Cloning and nucleotide sequence of the bglA gene from Erwinia herbicola and expression of β-glucosidase activity in Escherichia coli

Abstract Genomic DNA fragments encoding β-glucosidase activity from the wild-type strain WD4 of Erwinia herbicola were cloned into Escherichia coli . Two clones containing a common fragment encoded a polypeptide of 58000 Da. Cloned β-glucosidase, expressed in E. coli , showed activity against natural β-glucoside sugars except for cellobiose. An open reading frame of 1442 bp termed bglA was identified by nucleotide sequencing and it coded for a protein of 480 amino acids ( M _r 53896) which showed significant homology with β-glucosidases from glycosyl hydrolase family 1.     

A piperacillin-tazobactam resistant Escherichia coli strain isolated from a faecal sample of a healthy volunteer

Abstract As part of a surveillance programme of the prevalence of antibiotic resistance, the faecal bacteria of healthy people ( n = 1348) were examined, and the antibiotic resistance of the Escherichia coli strains determined. One strain out of 142 amoxycillin-resistant isolates, E. coli strain 1662, was also resistant to piperacillin-tazobactam but susceptible to amoxycillin-clavulanic acid. The piperacillin-tazobactam resistance determinant was transferable to standard E. coli strains by conjugation. However, the strain produced a β-lactamase with several characteristics very similar to those of the TEM-1 β-lactamase, i.e. p I of 5.4, an M _r value of 22 000 and a comparable substrate profile. The enzyme was as efficiently inhibited by clavulanic acid and tazobactam as the TEM-1 and TEM-2 β-lactamases but more than the amoxycillin-clavulanic acid-resistant TRC-1 enzyme. The transferable resistance to piperacillin-tazobactam appears to be mediated by a novel resistance mechanism that has previously not been described.     

Penicillin-binding proteins of pathogenic Escherichia coli strains

The penicillin-binding proteins of 11 pathogenic Escherichia coli strains, including enteropathogenic, enterotoxigenic, enteroinvasive, enteroaggregative, and enterohemorrhagic E. coli, were detected in gels following the labeling of isolated cell envelopes with [³H]benzylpenicillin. The electrophoretic profiles, sensitivities to and morphological changes induced by β-lactam antibiotics showed that the penicillin-binding proteins of most pathogenic E. coli possess structural and physiological functions similar to those of E. coli K12.     

Antagonistic effect of Erwinia herbicola on in vitro spore germination and germ tube elongation of Botrytis cinerea and Penicillium expansum

Interaction between Erwinia herbicola and Botrytis cinerea and Penicillium expansum was studied in liquid culture. The results show that the bacteria directly inhibited spore germination of both fungi, especially during the first hours of the paired cultivation. The distinct taxis of bacteria to spores and germ tubes was frequently followed by their lysis. It is likely that bacteria act also by competition for nutrients. The rate of antagonistic activity of the bacteria against both fungi depended on their concentration in the mixture. Formation of chlamydospore-like structures at the apical end of B. cinerea germ tube suggests induction of a defence mechanism of this fungus while in unfavourable conditions.     

Complementation of growth defect in an ampC deletion mutant of Escherichia coli

Abstract β-Lactamase genes of class-A ( Rtem ) and class-C ( ampC ) were placed under control of an inducible tac -promoter and expressed in Escherichia coli . Expression of RTEM had no observable effect on the growth properties of E. coli strains HB101 ( ampC ⁺) or MI1443 (Δ ampC ). E. coli MI1443 exhibited a decline in growth rate at mid-exponential phase which could be delayed by expression of AmpC at early-exponential phase. AmpC expression otherwise inhibited growth, particularly during the transition into exponential phase where growth was prevented altogether. We suggest that the AmpC β-lactamase, but not RTEM, may have an additional cellular function as a peptidoglycan hydrolase.     

Involvement of O8-antigen in altering β-lactam antibiotic susceptibilities in Escherichia coli

In spite of being dispensable, O-antigens are believed to facilitate various cellular processes and alter antibiotic sensitivities. Escherichia coli K-12 (CS109) strains are lacking in O-antigens and are reported to be sensitive to antibiotics. To our surprise, E. coli 2443 (expressing O8-antigen) manifested two- to fourfold higher sensitivities toward penicillin and its derivatives than strain CS109. However, sensitivities toward other structurally unrelated antibiotics remained unchanged. To understand the rationale behind such observations, we replaced the rfb locus of strain 2443 with that of E. coli K-12. The β-lactam sensitivities of 2443 cells with replaced rfb locus appeared to be identical to those for CS109. Therefore, it is quite reasonable to hypothesize the possible involvement of O8-antigen in β-lactam sensitization.     

