First report of multidrug-resistant carbapenemase-producing Aeromonas caviae co-harboring mcr-3.43 and mcr-7.2.

Hospital sewage serves as a crucial reservoir for antibiotic resistance genes. As colistin and carbapenems are the last-resort antibiotics, the emergence of their resistance genes has become a significant concern in clinical settings. In this study, we found that two novel mcr alleles (mcr-3.43 and mcr-7.2) with two carbapenemase genes (blaNDM-1 and blaKPC-2) were encoded in a single Aeromonas caviae strain isolated from hospital sewage. Our phylogenetic analysis revealed that the mcr-3.43 gene clustered with mcr-3.17 (with 95.55% amino acid identity), while the mcr-7.2 gene clustered with mcr-7.1 (with 68.68% amino acid identity). BLAST search against GenBank showed that mcr-7.2 was exclusively detected in Aeromonas spp. Mobile genetic elements were not found in the genetic context of mcr-7.2, suggesting that the dissemination of mcr-7.2 in Aeromonas spp. may be dependent on vertical transfer or recombination. The blaNDM-1 was adjacent to a recombinase gene and flanked by two IS91 elements, indicating a potential mobilization mechanism mediated by recombination and/or ISs. The blaKPC-2 gene was located on an IncU plasmid and adjacent to an ISKpn6. In summary, our study provides evidence for Aeromonas spp. as one of the potential reservoirs of colistin and carbapenem resistance genes.IMPORTANCEThe study discovered two novel mcr genes (mcr-3.43 and mcr-7.2) and two carbapenemase genes (blaNDM-1 and blaKPC-2) in a single Aeromonas caviae strain retrieved from hospital sewage. Using phylogenetic analysis and comparative data evaluation, the study revealed the genetic relatedness and dissemination potential of the detected resistance genes. With the exclusive discovery that mcr-7.2 is only present in Aeromonas spp. and the lack of mobile genetic elements in its genetic context, there is a strong indication of limited dissemination. The identification of these four resistance genes in a single strain of Aeromonas provided valuable insights into their potential presence in this genus. This study revealed that hospital sewage functions as a significant reservoir for antibiotic resistance genes, including colistin and carbapenem resistance genes.

Reconstitution and optimisation of the biosynthesis of bacterial sugar pseudaminic acid (Pse5Ac7Ac) enables preparative enzymatic synthesis of CMP-Pse5Ac7Ac.

Pseudaminic acids present on the surface of pathogenic bacteria, including gut pathogens Campylobacter jejuni and Helicobacter pylori, are postulated to play influential roles in the etiology of associated infectious diseases through modulating flagella assembly and recognition of bacteria by the human immune system. Yet they are underexplored compared to other areas of glycoscience, in particular enzymes responsible for the glycosyltransfer of these sugars in bacteria are still to be unambiguously characterised. This can be largely attributed to a lack of access to nucleotide-activated pseudaminic acid glycosyl donors, such as CMP-Pse5Ac7Ac. Herein we reconstitute the biosynthesis of Pse5Ac7Ac in vitro using enzymes from C. jejuni (PseBCHGI) in the process optimising coupled turnover with PseBC using deuterium wash in experiments, and establishing a method for co-factor regeneration in PseH tunover. Furthermore we establish conditions for purification of a soluble CMP-Pse5Ac7Ac synthetase enzyme PseF from Aeromonas caviae and utilise it in combination with the C. jejuni enzymes to achieve practical preparative synthesis of CMP-Pse5Ac7Ac in vitro, facilitating future biological studies.

Purification and characterization of a novel extracellular, alkaline, thermoactive, and detergent-compatible lipase from Aeromonas caviae LipT51 for application in detergent industry.

