Project description:Metals at high concentrations can exert toxic effects on microorganisms. It has been widely reported that lowering environmental pH reduces effects of cadmium toxicity in bacteria. Understanding the effects of pH-mediated cadmium toxicity on bacteria would be useful for minimizing cadmium toxicity in the environment and gaining insight into the interactions between organic and inorganic components of life. Growth curve analysis confirmed that cadmium was less toxic to Escherichia coli at pH 5 than at pH 7 in M9 minimal salts medium. To better understand the cellular mechanisms by which lowering pH decreases cadmium toxicity, we used DNA microarrays to characterize global gene expression patterns in E. coli in response to cadmium exposure at moderately acidic (5) and neutral (7) values of pH. Higher expression of several stress response genes including hdeA, otsA, and yjbJ at pH 5 after only 5 minutes was observed and may suggest that acidic pH more rapidly induces genes that confer cadmium resistance. Genes involved in transport were more highly expressed at pH 7 than at pH 5 in the presence of cadmium. Of the genes that showed an interaction between pH and cadmium effects, 46% encoded hypothetical proteins, which may have novel functions involved in mitigating cadmium toxicity.
Project description:In Escherichia coli, pH-dependent gene expression varies with oxygen level. Anaerobic pH-dependent expression ratios were analyzed and compared to the published analysis of aerated cultures (Maurer et al, 2005). E. coli K-12 strain W3110 was cultured in closed tubes containing LBK broth buffered at pH 5.7, pH 7.0, and pH 8.5. Gene expression profiles were obtained by cDNA hybridization to Affymetrix arrays. pH-dependent expression was seen for 1,394 genes, of which 1,002 show no pH dependence under aeration. Four intergenic regions containing regulatory sRNAs were up-regulated by acid anaerobically (ryeA, csrB, gadY, rybC) and one sRNA (ryhA) by acid with aeration. Acid and anaerobiosis co-regulated the gad regulon; drug transporters (mdtEF, mdtL); catabolism of sugar derivatives whose fermentation minimized acid production; and all hydrogenases (hya, hyb, hyc, hyf, hyp). The hydrogenases however were up-regulated at high pH under aeration (observed by real-time PCR). Acid with anaerobiosis down-regulated penicillin-binding proteins (dacACD, mreBC) and ribosome biosynthesis. Ribosome down-regulation may be caused by restriction of anaerobic metabolism at low pH. A core group of 236 genes showed similar pH response with or without aeration. Core genes up-regulated by acid included fimbriae (fimAC), periplasmic chaperones (hdeAB), cyclopropane fatty acid synthase (cfa), the “constitutive” Na+/H+ antiporter (nhaB), and over thirty unidentified proteins. Core genes at high pH included maltodextrin transport (lamB, malEFGKMPQT), ATP synthase, and DNA repair (recA and mutL). Overall, pH and anaerobiosis co-regulated metabolism and transport so as to maximize alternative catabolic options while minimizing acidification or alkalinization of the cytoplasm. Keywords: Steady State
Project description:The purpose of this study is to determine whether the presence of pathogenic Escherichia coli in colon is associated with psychiatric disorders.
Project description:Gene expression profiles of Escherichia coli K-12 W3110 were compared as a function of steady-state external pH. Cultures were grown with aeration to an optical density at 600 nm of 0.3 in potassium-modified Luria-Bertani medium buffered at pH 5.0, 7.0, and 8.7. For each of the three pH conditions, cDNA from RNA of five independent cultures was hybridized to Affymetrix E. coli arrays. Analysis of variance with a significance level of 0.001 resulted in 98% power to detect genes showing a twofold difference in expression. Normalized expression indices were calculated for each gene and intergenic region (IG). Differential expression among the three pH classes was observed for 763 genes and 353 IGs. Hierarchical clustering yielded six well-defined clusters of pH profiles, designated Acid High (highest expression at pH 5.0), Acid Low (lowest expression at pH 5.0), Base High (highest at pH 8.7), Base Low (lowest at pH 8.7), Neutral High (highest at pH 7.0, lower in acid or base), and Neutral Low (lowest at pH 7.0, higher at both pH extremes). Flagellar and chemotaxis genes were repressed at pH 8.7 (Base Low cluster), where the cell's transmembrane proton potential is diminished by the maintenance of an inverted pH gradient. High pH also repressed the proton pumps cytochrome o (cyo) and NADH dehydrogenases I and II. By contrast, the proton-importing ATP synthase F1Fo and the microaerophilic cytochrome d (cyd), which minimizes proton export, were induced at pH 8.7. These observations are consistent with a model in which high pH represses synthesis of flagella, which expend proton motive force, while stepping up electron transport and ATPase components that keep protons inside the cell. Acid-induced genes, on the other hand, were coinduced by conditions associated with increased metabolic rate, such as oxidative stress. All six pH-dependent clusters included envelope and periplasmic proteins, which directly experience external pH. Overall, this study showed that (i) low pH accelerates acid consumption and proton export, while coinducing oxidative stress and heat shock regulons; (ii) high pH accelerates proton import, while repressing the energy-expensive flagellar and chemotaxis regulons; and (iii) pH differentially regulates a large number of periplasmic and envelope proteins. Keywords: Steady State
Project description:Escherichia coli (E. coli) amine oxidase (ECAO) encoded by tynA gene has been one of the model enzymes to study the mechanism of oxidative deamination of amines to the corresponding aldehydes by amine oxidases. The biological roles of ECAO have been less addressed. Therefore we have constructed a gene deletion Escherichia coli K-12 strain, E. coli tynA-, and used the microarray technique to address its function by comparing the total RNA gene expression to the one of the wt. Our results suggest that tynA is a reserve gene for stringent environmental conditions and its gene product ECAO a growth advantage compared to other bacteria due to H2O2 production.
Project description:Despite the characterization of many aetiologic genetic changes. The specific causative factors in the development of sporadic colorectal cancer remain unclear. This study was performed to detect the possible role of Enteropathogenic Escherichia coli (EPEC) in developing colorectal carcinoma.