Using synthetic biology to overcome barriers to stable expression of nitrogenase in eukaryotic organelles.

Engineering biological nitrogen fixation in eukaryotic cells by direct introduction of nif genes requires elegant synthetic biology approaches to ensure that components required for the biosynthesis of active nitrogenase are stable and expressed in the appropriate stoichiometry. Previously, the NifD subunits of nitrogenase MoFe protein from Azotobacter vinelandii and Klebsiella oxytoca were found to be unstable in yeast and plant mitochondria, respectively, presenting a bottleneck to the assembly of active MoFe protein in eukaryotic cells. In this study, we have delineated the region and subsequently a key residue, NifD-R98, from K. oxytoca that confers susceptibility to protease-mediated degradation in mitochondria. The effect observed is pervasive, as R98 is conserved among all NifD proteins analyzed. NifD proteins from four representative diazotrophs, but not their R98 variants, were observed to be unstable in yeast mitochondria. Furthermore, by reconstituting mitochondrial-processing peptidases (MPPs) from yeast, Oryza sativa, Nicotiana tabacum, and Arabidopsis thaliana in Escherichia coli, we demonstrated that MPPs are responsible for cleavage of NifD. These results indicate a pervasive effect on the stability of NifD proteins in mitochondria resulting from cleavage by MPPs. NifD-R98 variants that retained high levels of nitrogenase activity were obtained, with the potential to stably target active MoFe protein to mitochondria. This reconstitution approach could help preevaluate the stability of Nif proteins for plant expression and paves the way for engineering active nitrogenase in plant organelles.

A novel ß-galactosidase from Klebsiella oxytoca ZJUH1705 for efficient production of galacto-oligosaccharides from lactose.

Galacto-oligosaccharides (GOS), which can be produced by enzymatic transgalactosylation of lactose with ß-galactosidases, have attracted much attention in recent years because of their prebiotic functions and wide uses in infant formula, infant foods, livestock feed, and pet food industries. In this study, a novel ß-galactosidase-producing Klebsiella oxytoca ZJUH1705, identified by its 16S rRNA sequence (GenBank accession no. MH981243), was isolated. Two ß-galactosidase genes, bga 1 encoding a 2058-bp fragment (GenBank accession no. MH986613) and bga 2 encoding a 3108-bp fragment (GenBank accession no. MN182756), were cloned from K. oxytoca ZJUH1705 and expressed in E. coli. The purified ß-gal 1 and ß-gal 2 had the specific activity of 217.56 U mg-1 and 57.9 U mg-1, respectively, at the optimal pH of 7.0. The reaction kinetic parameters Km, Vmax, and Kcat with oNPG as the substrate at 40 °C were 5.62 mM, 167.1 µmol mg-1 min-1, and 218.1 s-1, respectively, for ß-gal 1 and 3.91 mM, 14.6 µmol mg-1 min-1, and 28.9 s-1, respectively, for ß-gal 2. Although ß-gal 1 had a higher enzyme activity for lactose hydrolysis, only ß-gal 2 had a high transgalactosylation capacity. Using ß-gal 2 with the addition ratio of ~ 2.5 U g-1 lactose, a high GOS yield of 45.5 ± 2.3% (w/w-1) was obtained from lactose (40% w/w-1 or 480 g L-1) in a phosphate buffer (100 mM, pH 7.0) at 40 °C in 48 h. Thus, the ß-gal 2 from K. oxytoca ZJUH1705 would be a promising biocatalyst for GOS production from lactose.Key Points• A novel bacterial ß-galactosidase producer was isolated and identified.• ß-Galactosidases were cloned and expressed in heterologous strain and characterized.• Both enzymes have hydrolytic activity but only one have transglycosilation activity.• The developed process with ß-gal 2 could provide an alternative for GOS production.

Biochemical and structural investigation of sulfoacetaldehyde reductase from Klebsiella oxytoca.

