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PubMed1979

Biochemical properties of a new flexuous bacteriocin, pyocin F1, produced by Pseudomonas aeruginosa.

Pseudomonas aeruginosa strain P15 produces not only pyocin R1 and phage PS10, but also a substance having a flexuous rod structure, the nature of which is so far unknown. A variant strain (P15--40) was obtained which produced these flexuous particles more effectively than the original strain, and the particles were purified to homogeneity and investigated. Several strains of P. aeruginosa were found to be killed by the particles. It was concluded that the flexuous rod-like particles are not related to pyocin R1 or phage PS10, but represent a new pyocin, which we have designated as pyocin F1. Pyocin F1 showed a different action spectrum and a different pattern on SDS-polyacrylamide gel electrophoresis from either pyocin R1 or phage PS10. The killing activity of pyocin F1 was of single-hit type. The activity was not affected by anti-R1, anti-R1-core or anti-PS10, or by DNase, RNase, pronase or trypsin, but was completely destroyed by treatment at 70 degrees C for 10 min. Some cofactor was required for the adsorption of this pyocin on sensitive bacteria. Another flexuous bacteriocin was also found and named pyocin F2.

Bacteriocins↗

PubMed1996

Characterisation of the pvdE gene which is required for pyoverdine synthesis in Pseudomonas aeruginosa.

Pseudomonas aeruginosa (Pa) strain PAO synthesises a siderophore, pyoverdine (Pvd), when grown under conditions of iron starvation. Pvd consists of a dihydroxyquinoline group attached to an 8-amino-acid-residue peptide. DNA spanning at least 78 kb of the chromosome is required for Pvd synthesis, but to date only three genes involved in this process have been characterised. We report the characterisation of a fourth Pa gene, pvdE, which we show to be required for Pvd synthesis. The deduced amino acid sequence of PvdE indicates that the protein is a member of the ATP-binding-cassette (ABC) family of membrane transporter proteins, and this is the first example of the involvement of an ABC-type protein in siderophore synthesis.

ATP-Binding Cassette Transporters↗

PubMed1998

Formation of oligomeric rings by XcpQ and PilQ, which are involved in protein transport across the outer membrane of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is able to translocate proteins across both membranes of the cell envelope. Many of these proteins are transported via the type II secretion pathway and adopt their tertiary conformation in the periplasm, which implies the presence of a large transport channel in the outer membrane. The outer membrane protein, XcpQ, which is involved in transport of folded proteins across the outer membrane of P. aeruginosa, was purified as a highly stable homomultimer. Insertion and deletion mutagenesis of xcpQ revealed that the C-terminal part of XcpQ is sufficient for the formation of the multimer. However, linker insertions in the N-terminal part can disturb complex formation completely. Furthermore, complex formation is strictly correlated with lethality, caused by overexpression of xcpQ. Electron microscopic evaluation of the XcpQ multimers revealed large, ring-shaped structures with an apparent central cavity of 95 A. Purified PilQ, a homologue of XcpQ involved in the biogenesis of type IV pili, formed similar structures. However, the apparent cavity formed by PilQ was somewhat smaller, 53 A. The size of this cavity could allow for the transport of intact type IV pili.

