Acid response of exponentially growing Escherichia coli K-12

Abstract

Induction of acid tolerance response (ATR) of exponential-phase Escherichia coli K-12 cells grown and adapted at different conditions was examined. The highest level of protection against pH 2.5 challenges was obtained after adaptation at pH 4.5-4.9 for 60 min. To study the genetic systems, which could be involved in the development of log-phase ATR, we investigated the acid response of E. coli acid resistance (AR) mutants. The activity of the glutamate-dependent system was observed in exponential cells grown at pH 7.0 and acid adapted at pH 4.5 in minimal medium. Importantly, log-phase cells exhibited significant AR when grown in minimal medium pH 7.0 and challenged at pH 2.5 for 2 h without adaptation. This AR required the glutamate-dependent AR system. Acid protection was largely dependent on RpoS in unadapted and adapted cells grown in minimal medium. RpoS-dependent oxidative, glutamate and arginine-dependent decarboxylase AR systems were not involved in triggering log-phase ATR in cells grown in rich medium. Cells adapted at pH 4.5 in rich medium showed a higher proton accumulation rate than unadapted cells as determined by proton flux assay. It is clear from our study that highly efficient mechanisms of protection are induced, operate and play the main role during log-phase ATR.

YfdW and YfdU Are Required for Oxalate-Induced Acid Tolerance in Escherichia coli K-12

“…Repression of RpoS had no effect on the survival of cells adapted in oxalate, and deletion of the rpoS gene did not increase cell susceptibility to acid as it does for the oxidative AR1 and amino-aciddependent systems AR2 and AR3 (3,5). In addition, our deletion data show that knockout of YdeO, GadX, and GadW had no significant effect on the oxalate-dependent ATR in stationary-phase E. coli cells (Fig.…”

Global Transcriptome and Mutagenic Analyses of the Acid Tolerance Response of Salmonella enterica Serovar Typhimurium

“…6A). For the same reason and to facilitate a better comparison, the ATR was also performed in LB medium (49,50) (Fig. 6A).…”

ATP Requirement for Acidic Resistance in Escherichia coli

“…The DNA damage in the purA and purB mutants was higher than that in the wild type. These results demonstrated that metabolic processes that require ATP participate in survival under extremely acidic conditions, and that one such system is the ATP-dependent DNA repair system.Since the normal human stomach averages pH 2 for approximately 2 h after it becomes empty, to survive in the mammalian host both commensal and pathogenic enteric bacteria have resistance systems to protect themselves against acidic stress (5,32,36).Four acidic resistance (AR) systems that are induced under different conditions have been proposed for Escherichia coli (5). Acidic resistance system 1 (AR1), which is induced in cells grown to stationary phase in a moderately acidic medium, requires the sigma factor RpoS (3, 27) and the cyclic AMP receptor protein CRP (2).…”

“…Since the normal human stomach averages pH 2 for approximately 2 h after it becomes empty, to survive in the mammalian host both commensal and pathogenic enteric bacteria have resistance systems to protect themselves against acidic stress (5,32,36).…”