Sulfoacetaldehyde reductase (IsfD) is a member of the short-chain dehydrogenase/reductase (SDR) family, involved in nitrogen assimilation from aminoethylsulfonate (taurine) in certain environmental and human commensal bacteria. IsfD catalyzes the reversible NADPH-dependent reduction of sulfoacetaldehyde, which is generated by transamination of taurine, forming hydroxyethylsulfonate (isethionate) as a waste product. In the present study, the crystal structure of Klebsiella oxytoca IsfD in a ternary complex with NADPH and isethionate was solved at 2.8 Å, revealing residues important for substrate binding. IsfD forms a homotetramer in both crystal and solution states, with the C-terminal tail of each subunit interacting with the C-terminal tail of the diagonally opposite subunit, forming an antiparallel ß sheet that constitutes part of the substrate-binding site. The sulfonate group of isethionate is stabilized by a hydrogen bond network formed by the residues Y148, R195, Q244 and a water molecule. In addition, F249 from the diagonal subunit restrains the conformation of Y148 to further stabilize the orientation of the sulfonate group. Mutation of any of these four residues into alanine resulted in a complete loss of catalytic activity for isethionate oxidation. Biochemical investigations of the substrate scope of IsfD, and bioinformatics analysis of IsfD homologs, suggest that IsfD is related to the promiscuous 3-hydroxyacid dehydrogenases with diverse metabolic functions.

Characterization of Carbapenemase-Producing Klebsiella oxytoca in Spain, 2016-2017.

There is little information about carbapenemase-producing (CP) Klebsiella oxytoca, an important nosocomial pathogen. We characterized CP K. oxytoca isolates collected from different Spanish hospitals between January 2016 and October 2017. During the study period, 139 nonduplicate CP K. oxytoca isolates were identified; of these, 80 were studied in detail. Carbapenemase and extended-spectrum ß-lactamase genes were identified by PCR and sequencing. Genetic relatedness was studied by pulsed-field gel electrophoresis (PFGE). Whole-genome sequencing (WGS), carried out on 12 representative isolates, was used to identify the resistome, to elucidate the phylogeny, and to determine the plasmids harboring carbapenemase genes. Forty-eight (60%) isolates produced VIM-1, 30 (37.5%) produced OXA-48, 3 (3.7%) produced KPC-2, 2 (2.5%) produced KPC-3, and 1 (1.2%) produced NDM-1; 4 isolates coproduced two carbapenemases. By PFGE, 69 patterns were obtained from the 80 CP K. oxytoca isolates, and four well-defined clusters were detected: cluster 1 consisted of 11 OXA-48-producing isolates, and the other three clusters included VIM-1-producing isolates (5, 3, and 3 isolates, respectively). In the 12 sequenced isolates, the average number of acquired resistance genes was significantly higher in VIM-1-producing isolates (10.8) than in OXA-48-producing isolates (2.3). All 12 isolates had chromosomally encoded genes of the blaOXY-2 genotype, and by multilocus sequence typing, most belonged to sequence type 2 (ST2). Carbapenemase genes were carried by IncL, IncHI2, IncFII, IncN, IncC, and IncP6 plasmid types. The emergence of CP K. oxytoca was principally due to the spread of VIM-1- and OXA-48-producing isolates in which VIM-1- and OXA-48 were carried by IncL, IncHI2, IncFII, and IncN plasmids. ST2 and the genotype blaOXY-2 predominated among the 12 sequenced isolates.

The Washing Machine as a Reservoir for Transmission of Extended-Spectrum-Beta-Lactamase (CTX-M-15)-Producing Klebsiella oxytoca ST201 to Newborns.

During the period from April 2012 to May 2013, 13 newborns (1 to 4 weeks of age) and 1 child in a pediatric hospital ward in Germany were colonized with Klebsiella oxytoca producing an extended-spectrum beta-lactamase (ESBL) (CTX-M-15). A microbiological source-tracking analysis with human and environmental samples was carried out to identify the source and transmission pathways of the K. oxytoca clone. In addition, different hygienic intervention methods were evaluated. K. oxytoca isolates were detected in the detergent drawer and on the rubber door seal of a domestic washer-extractor machine that was used in the same ward to wash laundry for the newborns, as well as in two sinks. These strains were typed using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing. The environmental findings were compared with those for the human strains and the isolates detected on clothing. The results from both techniques showed that the strains were identical (sequence type 201 and PFGE type 00531, a clone specific to this hospital and not previously isolated in Germany), emphasizing the washing machine as a reservoir and fomite for the transmission of these multidrug-resistant bacteria. After the washing machine was taken out of use, no further colonizations were detected during the subsequent 4-year period.IMPORTANCE Washing machines should be further investigated as possible sites for horizontal gene transfer (ESBL genes) and cross-contamination with clinically important Gram-negative strains. Particularly in the health care sector, the knowledge of possible (re-)contamination of laundry (patients' clothes and staff uniforms) with multidrug-resistant Gram-negative bacteria could help to prevent and to control nosocomial infections. This report describes an outbreak with a single strain of a multidrug-resistant bacterium (Klebsiella oxytoca sequence type 201) in a neonatal intensive care unit that was terminated only when the washing machine was removed. In addition, the study implies that changes in washing machine design and processing are required to prevent accumulation of residual water where microbial growth can occur and contaminate clothes.

