Site-Specific and Asymmetric Hydrolysis of Prochiral 2-Phenyl-1,3-propanediol Diacetate by a Bacterial Esterase from an Isolated Strain

Bacillus cereus 809A and Burkholderia sp. 711C were isolated from soil. These strains demonstrate hydrolysis activity towards prochiral 2-phenyl-1,3-propanediol diacetate and accumulated the corresponding chiral monoacetates into the reaction mixture. When 2-phenyl 1,3-propanediol diacetate was used as a substrate, the produced monoacetates with Burkholderia sp. 711C were obtained in a racemic form but that produced by Bacillus cereus 809A showed an excess of the (S)-form. The resting cell reaction revealed that for Bacillus cereus 809A, there was an enrichment of one of the enantiomers of the monoacetate such that the enantiomeric excess (e.e.) of the (S)-form was over 95%. The purified enzyme from Bacillus cereus 809A hydrolyzed diacetate to monoacetate, and the e.e. value of the (S)-form increased by prolonged reaction in a way similar to the resting cell reaction. From N-terminal amino acids, this esterase is conserved in some strains of Bacillus for which the genomic sequences have been reported.

Directed Evolution to Enhance Secretion Efficiency and Thermostability of Chitosanase fromMitsuaria chitosanitabida3001

Chitosanase (ChoA) from Mitsuaria chitosanitabida 3001 was successfully evolved with secretion efficiency and thermal stability. The inactive ChoA mutant (G151D) gene was used to mutate by an error-prone PCR technique and mutant genes that restored chitosanase activity were isolated. Two desirable mutants, designated M5S and M7T, were isolated. Two amino acids, Leu74 and Val75, in the signal peptide of ChoA were changed to Gln and Ile respectively in the M7T mutant, in addition to the G151D mutation. The L74Q/V75I double ChoA mutant was 1.5-fold higher in specific activity than wild-type ChoA due to efficient secretion of ChoA. One amino acid Asn222 was changed to Ser in the M5S mutant in addition to the G151D mutation. The N222S single ChoA mutant was 1.2-fold higher in specific activity and showed a 17% increase in thermal stability at 50 degrees C as compared with wild-type ChoA. This is the first study to achieve an evolutional increase in enzyme capability among chitosanses.

Expression, purification, crystallization and preliminary X-ray diffraction analysis of the novel modular DNA-binding protein BurrH in its apo form and in complex with its target DNA

Different genome-editing strategies have fuelled the development of new DNA-targeting molecular tools allowing precise gene modifications. Here, the expression, purification, crystallization and preliminary X-ray diffraction of BurrH, a novel DNA-binding protein from Burkholderia rhizoxinica, are reported. Crystallization experiments of BurrH in its apo form and in complex with its target DNA yielded crystals suitable for X-ray diffraction analysis. The crystals of the apo form belonged to the primitive hexagonal space group P3(1) or its enantiomorph P3(2), with unit-cell parameters a = b = 73.28, c = 268.02 Å, α = β = 90, γ = 120°. The BurrH-DNA complex crystallized in the monoclinic space group P2(1), with unit-cell parameters a = 70.15, b = 95.83, c = 76.41 Å, α = γ = 90, β = 109.51°. The self-rotation function and the Matthews coefficient suggested the presence of two protein molecules per asymmetric unit in the apo crystals and one protein-DNA complex in the monoclinic crystals. The crystals diffracted to resolution limits of 2.21 and 2.65 Å, respectively, using synchrotron radiation.

Kinetics of transesterification of olive oil with methanol catalyzed by immobilized lipase derived from an isolated Burkholderia sp. strain

This work was carried out to investigate the acyl migration phenomena which has been considered as the factor having significant impact on kinetics of transesterification of oils catalyzed by a Burkholderia lipase with 1,3-regioselectivity. Transesterification of olive oil with methanol catalyzed by the immobilized lipase produces various intermediates, including 1-monoglyceride, 2-monoglyceride, 1,2-diglyceride, and 1,3-diglyceride. Migration kinetics of fatty acid groups from sn-2 of 2-monoglyceride and 1,2-diglyceride to 1-monoglyceride and 1,3-diglyceride were investigated for the temperature range of 25-65°C. The kinetics of transesterification of olive oil with methanol involving acyl migration in the presence of water was also systematically studied at 25, 40, and 65°C. Increasing temperature could increase the acyl migration rate. The overall biodiesel conversion was improved from 73.4% (at 25°C) to 90.0% and 92.4% when conducting at 40 and 65°C, respectively. Thermodynamics aspects of equilibrium state of the immobilized lipase-catalyzed transesterification were also discussed.

