Pseudomonas aeruginosa contains an inducible methylcitrate synthase

Assaying for enzymes of propionyl-CoA catabolism in crude extracts ofPseudomonas aeruginosa was complicated by the presence of a short-chain acyl-CoA hydrolase. Interference by the hydrolase was avoided by using permeabilized whole cells. Cells treated this way exhibited low or undetectable levels of propionyl-CoA carboxylase, propionyl-CoA dehydrogenase, and α-hydroxyglutarate synthase, enzymes initiating propionyl-CoA catabolism in many prokaryotes, but did contain high levels of methylcitrate synthase, an enzyme of the methylcitrate cycle for propionyl-CoA catabolism. Gel filtration experiments revealed a peak of methylcitrate synthase distinct from the citrate synthase of the bacterium. The enzyme was induced by growth on propionate and on propanol and heptanoate, precursors of propionate. These results suggest thatP. aeruginosa may utilize the methylcitrate cycle to metabolize propionate, a pathway heretofore only described in the yeastCandida lipolytica.     

Aspergillus contains multiple tubulin genes

Previous work with benomyl-resistant mutants of Aspergillus nidulans has demonstrated that the benA locus is a structural gene for beta-tubulin. Two of the benA mutants, benA22 and benA85, show altered electrophoretic mobilities on two-dimensional gels for two beta-tubulins (designated beta 1 and beta 2). These shifts of the beta 1- and beta 2-tubulins uncover a spot in the region where wild-type beta-tubulins migrate that is occluded on gels of wild-type extracts by the beta 1- and beta 2-tubulins. Evidence has now been obtained indicating that this spot represents an additional beta-tubulin (designated beta 3). Tubulin was partially purified from Aspergillus and run on one- and two-dimensional gels and the band or spot uncovered by the shift of the beta 1- and beta 2-tubulins was identified as a beta-tubulin by immunoblotting with monoclonal and affinity-purified polyclonal anti-tubulin antibodies and by one-dimensional peptide mapping. These observations show that Aspergillus contains at least two structural genes for beta-tubulins. Similar techniques have also been applied to a mutant showing altered alpha-tubulins to confirm and modify earlier observations suggesting that at least two structural genes for alpha-tubulins are also present.     

Pseudomonas aeruginosa contains a novel type V porphobilinogen synthase with no required catalytic metal ions.

Porphobilinogen synthases (PBGS) are metalloenzymes that catalyze the first common step in tetrapyrrole biosynthesis. The PBGS enzymes have previously been categorized into four types (I-IV) by the number of Zn(2+) and/or Mg(2+) utilized at three different metal binding sites termed A, B, and C. In this study Pseudomonas aeruginosa PBGS is found to bind only four Mg(2+) per octamer as determined by atomic absorption spectroscopy, in the presence or absence of substrate/product. This is the lowest number of bound metal ions yet found for PBGS where other enzymes bind 8-16 divalent ions. These four Mg(2+) allosterically stimulate a metal ion independent catalytic activity, in a fashion dependent upon both pH and K(+). The allosteric Mg(2+) of PBGS is located in metal binding site C, which is outside the active site. No evidence is found for metal binding to the potential high-affinity active site metal binding sites A and/or B. P. aeruginosa PBGS was investigated using Mn(2+) as an EPR probe for Mg(2+), and the active site was investigated using [3,5-(13)C]porphobilinogen as an NMR probe. The magnetic resonance data exclude the direct involvement of Mg(2+) in substrate binding and product formation. The combined data suggest that P. aeruginosa PBGS represents a new type V enzyme. Type V PBGS has the remarkable ability to synthesize porphobilinogen in a metal ion independent fashion. The total metal ion stoichiometry of only 4 per octamer suggests half-sites reactivity.     

FolX from Pseudomonas aeruginosa is octameric in both crystal and solution

FolX encodes an epimerase that forms one step of the tetrahydrofolate biosynthetic pathway, which is of interest as it is an established target for important drugs. Here we report the crystal structure of FolX from the bacterial opportunistic pathogen Pseudomonas aeruginosa, as well as a detailed analysis of the protein in solution, using analytical ultracentrifugation (AUC) and small-angle X-ray scattering (SAXS). In combination, these techniques confirm that the protein is an octamer both in the crystal structure, and in solution.     

Transfer and integration of chromosomal genes from Pseudomonas glycinea into Pseudomonas aeruginosa.