Amino Acid Sequence↗

PubMed1997

Modulation of macrophage function for defence of the lung against Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a common respiratory tract pathogen in certain groups of compromised hosts, most notably those with cystic fibrosis. The pathogenicity of P. aeruginosa may depend in part upon its capacity to resist normal phagocytic cell clearance. We have recently shown that phagocytosis of P. aeruginosa by macrophages is a unique two-step process; binding is glucose-independent but ingestion occurs only in the presence of D-glucose or D-mannose. P. aeruginosa is the only particle we have found which is ingested by macrophages in a glucose-dependent manner. Since glucose is present in only negligible quantities in the endobronchial space, P. aeruginosa may be pathogenic by virtue of its capacity to exploit the opportunity presented in the lower airway to resist normal nonspecific phagocytic defences. The purpose of the studies reported here is to better understand the glucose-dependent phagocytosis of P. aeruginosa and to design novel therapies to facilitate phagocytic cell clearance of it from the lower respiratory tract. We have shown that phagocytosis of unopsonized P. aeruginosa depends upon facilitated transport of glucose into macrophages via the GLUT1 isoform. After transport into the macrophage, the glucose must be metabolized to trigger phagocytosis of P. aeruginosa; pretreatment with 2-deoxyglucose or 5-thioglucose abrogates glucose-dependent ingestion. We have recently demonstrated that pulmonary alveolar macrophages (as opposed to all other macrophage phenotypes studied) lack the capacity to transport glucose and to phagocytose unopsonized P. aeruginosa; however, after the cells have been cultured in vitro for 48 hours, they are able to perform both functions. Whereas most macrophages (such as peritoneal cells) primarily depend upon glycolysis for metabolic energy, pulmonary alveolar macrophages reside in a high oxygen tension environment and appear to utilize oxidative phosphorylation. Treatment of freshly explanted pulmonary alveolar macrophages with sodium azide (to poison oxidative respiration) dramatically enhances both glucose transport and glucose-dependent phagocytosis of P. aeruginosa. We are currently investigating the compromised phagocytic function of pulmonary alveolar macrophages and the mechanism by which azide enhances glucose transport and phagocytosis of P. aeruginosa. Although physiological measurements have indicated that glucose is removed from the endobronchial space by an active transport process of the lung epithelium, the types of glucose transporters that are expressed in the lung are as yet unknown. Using RT-PCR, we have amplified a product from human and murine lung RNA which has a high degree of homology with members of the sodium-dependent glucose transporter (SGLT) family. The ultimate goal of these studies is to design novel agents for enhancing the phagocytic function of pulmonary alveolar macrophages. Delivery of simple glucose by aerosol would not be effective because (i) it would be exported by sodium-dependent active transport and (ii) pulmonary alveolar macrophages lack the capacity to transport glucose. Various approaches for targeting glucose to alveolar macrophages by receptor-mediated endocytosis are under investigation.

Animals↗

PubMed2001

Synthesis and activities of pyoverdin-quinolone adducts: a prospective approach to a specific Therapy against Pseudomonas aeruginosa.

Pseudomonas aeruginosa is particularly resistant to most all the antibiotics presently available, essentially because of the very low permeability of its outer membrane. To overcome this, we synthesized four siderophore-based antibiotics formed by two quinolones - norfloxacin and benzonaphthyridone - bound to the pyoverdin of P. aeruginosa ATCC 15692 via two types of spacer arms: one stable and the other readily hydrolyzable. From the comparison of their antibacterial properties with those of the two unbound quinolones, we reached the following conclusions: (a) The adducts inhibit Escherichia coli's gyrase showing that the dissociation of the compounds is not necessary for their activity. However, the presence of the pyoverdin moiety on the molecule decreases the inhibition activity compared to the antibiotic alone. (b) They facilitate the uptake of (55)Fe using the specific pyoverdin-mediated iron-transport system of the bacterium. No uptake was observed either with P. aeruginosa ATCC 27853, which produces a structurally different pyoverdin, or with P. aeruginosa K690, which is a mutant of P. aeruginosa ATCC 15692 lacking FpvA, the outer-membrane pyoverdin receptor. (c) MIC determinations have shown that only strains P. aeruginosa ATCC 15692 and the derived outer-membrane receptor-producing but pyoverdin-deficient P. aeruginosa IA1 mutant present higher susceptibility to the pyoverdin-quinolone adducts, whereas P. aeruginosa ATCC 27853 and K690 are much more resistant. (d) Growth inhibition by these adducts confirmed these results and showed that the adducts with the hydrolyzable spacer arm have better activity than those with the stable one and that the labile spacer arm adducts present much higher activity than the quinolones alone. These results show clearly that the penetration of the antibiotic into the cells is favored when this latter is coupled with pyoverdin: Only the strains possessing the appropriate outer-membrane receptor present higher susceptibility to the adduct. In this case the antibiotic uses the pyoverdin-mediated iron-transport system. Furthermore, better efficiency is obtained when the spacer arm is labile and favors the antibiotic release inside the cell, allowing better inhibition of gyrase.