The lid domain of the MCP hydrolase DxnB2 contributes to the reactivity toward recalcitrant PCB metabolites

DxnB2 and BphD are meta-cleavage product (MCP) hydrolases that catalyze C-C bond hydrolysis of the biphenyl metabolite 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA). BphD is a bottleneck in the bacterial degradation of polychlorinated biphenyls (PCBs) by the Bph catabolic pathway due in part to inhibition by 3-Cl HOPDAs. By contrast, DxnB2 from Sphingomonas wittichii RW1 catalyzes the hydrolysis of 3-Cl HOPDAs more efficiently. X-ray crystallographic studies of the catalytically inactive S105A variant of DxnB2 complexed with 3-Cl HOPDA revealed a binding mode in which C1 through C6 of the dienoate are coplanar. The chlorine substituent is accommodated by a hydrophobic pocket that is larger than the homologous site in BphDLB400 from Burkholderia xenovorans LB400. The planar binding mode observed in the crystalline complex was consistent with the hyper- and hypsochromically shifted absorption spectra of 3-Cl and 3,9,11-triCl HOPDA, respectively, bound to S105A in solution. Moreover, ES(red), an intermediate possessing a bathochromically shifted spectrum observed in the turnover of HOPDA, was not detected, suggesting that substrate destabilization was rate-limiting in the turnover of these PCB metabolites. Interestingly, electron density for the first α-helix of the lid domain was poorly defined in the dimeric DxnB2 structures, unlike in the tetrameric BphDLB400. Structural comparison of MCP hydrolases identified the NC-loop, connecting the lid to the α/β-hydrolase core domain, as a determinant in the oligomeric state and suggests its involvement in catalysis. Finally, an increased mobility of the DxnB2 lid may contribute to the enzyme's ability to hydrolyze PCB metabolites, highlighting how lid architecture contributes to substrate specificity in α/β-hydrolases.

A simple and sensitive biosensor strain for detecting toxoflavin using β-galactosidase activity

In this study, we developed a simple and sensitive biosensor for the determination of toxoflavin (which is toxic to various plants, fungi, animals, and bacteria) in natural samples based on β-galactosidase activity. The proposed toxoflavin detection method for toxin-producing bacteria or toxin-contaminated foods is simple and cost effective. Burkholderia glumae, a species known to cause rice grain rot and wilt in various field crops, produces toxoflavin under the control of a LysR-type transcriptional regulator ToxR and its ligand toxoflavin. As the expression of toxoflavin biosynthetic genes requires toxoflavin as a co-activator of ToxR, a novel biosensor stain was constructed based on lacZ reporter gene integration into the first gene of the toxoflavin biosynthesis operon, toxABCDE of B. glumae. The biosensor was composed of a sensor strain (COK71), substrates (X-gal or ONPG), and culture medium, without any complex preparation process. We demonstrated that the biosensor strain is highly specific to toxoflavin, and can quantify relative amounts of toxoflavin compared with known concentrations of toxoflavin. The proposed method was reliable and simple; samples containing 50-500 nM of toxoflavin could be analyzed. More importantly, the proposed biosensor strain could identify toxoflavin-producing bacteria in real samples. The excellent performance of this biosensor is useful for diagnostic purposes, such as detecting toxoflavin-contaminated foods and environmental samples.

Microalgae harvesting and subsequent biodiesel conversion

Chlorella vulgaris ESP-31 containing 22.7% lipid was harvested by coagulation (using chitosan and polyaluminium chloride (PACl) as the coagulants) and centrifugation. The harvested ESP-31 was directly employed as the oil source for biodiesel production via transesterification catalyzed by immobilized Burkholderia lipase and by a synthesized solid catalyst (SrO/SiO2). Both enzymatic and chemical transesterification were significantly inhibited in the presence of PACl, while the immobilized lipase worked well with wet chitosan-coagulated ESP-31, giving a high biodiesel conversion of 97.6% w/w oil, which is at a level comparable to that of biodiesel conversion from centrifugation-harvested microalgae (97.1% w/w oil). The immobilized lipase can be repeatedly used for three cycles without significant loss of its activity. The solid catalyst SrO/SiO2 worked well with water-removed centrifuged ESP-31 with a biodiesel conversion of 80% w/w oil, but the conversion became lower (55.7-61.4% w/w oil) when using water-removed chitosan-coagulated ESP-31 as the oil source.