The Metal Drives the Chemistry: Dual Functions of Acireductone Dioxygenase.

Acireductone dioxygenase (ARD) from the methionine salvage pathway (MSP) is a unique enzyme that exhibits dual chemistry determined solely by the identity of the divalent transition-metal ion (Fe2+ or Ni2+) in the active site. The Fe2+-containing isozyme catalyzes the on-pathway reaction using substrates 1,2-dihydroxy-3-keto-5-methylthiopent-1-ene (acireductone) and dioxygen to generate formate and the ketoacid precursor of methionine, 2-keto-4-methylthiobutyrate, whereas the Ni2+-containing isozyme catalyzes an off-pathway shunt with the same substrates, generating methylthiopropionate, carbon monoxide, and formate. The dual chemistry of ARD was originally discovered in the bacterium Klebsiella oxytoca, but it has recently been shown that mammalian ARD enzymes (mouse and human) are also capable of catalyzing metal-dependent dual chemistry in vitro. This is particularly interesting, since carbon monoxide, one of the products of off-pathway reaction, has been identified as an antiapoptotic molecule in mammals. In addition, several biochemical and genetic studies have indicated an inhibitory role of human ARD in cancer. This comprehensive review describes the biochemical and structural characterization of the ARD family, the proposed experimental and theoretical approaches to establishing mechanisms for the dual chemistry, insights into the mechanism based on comparison with structurally and functionally similar enzymes, and the applications of this research to the field of artificial metalloenzymes and synthetic biology.

Cloning and characterization of a Flavin-free oxygen-insensitive azoreductase from Klebsiella oxytoca GS-4-08.

OBJECTIVES: This study reports the identification of a new bacterial azoreductase (AzoR) from Klebsiella oxytoca GS-4-08, its heterologous production in Escherichia coli and the decolorization of azo dyes. RESULTS: The AzoR, as a flavin-free, oxygen-insensitive enzyme, has a molecular mass of 22 kDa and a high substrate specificity for methyl red (MR). In the presence of 5 mM of NADH, the enzyme activity for decolorization of 50 mg l-1 of MR reached 5.61 µmol min-1 mg protein-1. Double-reciprocal plots indicated that the NADH and MR reductions proceed by ping-pong mechanism. The calculated Vm was 8.17 µM min-1 mg protein-1, and the AzoR retained over 75% of relative activity under temperature range from 20 to 50 °C. CONCLUSION: This study for the first time identified an AzoR from Klebsiella oxytoca strain, which enabled efficient degradation of azo dyes by strain GS-4-08.

Carbapenemase-producing Enterobacteriaceae in Mexico: report of seven non-clonal cases in a pediatric hospital.

BACKGROUND: Carbapenemases-producing Enterobacteriaceae (CPE) are a worldwide public health emergency. In Mexico, reports of CPE are limited, particularly in the pediatric population. Here, we describe the clinical, epidemiological, and molecular characteristics of seven consecutive cases in a third-level pediatric hospital in Mexico City over a four-month period during 2016. RESULTS: The Enterobacteriaceae identified were three Escherichia coli strains (producing OXA-232, NDM-1 and KPC-2), two Klebsiella pneumoniae strains (producing KPC-2 and NDM-1), one Klebsiella oxytoca strain producing OXA-48 and one Enterobacter cloacae strain producing NDM-1. The majority of patients had underlying disesases, three were immunocompromised, and three had infections involved the skin and soft tissues. Half patients died as a result of CPE infection. CONCLUSIONS: This study represents the first report of E. coli ST131-O25b clone producing NDM-1 in Latin America. In addition, this study is the first finding of K. oxytoca producing OXA-48 and E. coli producing OXA-232 in Mexican pediatric patients.

