pH-Dependent Expression of Periplasmic Proteins and Amino Acid Catabolism inEscherichia coli

Abstract

Escherichia coli grows over a wide range of pHs (pH 4.4 to 9.2), and its own metabolism shifts the external pH toward either extreme, depending on available nutrients and electron acceptors. Responses to pH values across the growth range were examined through two-dimensional electrophoresis (2-D gels) of the proteome and through lac gene fusions. Strain W3110 was grown to early log phase in complex broth buffered at pH 4.9, 6.0, 8.0, or 9.1. 2-D gel analysis revealed the pH dependence of 19 proteins not previously known to be pH dependent. At low pH, several acetate-induced proteins were elevated (LuxS, Tpx, and YfiD), whereas acetaterepressed proteins were lowered (Pta, TnaA, DksA, AroK, and MalE). These responses could be mediated by the reuptake of acetate driven by changes in pH. The amplified proton gradient could also be responsible for the acid induction of the tricarboxylic acid (TCA) enzymes SucB and SucC. In addition to the autoinducer LuxS, low pH induced another potential autoinducer component, the LuxH homolog RibB. pH modulated the expression of several periplasmic and outer membrane proteins: acid induced YcdO and YdiY; base induced OmpA, MalE, and YceI; and either acid or base induced OmpX relative to pH 7. Two pH-dependent periplasmic proteins were redox modulators: Tpx (acid-induced) and DsbA (base-induced). The locus alx, induced in extreme base, was identified as ygjT, whose product is a putative membrane-bound redox modulator. The cytoplasmic superoxide stress protein SodB was induced by acid, possibly in response to increased iron solubility. High pH induced amino acid metabolic enzymes (TnaA and CysK) as well as lac fusions to the genes encoding AstD and GabT. These enzymes participate in arginine and glutamate catabolic pathways that channel carbon into acids instead of producing alkaline amines. Overall, these data are consistent with a model in which E. coli modulates multiple transporters and pathways of amino acid consumption so as to minimize the shift of its external pH toward either acidic or alkaline extreme.

Bifidobacterium lactisDSM 10140: Identification of theatp(atpBEFHAGDC) Operon and Analysis of Its Genetic Structure, Characteristics, and Phylogeny

“…Other short palindromic sequences were detected in the operon sequences, at positions corresponding to those described in the L. acidophilus and E. coli atp operons (36,44). In the ATPases complexes of these bacteria these palindromic sequences have been found to increase the mRNA stability and thus enhance the translational efficiency of the corresponding genes (21).…”

Characterization of a yjjQ mutant of avian pathogenic Escherichia coli (APEC)

“…In addition, several proteins involved in molecular chaperoning (DnaK) (Slepenkov & Witt, 2002), acid tolerance response (YfiD) (Stancik et al, 2002), LPS core region biosynthesis (RfaE) (Valvano et al, 2000), transcriptional regulation and other functions were identified. Interestingly, YbeJ, a putative glutamate/aspartate periplasmic binding and transport protein (Tremoulet et al, 2002) was represented by one of the five unique spots from the wild-type.…”

Optimization of culture conditions to improve the expression level of beta1–epsilon toxin ofClostridium perfringenstype B inEscherichia coli

“…pH also influences the culture conditions, including oxygenation, growth phase and metabolite composition. [16] Cell growth rate is also affected by pH, and low cell growth rate occurs at low pH. [17] Several enzymes related to the formation of acetate are induced at the pH extremes, including the proteins encoded by pta, sucB and sucC.…”

“…[17] Several enzymes related to the formation of acetate are induced at the pH extremes, including the proteins encoded by pta, sucB and sucC. [16] Components of the tricarboxylic acid (TCA) cycle, such as sucB and sucC, are induced at low pH, which would be expected to result in utilization of the high proton potential and in increase of the TCA cycle capacity. [16,18] The key gene pta, which regulates pH, is involved in the synthesis of acetate and is induced at high pH that would be changed by the concentration of acetate.…”