Deletion of sigma54 (rpoN) alters the rate of autolysis and biofilm formation in Enterococcus faecalis

Transcription initiation is a critical step in bacterial gene regulation and is often controlled by transcription regulators. The alternate sigma factor (sigma54) is one such regulator that facilitates activator-dependent transcription initiation and thus modulates the expression of a variety of genes involved in metabolism and pathogenesis in bacteria. This study describes the role of sigma54 in the nosocomial pathogen Enterococcus faecalis. Biofilm formation is one of the important pathogenic mechanisms of E. faecalis, as it elevates the organism’s potential to cause surgical site and urinary tract infections. Lysis of bacterial cells within the population contributes to biofilm formation by providing extracellular DNA (eDNA) as a key component of the biofilm matrix. Deletion of rpoN rendered E. faecalis resistant to autolysis, which in turn impaired eDNA release. Despite the significant reduction in eDNA levels compared to the parental strain, the rpoN mutant formed more robust biofilms as observed using laser scanning confocal microscopy and Comstat analysis, indicating and emphasizing the presence of other matrix components. Initial adherence to a polystyrene surface was also enhanced in the mutant. Proteinase K treatment at early stages of biofilm development significantly reduced the accumulation of biofilm by the rpoN mutant. In conclusion, our data indicate that other factors in addition to eDNA might contribute to the overall composition of the enterococcal biofilm and that the regulatory role of sigma54 governs the nature and composition of the biofilm matrix

Misregulation of the arginase pathway in tissues of spontaneously hypertensive rats.

International audienceThere is a growing evidence that arginase has a role in the pathophysiology of cardiovascular diseases including hypertension. We recently reported arginase upregulation in aortas from hypertensive spontaneously hypertensive rats (SHRs). The aim of this study was to determine whether arginase abnormalities occur in other tissues of SHR, including the target organs of hypertension. Experiments were conducted on 5-, 10-, 19- and 26-week-old SHRs and Wistar-Kyoto (WKY) rats. Arginase activity and expression were evaluated in heart, kidney, liver, lung and brain tissue extracts. To investigate the role of blood pressure by itself in arginase abnormalities, arginase activity was determined in 10-week-old SHRs previously treated with hydralazine (20 mg kg(-1) per day, for 5 weeks). Compared with WKY rats, cardiac arginase activity was higher in hypertensive SHRs aged 10 weeks (+46%, P<0.05), 19 weeks (+29%, P<0.05) and 26 weeks (+23%, NS). Similar results were found in lungs in which arginase activity was increased in SHRs aged 10 weeks (+39%, P<0.05), 19 weeks (+49%, P<0.05) and 26 weeks (+36%, P<0.05) compared with WKY rats. The changes in arginase activity in these tissues were not associated with changes in enzyme expression. The prevention of hypertension by hydralazine blunted the increase in arginase activity in the hearts but not in the lungs. No change in arginase activity/expression was found in the kidney, liver or brain. In conclusion, this study shows that increased arginase activity is not restricted to large vessels in SHRs and suggests that cardiac arginase activity is hemodynamic sensitive