Lipase producer bacterium isolated from Erzurum was identified as Aeromonas caviae LipT51 (GenBank ID: MN818567.1) by 16S rDNA sequencing and conventional methods. Extracellular lipase was purified by ammonium sulphate precipitation, centrifugal filtration, and anion-exchange chromatography resulting in 6.1-fold purification with 28% final yield. Molecular weight was 31.6 kDa on SDS-PAGE. Lipase was stable over a broad range of pH (6-11) and temperature (25-70 °C), and showed optimum activity at pH 9 and 60 °C. Km and Vmax for pNPP hydrolysis were 0.88 mM and 34.2 U/mg protein, respectively. Ba2+, Ca2+, Co2+, Cu2+, Fe3+, and Mg2+ increased activity, while Mn2+, Mo2+, Ni2+, Zn2+, and other additives partially decreased. Activity and stability increased with laundry detergent and slightly decreased with handwash and dishwashing detergents. Alkaline and thermostable lipase from newly isolated A. caviae has been shown for the first time to be remarkably compatible with laundry detergent and improve washing performance by enhanced oil-stain removal.

Microbial Secretion Platform for 3-Hydroxybutyrate Oligomer and Its End-Capped Forms Using Chain Transfer Reaction-Mediated Polyhydroxyalkanoate Synthases.

The biodegradable polyester 3-hydroxybutyrate (3HB) polymer [P(3HB)] is intracellularly synthesized and accumulated in recombinant Escherichia coli. In this study, native polyhydroxyalkanoate (PHA) synthases are used to attempt to microbially secrete 3HB homo-oligomers (3HBOs), which are widely distributed in nature as physiologically active substances. High secretory production is observed, especially for the two PHA synthases from Aeromonas caviae and Bacillus cereus YB4. Surprisingly, an ethyl ester at the carboxy terminus (ethyl ester form) of 3HBOs is identified for most of the PHA synthases tested. Next, 3HBOs with a functional carboxyl group (carboxyl form of 3HBO) are obtained by using the alcohol dehydrogenase gene (adhE)-deficient mutant strain, suggesting that the endogenous ethanol produced in E. coli acts as a chain transfer (CT) agent in the generation of 3HBOs. Furthermore, an in vitro polymerization assay reveals that CT agents such as ethanol and free 3HB are involved in the generation of ethyl ester and carboxyl form of 3HBO, respectively. The microbial platform established herein allows the secretion of 3HBOs with desirable end structures by supplementation with various CT agents. The obtained 3HBOs and their end-capped forms may be used as physiologically active substances and building blocks for polymeric materials.

Bioproduction of N-acetyl-glucosamine from colloidal α-chitin using an enzyme cocktail produced by Aeromonas caviae CHZ306.

N-acetyl-D-glucosamine (GlcNAc) is an important amino-monosaccharide with great potential for biotechnological applications. It has traditionally been produced by the chemical hydrolysis of chitin, despite certain industrial and environmental drawbacks, including acidic wastes, low yields and high costs. Therefore, enzymatic production has gained attention as a promising environmentally-friendly alternative to the chemical processes. In this study we demonstrate the GlcNAc bioproduction from colloidal α-chitin using an enzyme cocktail containing endochitinases and exochitinases (chitobiosidases and N-acetyl-glucosaminidases). The enzyme cocktail was extracted after fermentation in a bioreactor by Aeromonas caviae CHZ306, a chitinolytic marine bacterium with great potential for chitinase production. Hydrolysis parameters were studied in terms of temperature, pH, enzyme and substrate concentration, and reaction time, achieving over 90% GlcNAc yield within 6 h. The use of colloidal α-chitin as substrate showed a substantial improvement of GlcNAc yields, when compared with ß-chitin and α-chitin polymorphs. Such result is directly related to a significant decrease in crystallinity and viscosity from natural α-chitin, providing the chitinase with greater accessibility to the depolymerized chains. This study provides valuable information on the GlcNAc bioproduction from chitin using an enzymatic approach, addressing the key points for its production, including the enzyme cocktail composition and the substrate structures.

Potential KPC-2 carbapenemase reservoir of environmental Aeromonas hydrophila and Aeromonas caviae isolates from the effluent of an urban wastewater treatment plant in Japan.