Kinetic properties analysis of beta-mannanase from Klebsiella oxytoca KUB-CW2-3 expressed in Escherichia coli.

Endo-1,4-ß-mannanase is an enzyme that can catalyze the random hydrolysis of ß-1,4-mannosidic linkages in the main chain of mannans, glucomannans and galactomannans and offers many applications in different biotechnology industries. Purification and kinetic properties of the endo-1,4-ß-mannanase from recombinant Escherichia coli strain KMAN-3 were examined. Recombinant ß-mannanase (KMAN-3) was purified 50.5 fold using Ni-NTA Agarose resin and specific activity of 11900 U/mg protein was obtained. Purified KMAN-3 showed a single band on SDS-PAGE with a molecular weight of 43 kDa. Km and Vmax values of KMAN-3 on ivory nut mannan, locust bean gum, defatted copra meal and konjac glucomannan were 243, 3.83 × 105 37 and 2.13 × 106 mg ml-1 and 2940, 61,100, 3930 and 1.56 × 1010 mg-1, respectively. Carboxymethyl cellulose was not digested by KMAN-3.

VIM-Klebsiella oxytoca outbreak in a Neonatal Intensive Care Unit. This time it wasn't the drain.

OBJECTIVE: We describe an outbreak of VIM-carbapenemase Klebsiella oxytoca (VIM-Kox) in a NICU. MATERIALS AND METHODS: Prospective Epidemiological Surveillance:Systematically (weekly screening cultures) or on admission, if the patient had a history of previous colonization by VIM-Kox.Clinical cultures, done if infection was suspected.Other possible microorganism sources were investigated: their mothers (rectal microbiota), milk packages and preparation apparata in the lactodietary section, echocardiagram transductors, cribs, the sinks (faucets and drains), washing bowls, etc.Molecular typing was performed using the DiversiLab (bioMérieux) system on all VIM-Kox isolated from environment or patients (one by neonate). RESULTS: We identified 20 VIM-Kox cases, the most only presented colonization, but 4 showed infection. Three of the ten sinks (drains) in our NICU, were positive for VIM-Kox. Another four drains harbored P.aeruginosa, S. maltophilia and/or Enterobacter sp. Nevertheless the VIM-Kox bacteria in the sinks (drains) were not the same as those in the patients, who showed three different strains. CONCLUSIONS: A VIM-Kox colonization or infection outbreak in a NICU is described. Rather than environment, not even drains, the source of the outbreak was other patients. The outbreak was relatively brief, as a result of the rapidness with which appropriate measures were taken and followed.

Diol Dehydratase-Reactivase Is Essential for Recycling of Coenzyme B12 in Diol Dehydratase.

Holoenzymes of adenosylcobalamin-dependent diol and glycerol dehydratases undergo mechanism-based inactivation by glycerol and O2 inactivation in the absence of substrate, which accompanies irreversible cleavage of the coenzyme Co-C bond. The inactivated holodiol dehydratase and the inactive enzyme·cyanocobalamin complex were (re)activated by incubation with NADH, ATP, and Mg(2+) (or Mn(2+)) in crude extracts of Klebsiella oxytoca, suggesting the presence of a reactivating system in the extract. The reducing system with NADH could be replaced by FMNH2. When inactivated holoenzyme or the enzyme·cyanocobalamin complex, a model of inactivated holoenzyme, was incubated with purified recombinant diol dehydratase-reactivase (DD-R) and an ATP:cob(I)alamin adenosyltransferase in the presence of FMNH2, ATP, and Mg(2+), diol dehydratase activity was restored. Among the three adenosyltransferases (PduO, EutT, and CobA) of this bacterium, PduO and CobA were much more efficient for the reactivation than EutT, although PduO showed the lowest adenosyltransfease activity toward free cob(I)alamin. These results suggest that (1) diol dehydratase activity is maintained through coenzyme recycling by a reactivating system for diol dehydratase composed of DD-R, PduO adenosyltransferase, and a reducing system, (2) the releasing factor DD-R is essential for the recycling of adenosycobalamin, a tightly bound, prosthetic group-type coenzyme, and (3) PduO is a specific adenosylating enzyme for the DD reactivation, whereas CobA and EutT exert their effects through free synthesized coenzyme. Although FMNH2 was mainly used as a reductant in this study, a natural reducing system might consist of PduS cobalamin reductase and NADH.