Anti-Infective Agents↗

PubMed1998

[Antibiotic efflux, a mechanism of multiple resistance in Pseudomonas aeruginosa].

Pseudomonas aeruginosa displays three active efflux systems, made of three components: an inner membrane protein acting as a proton motive pump, a periplasmic linking protein and an outer membrane protein acting as an efflux porin. All three proteins are encoded by genes organised as an operon, with a regulator gene in the vicinity. Efflux systems produce phenotypes of multidrug resistance. The constitutively produced system MexAB-OprM generates intrinsic resistance to most beta-lactams, quinolones, tetracycline, chloramphenicol, trimethoprim and sulfamethoxazole; in addition, genetic derepression causes acquired resistance to the same drugs. The non constitutive MexCD-OprJ and MexEF-OprN can be expressed by mutation, producing then slightly different multidrug resistant phenotypes. Efflux systems are responsible for low level resistance, and seem to promote selection of mutations responsible for higher level resistance. The multidrug resistance associated to active efflux systems should be taken into account in our antibiotic policies, both at the individual and at the institutional level.

Anti-Bacterial Agents↗

PubMed1988

Interaction between piperacillin and pefloxacin or amikacin on the selection of resistant mutants of Pseudomonas aeruginosa.

Pseudomonas aeruginosa mutants were selected with piperacillin, pefloxacin, amikacin and the combinations pefloxacin-piperacillin and amikacin-piperacillin. With amikacin and the piperacillin-amikacin combination no mutants were selected. With piperacillin (1-32 x MIC) mutants resistant to carboxypenicillins, ureidopenicillins, monobactam and cephalosporins were selected. With pefloxacin, three different types of mutant were observed which showed different patterns of cross-resistance to pefloxacin, sulphonamides, imipenem, piperacillin and other beta-lactam antibiotics. With the pefloxacin-piperacillin association, mutants similar to one of the types selected by pefloxacin alone and resistant to both of the selective antibiotic were predominantly obtained. No mutants were selected with this combination if one of the antibiotics was used at a concentration equal to its MIC for the wild type strain and the other at concentrations above 4 x MIC. Since the association of piperacillin and pefloxacin was only moderately bactericidal against the predominantly cross-resistant mutant selected, the concentration of these antibiotics may have to be carefully controlled to prevent the emergence of such mutants.

Amikacin↗

PubMed2003

Substrate specificity of the nonribosomal peptide synthetase PvdD from Pseudomonas aeruginosa.

Pseudomonas aeruginosa PAO1 secretes a siderophore, pyoverdine(PAO), which contains a short peptide attached to a dihydroxyquinoline moiety. Synthesis of this peptide is thought to be catalyzed by nonribosomal peptide synthetases, one of which is encoded by the pvdD gene. The first module of pvdD was overexpressed in Escherichia coli, and the protein product was purified. L-Threonine, one of the amino acid residues in pyoverdine(PAO), was an effective substrate for the recombinant protein in ATP-PP(i) exchange assays, showing that PvdD has peptide synthetase activity. Other amino acids, including D-threonine, L-serine, and L-allo-threonine, were not effective substrates, indicating that PvdD has a high degree of substrate specificity. A three-dimensional modeling approach enabled us to identify amino acids that are likely to be critical in determining the substrate specificity of PvdD and to explore the likely basis of the high substrate selectivity. The approach described here may be useful for analysis of other peptide synthetases.

