Prevention of Surface-Associated Calcium Phosphate by the Pseudomonas syringae Two-Component System CvsSR

CvsSR is a Ca²⁺-induced two-component system (TCS) in the plant pathogen Pseudomonas syringae pv. tomato DC3000. Here, we discovered that CvsSR is induced by Fe³⁺, Zn²⁺, and Cd²⁺ However, only supplementation of Ca²⁺ to medium resulted in rugose, opaque colonies in ΔcvsS and ΔcvsR strains. This phenotype corresponded to formation of calcium phosphate precipitation on the surface of ΔcvsS and ΔcvsR colonies. CvsSR regulated swarming motility in P. syringae pv. tomato in a Ca²⁺-dependent manner, but swarming behavior was not influenced by Fe³⁺, Zn²⁺, or Cd²⁺ We hypothesized that reduced swarming displayed by ΔcvsS and ΔcvsR strains was due to precipitation of calcium phosphate on the surface of ΔcvsS and ΔcvsR cells grown on agar medium supplemented with Ca²⁺ By reducing the initial pH or adding glucose to the medium, calcium precipitation was inhibited, and swarming was restored to ΔcvsS and ΔcvsR strains, suggesting that calcium precipitation influences swarming ability. Constitutive expression of a CvsSR-regulated carbonic anhydrase and a CvsSR-regulated putative sulfate major facilitator superfamily transporter in ΔcvsS and ΔcvsR strains inhibited formation of calcium precipitates and restored the ability of ΔcvsS and ΔcvsR bacteria to swarm. Lastly, we found that glucose inhibited Ca²⁺-based induction of CvsSR. Hence, CvsSR is a key regulator that controls calcium precipitation on the surface of bacterial cells.IMPORTANCE Bacteria are capable of precipitating and dissolving minerals. We previously reported the characterization of the two-component system CvsSR in the plant-pathogenic bacterium Pseudomonas syringae CvsSR responds to the presence of calcium and is important for causing disease. Here, we show that CvsSR controls the ability of the bacterium to prevent calcium phosphate precipitation on the surface of cells. We also identified a carbonic anhydrase and transporter that modulate formation of surface-associated calcium precipitates. Furthermore, our results demonstrate that the ability of the bacterium to swarm is controlled by the formation and dissolution of calcium precipitates on the surface of cells. Our study describes new mechanisms for microbially induced mineralization and provides insights into the role of mineral deposits on bacterial physiology. The discoveries may lead to new technological and environmental applications.