Activity of Ceftazidime-Avibactam against Extended-Spectrum- and AmpC ß-Lactamase-Producing Enterobacteriaceae Collected in the INFORM Global Surveillance Study from 2012 to 2014.

The in vitro activity of ceftazidime-avibactam was evaluated against 34,062 isolates of Enterobacteriaceae from patients with intra-abdominal, urinary tract, skin and soft-tissue, lower respiratory tract, and blood infections collected in the INFORM (International Network For Optimal Resistance Monitoring) global surveillance study (176 medical center laboratories in 39 countries) in 2012 to 2014. Overall, 99.5% of Enterobacteriaceae isolates were susceptible to ceftazidime-avibactam using FDA approved breakpoints (susceptible MIC of ≤8 µg/ml; resistant MIC of ≥16 µg/ml). For individual species of the Enterobacteriaceae, the ceftazidime-avibactam MIC inhibiting ≥90% of isolates (MIC90) ranged from 0.06 µg/ml for Proteus species to 1 µg/ml for Enterobacter spp. and Klebsiella pneumoniae Carbapenem-susceptible isolates of Escherichia coli, K. pneumoniae, Klebsiella oxytoca, and Proteus mirabilis with a confirmed extended-spectrum ß-lactamase (ESBL) phenotype, or a ceftazidime MIC of ≥16 µg/ml if the ESBL phenotype was not confirmed by clavulanic acid inhibition, were characterized further to identify the presence of specific ESBL- and plasmid-mediated AmpC ß-lactamase genes using a microarray-based assay and additional PCR assays. Ceftazidime-avibactam demonstrated potent activity against molecularly confirmed ESBL-producing (n = 5,354; MIC90, 0.5 µg/ml; 99.9% susceptible), plasmid-mediated AmpC-producing (n = 246; MIC90, 0.5 µg/ml; 100% susceptible), and ESBL- and AmpC-producing (n = 152; MIC90, 1 µg/ml; 100% susceptible) isolates of E. coli, K. pneumoniae, K. oxytoca, and P. mirabilis We conclude that ceftazidime-avibactam demonstrates potent in vitro activity against globally collected clinical isolates of Enterobacteriaceae, including isolates producing ESBLs and AmpC ß-lactamases.

Crystal structure of a novel two domain GH78 family α-rhamnosidase from Klebsiella oxytoca with rhamnose bound.

The crystal structure of the GH78 family α-rhamnosidase from Klebsiella oxytoca (KoRha) has been determined at 2.7 Å resolution with rhamnose bound in the active site of the catalytic domain. Curiously, the putative catalytic acid, Asp 222, is preceded by an unusual non-proline cis-peptide bond which helps to project the carboxyl group into the active centre. This KoRha homodimeric structure is significantly smaller than those of the other previously determined GH78 structures. Nevertheless, the enzyme displays α-rhamnosidase activity when assayed in vitro, suggesting that the additional structural domains found in the related enzymes are dispensible for function.

Contaminated handwashing sinks as the source of a clonal outbreak of KPC-2-producing Klebsiella oxytoca on a hematology ward.

We investigated sinks as possible sources of a prolonged Klebsiella pneumonia carbapenemase (KPC)-producing Klebsiella oxytoca outbreak. Seven carbapenem-resistant K. oxytoca isolates were identified in sink drains in 4 patient rooms and in the medication room. Investigations for resistance genes and genetic relatedness of patient and environmental isolates revealed that all the isolates harbored the blaKPC-2 and blaTEM-1 genes and were genetically indistinguishable. We describe here a clonal outbreak caused by KPC-2-producing K. oxytoca, and handwashing sinks were a possible reservoir.

Predominance of KPC-3 in a survey for carbapenemase-producing Enterobacteriaceae in Portugal.

Among the 2,105 Enterobacteriaceae tested in a survey done in Portugal, 165 were nonsusceptible to carbapenems, from which 35 (26 Klebsiella pneumoniae, 3 Escherichia coli, 2 Enterobacter aerogenes, and 3 Enterobacter cloacae isolates and 1 Klebsiella oxytoca isolate) were confirmed to be carbapenemase producers by the presence of 30 Tn4401d-blaKPC-3, 4 intI3-blaGES-5, and one intI1-blaVIM-2 gene, alone or in combination with other bla genes. The dissemination of blaKPC-3 gene carried by an IncF plasmid suggests lateral gene transfer as a major mechanism of dissemination.