Amino Acid Sequence↗

PubMed2006

Polyamines increase antibiotic susceptibility in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic human pathogen. Treatment is complicated by frequent acquired resistance to antipseudomonal therapies. Polyamines (cadaverine, putrescine, spermidine, and spermine) are ubiquitous polycationic compounds essential for all living organisms. In a dose-dependent manner, polyamines increased the susceptibility of P. aeruginosa to 14 beta-lactam antibiotics, chloramphenicol, nalidixic acid, and trimethoprim as demonstrated by a reduction in MIC of up to 64-fold. This effect was partially antagonized (25 to 50%) by the presence of 10 mM of Mg(2+) or Ca(2+). In contrast, the effects of the outer membrane permeabilizers, polymyxin B nonapeptide and EDTA, were completely abolished by 3 mM Mg(2+) or Ca(2+). Changes on the outer membrane barrier by these compounds were assessed by activity measurements of periplasmic beta-lactamase. The results showed that while EDTA and polymyxin B serve as outer membrane disorganizing agents as expected, exogenous spermidine and spermine did not exhibit any apparent effect on outer membrane permeability or rupture. In summary, these results strongly suggest that the increased antibiotic susceptibility by polyamines is exerted by a mechanism that differs from that of EDTA and polymyxin B. Polyamines might be potentially useful in antipseudomonal therapies by increasing the effectiveness of certain beta-lactam antibiotics.

Anti-Bacterial Agents↗

PubMed1996

Recognition of mucin by the adhesin-flagellar system of Pseudomonas aeruginosa.

Pseudomonas aeruginosa colonizes the mucus of patients with chronic lung diseases by a specific mechanism involving an adhesin-receptor system. Several adhesins have been implicated in the adhesion of P. aeruginosa to cells, but the identity of the principal adhesin(s) involved in adhesion to mucin is unknown. Mutagenesis studies have indicated that P. aeruginosa adhesion is under the control of the rpoN gene, which also regulates pilin synthesis, flagellum formation, and other functions. Mutagenesis of certain flagellar genes that are not controlled by RpoN, e.g., flif, also indicates a close relationship between adhesion and flagellar genes and not necessarily an independent effect of rpoN on adhesion. Mutants of certain early flagellar genes lead to the loss of both adhesion and motility, whereas mutants of certain late genes, e.g., fliC, the gene for flagellin, lose motility but retain adhesion. Recent studies indicate that both motility and adhesion are regulated by a two-component regulatory system called fleS-R, which in turn is controlled by another regulator in a cascade that involves rpoN. A fleR mutant possessing pili adheres poorly to mucins, definitively showing that pili do not play a major role in adhesion to mucin. It is unclear whether the adhesin is a flagellar protein or another protein that uses the flagellar export apparatus for localization or both. Finding the gene under control of rpoN may provide answers to these questions.

Adhesins, Bacterial↗

PubMed1997

Identification and functional characterization of an ABC transport system involved in polysaccharide export of A-band lipopolysaccharide in Pseudomonas aeruginosa.