Aeromonas hydrophila and Aeromonas caviae adapt to saline water environments and are the most predominant Aeromonas species isolated from estuaries. Here, we isolated antimicrobial-resistant (AMR) Aeromonas strains (A. hydrophila GSH8-2 and A. caviae GSH8M-1) carrying the carabapenemase blaKPC-2 gene from a wastewater treatment plant (WWTP) effluent in Tokyo Bay (Japan) and determined their complete genome sequences. GSH8-2 and GSH8M-1 were classified as newly assigned sequence types ST558 and ST13, suggesting no supportive evidence of clonal dissemination. The strains appear to have acquired blaKPC-2 -positive IncP-6-relative plasmids (pGSH8-2 and pGSH8M-1-2) that share a common backbone with plasmids in Aeromonas sp. ASNIH3 isolated from hospital wastewater in the United States, A. hydrophila WCHAH045096 isolated from sewage in China, other clinical isolates (Klebsiella, Enterobacter and Escherichia coli), and wastewater isolates (Citrobacter, Pseudomonas and other Aeromonas spp.). In addition to blaKPC-2 , pGSH8M-1-2 carries an IS26-mediated composite transposon including a macrolide resistance gene, mph(A). Although Aeromonas species are opportunistic pathogens, they could serve as potential environmental reservoir bacteria for carbapenemase and AMR genes. AMR monitoring from WWTP effluents will contribute to the detection of ongoing AMR dissemination in the environment and might provide an early warning of potential dissemination in clinical settings and communities.

PHA synthase (PhaC): interpreting the functions of bioplastic-producing enzyme from a structural perspective.

Polyhydroxyalkanoates (PHAs) are biopolymers synthesized by a wide range of bacteria, which serve as a promising candidate in replacing some conventional petrochemical-based plastics. PHA synthase (PhaC) is the key enzyme in the polymerization of PHA, and the crystal structures were successfully determined using the catalytic domain of PhaC from Cupriavidus necator (PhaCCn-CAT) and Chromobacterium sp. USM2 (PhaCCs-CAT). Here, we review the beneficial mutations discovered in PhaCs from a structural perspective. The structural comparison of the residues involved in beneficial mutation reveals that the residues are near to the catalytic triad, but not inside the catalytic pocket. For instance, Ala510 of PhaCCn is near catalytic His508 and may be involved in the open-close regulation, which presumably play an important role in substrate specificity and activity. In the class II PhaC1 from Pseudomonas sp. 61-3 (PhaC1Ps), Ser325 stabilizes the catalytic cysteine through hydrogen bonding. Another residue, Gln508 of PhaC1Ps is located in a conserved hydrophobic pocket which is next to the catalytic Asp and His. A class I, II-conserved Phe420 of PhaCCn is one of the residues involved in dimerization and its mutation to serine greatly reduced the lag phase. The current structural analysis shows that the Phe362 and Phe518 of PhaC from Aeromonas caviae (PhaCAc) are assisting the dimer formation and maintaining the integrity of the core beta-sheet, respectively. The structure-function relationship of PhaCs discussed in this review will serve as valuable reference for future protein engineering works to enhance the performance of PhaCs and to produce novel biopolymers.

Bioconversion of α-chitin into N-acetyl-glucosamine using chitinases produced by marine-derived Aeromonas caviae isolates.

N-Acetyl-D-glucosamine (GlcNAc) is a monosaccharide with great application potential in the food, cosmetic, pharmaceutical, and biomaterial areas. GlcNAc is currently produced by chemical hydrolysis of chitin, but the current processes are environmentally unfriendly, have low yield and high cost. This study demonstrates the potential to produce GlcNAc from α-chitin using chitinases of ten marine-derived Aeromonas isolates as a sustainable alternative to the current chemical process. The isolates were characterized as Aeromonas caviae by multilocus sequence analysis (MLSA) using six housekeeping genes (gltA, groL, gyrB, metG, ppsA, and recA), not presented the virulence genes verified (alt, act, ast, ahh1, aer, aerA, hlyA, ascV and ascFG), but showed hemolytic activity on blood agar. GlcNAc was produced at 37 °C, pH 5.0, 2% (w/v) colloidal chitin and crude chitinase extracts (0.5 U mL-1) by all the isolates with yields from 14 to 85% at 6 h, 17-89% at 12 h and 19-93% after 24 h. The highest yield of GlcNAc was observed by A. caviae CH129 (93%). This study demonstrates one of the most efficient chitin enzymatic hydrolysis procedures and A. caviae isolates with great potential for chitinases expression and GlcNAc production.

