Calcium (Ca2+) homeostasis is tightly regulated in eukaryotes, where Ca2+ acts as a cellular messenger regulating a number of essential processes. We aim to characterize intracellular Ca2+ (Ca2+in) homeostasis in PAO1 and identify proteins responsible for Ca2+ transport. By using Ca2+-binding photoprotein aequorin, we showed that P. aeruginosa maintains intracellular Ca2+ homeostasis and generates a transient [Ca2+]in increase in response to elevated external Ca2+. Multiple transporters play a major role in such maintenance, including P-type ATPase that is also required for Ca2+-induced swarming. Currently, we study the role of these proteins in cell tolerance to high Ca2+and Ca2+-induced virulence. Identification of Ca2+ transporters enables further studies aiming to elucidate the regulatory role of Ca2+ in physiology and virulence of P. aeruginosa.
Abnormalities in Ca2+ homeostasis in a human body may lead to soft tissue calcification commonly associated with diseases. However the origin and the mechanisms of such calcification remain unknown. Our hypothesis is that P. aeruginosa carbonic anhydrases (CA) may be involved in CaCO3 deposition. CAs are zinc metalloenzymes catalyzing reversible hydration of CO2. Using transmission electron microscopy with X-Ray elemental analysis we detected the ability of P. aeruginosa to deposit extracellular Ca2+, which may trigger soft tissue calcification in a host and thus contribute to P. aeruginosa pathogenicity. We purified and characterized three β-carbonic anhydrases, two of which are induced by Ca2+ and play a major role in this deposition. Currently, the role of the CAs in Ca2+-induced virulence is tested. Further studies include structure-function analyses of the proteins, which may enable the development of at least one of these proteins into potential new antimicrobial target against this pathogen.