Crystal structure of a novel N-substituted L-amino acid dioxygenase from Burkholderia ambifaria AMMD

A novel dioxygenase from Burkholderia ambifaria AMMD (SadA) stereoselectively catalyzes the C3-hydroxylation of N-substituted branched-chain or aromatic L-amino acids, especially N-succinyl-L-leucine, coupled with the conversion of α-ketoglutarate to succinate and CO₂. To elucidate the structural basis of the substrate specificity and stereoselective hydroxylation, we determined the crystal structures of the SadA.Zn(II) and SadA.Zn(II).α-KG complexes at 1.77 Å and 1.98 Å resolutions, respectively. SadA adopted a double-stranded β-helix fold at the core of the structure. In addition, an HXD/EX_nH motif in the active site coordinated a Zn(II) as a substitute for Fe(II). The α-KG molecule also coordinated Zn(II) in a bidentate manner via its 1-carboxylate and 2-oxo groups. Based on the SadA.Zn(II).α-KG structure and mutation analyses, we constructed substrate-binding models with N-succinyl-L-leucine and N-succinyl-L-phenylalanine, which provided new insight into the substrate specificity. The results will be useful for the rational design of SadA variants aimed at the recognition of various N-succinyl L-amino acids.

Effect of solvents and oil content on direct transesterification of wet oil-bearing microalgal biomass of Chlorella vulgaris ESP-31 for biodiesel synthesis using immobilized lipase as the biocatalyst

In this work, a one-step extraction/transesterification process was developed to directly convert wet oil-bearing microalgal biomass of Chlorella vulgaris ESP-31 into biodiesel using immobilized Burkholderia lipase as the catalyst. The microalgal biomass (water content of 86-91%; oil content 14-63%) was pre-treated by sonication to disrupt the cell walls and then directly mixed with methanol and solvent to carry out the enzymatic transesterification. Addition of a sufficient amount of solvent (hexane is most preferable) is required for the direct transesterification of wet microalgal biomass, as a hexane-to-methanol mass ratio of 1.65 was found optimal for the biodiesel conversion. The amount of methanol and hexane required for the direct transesterification process was also found to correlate with the lipid content of the microalga. The biodiesel synthesis process was more efficient and economic when the lipid content of the microalgal biomass was higher. Therefore, using high-lipid-content microalgae as feedstock appears to be desirable.

The Burkholderia contaminans MS14 ocfC gene encodes a xylosyltransferase for production of the antifungal occidiofungin

Burkholderia contaminans strain MS14 produces the antifungal compound occidiofungin, which is responsible for significant antifungal activities against a broad range of plant and animal fungal pathogens. Occidiofungin is a cyclic glycolipopeptide made up of eight amino acids and one xylose. A 56-kb ocf gene cluster was determined to be essential for occidiofungin production. In this study, the ocfC gene, which is located downstream of ocfD and upstream of the ocfB gene in the ocf gene cluster, was examined. Antifungal activity of the ocfC gene mutant MS14KC1 was reduced against the indicator fungus Geotrichum candidum compared with that of the wild-type strain. Furthermore, the analysis of the protein sequence suggests that the ocfC gene encodes a glycosyltransferase. Biochemical analyses using nuclear magnetic resonance (NMR) and mass spectroscopy revealed that the ocfC mutant produced the occidiofungin without the xylose. The purified ocfC mutant MS14KC1 product had a level of bioactivity similar to that of the wild-type product. The revertant MS14KC1-R of the ocfC mutant produced the same antifungal activity level on plate assays and the same antifungal compound based on high-performance liquid chromatography (HPLC) and mass spectroscopy analysis as wild-type strain MS14. Collectively, the study demonstrates that the ocfC gene encodes a glycosyltransferase responsible to add a xylose to the occidiofungin molecule and that the presence of the xylose is not important for antifungal activity against Candida species. The finding provides a novel variant for future studies aimed at evaluating its use for inhibiting clinical and agricultural fungi, and the finding could also simplify the chemical synthesis of occidiofungin variants.