Pseudomonas aeruginosa coexpresses two distinct lipopolysaccharide (LPS) molecules known as A band and B band. B band is the serospecific LPS, while A band is the common LPS antigen composed of a D-rhamnose O-polysaccharide region. An operon containing eight genes responsible for A-band polysaccharide biosynthesis and export has recently been identified and characterized (H. L. Rocchetta, L. L. Burrows, J. C. Pacan, and J. S. Lam, unpublished data; H. L. Rocchetta, J. C. Pacan, and J. S. Lam, unpublished data). In this study, we report the characterization of two genes within the cluster, designated wzm and wzt. The Wzm and Wzt proteins have predicted sizes of 29.5 and 47.2 kDa, respectively, and are homologous to a number of proteins that comprise ABC (ATP-binding cassette) transport systems. Wzm is an integral membrane protein with six potential membrane-spanning domains, while Wzt is an ATP-binding protein containing a highly conserved ATP-binding motif. Chromosomal wzm and wzt mutants were generated by using a gene replacement strategy in P. aeruginosa PAO1 (serotype 05). Western blot analysis and immunoelectron microscopy using A-band- and B-band-specific monoclonal antibodies demonstrated that the wzm and wzt mutants were able to synthesize A-band polysaccharide, although transport of the polymer to the cell surface was inhibited. The inability of the polymer to cross the inner membrane resulted in the accumulation of cytoplasmic A-band polysaccharide. This A-band polysaccharide is likely linked to a carrier lipid molecule with a phenol-labile linkage. Chromosomal mutations in wzm and wzt were found to have no effect on B-band LPS synthesis. Rather, immunoelectron microscopy revealed that the presence of A-band LPS may influence the arrangement of B-band LPS on the cell surface. These results demonstrate that A-band and B-band O-antigen assembly processes follow two distinct pathways, with the former requiring an ABC transport system for cell surface expression.

ATP-Binding Cassette Transporters↗

PubMed2000

Assignment of the substrate-selective subunits of the MexEF-OprN multidrug efflux pump of Pseudomonas aeruginosa.

Pseudomonas aeruginosa expresses a low level of the MexAB-OprM efflux pump and shows natural resistance to many structurally and functionally diverse antibiotics. The mutation that has been referred to previously as nfxC expresses an additional efflux pump, MexEF-OprN, exhibiting resistance to fluoroquinolones, imipenem, and chloramphenicol and hypersusceptibility to beta-lactam antibiotics. To address the antibiotic specificity of the MexEF-OprN efflux pump, we introduced a plasmid carrying the mexEF-oprN operon into P. aeruginosa lacking the mexAB-oprM operon. The transformants exhibited resistance to fluoroquinolones, trimethoprim, and chloramphenicol but, unlike most nfxC-type mutants, did not show beta-lactam hypersusceptibility. The transformants exhibited additional resistance to tetracycline. In the next experiment, we analyzed the MexEF-OprN pump subunit(s) responsible for substrate selectivity by expressing MexE, MexF, OprN, and MexEF in strains lacking MexA, MexB, OprM, and MexAB, respectively. The MexEF-OprM/DeltaMexAB transformants exhibited MexEF-OprN-type pump function that rendered the strains resistant to fluoroquinolones and chloramphenicol but did not change susceptibility to beta-lactam antibiotics compared with the host strain. The MexAB-OprN/DeltaOprM, MexAF-OprM/DeltaMexB, and MexEB-OprM/DeltaMexA mutants exhibited antibiotic susceptibility indistinguishable from that in the mutant lacking both types of efflux pumps. The results imply that the MexEF-OprM pump selects substrates by a MexEF functional unit. Interestingly, OprN did not link functionally with the MexAB complex, despite the fact that OprM interacted functionally with MexEF.

Anti-Bacterial Agents↗

PubMed2003

Induction of apoptosis in macrophage cell line, J774, by the cell-free supernatant from Pseudomonas aeruginosa.

Pseudomonas aeruginosa is able to secrete many virulence factors that are cytotoxic towards eukaryotic cells. To investigate the effect of the bacterium on macrophages, we obtained cell-free supernatants from P. aeruginosa (Pa) IID1117 (elastase-positive and protease-positive) and Pa IID1130 (elastase-positive and protease-negative). After 6 hr of incubation with the cell-free supernatant from the Pa IID1117 strain, the viability of J774 macrophages was shown to be significantly reduced (47.5+/-11%), but not Pa IID1130 (96.4+/-1.6%) at a concentration of 10% (v/v) compared to control J774 macrophages without any supernatant (97.2+/-1.7%) by the detection of trypan blue dye exclusion. The death of cells was further demonstrated to be due to apoptosis characterized by chromatin condensation and apoptotic bodies by Hoechst 33258 staining, DNA fragmentation by agarose gel electrophoresis and terminal deoxynucleotidyl transferase-mediated d-UTP nick end labeling (TUNEL). An activated subunit was found to be released from procaspase-3 in cell lysate. But in the presence of protease inhibitor, the apoptosis was completely blocked. The findings indicate that the Pa IID1117 strain is capable of inducing apoptosis in J774 macrophages. The apoptosis induced by the cell-free supernatant from Pa IID1117 strain is suggested to be dependent on protease, but not elastase.

