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Positive Effect of Carbon Sources on Natural Transformation in Escherichia coli: Role of Low-Level Cyclic AMP (cAMP)-cAMP Receptor Protein in the Derepression of rpoS.

ABSTRACT:

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Natural plasmid transformation of Escherichia coli is a complex process that occurs strictly on agar plates and requires the global stress response factor ?(S). Here, we showed that additional carbon sources could significantly enhance the transformability of E. coli. Inactivation of phosphotransferase system genes (ptsH, ptsG, and crr) caused an increase in the transformation frequency, and the addition of cyclic AMP (cAMP) neutralized the promotional effect of carbon sources. This implies a negative role of cAMP in natural transformation. Further study showed that crp and cyaA mutations conferred a higher transformation frequency, suggesting that the cAMP-cAMP receptor protein (CRP) complex has an inhibitory effect on transformation. Moreover, we observed that rpoS is negatively regulated by cAMP-CRP in early log phase and that both crp and cyaA mutants show no transformation superiority when rpoS is knocked out. Therefore, it can be concluded that both the crp and cyaA mutations derepress rpoS expression in early log phase, whereby they aid in the promotion of natural transformation ability. We also showed that the accumulation of RpoS during early log phase can account for the enhanced transformation aroused by additional carbon sources. Our results thus demonstrated that the presence of additional carbon sources promotes competence development and natural transformation by reducing cAMP-CRP and, thus, derepressing rpoS expression during log phase. This finding could contribute to a better understanding of the relationship between nutrition state and competence, as well as the mechanism of natural plasmid transformation in E. coli.

Importance

Escherichia coli, which is not usually considered to be naturally transformable, was found to spontaneously take up plasmid DNA on agar plates. Researching the mechanism of natural transformation is important for understanding the role of transformation in evolution, as well as in the transfer of pathogenicity and antibiotic resistance genes. In this work, we found that carbon sources significantly improve transformation by decreasing cAMP. Then, the low level of cAMP-CRP derepresses the general stress response regulator RpoS via a biphasic regulatory pattern, thereby contributing to transformation. Thus, we demonstrate the mechanism by which carbon sources affect natural transformation, which is important for revealing information about the interplay between nutrition state and competence development in E. coli.

SUBMITTER: Guo M

PROVIDER: S-EPMC4573726 | biostudies-literature | 2015 Oct

REPOSITORIES: biostudies-literature

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Positive Effect of Carbon Sources on Natural Transformation in Escherichia coli: Role of Low-Level Cyclic AMP (cAMP)-cAMP Receptor Protein in the Derepression of rpoS.

Guo Mengyue M Wang Huanyu H Xie Nengbin N Xie Zhixiong Z

Journal of bacteriology 20150810 20

<h4>Unlabelled</h4>Natural plasmid transformation of Escherichia coli is a complex process that occurs strictly on agar plates and requires the global stress response factor σ(S). Here, we showed that additional carbon sources could significantly enhance the transformability of E. coli. Inactivation of phosphotransferase system genes (ptsH, ptsG, and crr) caused an increase in the transformation frequency, and the addition of cyclic AMP (cAMP) neutralized the promotional effect of carbon sources ...[more]

PMID: 26260461

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Project description:For heterotrophic microbes, limited availability of carbon and energy sources is one of the major nutritional factors restricting the rate of growth in most ecosystems. Physiological adaptation to this hunger state requires metabolic versatility which usually involves expression of a wide range of different catabolic pathways and of high-affinity carbon transporters; together, this allows for simultaneous utilization of mixtures of carbonaceous compounds at low concentrations. In Escherichia coli the stationary phase sigma factor RpoS and the signal molecule cAMP are the major players in the regulation of transcription under such conditions; however, their interaction is still not fully understood. Therefore, during growth of E. coli in carbon-limited chemostat culture at different dilution rates, the transcriptomes, expression of periplasmic proteins and catabolomes of strains lacking one of these global regulators, either rpoS or adenylate cyclase (cya), were compared to those of the wild-type strain. The inability to synthesize cAMP exerted a strong negative influence on the expression of alternative carbon source uptake and degradation systems. In contrast, absence of RpoS increased the transcription of genes belonging to high-affinity uptake systems and central metabolism, presumably due to reduced competition of σ(D) with σ(S). Phenotypical analysis confirmed this observation: The ability to respire alternative carbon substrates and to express periplasmic high-affinity binding proteins was eliminated in cya and crp mutants, while these properties were not affected in the rpoS mutant. As expected, transcription of numerous stress defence genes was negatively affected by the rpoS knock-out mutation. Interestingly, several genes of the RpoS stress response regulon were also down-regulated in the cAMP-negative strain indicating a coordinated global regulation. The results demonstrate that cAMP is crucial for catabolic flexibility during slow, carbon-limited growth, whereas RpoS is primarily involved in the regulation of stress response systems necessary for the survival of this bacterium under hunger conditions.