The plasmids FP2 and R68.45 were shown to function as chromosome-mobilizing plasmids in a series of interspecific crosses between the phytopathogen Pseudomonas glycinea and the human pathogen Pseudomonas aeruginosa. At least four of seven loci tested were transferred from P. glycinea donors to P. aeruginosa auxotrophic recipients. Transductional analysis indicates that a leu+ locus of the P. glycinea chromosome transferred is stably integrated into the P. aeruginosa chromosome.     

Cloning and characterization of elastase genes from Pseudomonas aeruginosa.

A gene bank was constructed from Pseudomonas aeruginosa PAO1 and used to complement three P. aeruginosa elastase-deficient strains. One clone, pRF1, contained a gene which restored elastase production in two P. aeruginosa isolates deficient in elastase production (PA-E15 and PAO-E105). This gene also encoded production of elastase antigen and activity in Escherichia coli and is the structural gene for Pseudomonas elastase. A second clone, pHN13, contained a 20-kilobase (kb) EcoRI insert which was not related to the 8-kb EcoRI insert of pRF1 as determined by restriction analysis and DNA hybridization. A 2.2-kb SalI-HindIII fragment from pHN3 was subcloned into pUC18, forming pRB1822-1. Plasmid pRB1822-1 restored normal elastolytic activity to PAO-E64, a mutant for elastase activity. Clones derived from pHN13 failed to elicit elastase antigen or enzymatic activity in E. coli.     

铜绿假单胞菌必需基因的研究进展

铜绿假单胞菌为专性需氧非发酵革兰氏阴性杆菌,是医院感染的常见条件致病菌之一,可引起呼吸道、泌尿道、烧伤创面和菌血症等严重感染.铜绿假单胞菌耐药形势日益严峻,给临床治疗带来困难.必需基因是生长过程中必不可少的看家基因,对铜绿假单胞菌必需基因进行深入研究,不仅有助于了解细菌的生长、毒力等基本特性,也有助于筛选新的抗菌药物靶...     

Mapping of ben genes of Pseudomonas aeruginosa

Abstract Four ben genes responsible for the conversion of benzoate to catechol in Pseudomonas aeruginosa PAO have been mapped to a 4.6 kb Kpn I fragment. ben -1 and ben -4 were known to be separate genes but now ben-1508 has been found to be different from ben-2 . The two genes were distinguished by Tn 5 mutagenesis of a cosmid clone and deletion mapping. It is likely that the four genes mapped ( ben-4, ben-2, ben-1508 and ben-1 ) correspond to the previously characterized benR (regulatory gene) and benABC (benzoate dioxygenase) respectively.     

Comparison of flagellin genes from clinical and environmental Pseudomonas aeruginosa isolates

Pseudomonas aeruginosa, an important opportunistic pathogen, was isolated from environmental samples and compared to clinically derived strains. While P. aeruginosa was isolated readily from an experimental mushroom-growing unit, it was found only rarely in other environmental samples. A flagellin gene PCR-restriction fragment length polymorphism analysis of the isolates revealed that environmental and clinical P. aeruginosa strains are not readily distinguishable. The variation in the central regions of the flagellin genes of seven of the isolates was investigated further. The strains used included two strains with type a genes (998 bp), four strains with type b genes (1,258 bp), and one strain, K979, with a novel flagellin gene (2,199 bp). The route by which flagellin gene variation has occurred in P. aeruginosa is discussed.     

Crystal structure at 1.45 A resolution of alanine racemase from a pathogenic bacterium, Pseudomonas aeruginosa, contains both internal and external aldimine forms

The structure of the catabolic alanine racemase, DadX, from the pathogenic bacterium Pseudomonas aeruginosa, reported here at 1.45 A resolution, is a dimer in which each monomer is comprised of two domains, an eight-stranded alpha/beta barrel containing the PLP cofactor and a second domain primarily composed of beta-strands. The geometry of each domain is very similar to that of Bacillus stearothermophilus alanine racemase, but the rotation between domains differs by about 15 degrees. This change does not alter the structure of the active site in which almost all residues superimpose well with a low rms difference of 0.86 A. Unexpectedly, the active site of DadX contains a guest substrate that is located where acetate and propionate have been observed in the Bacillus structures. It is modeled as d-lysine and oriented such that its terminal NZ atom makes a covalent bond with C4' of PLP. Since the internal aldimine bond between the protein lysine, Lys33, and C4' of PLP is also unambiguously observed, there appears to be an equilibrium between both internally and externally reacted forms. The PLP cofactor adopts two partially occupied conformational states that resemble previously reported internal and external aldimine complexes.     