Changes in carotenoids but not in D1 protein in response to nitrogen depletion and recovery in a cyanobacterium

Abstract In Synechococcus PCC 6301 ( Anacystis nidulans ) the imposition of nitrogen stress resulted in substantial losses of phycobiliproteins, lesser changes in chlorophyll-proteins and a dramatic change in carotenoid composition. In nitrogen-depleted cultures carotenoids continued to be synthesised, with the increase being accounted for by zeaxanthin with β-carotene content declining slightly. In these cultures zeaxanthin accounted for 75% of the carotenoid present compared to 43% in nitrogen-replete cells. Amounts of D1, a protein associated with the Photosystem II reaction centre, were similar in nitrogen-replete and nitrogen-starved cells; this retention was in accord with those of β-carotene and chlorophyll. On nitrate replenishment, zeaxanthin was not produced for 36 h, by which time β-carotene level had increased to restore the carotenoid composition characteristic of an exponential culture, and normal phycocyanin and chlorophyll levels had also been recovered. Throughout, the ratio of β-carotene to chlorophyll remained more-or-less constant.     

Expression of pRW83 (penP) and pBR322-encoded β-lactamases in Escherichia coli

Abstract Plasmid pBR322 and penP -encoded β-lactamase activities were examined in cell fractions from wild-type and murein lipoprotein-deficient Escherichia coli strains. The specific activity of the Bacillus licheniformis penP gene product, a lipoprotein when expressed in E. coli , was increased in the outer membrane of a murein-lipoprotein deficient mutant. The activities of the 2 enzymes in wild-type E. coli exposed to the translational inhibitor puromycin were also investigated. Synthesis of penP was more susceptible to inhibition by puromycin than the pBR322-encoded TEM1 β-lactamase. The implications of these results for mechanisms of secretion and insertion of lipoproteins into the E. coli outer membrane are discussed.     

Two variants of transferrable extended-spectrum TEM-β-lactamase successively isolated from a clinical Escherichia coli isolate

In a leukaemic patient presenting a septicaemia treated with ceftazidime and amikacin, two clinical Escherichia coli isolates distinguished by their level of resistance to oxyimino-beta-lactams were isolated at an interval of 24 h. The isolates were identified by biotyping and esterase electrophoretic typing and the two host strains were shown to be identical. However, each of these strains exhibited a different transferrable extended-spectrum beta-lactamase. These enzymes had different pI values (5.25 and 5.58), but were both blaTEM-1 mutants. The enzyme with pI 5.25 was identical to TEM-101 (TEM-12) (serine 162 substitution). The enzyme with pI 5.58 showed an additional amino acid substitution (lysine residue instead of an arginine at position 237) and was denominated TEM-23. These data indicate that point-mutations can be successively cumulated in vivo by blaTEM mutants, leading to expression of beta-lactamases with increased hydrolysis rates.     

Contribution of extended-spectrum AmpC (ESAC) beta-lactamases to carbapenem resistance in Escherichia coli

ESAC beta-lactamases have increased catalytic efficiencies toward extended-spectrum cephalosporins and to a lesser extent toward imipenem as compared with the wild-type cephalosporinases. We show here that ESAC expression associated with the loss of both OmpC and OmpF porins conferred in Escherichia coli a high level of resistance to ertapenem and reduced the susceptibility to imipenem. On the contrary, ESAC expressed in the OmpC- or OmpF-deficient E. coli strains or narrow-spectrum cephalosporinase expressed in the OmpC-and OmpF-deficient strain do not confer reduced susceptibility to any of the carbapenems. The production of ESAC beta-lactamase in favorable E. coli background may represent an additional mechanism of resistance to ertapenem.     

Identification of a new mutation in Escherichia coli that suppresses a pbpB (Ts) phenotype in the presence of penicillin-binding protein 1B

Analysis of the functional role of penicillin-binding protein 1B (PBP1B) of Escherichia coli led us to find a new mutation able to suppress thermosensitive growth of the pbpB2158(Ts) mutant strain, which harbors a thermosensitive PBP3 protein only in the presence of a ponB+ background. The mutation, originally isolated in a strain with a high dosage of PBP1B, could also suppress the pbpB(Ts) phenotype when a single copy of the ponB gene was introduced. These results clearly give further support to the implication of PPB1B in the septation process in Escherichia coli.     

A simple and reliable method to conduct and monitor expression cassette integration into the Escherichia coli chromosome

We report a method for the integration of expression cassettes into the Escherichia coli chromosome using rare and dispensable sugar degradation gene loci as sites for integration. Clones carrying successfully recombined DNA fragments in the chromosome are easily screened using a solid differential medium containing the respective sugar compound. As an example for the heterologous expression of a complex natural product biosynthesis pathway, we show the stepwise chromosomal integration of the zeaxanthin biosynthesis pathway from Pantoea ananatis into E. coli.     