Apoptosis↗

PubMed1994

Cloning and heterologous expression of a gene encoding an alkane-induced extracellular protein involved in alkane assimilation from Pseudomonas aeruginosa.

Pseudomonas aeruginosa PG201 produces a 16-kDa extracellular protein in media containing n-hexadecane as a carbon source but not in media containing glycerol or glucose. This protein was purified, and the N-terminal amino acid sequence was determined. The amino acid composition of the protein was found to be very similar to that of the so-called protein-like activator for n-alkane oxidation (PA) from P. aeruginosa S7B1. This extracellular protein was previously characterized (K. Hisatsuka, T. Nakahara, Y. Minoda, and K. Yamada, Agric. Biol. Chem. 41:445-450, 1977) and found to stimulate the growth of P. aeruginosa on n-hexadecane and to possess emulsifying activity. To study the role(s) of the PA protein and to make it accessible for possible future applications, we have cloned the PA-encoding (pra) gene and determined its nucleotide sequence. This analysis revealed a protein-coding region of 162 amino acids, with the first 25 residues being reminiscent of those of a typical bacterial signal sequence. The pra gene was inactivated by insertional mutagenesis, and the resulting strain was found to lack extracellular PA protein and to be retarded in its growth in n-hexadecane-containing media. These results are consistent with the growth stimulatory role of the PA protein. The pra gene was expressed in Escherichia coli, and substantial amounts of the recombinant protein were found in the extracellular growth medium. The recombinant protein was purified by metal chelate affinity chromatography. The ability to produce secreted PA protein by E. coli provides a simple and safe means to analyze its function(s) in alkane assimilation in the future.

Alkanes↗

PubMed1999

Characterization of a Hank's type serine/threonine kinase and serine/threonine phosphoprotein phosphatase in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic pathogen that causes infections in eye, urinary tract, burn, and immunocompromised patients. We have cloned and characterized a serine/threonine (Ser/Thr) kinase and its cognate phosphoprotein phosphatase. By using oligonucleotides from the conserved regions of Ser/Thr kinases of mycobacteria, an 800-bp probe was used to screen P. aeruginosa PAO1 genomic library. A 20-kb cosmid clone was isolated, from which a 4.5-kb DNA with two open reading frames (ORFs) were subcloned. ORF1 was shown to encode Ser/Thr phosphatase (Stp1), which belongs to the PP2C family of phosphatases. Overlapping with the stp1 ORF, an ORF encoding Hank's type Ser/Thr kinase was identified. Both ORFs were cloned in pGEX-4T1 and expressed in Escherichia coli. The overexpressed proteins were purified by glutathione-Sepharose 4B affinity chromatography and were biochemically characterized. The Stk1 kinase is 39 kDa and undergoes autophosphorylation and can phosphorylate eukaryotic histone H1. A site-directed Stk1 (K86A) mutant was shown to be incapable of autophosphorylation. A two-dimensional phosphoamino acid analysis of Stk1 revealed strong phosphorylation at a threonine residue and weak phosphorylation at a serine residue. The Stp1 phosphatase is 27 kDa and is an Mn(2+)-, but not a Ca(2+)- or a Mg(2+)-, dependent Ser/Thr phosphatase. Its activity is inhibited by EDTA and NaF, but not by okadaic acid, and is similar to that of PP2C phosphatase.

