Pyruvate-Associated Acid Resistance in Bacteria

Abstract

dGlucose confers acid resistance on exponentially growing bacteria by repressing formation of the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex and consequently activating acid resistance genes. Therefore, in a glucose-rich growth environment, bacteria are capable of resisting acidic stresses due to low levels of cAMP-CRP. Here we reveal a second mechanism for glucose-conferred acid resistance. We show that glucose induces acid resistance in exponentially growing bacteria through pyruvate, the glycolysis product. Pyruvate and/or the downstream metabolites induce expression of the small noncoding RNA (sncRNA) Spot42, and the sncRNA, in turn, activates expression of the master regulator of acid resistance, RpoS. In contrast to glucose, pyruvate has little effect on levels of the cAMP-CRP complex and does not require the complex for its effects on acid resistance. Another important difference between glucose and pyruvate is that pyruvate can be produced by bacteria. This means that bacteria have the potential to protect themselves from acidic stresses by controlling glucose-derived generation of pyruvate, pyruvate-acetate efflux, or reversion from acetate to pyruvate. We tested this possibility by shutting down pyruvate-acetate efflux and found that the resulting accumulation of pyruvate elevated acid resistance. Many sugars can be broken into glucose, and the subsequent glycolysis generates pyruvate. Therefore, pyruvate-associated acid resistance is not confined to glucose-grown bacteria but is functional in bacteria grown on various sugars. G astric acid (pH 2) in the stomach of the host efficiently kills or inhibits the growth of bacterial pathogens. After being swallowed, enteric organisms have to overcome the low pH of gastric acid. Acidic stresses also come from bacterial growth per se. It is well established that bacteria such as Escherichia coli utilize the phosphotransacetylase (Pta)-acetate kinase (AckA) pathway to generate ATP from acetate production in glucose-containing environments even in the presence of ample oxygen (1). The phenomenon of overflow metabolism has been attributed to an imbalance between the fluxes of glucose uptake and those for energy production and biosynthesis (2), probably caused by improperly controlled glucose uptake and/or limited activity of the tricarboxylic acid (TCA) cycle (3). As a weak acid, acetate is toxic to bacteria and has been found to uncouple the transmembrane pH gradient (4, 5), acidify the cytoplasm, and interfere with methionine biosynthesis (6-8). Therefore, acid resistance (AR) is an important ability that E. coli possesses to survive low pH and flourish. Indeed, E. coli organisms can be so resistant to low pH that they survive gastric acid, colonize the gut, and cause diseases even though small numbers of them (10 to 100) are ingested (9, 10).The cyclic AMP (cAMP) receptor protein (CRP) is a crucial regulator of AR in E. coli. It has been demonstrated that CRP negatively regulates AR by repressing a set of AR genes (11,12). CRP has to form a complex ...

cAMP receptor protein regulates mouse colonization, motility, fimbria-mediated adhesion, and stress tolerance in uropathogenic Proteus mirabilis

“…Crp has been reported to regulate the expression of the general stress response regulator RpoS of E . coli 40 . We demonstrated that loss of rpoS rendered P .…”

“…In addition, rpoS transcription was demonstrated to be regulated by Crp-cAMP 56 , and Crp could inhibit RpoS expression through Spf, an Hfq-dependent sRNA that facilitates acid resistance by activating RpoS expression in E . coli 40 . Our unpublished data also revealed that P .…”

“…Acid resistance assay was performed as described by Wu et al . with some modifications 40 . Overnight cultures were diluted 500-fold in fresh LB broth and incubated at 37 °C with shaking at 250 rpm for 4 h. After adjusting the LB broth with HCl to pH 3.0, bacterial cells were treated statically with acid for 2 h. Cells were washed with PBS (pH 7.2) and plated on LSW − plates to determine the CFU.…”

The LysR‐type transcriptional regulator, CidR, regulates stationary phase cell death in Staphylococcus aureus

“…The cellular toxicity attributed to pyruvate under acid stress is controversial. While some studies point to a beneficial role for intracellular pyruvate following acidic stress, others have alluded to a more toxic nature for this metabolite (Harvey & Collins, 1963;Tsau et al, 1992;Repizo et al, 2011;Wu et al, 2014). Hence, to test whether intracellular pyruvate affects S. aureus under acidic stress, we challenged the wild-type strain with increasing concentrations of sodium pyruvate in Tryptic Soy broth (TSB) that was acidified to an initial pH of 4.5 and monitored growth at a wavelength of 600 nm (OD 600 ) for 24 h. Because of the weak acid properties of pyruvic acid (pKa5 2.49), this approach not only allows a small percentage (<1%; estimate based on the Henderson-Hasselbalch equation) of extracellular pyruvic acid to diffuse freely into cells and ensure cytoplasmic acidification, but also simultaneously increases the levels of intracellular pyruvate (upon disassociation of pyruvic acid within the cytoplasm) in the acid stressed cells.…”

Expression of stress-related proteins inSediminibacteriumsp. growing under planktonic conditions

“…Interestingly, a recent report demonstrated that hydrogen peroxide stress in Pseudomonas fluorescens provoked a metabolic reprogramming that enhanced the production of pyruvate . Pyruvate also induces acid resistance in bacteria by the expression of the small noncoding RNAs, which in turn activates expression of RpoS .…”