Nitrogen Fixation in a Biotype of Erwinia herbicola Resembling Escherichia coli

Two nitrogen-fixing members of the Enterobacteriaceae have been isolated from paper mill process water and compost. Although they closely resembled Escherichia coli , detailed biochemical characterization of these and 7 other isolates established that they should be assigned to a biotype of Erwinia herbicola . They may be distinguished from E. coli by their lack of amino acid decarboxylase activity, their ability to utilize cellobiose and malonate and to ferment cellobiose and amygdalin. In one of them, the capacity to fix nitrogen, ferment cellobiose and utilize malonate was resistant to the effects of ethidium bromide, acridine orange and sodium dodecyl sulphate, and the ability to utilize cellobiose could not be transferred on to E. coli or Salmonella typhi . It is therefore concluded that these characters are not carried on transferable plasmids. Forty-eight strains of E. coli of varying origin were examined for acetylene reducing activity and all were found to be negative. It is concluded that hitherto no naturally occurring strains of E. coli have been shown to fix nitrogen.     

Crystalline 3-methylaspartase from a facultative anaerobe, Escherichia coli strain YG1002

Abstract Crystalline 3-methylaspartase (EC 4.3.1.2) from Escherichia coli strain YG1002 that had been isolated from soil was characterized. The enzyme activity was induced when the organism was grown statically on medium containing ( S )-glutamic acid. Its molecular mass is about 84 kDa, and it may be composed of two identical subunits of 42 kDa. The enzyme requires both divalent and monovalent cations such as Mg²⁺ and K⁺, respectively. The enzyme catalyzes reversible amination-deamination between mesaconic acid and (2 S ,3 S )-methylaspartic acid, which is the best substrate.     

Mutagenic effect of acridine orange on the expression of penicillin G acylase and beta-lactamase in Escherichia coli

AIMS: The present work aimed to improve the production of penicillin G acylase (PGA) and reduce the beta-lactamase activity through acridine orange (AO) induced mutation in Escherichia coli. METHODS AND RESULTS: Three wild E. coli strains BDCS-N-FMu10, BDCS-N-S21 and BDCS-N-W50, producing both the enzymes PGA and beta-lactamase were treated by AO. Minimum inhibitory concentration of AO was 10 microg ml(-1) and it was noted that bacterial growth was gradually suppressed by increasing the concentration of AO from 10 to 100 microg ml(-1). The highest concentration that gave permissible growth rate was 50 microg ml(-1). The isolated survivals were screened on the bases of PGA and beta-lactamase activities. Among the retained mutants, the occurrence of beta-lactamase deficient ones (91%) was significantly higher than penicillin acylase deficient ones (27%). CONCLUSIONS: In seven of the mutants, PGA activity was enhanced with considerable decrease in beta-lactamase activity. One of the mutant strains (BDCS-N-M36) exhibited very negligible expression of beta-lactamase activity and twofold increase in PGA activity [12.7 mg 6-amino-penicillanic acid (6-APA) h(-1) mg(-1) wet cells] compared with that in the wild-type strain (6.3 mg 6-APA h(-1) mg(-1) wet cells). SIGNIFICANCE AND IMPACT OF THE STUDY: The treatment of E. coli cells with AO resulted in mutants with enhanced production of PGA and inactivation of beta-lactamase. These mutants could be used for industrial production of PGA.     

Metabolic engineering of Escherichia coli for the production of medium-chain-length polyhydroxyalkanoates rich in specific monomers

The Escherichia coli fabG(Ec) gene and the Pseudomonas aeruginosa rhlG(Pa) gene, which encode 3-ketoacyl-acyl carrier protein reductase, were expressed in E. coli W3110 and its fadA mutant strain WA101 to examine their roles in medium-chain-length (MCL) polyhydroxyalkanoate (PHA) biosynthesis from fatty acids. When one of these 3-ketoacyl-acyl carrier protein reductase genes was co-expressed with the Pseudomonas sp. 61-3 PHA synthase gene (phaC2(Ps)) in E. coli W3110, MCL-PHA composed mainly of 3-hydroxyoctanoate and 3-hydroxydecanoate was synthesized from sodium decanoate. When the fabG(Ec) gene and the phaC2(Ps) gene were co-expressed in the fadA mutant E. coli strain WA101, MCL-PHA rich in 3-hydroxydecanoate monomer up to 93 mol% was accumulated from sodium decanoate. This was possible by efficiently redirecting 3-ketoacyl-coenzymes A from the beta-oxidation pathway to the PHA biosynthesis pathway without losing two carbon units, the strategy of which can be extended for the production of MCL-PHAs rich in other specific monomers.     

SAR-2: Identification of a novel plasmid-encoded β-lactamase from India

A novel beta-lactamase has been identified in an Escherichia coli strain isolated in South India. The beta-lactamase gene was carried on a plasmid (pUK734) along with resistance determinants to sulphonamides and tetracycline. The novel enzyme has a pI of 8.3 and an Mr of 36,000. The enzyme has a broad-spectrum of activity against both penicillins and cephalosporins. It is also active against oxacillin and methicillin.