Butyrate production under aerobic growth conditions by engineered Escherichia coli.

Butyrate is an important industrial platform chemical. Although several groups have reported butyrate production under oxygen-limited conditions by a native producer, Clostridium tyrobutylicum, and by a metabolically engineered Escherichia coli, efforts to produce butyrate under aerobic growth conditions have met limited success. Here, we constructed a novel butyrate synthetic pathway that functions under aerobic growth conditions in E. coli, by modifying the 1-butanol synthetic pathway reported previously. The pathway consists of phaA (acetyltransferase) and phaB (NADPH-dependent acetoacetyl-CoA reductase) from Ralstonia eutropha, phaJ ((R)-specific enoyl-CoA hydratase) from Aeromonas caviae, ter (trans-enoyl-CoA reductase) from Treponema denticola, and endogenous thioesterase(s) of E. coli. To evaluate the potential of this pathway for butyrate production, culture conditions, including pH, oxygen supply, and concentration of inorganic nitrogen sources, were optimized in a mini-jar fermentor. Under the optimal conditions, butyrate was produced at a concentration of up to 140 mM (12.3 g/L in terms of butyric acid) after 54 h of fed-batch culture.

Production, characterization, and immobilization of partially purified surfactant-detergent and alkali-thermostable protease from newly isolated Aeromonas caviae.

Proteolytic Aeromonas caviae P-1-1 growing at wide-ranging pH (7.0-11.0) and moderate salinity (0-5% NaCl) was isolated from cattle shed of Thanjavur, India. It produced lipase, gelatinase, and polyhydroxybutyrate. Different culture conditions, incubation time, carbon and nitrogen sources, vitamins, amino acids, surfactants, and metal ions for optimal growth and protease production of P-1-1 were examined. Maximum protease (0.128 U/mL) production was achieved with 1% fructose, 1% yeast extract, 0.1% ammonium sulfate, 3% NaCl, 0.1% CaCl2 · 2H2O, 1% glycine, 0.1% vitamin E, and 0.1% Tween-40 at pH 8.0 after 42 hr of incubation at 37°C. It was active over broad range of pH (7.0-12.0), temperature (15-100°C), and salinity (0-9% NaCl) with optima at pH 10.0, 55°C, and 3% NaCl. It retained 65 and 48% activities at pH 12.0 and 100°C, respectively. Partially purified protease was highly stable (100%) within pH range 7.0-12.0 and salinities of 0-5% NaCl for 48 hr. Cu2+, Mn2+, Co2+, and Ca2+ did not inhibit its activity. Its stability at extreme pHs, temperatures, and in the presence of surfactants and commercial detergents suggests its possible application in laundry detergents. Partially purified protease was immobilized and reused. This is the first report of alkali-thermotolerant, surfactant-detergent-stable partially purified extracellular protease from A. caviae.

Regulation of 3-hydroxyhexanoate composition in PHBH synthesized by recombinant Cupriavidus necator H16 from plant oil by using butyrate as a co-substrate.