Amino Acid Sequence↗

PubMed2007

Interrelationships between colonies, biofilms, and planktonic cells of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a gram-negative bacterium and an opportunistic human pathogen that causes chronic infections in immunocompromised individuals. These infections are hard to treat, partly due to the high intrinsic resistance of the bacterium to clinically used antibiotics and partly due to the formation of antibiotic-tolerant biofilms. The three most common ways of growing bacteria in vitro are as planktonic cultures, colonies on agar plates, and biofilms in continuous-flow systems. Biofilms are known to express genes different from those of planktonic cells, and biofilm cells are generally believed to closely resemble planktonic cells in stationary phase. However, few, if any, studies have examined global gene expression in colonies. We used a proteomic approach to investigate the interrelationships between planktonic cells, colonies, and biofilms under comparable conditions. Our results show that protein profiles in colonies resemble those of planktonic cells. Furthermore, contrary to what has been reported previously, the protein profiles of biofilms were found to more closely resemble those of exponentially growing planktonic cells than those of planktonic cells in the stationary phase. These findings raise some intriguing questions about the true nature of biofilms.

Agar↗

PubMed1990

Molecular comparison of a nonhemolytic and a hemolytic phospholipase C from Pseudomonas aeruginosa.

Pseudomonas aeruginosa produces two secreted phospholipase C (PLC) enzymes. The expression of both PLCs is regulated by Pi. One of the PLCs is hemolytic, and one is nonhemolytic. Low-stringency hybridization studies suggested that the genes encoding these two PLCs shared DNA homology. This information was used to clone plcN, the gene encoding the 77-kilodalton nonhemolytic PLC, PLC-N. A fragment of plcN was used to mutate the chromosomal copy of plcN by the generation of a gene interruption mutation. This mutant produces 55% less total PLC activity than the wild type, confirming the successful cloning of plcN. plcN was sequenced and encodes a protein which is 40% identical to the hemolytic PLC (PLC-H). The majority of the homology lies within the NH2 two-thirds of the proteins, while the remaining third of the amino acid sequence of the two proteins shows very little homology. Both PLCs hydrolyze phosphatidylcholine; however, each enzyme has a distinct substrate specificity. PLC-H hydrolyzes sphingomyelin in addition to phosphatidylcholine, whereas PLC-N is active on phosphatidylserine as well as phosphatidylcholine. These studies suggest structure-function relationships between PLC activity and hemolysis.

Amino Acid Sequence↗

PubMed1986

Siderophore-mediated iron acquisition from transferrin by Pseudomonas aeruginosa.

Pseudomonas aeruginosa placed across a dialysis membrane from [55Fe]transferrin caused the mobilization of the iron from the transferrin side to the bacterial or dialysate side of the membrane. Although the bacteria were capable of obtaining iron from transferrin for growth, the siderophores of P. aeruginosa failed to convert iron bound to transferrin into dialyzable, low-molecular-weight chelates. The crucial factor produced by the bacteria which was not present when the siderophores were added alone was the acid produced from the glucose minimal medium. The siderophores mobilized considerable iron from transferrin when used in the dialysis assay at pH values between 5.0 and 6.0, values which were commonly found during incubation of bacteria in the assays. When the siderophores were tested individually, pyoverdin was more effective than pyochelin in mobilizing iron across dialysis membranes at pH values of 5.0 and 6.0, but neither had appreciable activity at pH 7.4. The amounts of iron mobilized from conalbumin were comparable to the amounts from transferrin, but there was negligible release from lactoferrin at the three pH values. When the two siderophores were combined, the level of iron mobilization was identical to that demonstrated by pyoverdin alone. When the dialysis membrane was removed and the bacteria were mixed with the siderophores and transferrin, pyoverdin was again more active than pyochelin in mediating iron transport. Although no pyochelin-mediated iron mobilization could be detected at pH 7.4, there was transport. Therefore, the bacteria appeared to be aiding the siderophores in iron mobilization from transferrin.

Conalbumin↗