Pseudomonas aeruginosa (PA) is a primary cause of nosocomial infections. A key element in PA pathogenicity is its ability to form biofilms that withstand eradication by antibiotics and the immune system. Biofilm formation is controlled by phosphate signaling and here we evidence that PstS, a subunit of the PA Pst phosphate transporter has a surprising role in this process. Using X-ray crystallography, we characterized the unique underpinnings of PstS phosphate binding and identified an unusual 15-residue N` loop extension.
Structure-based experiments showed that PstS-mediated phosphate uptake and biofilm formation are in fact two distinct functions. Specifically, a point mutation that abrogated phosphate binding did not eliminate biofilm formation and, conversely, truncation of the N` loop diminished the ability of PA to form biofilms but had no effect on phosphate binding and uptake. This places PstS at a junction that separately controls phosphate sensing, uptake and the ultra-structure organization of bacteria.