A (R)-3-hydroxyhexanoate (3HH) composition-regulating technology for poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) production was developed using recombinant Cupriavidus necator H16 with butyrate as a co-substrate. A new (R)-3-hydroxyhexanoyl-CoA ((R)-3HH-CoA) synthesis pathway was designed and enhanced by replacing the PHA synthase gene (phaC1) of C. necator by the phaCAcNSDG (encoding the N149S and D171G mutant of PHA synthase from Aeromonas caviae) and deactivation of the phaA gene (encoding (ß-ketothiolase) from C. necator H16 chromosome). The effect of butyrate as co-substrate was assessed in high-cell-density fed-batch cultures of several C. necator mutants, and the 3HH fraction was successfully increased by adding butyrate to the culture. Moreover, overexpression of BktB (encoding the second ß-ketothiolase with broad substrate specificity) enhanced the (R)-3HH-CoA synthesis pathway in the phaA deactivated mutant of C. necator by promoting the condensation of acetyl-CoA and butyryl-CoA into 3-ketohexanoyl-CoA. Consequently, PHBH containing 4.2-13.0 mol% 3HH was produced from butyrate and palm kernel oil by the genetically modified C. necator H16 strains.

Maf-dependent bacterial flagellin glycosylation occurs before chaperone binding and flagellar T3SS export.

Bacterial swimming is mediated by rotation of a filament that is assembled via polymerization of flagellin monomers after secretion via a dedicated flagellar Type III secretion system. Several bacteria decorate their flagellin with sialic acid related sugars that is essential for motility. Aeromonas caviae is a model organism for this process as it contains a genetically simple glycosylation system and decorates its flagellin with pseudaminic acid (Pse). The link between flagellin glycosylation and export has yet to be fully determined. We examined the role of glycosylation in the export and assembly process in a strain lacking Maf1, a protein involved in the transfer of Pse onto flagellin at the later stages of the glycosylation pathway. Immunoblotting, established that glycosylation is not required for flagellin export but is essential for filament assembly since non-glycosylated flagellin is still secreted. Maf1 interacts directly with its flagellin substrate in vivo, even in the absence of pseudaminic acid. Flagellin glycosylation in a flagellin chaperone mutant (flaJ) indicated that glycosylation occurs in the cytoplasm before chaperone binding and protein secretion. Preferential chaperone binding to glycosylated flagellin revealed its crucial role, indicating that this system has evolved to favour secretion of the polymerization competent glycosylated form.

Biosynthesis of polyhydroxyalkanoate copolymers from methanol by Methylobacterium extorquens AM1 and the engineered strains under cobalt-deficient conditions.

Methylobacterium extorquens AM1 has been shown to accumulate polyhydroxyalkanoate (PHA) composed solely of (R)-3-hydroxybutyrate (3HB) during methylotrophic growth. The present study demonstrated that the wild-type strain AM1 grown under Co²âº-deficient conditions accumulated copolyesters of 3HB and a C5-monomer, (R)-3-hydroxyvalerate (3HV), using methanol as the sole carbon source. The 3HV unit was supposed to be derived from propionyl-CoA, synthesized via the ethylmalonyl-CoA pathway impaired by Co²âº limitation. This assumption was strongly supported by the dominant incorporation of the 3HV unit into PHA when a strain lacking propionyl-CoA carboxylase was incubated with methanol. Further genetic engineering of M. extorquens AM1 was employed for the methylotrophic synthesis of PHA copolymers. A recombinant strain of M. extorquens AM1C(Ac) in which the original PHA synthase gene phaC(Me) had been replaced by phaC(Ac), encoding an enzyme with broad substrate specificity from Aeromonas caviae, produced a PHA terpolymer composed of 3HB, 3HV, and a C6-monomer, (R)-3-hydroxyhexanoate, from methanol. The cellular content and molecular weight of the PHA accumulated in the strain AM1C(Ac) were higher than those of PHA in the wild-type strain. The triple deletion of three PHA depolymerase genes in M. extorquens AM1C(Ac) showed no significant effects on growth and PHA biosynthesis properties. Overexpression of the genes encoding ß-ketothiolase and NADPH-acetoacetyl-CoA reductase increased the cellular PHA content and 3HV composition in PHA, although the cell growth on methanol was decreased. This study opens up the possibility of producing practical PHA copolymers with methylotrophic bacteria using methanol as a feedstock.

Emergence of VIM-producing Aeromonas caviae in Israeli hospitals.

