All these genes are organized in the same orientation and close enough to each other to be part of the same transcript. However, our finding of a ChvI binding site in SMc00262, after the gene encoding the IclR regulator, suggests a complex regulation of these genes. In fact, a N-Acyl homoserine lactone (AHL) also impacts on their expression [38]. The fatty-acid-CoA ligase (SMc00261) has been found differentially accumulated in early log phase

cultures of S. meliloti Rm1021 treated selleck chemicals llc for 2 hours with 3-oxo-C16:1-HL while the periplasmic binding protein (SMc00265) accumulated in stationary phase cultures independently of the presence of AHLs. Perhaps under conditions that activate

ChvI, the first part of the gene cluster is upregulated to allow the import of an organic acid but the second part responsible for its degradation and entry in the TCA cycle is downregulated. This hypothesis would suggest the use of this organic acid, under certain conditions, as a readily available building block rather than an energy source. An important finding from this work is that uracil and proline improved the growth of the chvI mutant. This finding now allows us to culture the mutant strain in liquid media, greatly facilitating experimental analysis. Binding of ChvI in thiC (SMb20615) and in hisB (SMc02574), perhaps to repress the thiamine and

histidine biosynthesis operons, EPZ-6438 supplier made us hypothesize that a derepression of these operons in exoS or chvI mutants could Celecoxib lead to a deficiency in UTP formation and could explain the pleiotropy of these mutants. Rhizobial purine and pyrimidine auxotrophic mutants have been found affected in polysaccharides synthesis and plant invasion [39–42]. Further work needs to be done to confirm that chvI mutant auxotrophy is truly caused by a derepression of operons for thiamine and histidine biosynthesis. Conclusions We have identified a number of putative direct targets of ChvI, many of which are consistent with the pleotropic phenotype of exoS and chvI mutants. We also demonstrated that ChvI may act as a repressor or activator of gene expression, and surprisingly ChvI seems to often bind within predicted protein coding sequences. The bias is often to only consider intergenic regions for locations of potential regulatory sites. However, we note that the Fur regulator of Helicobacter pylori is just one example of a transcriptional regulatory protein that has targets within polycistronic operons and acts as a repressor and an activator of gene expression [43]. The tendency to search for transcriptional cis-regulatory elements in intergenic areas rather than considering equally regions internal to ORFs may need to be revisited. GD.