Characterization of IncI1 sequence type 71 epidemic plasmid lineage responsible for the recent dissemination of CTX-M-65 extended-spectrum ß-lactamase in the Bolivian Chaco region.

During the last decade, a significant diffusion of CTX-M-type extended-spectrum ß-lactamases (ESBLs) was observed in commensal Escherichia coli from healthy children in the Bolivian Chaco region, with initial dissemination of CTX-M-2, which was then replaced by CTX-M-15 and CTX-M-65. In this work, we demonstrate that the widespread dissemination of CTX-M-65 observed in this context was related to the polyclonal spreading of an IncI1 sequence type 71 (ST71) epidemic plasmid lineage. The structure of the epidemic plasmid population was characterized by complete sequencing of four representatives and PCR mapping of the remainder (n = 16). Sequence analysis showed identical plasmid backbones (similar to that of the reference IncI1 plasmid, R64) and a multiresistance region (MRR), which underwent local microevolution. The MRR harbored genes responsible for resistance to ß-lactams, aminoglycosides, florfenicol, and fosfomycin (with microevolution mainly consisting of deletion events of resistance modules). The bla CTX-M-65 module harbored by the IncI1 ST71 epidemic plasmid was apparently derived from IncN-type plasmids, likely via IS26-mediated mobilization. The plasmid could be transferred by conjugation to several different enterobacterial species (Escherichia coli, Cronobacter sakazakii, Enterobacter cloacae, Klebsiella oxytoca, Klebsiella pneumoniae, and Salmonella enterica) and was stably maintained without selective pressure in these species, with the exception of K. oxytoca and S. enterica. Fitness assays performed in E. coli recipients demonstrated that the presence of the epidemic plasmid was apparently not associated with a significant biological cost.

OXY-2-15, a novel variant showing increased ceftazidime hydrolytic activity.

OBJECTIVES: Klebsiella oxytoca is a member of the family of Enterobacteriaceae and often contains the ß-lactamase blaOXY gene. Although this ß-lactamase does not naturally hydrolyse ceftazidime, this study describes possible in vivo selection of a clinical K. oxytoca isolate showing increased MICs of ceftazidime. METHODS: To reveal the molecular mechanism underlying this unusual resistance phenotype, WGS, cloning, overexpression, MIC and steady-state kinetic studies were performed. RESULTS: A patient was treated for a septic episode with ceftazidime (4 g/day). This therapy was based on earlier culture results in which, amongst others, a K. oxytoca (Velp-1) isolate was identified. After 11 days of treatment, K. oxytoca Velp-2 was isolated from a pus sample drained from the wound. The isolate showed increased resistance to ceftazidime (MIC ≥64 mg/L) compared with the original K. oxytoca isolate (Velp-1). WGS revealed the presence of a novel blaOXY-2 allele, designated blaOXY-2-15, with a two amino acid deletion at Ambler positions 168 and 169 compared with OXY-2-2. Cloning blaOXY-2-15 into Escherichia coli TOP10 resulted in increased MICs of ceftazidime, but reduced MICs of most other ß-lactams compared with OXY-2-2. Steady-state kinetics confirmed the results of the MIC data, showing clearly significant ceftazidime hydrolysis. CONCLUSIONS: This report shows the risk of in vivo selection of ceftazidime-resistant K. oxytoca isolates after prolonged ceftazidime treatment. Furthermore, it is the first known report of a K. oxytoca isolate conferring resistance to ceftazidime by a two amino acid deletion in the omega loop of OXY-2-2.

High prevalence of CTX-M-15 and first report of CTX-M-3, CTX-M-22, CTX-M-28 and plasmid-mediated AmpC beta-lactamase producing Enterobacteriaceae causing urinary tract infections in Bosnia and Herzegovina in hospital and community settings.