OBJECTIVES: Resistance to carbapenems in Aeromonas species is rare and mediated mostly by the chromosomal cphA gene. Our aims were to describe the molecular characteristics of the first cases of VIM-producing Aeromonas caviae isolated from human samples. METHODS: Carbapenem-resistant Aeromonas (CRA) spp. were isolated from rectal surveillance cultures. Bacterial identification was done by dnaJ sequencing. Detection of metallo-carbapenemase and other ß-lactamase genes was done by PCR. Molecular typing was done by PFGE. The genetic environment of the blaVIM gene was determined by sequencing. RESULTS: Five CRA were isolated from surveillance cultures in 2010-13; four were from Shaare Zedek Medical Center and one was from Laniado Hospital. All five isolates were identified as A. caviae and comprised four different pulsotypes. MICs ranged from 0.5 to 8 mg/L for imipenem and from 0.25 to 8 mg/L for meropenem. All isolates were resistant to gentamicin, susceptible to amikacin and ciprofloxacin (except one), and were positive for carbapenemase production in the modified Hodge and Carba NP tests. The carbapenemase genes blaVIM-1 and blaVIM-35 were located inside a class I integron with two different sizes to its variable region. CONCLUSIONS: This is the first report of blaVIM in A. caviae from human samples and the first report of VIM-producing Gram-negative bacteria in Israel. This finding is alarming as this species may spread via water or sewage systems. Although infection due to Aeromonas spp. is rare, the presence of the gene on a mobile element is of concern due to the potential for dissemination to clinically important Gram-negative pathogens.

In vitro evidence of chain transfer to tetraethylene glycols in enzymatic polymerization of polyhydroxyalkanoate.

A polyhydroxyalkanoate (PHA) was enzymatically synthesized in vitro, and the end structure of PHA associated with a chain transfer (CT) reaction was investigated. In the CT reaction, PHA chain transfers from PHA synthase (PhaC) to a CT agent, resulting in covalent bonding of CT agent to the PHA chain at its carboxyl end. In vitro CT reaction has never been demonstrated because of relatively low yields of in vitro synthesized poly[(R)-3-hydroxybutyrate)] (P(3HB)), which makes it difficult to characterize the end structures of the polymers by nuclear magnetic resonance (NMR). To overcome these difficulties, a novel in vitro synthesis method that produced relatively larger amounts of P(3HB) was developed by employing PhaCDa from Delftia acidovorans and two enantioselective enoyl-coenzyme A (CoA) hydratases which were R-hydratase (PhaJAc) from Aeromonas caviae and S-hydratase (FadB1x) from Pseudomonas putida KT2440 with ß-butyrolactone and CoA as starting materials. Using this method, P(3HB) synthesis was performed with tetraethylene glycols (TEGs) as a discriminable CT agent, and the resultant P(3HB) was characterized by (1)H-NMR. NMR analysis revealed that the carboxylic end of P(3HB) was covalently linked to TEGs, providing the first direct evidence of in vitro CT reaction.

Active intermediates of polyhydroxyalkanoate synthase from Aeromonas caviae in polymerization reaction.

Polyhydroxyalkanoate (PHA) synthase from Aeromonas caviae FA440 (PhaC(Ac), BAA21815) is one of the most valuable PHA synthase, because of its function to synthesize a practical bioplastic, poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] [P(3HB-co-3HHx)]. However, biochemical activity and active intermediates of PhaC(Ac) have not been clarified until now. In the present study, a gene of PhaC(Ac) was cloned and overexpressed by a cell-free protein expression system. Both the polymerization activity and oligomerization behavior of the purified PhaC(Ac) were characterized in order to clarify the active intermediates of PhaC(Ac) based on the hydrodynamic diameters and specific activities of PhaC(Ac). The influences of a substrate, (R)-3-hydroxybutyryl-CoA (3HB-CoA), on the oligomerization of PhaC(Ac) (7.5 µM) were also investigated, and then the Hill coefficient (n = 2.6 ± 0.4) and the microscopic dissociation constant (K(m) = 77 ± 5 µM) were determined. Based on the results, the active intermediate of PhaC(Ac) was concluded to be the dimeric PhaC(Ac) containing 3HB-CoA as an activator for its dimerization. This information is critical for revealing the relationships between its dimerization and function in PHA synthesis.

