Escherichia coli K-12 survives anaerobic exposure at pH 2 without RpoS, Gad, or hydrogenases, but shows sensitivity to autoclaved broth products

• Published in: PloS one Vol. 8; no. 3; p. e56796
• Main Authors: Riggins, Daniel P, Narvaez, Maria J, Martinez, Keith A, Harden, Mark M, Slonczewski, Joan L
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 08-03-2013; Public Library of Science (PLoS)
• Subjects: Aeration; Amino acids; Anaerobiosis - physiology; Autoclaving; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biology; Carbon dioxide; Catalase; Catalase - genetics; Catalase - metabolism; Colicins; Culture Media - pharmacology; Cyclopropane; Cyclopropane compounds; Dilution; E coli; Escherichia coli; Escherichia coli K12 - genetics; Escherichia coli K12 - metabolism; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; Exposure; Fatty acid synthesis; Fatty acids; Fatty-acid synthase; Gene Deletion; Genes; Glutamate; Glutamate decarboxylase; Glutamate Decarboxylase - genetics; Glutamate Decarboxylase - metabolism; Hydrogen ions; Hydrogen peroxide; Hydrogen Peroxide - pharmacology; Hydrogen-Ion Concentration; Hydrogenase - genetics; Hydrogenase - metabolism; Intestine; Metabolism; Methyltransferases - genetics; Methyltransferases - metabolism; Mortality; Oxidants - pharmacology; Oxidative stress; Oxygen; Oxygen - metabolism; pH effects; Proteins; RNA polymerase; Sigma Factor - genetics; Sigma Factor - metabolism; Stomach; Strains (organisms); Stress response; Survival; Transcription; Transcription (Genetics); Yeast; Ohio
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0056796

Escherichia coli and other enteric bacteria survive exposure to extreme acid (pH 2 or lower) in gastric fluid. Aerated cultures survive via regulons expressing glutamate decarboxylase (Gad, activated by RpoS), cyclopropane fatty acid synthase (Cfa) and others. But extreme-acid survival is rarely tested under low oxygen, a condition found in the stomach and the intestinal tract. We observed survival of E. coli K-12 W3110 at pH 1.2-pH 2.0, conducting all manipulations (overnight culture at pH 5.5, extreme-acid exposure, dilution and plating) in a glove box excluding oxygen (10% H2, 5% CO2, balance N2). With dissolved O2 concentrations maintained below 6 µM, survival at pH 2 required Cfa but did not require GadC, RpoS, or hydrogenases. Extreme-acid survival in broth (containing tryptone and yeast extract) was diminished in media that had been autoclaved compared to media that had been filtered. The effect of autoclaved media on extreme-acid survival was most pronounced when oxygen was excluded. Exposure to H2O2 during extreme-acid treatment increased the death rate slightly for W3110 and to a greater extent for the rpoS deletion strain. Survival at pH 2 was increased in strains lacking the anaerobic regulator fnr. During anaerobic growth at pH 5.5, strains deleted for fnr showed enhanced transcription of acid-survival genes gadB, cfa, and hdeA, as well as catalase (katE). We show that E. coli cultured under oxygen exclusion (<6 µM O2) requires mechanisms different from those of aerated cultures. Extreme acid survival is more sensitive to autoclave products under oxygen exclusion.