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Pseudomonas aeruginosa is a facultative human pathogen, and a major cause of nosocomial infections and severe chronic infections in endocarditis and in cystic fibrosis (CF) patients. Calcium (Ca2+) accumulates in pulmonary fluids of CF patients, and plays a role in the hyperinflamatory response to bacterial infection. Earlier we showed that P. aeruginosa responds to increased Ca2+ levels, primarily through the increased production of secreted virulence factors. Here we describe the role of putative Ca2+-binding protein, with an EF-hand domain, PA4107 (EfhP), in this response. Deletion mutations of efhP were generated in P. aeruginosa strain PAO1 and CF pulmonary isolate, strain FRD1. The lack of EfhP abolished the ability of P. aeruginosa PAO1 to maintain intracellular Ca2+ homeostasis. Quantitative high-resolution 2D-PAGE showed that the efhP deletion also affected the proteomes of both strains during growth with added Ca2+. The greatest proteome effects occurred when the pulmonary isolate was cultured in biofilms. Among the proteins that were significantly less abundant or absent in the mutant strains were proteins involved in iron acquisition, biosynthesis of pyocyanin, proteases, and stress response proteins. In support, the phenotypic responses of FRD1 ΔefhP showed that the mutant strain lost its ability to produce pyocyanin, developed less biofilm, and had decreased resistance to oxidative stress (H2O2) when cultured at high [Ca2+]. Furthermore, the mutant strain was unable to produce alginate when grown at high [Ca2+] and no iron. The effect of the ΔefhP mutations on virulence was determined in a lettuce model of infection. Growth of wild-type P. aeruginosa strains at high [Ca2+] causes an increased area of disease. In contrast, the lack of efhP prevented this Ca2+-induced increase in the diseased zone. The results indicate that EfhP is important for Ca2+ homeostasis and virulence of P. aeruginosa when it encounters host environments with high [Ca2+].

Bacterial b-class carbonic anhydrases (CAs) are zinc metalloenzymes catalysing reversible hydration of CO 2. They maintain the intracellular balance of CO 2 /bicarbonate required for biosynthetic reactions and represent a new group of antimicrobial drug targets. Genome sequence analysis of Pseudomonas aeruginosa PAO1, an opportunistic human pathogen causing life threatening infections, identified three genes, PAO102, PA2053 and PA4676, encoding putative b-CAs that share 28-45 % amino acid sequence identity and belong to clades A and B. The genes are conserved among all sequenced pseudomonads. The CAs were cloned, heterologously expressed and purified. Metal and enzymic analyses confirmed that the proteins contain Zn 2+ and catalyse hydration of CO 2 to bicarbonate. PAO102 (psCA1) was 19-26-fold more active, and together with PA2053 (psCA2) showed CA activity at both pH 7.5 and 8.3, whereas PA4676 (psCA3) was active only at pH 8.3. Circular dichroism spectroscopy suggested that psCA2 and psCA3 undergo pH-dependent structural changes. Taken together, the data suggest that psCA1 may belong to type I and psCA3 to type II b-CAs. Immunoblot analysis showed that all three CAs are expressed in PAO1 cells when grown in ambient air and at 5 % CO 2 ; psCA1 appeared more abundant under both conditions. Growth studies of transposon mutants showed that the disruption of psCA1 impaired PAO1 growth in ambient air and caused a minor defect at high CO 2 . Thus, psCA1 contributes to the adaptation of P. aeruginosa to low CO 2 conditions and will be further studied for its role in virulence and as a potential antimicrobial drug target in this organism.

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High-yield syntheses of N-piperidine-cyanacetamide (1), N-morpholyl-cyanacetamide (4) and their oxime derivatives N-piperidine-2-cyano-2-oximino-acetamide (HPiPCO, 2) and N-morpholyc-2-cyano-2-oximino-acetamide (HMCO, 5) were developed using two-step preparations. At first, the reactions of neat cyanoacetic acid esters and the respective cyclic secondary amines such as piperideine and morpholine afforded pure cyanacetamides, which were converted into cyanoximes at room temperature using the nitrosation reaction with gaseous CH3ONO. The synthesized compounds were investigated by means of IR, 1H, 13C and UV-visible spectroscopy. Crystal structures of two starting substituted cyan-acetamides and two target cyanoximes were determined. Silver(I) complexes of AgL composition (L = PipCO, 3; MCO, 6) were prepared in high yield. Both metal complexes are thermally stable above 100oC, and remarkably stable to high intensity visible light. The stability of dried AgL compounds towards short wavelength UV-radiation (a frequently used germicidal light) was examined using diffusion reflectance spectroscopy. Both complexes demonstrate slow photoreduction within ~3 hrs, observable as a gradual color change and darkening due to the formation of fine (nano-scale) particles of metallic silver. The complex Ag(MCO), 6, is about 2.6 times less stable towards UV-radiation than its more lypophyllic analog Ag(PipCO), 3. Antimicrobial and biofilm growth inhibition properties of the prepared solid acrylate-based polymeric composites containing embedded silver(I) cyanoximates were investigated using three human pathogens: P. aeruginosa PAO1 (wound isolate), S. aureus NRS70 (methicillin resistant respiratory isolate), and S. mutans UA159 (cariogenic dental isolate). Studies showed that both 3 and 6 compounds completely abolished the growth of PAO1 at 0.5 weight % concentration, and the growth of UA159 and NRS70 at 1% concentration. Moreover, data demonstrates that complexes 3 and 6 also inhibit both planktonic and biofilm growth of Gram-positive and Gram-negative bacterial pathogens. The demonstrated thermal stability and pronounced antimicrobial activity of both silver(I) cyanoximates indicates the strong potential for the studied complexes to be used as light insensitive antimicrobial additives to light-curable adhesives that set indwelling devices in place.