Abstract 1380 A Ferrous Iron Two-Component System in Pseudomonas aeruginosa

Pseudomonas aeruginosa (Pa) is an opportunistic and increasingly antibiotic-resistant Gram-negative bacterium that is one of the major causes of chronic nosocomial infections.The colonization of Pa within a host is often linked to the bioavailability of nutrients, such as iron, and Pa has multiple iron acquisition pathways that allow it to adapt readily to the variety of environments it may encounter within a human host.Pa responds to these dynamic environments through the use of two-component signal transduction systems (TCSs), and previous studies have identified a biofilm-and quorum-sensing TCS known as BqsRS (also known as CarRS) that regulates biofilm formation and decay in Pa through the sensing of extracytoplasmic Fe2+ and Ca2+.In this work, we characterize the BqsRS system to understand its function and selectivity.Using biophysical approaches, we show that the membrane His kinase BqsS binds a single iron ion at a dimeric interface using a unique ligation scheme.Binding of ferrous iron elicits activity changes in the His kinase to activate the response regulator, BqsR.We have determined the structure of the BqsR receiver domain to 1.3 resolution and have modeled its DNA-binding domain.Interestingly, BqsR shows a preference for binding iron itself, which has not been observed in other OmpR-like response regulators.Importantly, using in vitro DNA-binding assays, we show that BqsR can target the Pa ferrous iron uptake operon feo.Transcriptomic changes in PAO1 show that feo is among among the most differentially regulated genes by the BqsRS sytem.Taken together, these data suggest that the BqsRS system plays an important role in iron homeostasis of this infectious pathogen.