Purification and characterization of glyoxalase I from Pseudomonas putida

Glyoxalase I was purified to apparent homogeneity from Pseudomonas putida. The enzyme was a monomer with a molecular weight of 20,000. The enzyme was most active at pH 8.0. The Km values for methylglyoxal and 4,5-dioxovale-rate are 3.5 mM and 1.2 mM, respectively. Contrary to the case of eukaryotic enzymes, chelating agents showed little inhibitory effects on the enzyme activity. Among the metal ions tested, Zn++ specifically and completely inhibited the activity of the enzyme at a millimolar level. The properties of bacterial glyoxalase I were quite different from mammalian and yeast enzymes.     

Transposon mutagenesis of Pseudomonas aeruginosa exoprotease genes.

Transposon Tn5 was used to generate protease-deficient insertion mutants of Pseudomonas aeruginosa. The presence of Tn5 in the chromosome of P. aeruginosa was demonstrated by transduction and DNA-DNA hybridization. The altered protease production and kanamycin resistance were cotransduced into a wild-type P. aeruginosa strain. A radiolabeled probe of Tn5 DNA hybridized to specific BamHI fragments isolated from the insertion mutants. Two independently isolated Tn5 insertion mutants had reduced protease production, partially impaired elastase activity, and no immunologically reactive alkaline protease.     

Pseudomonas aeruginosa acid phosphatase contains an anionic site with a trimethyl subsite

Summary In this work the action of the following compounds upon Ps. aeruginosa acid phosphatase has been studied: 1) alkylammonium compounds; 2) aminoalcohols and aminoacids with different substituents (–H, –CH₃OH and –CH₃) attached to the nitrogen atom; 3) alcohols analogous to some compounds of the above series, but without the amino group.It was found that the enzyme inhibition was more effective with N-trimethylated compounds than with the triethylated ones. The degree of inhibition depended on the number of methyl groups bound to the nitrogen atom. Taking into account the choline and betaine series the hydroxyl derivatives showed more affinity for the enzyme than the carboxylated ones. In each series the Ki values increased with the decrease of methyl groups bound to the nitrogen atom. The presence of a positively charged nitrogen atom in the molecule of the effector was essential. These results enable us to confirm that in the molecule of Ps. aeruginosa acid phosphatase there exists an anionic site with one subsite with affinity for methyl groups.     

Iron reductases from Pseudomonas aeruginosa

Cell-free extracts of Pseudomonas aeruginosa contain enzyme activities which reduce Fe(III) to Fe(II) when iron is provided in certain chelates, but not when the iron is uncomplexed. Iron reductase activities for two substrates, ferripyochelin and ferric citrate, appear to be separate enzymes because of differences in heat stabilities, in locations in fractions of cell-free extracts, in reductant specificity, and in apparent sizes during gel filtration chromatography. Ferric citrate iron reductase is an extremely labile activity found in the cytoplasmic fraction, and ferripyochelin iron reductase is a more stable activity found in the periplasmic as well as cytoplasmic fraction of extracts. A small amount of activity detectable in the membrane fraction seemed to be loosely associated with the membranes. Although both enzymes have highest activity reduced nicotinamide adenine dinucleotide, reduced glutathione also worked with ferripyochelin iron reductase. In addition, oxygen caused an irreversible loss of a percentage of the ferripyochelin iron reductase following sparge of reaction mixtures, whereas the reductase for ferric citrate was not appreciably affected by oxygen.     

Heavy metal resistance of biofilm and planktonic Pseudomonas aeruginosa

A study was undertaken to examine the effects of the heavy metals copper, lead, and zinc on biofilm and planktonic Pseudomonas aeruginosa. A rotating-disk biofilm reactor was used to generate biofilm and free-swimming cultures to test their relative levels of resistance to heavy metals. It was determined that biofilms were anywhere from 2 to 600 times more resistant to heavy metal stress than free-swimming cells. When planktonic cells at different stages of growth were examined, it was found that logarithmically growing cells were more resistant to copper and lead stress than stationary-phase cells. However, biofilms were observed to be more resistant to heavy metals than either stationary-phase or logarithmically growing planktonic cells. Microscopy was used to evaluate the effect of copper stress on a mature P. aeruginosa biofilm. The exterior of the biofilm was preferentially killed after exposure to elevated concentrations of copper, and the majority of living cells were near the substratum. A potential explanation for this is that the extracellular polymeric substances that encase a biofilm may be responsible for protecting cells from heavy metal stress by binding the heavy metals and retarding their diffusion within the biofilm.