working at pH 2.5 to enhance the survival under such extremely acidic conditions.
Highlights
Escherichia coli has to pass through the extremely acidic stomach before entering the more hospitable gastro-intestinal tract, and resistance to extremely acidic environments (AR) is an important mechanism for E. coli to survive [1,2]
An adenosinedependent AR system was reported in E. coli, and this system was less active than AR2 but more potent than AR4 [10]
E. coli F1Fo-ATPase consists of two parts, F1 and Fo, which contain five subunits (a, b, c, d, and e) and three subunits (a, b, and c), respectively [34,35]
Summary
Escherichia coli has to pass through the extremely acidic stomach before entering the more hospitable gastro-intestinal tract, and resistance to extremely acidic environments (AR) is an important mechanism for E. coli to survive [1,2]. Multiple metabolic pathways have been reported to function for survival under extremely acidic conditions. Three amino acid-dependent systems have been identified as enhancing the AR in E. coli [1]. The most potent system is the glutamate-dependent system (AR2) [3,4]. An adenosinedependent AR system was reported in E. coli, and this system was less active than AR2 but more potent than AR4 [10]. These systems were proposed to regulate the intracellular pH (pHi) at a higher level than the pH of the surroundings [1,10]
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