AIM: To investigate molecular epidemiology of extended-spectrum ß-lactamase/ESBL and plasmid-mediated AmpC ß-lactamase/pAmpC producing Gram-negative bacteria causing urinary tract infections (UTIs) in Zenica-Doboj Canton, Bosnia and Herzegovina, in the period Decembar 2009-May 2010. METHODS: Antibiotic susceptibility was determined by disc diffusion and broth microdilution according to CLSI guidelines. Double-disk synergy test was performed in order to screen for ESBLs/pAmpC beta-lactamases. PCR was used to detect bla(ESBL)/bla(ampC)/bla(carb) genes. Genetic relatedness of the strains was determined by pulsed-field-gel-electrophoresis (PFGE). RESULTS: Among 85 patients with UTIs caused by ESBL producing isolates, 44 (51.8%) were from in-patients and 41 (48.2%) from outpatients. Klebsiella spp. was the most frequently isolated from in-patients, in 28 (63.6%) cases. Among outpatients, Klebsiella spp./Escherichia coli were the most frequently isolated, in 19 (46.3%)/16 (39.0%) cases. Twenty-one (75.0%) from hospital and nine (47.4%) from outpatient Klebsiella spp. isolates were positive for blaTEM, whereas 27 (96.4%) from in-patients and 6 (31.6%) from outpatient were bla(CTX-M) positive (18 hospital and five outpatient isolates were encoding bla(CTX-M-15)). One Klebsiella oxytoca and one Enterobacter cloacae inpatient isolates were positive for blaCTX-M-28. One Klebsiella pneumoniae outpatient isolate were positive for bla(CTX-M-22) and one E. coli for bla(CTX-M-3). One hospital Proteus mirabilis strain was positive for bla(CMY-2) and two Klebsiella spp. strains for blaDHA-1, whereas two E. coli, one K. oxytoca and one Proteus vulgaris outpatient strains were positive for bla(CMY-2). CONCLUSION: Identification of bla(CTX-M-3), bla(CTX-M-22) and bla(CTX-M-28) among Enterobacteriaceae is uncommon. In this study we report the emergency of CMY-2 and DHA-1 plasmid-mediated beta-lactamases.

Enhanced production of (R,R)-2,3-butanediol by metabolically engineered Klebsiella oxytoca.

Microbial fermentation produces a racemic mixture of 2,3-butanediol ((R,R)-BD, (S,S)-BD, and meso-BD), and the compositions and physiochemical properties vary from microorganism to microorganism. Although the meso form is much more difficult to transport and store because of its higher freezing point than those of the optically active forms, most microorganisms capable of producing 2,3-BD mainly yield meso-2,3-BD. Thus, we developed a metabolically engineered (R,R)-2,3-BD overproducing strain using a Klebsiella oxytoca ΔldhA ΔpflB strain, which shows an outstanding 2,3-BD production performance with more than 90 % of the meso form. A budC gene encoding 2,3-BD dehydrogenase in the K. oxytoca ΔldhA ΔpflB strain was replaced with an exogenous gene encoding (R,R)-2,3-BD dehydrogenase from Paenibacillus polymyxa (K. oxytoca ΔldhA ΔpflB ΔbudC::PBDH strain), and then its expression level was further amplified with using a pBBR1MCS plasmid. The fed-batch fermentation of the K. oxytoca ΔldhA ΔpflB ΔbudC::PBDH (pBBR-PBDH) strain with intermittent glucose feeding allowed the production of 106.7 g/L of (R,R)-2,3-BD [meso-2,3-BD, 9.3 g/L], with a yield of 0.40 g/g and a productivity of 3.1 g/L/h, which should be useful for the industrial application of 2,3-BD.

Construction of allitol synthesis pathway by multi-enzyme coexpression in Escherichia coli and its application in allitol production.

An engineered strain for the conversion of D-fructose to allitol was developed by constructing a multi-enzyme coupling pathway and cofactor recycling system in Escherichia coli. D-Psicose-3-epimerase from Ruminococcus sp. and ribitol dehydrogenase from Klebsiella oxytoca were coexpressed to form the multi-enzyme coupling pathway for allitol production. The cofactor recycling system was constructed using the formate dehydrogenase gene from Candida methylica for continuous NADH supply. The recombinant strain produced 10.62 g/l allitol from 100 mM D-fructose. To increase the intracellular concentration of the substrate, the glucose/fructose facilitator gene from Zymomonas mobilis was incorporated into the engineered strain. The results showed that the allitol yield was enhanced significantly to 16.53 g/l with a conversion rate of 92 %. Through optimizing conversion conditions, allitol was produced effectively on a large scale by the whole-cell biotransformation system; the yield reached 48.62 g/l when 500 mM D-fructose was used as the substrate.