Project description:The faecal indicator bacterium Escherichia coli K12 was used to study the effects of the global regulators RpoS and cAMP at the transcription level using microarray technology during short-term (physiological) adaptation to slow growth under limited nutrient supply. Effects due to the absence of one global regulator were assessed by comparing the mRNA levels isolated from rpoS or cya mutants under glucose-limited continuous culture at a dilution rate of 0.3 h-1 for the rpoS mutant or 0.16 h-1 for the cya mutant with those from wt E. coli grown under the same conditions. Wild-type Escherichia coli K12 MG1655 (ATCC 700926), E. coli delta-rpoS (MG1655 delta-rpoS::Tn10; Wick et al. (2002)) and AMS2 (MG1655 delta-cya-854; Schultz et al. (1988)) were grown at 37°C in mineral medium. Steady-state with respect to optical density was reached approximately 20 hours after switching on the medium feed. Samples for catabolic pathway assays and transcriptome analysis were taken 40 hours after switching to the continuous culture mode, and each experiment was done in triplicate. 800 ml of culture liquid was withdrawn from the chemostat, immediately cooled down on crushed ice and cells were collected by centrifugation at 4°C. Total RNA from E. coli cells was isolated (Sambrook et al., 1989). RNA in samples was quantified spectrophotometrically by measuring extinction at 260 nm, and purity (free from DNA) was checked by gel electrophoresis. Synthesis of cDNA from RNA was performed with the CyScribe First-Strand cDNA Labelling Kit (Amersham Bioscience, Little Chalfont, England). The purified cDNA was concentrated to 5 ul and was mixed with 120 ul of hybridization buffer (MWG-Biotech AG), heated to 95°C for 3 min and cooled down on ice for 3 min. The hybridization mixture was then added to the microarray slide and covered with a coverslip. The hybridization slide was incubated overnight at 42°C. After the hybridization step, the slide was washed three times, the first time for 5 min in 2x (times concentrated) SSC - 0.1 % SDS, the second time for 5 min in 1x SSC, and finally for 5 min in 0.1x SSC. SSC buffer was prepared as 20x solution containing 0.3M Na-citrate and 3M NaCl at pH 7.0. The slides were dried by centrifugation at room temperature for 2 min at 500g. Microarray slides were scanned using the Affymetrix 428TM Array Scanner (High Wycombe, UK). Spot intensities and corresponding background signals were quantified with the Affymetrix JaguarTM software version 2.0. Further data analysis was performed with the program GeneSpring from Silicon Genetics (Redwood City, USA). Induction factors were calculated from the Cy3 and Cy5 signal intensities of the spot. Spots with signal intensity below a value of 50 were excluded from the analysis and the minimal induction factor was set to 0.01. The normalization was performed with the 50th percentile distribution of remaining spots after background correction. The mean value of the induction factors of a specific gene was calculated from three replicates. Biological experiments were carried out three times, which provided three biological repeats. Data from the independent experiment were combined, genes that were differently regulated ?3 and ?-3 (t-test, p ? 0.2) were defined as being statistically significant.

Dataset Information

Positive Effect of Carbon Sources on Natural Transformation in Escherichia coli: Role of Low-Level Cyclic AMP (cAMP)-cAMP Receptor Protein in the Derepression of rpoS.

Unlabelled

Importance

Publications

Positive Effect of Carbon Sources on Natural Transformation in Escherichia coli: Role of Low-Level Cyclic AMP (cAMP)-cAMP Receptor Protein in the Derepression of rpoS.

Similar Datasets

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