Characterization and functional analyses of R-specific enoyl coenzyme A hydratases in polyhydroxyalkanoate-producing Ralstonia eutropha.

A genome survey of polyhydroxyalkanoate (PHA)-producing Ralstonia eutropha H16 detected the presence of 16 orthologs of R-specific enoyl coenzyme A (enoyl-CoA) hydratase, among which three proteins shared high homologies with the enzyme specific to enoyl-CoAs of medium chain length encoded by phaJ4 from Pseudomonas aeruginosa (phaJ4(Pa)). The recombinant forms of the three proteins, termed PhaJ4a(Re) to PhaJ4c(Re), actually showed enoyl-CoA hydratase activity with R specificity, and the catalytic efficiencies were elevated as the substrate chain length increased from C(4) to C(8). PhaJ4a(Re) and PhaJ4b(Re) showed >10-fold-higher catalytic efficiency than PhaJ4c(Re). The functions of the new PhaJ4 proteins were investigated using previously engineered R. eutropha strains as host strains; these strains are capable of synthesizing poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate) [P(3HB-co-3HHx)] from soybean oil. Deletion of phaJ4a(Re) from the chromosome resulted in significant decrease of 3HHx composition in the accumulated copolyester, whereas no change was observed with deletion of phaJ4b(Re) or phaJ4c(Re), indicating that only PhaJ4a(Re) was one of the major enzymes supplying the (R)-3HHx-CoA monomer through ß-oxidation. Introduction of phaJ4a(Re) or phaJ4b(Re) into the R. eutropha strains using a broad-host-range vector enhanced the 3HHx composition of the copolyesters, but the introduction of phaJ4c(Re) did not. The two genes were then inserted into the pha operon on chromosome 1 of the engineered R. eutropha by homologous recombination. These modifications enabled the biosynthesis of P(3HB-co-3HHx) composed of a larger 3HHx fraction without a negative impact on cell growth and PHA production on soybean oil, especially when phaJ4a(Re) or phaJ4b(Re) was tandemly introduced with phaJ(Ac) from Aeromonas caviae.

Expression of Aeromonas caviae polyhydroxyalkanoate synthase gene in Burkholderia sp. USM (JCM15050) enables the biosynthesis of SCL-MCL PHA from palm oil products.

AIMS: Burkholderia sp. USM (JCM15050) isolated from oil-polluted wastewater is capable of utilizing palm oil products and glycerol to synthesize poly(3-hydroxybutyrate) [P(3HB)]. To confer the ability to produce polymer containing 3-hydroxyhexanoate (3HHx), plasmid (pBBREE32d13) harbouring the polyhydroxyalkanoate (PHA) synthase gene of Aeromonas caviae (phaC(Ac)) was transformed into this strain. METHODS AND RESULTS: The resulting transformant incorporated approximately 1 ± 0·3 mol% of 3HHx in the polymer when crude palm kernel oil (CPKO) or palm kernel acid oil was used as the sole carbon source. In addition, when the transformed strain was cultivated in the mixtures of CPKO and sodium valerate, PHA containing 69 mol% 3HB, 30 mol% 3-hydroxyvalerate and 1 mol% 3HHx monomers was produced. Batch feeding of carbon sources with 0·5% (v/v) CPKO at 0 h and 0·25% (w/v) sodium valerate at 36 h yielded 6 mol% of 3HHx monomer by controlled-feeding strategies. CONCLUSIONS: Burkholderia sp. USM (JCM15050) has the metabolic pathways to supply both the short-chain length (SCL) and medium-chain length (MCL) PHA monomers. By transforming the strain with the Aer. caviae PHA synthase with broader substrate specificity, SCL-MCL PHA was produced. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study demonstrating the ability of transformant Burkholderia to produce P(3HB-co-3HHx) from a single carbon source.