SummaryThe cyanobacterial genes lexA , recA and ruvB were analysed in Synechocystis PCC6803, which is shown here to be more radiation resistant than the other unicellular model strain Synechococcus PCC7942. We found that cyanobacteria do not have an Escherichia coli -type SOS regulon. The Synechocystis lexA and recA promoters were found to be strong and UV insensitive, unlike the ruvB promoter, which is weak and UV-C inducible. Yet, lexA and recA are regulated by UV-C, but the control is negative and occurs at the post-transcriptional level. Two novel conserved elements were characterized in the lexA promoter: (i) an unusually long crucial box 5 ¢ ¢ ¢ ¢ -TAAAATTTTGTATCTTTT-3 ¢ ¢ ¢ ¢ ( ----64, ----47); and (ii) a negatively acting motif 5 ¢ ¢ ¢ ¢ -TAT GAT-3 ¢ ¢ ¢ ¢ ( ----42, ----37). These elements were not found in the recA promoter, which appeared to be unusually simple in harbouring only a single crucial element (i.e. the canonical ----10 box). RuvB, operating in recombination-dependent cellular processes, was found to be dispensable to cell growth, whereas LexA and RecA appeared to be critical to cell viability. Using DNA microarrays, we have identified 57 genes with expression that is altered, at least twofold, in response to LexA depletion. None of these genes is predicted to operate in DNA metabolism, arguing against the involvement of LexA in the regulation of DNA repair. Instead, most of the LexA-responsive genes were known to be involved in carbon assimilation or controlled by carbon availability. Consistently, the growth of the LexA-depleted strain was found to be strongly dependent on the availability of inorganic carbon.

The bacterial phosphoenolpyruvate phosphotransferase system (PTS) is a highly conserved phosphotransfer cascade whose components modulate many cellular functions in response to carbohydrate availability. Here, we further elucidate PTS control of Vibrio cholerae carbohydrate transport and activation of biofilm formation on abiotic surfaces. We then define the role of the PTS in V. cholerae colonization of the adult germfree mouse intestine. We report that V. cholerae colonizes both the small and large intestines of the mouse in a distribution that does not change over the course of a month-long experiment. Because V. cholerae possesses many PTS-independent carbohydrate transporters, the PTS is not essential for bacterial growth in vitro. However, we find that the PTS is essential for colonization of the germfree adult mouse intestine and that this requirement is independent of PTS regulation of biofilm formation. Therefore, competition for PTS substrates may be a dominant force in the success of V. cholerae as an intestinal pathogen. Because the PTS plays a role in colonization of environmental surfaces and the mammalian intestine, we propose that it may be essential to successful transit of V. cholerae through its life cycle of pathogenesis and environmental persistence.

Glucose is a universal energy source and a potent inducer of surface colonization for many microbial species. Highly efficient sugar assimilation pathways ensure successful competition for this preferred carbon source. One such pathway is the phosphoenolpyruvate phosphotransferase system (PTS), a multicomponent sugar transport system that phosphorylates the sugar as it enters the cell. Components required for transport of glucose through the PTS include enzyme I, histidine protein, enzyme IIA Glc , and enzyme IIBC Glc . In Escherichia coli, components of the PTS fulfill many regulatory roles, including regulation of nutrient scavenging and catabolism, chemotaxis, glycogen utilization, catabolite repression, and inducer exclusion. We previously observed that genes encoding the components of the Vibrio cholerae PTS were coregulated with the vps genes, which are required for synthesis of the biofilm matrix exopolysaccharide. In this work, we identify the PTS components required for transport of glucose and investigate the role of each of these components in regulation of biofilm formation. Our results establish a novel role for the phosphorylated form of enzyme I in specific regulation of biofilm-associated growth. As the PTS is highly conserved among bacteria, the enzyme I regulatory pathway may be relevant to a number of biofilm-based infections.

The bacterial phosphoenolpyruvate phosphotransferase system (PTS) is a highly conserved phosphotransfer cascade that participates in the transport and phosphorylation of selected carbohydrates and modulates many cellular functions in response to carbohydrate availability. It plays a role in the virulence of many bacterial pathogens. Components of the carbohydrate-specific PTS include the general cytoplasmic components enzyme I (EI) and histidine protein (HPr), the sugar-specific cytoplasmic components enzymes IIA (EIIA) and IIB (EIIB), and the sugar-specific membrane-associated multisubunit components enzymes IIC (EIIC) and IID (EIID). Many bacterial genomes also encode a parallel PTS pathway that includes the EI homolog EI Ntr , the HPr homolog NPr, and the EIIA homolog EIIA Ntr . This pathway is thought to be nitrogen specific because of the proximity of the genes encoding this pathway to the genes encoding the nitrogen-specific factor 54 . We previously reported that phosphorylation of HPr and FPr by EI represses Vibrio cholerae biofilm formation in minimal medium supplemented with glucose or pyruvate. Here we report two additional PTS-based biofilm regulatory pathways that are active in LB broth but not in minimal medium. These pathways involve the glucose-specific enzyme EIIA (EIIA Glc ) and two nitrogen-specific EIIA homologs, EIIA Ntr1 and EIIA Ntr2 . The presence of multiple, independent biofilm regulatory circuits in the PTS supports the hypothesis that the PTS and PTS-dependent substrates have a central role in sensing environments suitable for a surface-associated existence.

Background: Cadmium is a persistent pollutant that threatens most biological organisms, including cyanobacteria that support a large part of the biosphere. Using a multifaceted approach, we have investigated the global responses to Cd and other relevant stresses (H 2 O 2 and Fe) in the model cyanobacterium Synechocystis PCC6803.