The phosphoenopyruvate:carbohydrate phosphotransferase system (PTS) enables Vibrio cholerae – and other bacteria – to recognize and transport exogenous carbon sources for energy, including the six-carbon sugar alcohol, mannitol. The mannitol-specific PTS transporter is encoded by mtlA and its expression is expected to be regulated by the putative repressor encoded by the mtlR gene. Here, we show that mtlR overexpression inhibits V. cholerae growth in medium supplied with mannitol as the sole carbon source and represses MtlA-mediated biofilm formation. We demonstrate that when V. cholerae is grown in non-mannitol medium, knocking out mtlR leads to both increased MtlA protein and mtlA mRNA levels, with these increases being especially pronounced in non-glucose sugars. We propose that in non-mannitol, non-glucose growth conditions, MtlR is a major regulator of mtlA transcription. Surprisingly, with regard to mtlR expression, transcript and protein levels are highest in mannitol medium, conditions where mtlA expression should not be repressed. We further show that MtlR levels increase during growth of the bacteria and linger in cells switched from mannitol to non-mannitol medium. Our data suggests an expression paradigm for mtlA where MtlR acts as a transcriptional repressor responsible for calibrating MtlA levels during environmental transitions.
The Escherichia coli PhoB-PhoR two-component system responds to phosphate starvation and induces the expression of many genes. Previous studies suggested that phosphate starvation induces oxidative stress, but the involvement of the PhoB regulon in oxidative stress tolerance has not been clarified. Here, we showed that ytfK, one of the PhoB regulon genes, is involved in cell tolerance to a redox-cycling drug, menadione, and H2O2 in stationary-phase cells. A ytfK deletion mutant was sensitive to H2O2 when the cells were grown anaerobically or micro-aerobically in the presence of nitrate. Genetic analysis suggested that the ytfK gene has a functional relationship with the oxyR and fur genes, among the oxyR regulon, at least, a catalase-encoding katG gene and peroxidase-encoding ahpCF genes. Overproduction of YtfK resulted in a KatG-dependent decrease of H2O2 concentration in the cell suspension, suggesting that katG is one of the targets of YtfK. Using a katG′-lacZ reporter fusion, we showed that YtfK enhances the transcription of katG although it was not clarified whether YtfK functions directly or not. We also showed that ytfK disruption results in reduced viability of stationary-phase cells under phosphate starvation. These results indicated that YtfK is involved in H2O2 tolerance by stimulating directly or indirectly the transcription of at least the catalase gene, and that this system plays an important role in cellular survival during phosphate starvation.
Small RNA (sRNA)-mediated regulation of gene expression is a major tool to understand bacterial responses to environmental changes. In particular, pathogenic bacteria employ sRNAs to adapt to the host environment and establish infection. Members of the Burkholderia cepacia complex, normally present in soil microbiota, cause nosocomial lung infection especially in hospitalized cystic fibrosis patients. We sequenced the draft genome of Burkholderia cenocepacia KC-01, isolated from the coastal saline soil, and identified several potential sRNAs in silico. Expression of seven small RNAs (Bc_KC_sr1–7) was subsequently confirmed. Two sRNAs (Bc_KC_sr1 and Bc_KC_sr2) were upregulated in response to iron depletion by 2,2’-bipyridyl and another two (Bc_KC_sr3 and Bc_KC_sr4) responded to the presence of 60 µM H2O2 in the culture media. Bc_Kc_sr5, 6 and 7 remained unchanged under these conditions. Expression of Bc_KC_sr2, 3 and 4 also altered with a change in temperature and incubation time. A search in the Rfam and BSRD databases identified Bc_Kc_sr4 as candidate738 in B. pseudomallei D286 and assigned Bc_Kc_sr5 and 6 as tmRNA and 6S RNA, respectively. The novel sRNAs were conserved in Burkholderiaceae but did not have any homologue in other genera. Bc_KC_sr1 and 4 were transcribed independently while the rest were part of the 3′ UTR of their upstream genes. TargetRNA2 predicted that these sRNAs could target a host of cellular messages with very high stringency. Intriguingly, regions surrounding the translation initiation site for several enzymes involved in Fe–S cluster and siderophore biosynthesis, ROS homeostasis, porins, transcription and translation regulators, were among the suggested putative binding sites for these sRNAs.
Ethylene is a gaseous signal sensed by plants and bacteria. Heterologous expression of the ethylene-forming enzyme (EFE) from Pseudomonas syringae in cyanobacteria leads to the production of ethylene under photoautotrophic conditions. The recent characterization of an ethylene-responsive signalling pathway affecting phototaxis in the cyanobacterium Synechocystis sp. PCC 6803 implied that biotechnologically relevant ethylene synthesis may induce regulatory processes that are not related to changes in metabolism. Here, we provide data that indicate that endogenously produced ethylene accelerates the movement of cells towards light. Microarray analysis demonstrates that ethylene mainly deactivates transcription from the csiR1/lsiR promoter, which is under the control of the two-component system consisting of the ethylene- and UV-A-sensing histidine kinase UirS and the DNA-binding response regulator UirR. Surprisingly, ethylene production triggers a very specific transcriptional response and only a few other smaller transcriptional changes are detected in the microarray analysis.