Expression of the Pho regulon negatively regulates biofilm formation by Pseudomonas aureofaciens PA147‐2

Abstract

SummaryWe report the isolation of insertional mutations to the pstC and pstA genes of the phosphate-specific transport ( pst ) operon that results in loss of biofilm formation by Pseudomonas aureofaciens PA147-2. Consistent with the known roles of the Pst system in Escherichia coli and Pseudomonas aeruginosa, both P. aureofaciens pst mutants were demonstrated to have defects in inorganic phosphate (P i ) transport and repression of Pho regulon expression. Subsequently, biofilm formation by the wild type was shown to require a threshold concentration of extracellular P i . The two-component regulatory pair PhoR/PhoB is responsible for upregulation of Pho regulon expression in response to P i -limiting environments. By generating phoR mutants that were unable to express the Pho regulon, we were able to restore biofilm formation by P. aureofaciens in P i -limiting conditions. This result suggests that gene(s) within the Pho regulon act to regulate biofilm formation negatively in low-P i environments, and that phoR mutations uncouple PA147-2 from such regulatory constraints. Furthermore, the inability of pst mutants to repress Pho regulon expression accounts for their inability to form biofilms in non-limiting P i environments. Preliminary evidence suggests that the Pst system is also required for antifungal activity by PA147-2. During phenotypic analysis of pst mutants, we also uncovered novelties in relation to P i assimilation and Pho regulon control in P. aureofaciens.

The high-affinity phosphate transporter Pst in Proteus mirabilis HI4320 and its importance in biofilm formation

“…Since it has been shown that biofilm formation plays a role in early P. mirabilis UTIs and that gene products of the pst operon negatively regulate biofilm formation (Monds et al, 2001), quantitative biofilm microtitre assays were performed. After 48 h of static growth in pooled human urine, a 2.5-and eightfold reduction in biofilm formation between the HI4320 wild-type and the DpstA and DpstS mutants, respectively, was observed [wild-type, 1.65610 7 c.f.u.…”

“…Studies using null mutants in pstC and pstA genes have revealed that the Pst system negatively regulates biofilm formation in Pseudomonas aureofaciens PA147-2 (Monds et al, 2001). Since biofilm formation is critical for the establishment of P. mirabilis in the human host, mutations in the Pst system may explain Fig.…”

“…Since (i) earlier work has alluded to the importance of this system during biofilm formation (Monds et al, 2001(Monds et al, , 2007 and (ii) the formation of crystalline biofilms is a characteristic of UTIs associated with P. mirabilis, we hypothesized that the Pst system of P. mirabilis HI4320 is involved in biofilm formation during establishment of a UTI. To assess the role of the Pst system, this study focused upon determining previously undetected in vitro phenotypes of the Dpst mutants by comparing biofilm formation between the wild-type HI4320 and DpstA and DpstS mutants via confocal laser scanning microscopy (CLSM) and quantitative analysis of surface coverage, and by comparing in vitro protein expression of these strains grown planktonically and as a biofilm.…”

“…P. mirabilis HI4320 possesses a pst operon identical in gene organization to that observed in Escherichia coli. Previous studies have suggested that the roles of the Pst transport system in pathogenesis include regulation of invasion (Lucas et al, 2000;Mathew et al, 2001;Sinai & Bavoil, 1993), antibiotic resistance (Soualhine et al, 2005), colonization (Buckles et al, 2006;Daigle et al, 1995;Lamarche et al, 2005;Orihuela et al, 2001;Peirs et al, 2005;Runyen-Janecky et al, 2005), and biofilm formation (Monds et al, 2001).…”

“…P. mirabilis HI4320 possesses a pst operon identical in gene organization to that observed in Escherichia coli. Previous studies have suggested that the roles of the Pst transport system in pathogenesis include regulation of invasion (Lucas et al, 2000;Mathew et al, 2001;Sinai & Bavoil, 1993), antibiotic resistance (Soualhine et al, 2005), colonization (Buckles et al, 2006;Daigle et al, 1995;Lamarche et al, 2005;Orihuela et al, 2001;Peirs et al, 2005;Runyen-Janecky et al, 2005), and biofilm formation (Monds et al, 2001).Since (i) earlier work has alluded to the importance of this system during biofilm formation (Monds et al, 2001(Monds et al, , 2007 and (ii) the formation of crystalline biofilms is a characteristic of UTIs associated with P. mirabilis, we hypothesized that the Pst system of P. mirabilis HI4320 is involved in biofilm formation during establishment of a UTI. To assess the role of the Pst system, this study focused upon determining previously undetected in vitro phenotypes of the Dpst mutants by comparing biofilm formation between the wild-type HI4320 and DpstA and DpstS mutants via confocal laser scanning microscopy (CLSM) and quantitative analysis of surface coverage, and by comparing in vitro protein expression of these strains grown planktonically and as a biofilm.…”