Expression, purification, crystallization and preliminary X-ray analysis of a novel N-substituted branched-chain L-amino-acid dioxygenase from Burkholderia ambifaria AMMD

Ferrous ion- and α-ketoglutarate-dependent dioxygenase from Burkholderia ambifaria AMMD (SadA) catalyzes the C3-hydroxylation of N-substituted branched-chain L-amino acids, especially N-succinyl-L-leucine, coupled to the conversion of α-ketoglutarate to succinate and CO(2). SadA was expressed in Escherichia coli, purified and crystallized using the sitting-drop vapour-diffusion method at 293 K. Crystals of selenomethionine-substituted SadA were obtained using a reservoir solution containing PEG 3000 as the precipitant at pH 9.5 and diffracted X-rays to 2.4 Å resolution. The crystal belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 49.3, b = 70.9, c = 148.2 Å. The calculated Matthews coefficient (V(M) = 2.1 Å(3) Da(-1), 41% solvent content) suggested that the crystal contains two molecules per asymmetric unit.

Decoding the folding of Burkholderia glumae lipase: folding intermediates en route to kinetic stability

The lipase produced by Burkholderia glumae folds spontaneously into an inactive near-native state and requires a periplasmic chaperone to reach its final active and secretion-competent fold. The B. glumae lipase-specific foldase (Lif) is classified as a member of the steric-chaperone family of which the propeptides of α-lytic protease and subtilisin are the best known representatives. Steric chaperones play a key role in conferring kinetic stability to proteins. However, until present there was no solid experimental evidence that Lif-dependent lipases are kinetically trapped enzymes. By combining thermal denaturation studies with proteolytic resistance experiments and the description of distinct folding intermediates, we demonstrate that the native lipase has a kinetically stable conformation. We show that a newly discovered molten globule-like conformation has distinct properties that clearly differ from those of the near-native intermediate state. The folding fingerprint of Lif-dependent lipases is put in the context of the protease-prodomain system and the comparison reveals clear differences that render the lipase-Lif systems unique. Limited proteolysis unveils structural differences between the near-native intermediate and the native conformation and sets the stage to shed light onto the nature of the kinetic barrier.

Enzymatic transesterification of microalgal oil from Chlorella vulgaris ESP-31 for biodiesel synthesis using immobilized Burkholderia lipase

An indigenous microalga Chlorella vulgaris ESP-31 grown in an outdoor tubular photobioreactor with CO(2) aeration obtained a high oil content of up to 63.2%. The microalgal oil was then converted to biodiesel by enzymatic transesterification using an immobilized lipase originating from Burkholderia sp. C20. The conversion of the microalgae oil to biodiesel was conducted by transesterification of the extracted microalgal oil (M-I) and by transesterification directly using disrupted microalgal biomass (M-II). The results show that M-II achieved higher biodiesel conversion (97.3 wt% oil) than M-I (72.1 wt% oil). The immobilized lipase worked well when using wet microalgal biomass (up to 71% water content) as the oil substrate. The immobilized lipase also tolerated a high methanol to oil molar ratio (>67.93) when using the M-II approach, and can be repeatedly used for six cycles (or 288 h) without significant loss of its original activity.

Study of an aquifer contaminated by ethyl tert-butyl ether (ETBE): site characterization and on-site bioremediation

Ethyl tert-butyl ether (ETBE) was detected at high concentration (300mgL(-1)) in the groundwater below a gas-station. No significant carbon neither hydrogen isotopic fractionation of ETBE was detected along the plume. ETBE and BTEX biodegradation capacities of the indigenous microflora Pz1-ETBE and of a culture (MC-IFP) composed of Rhodococcus wratislaviensis IFP 2016, Rhodococcus aetherivorans IFP 2017 and Aquincola tertiaricarbonis IFP 2003 showed that ETBE and BTEX degradation rates were in the same range (ETBE: 0.91 and 0.83 mg L(-1)h(-1) and BTEX: 0.64 and 0.82 mg L(-1)h(-1), respectively) but tert-butanol (TBA) accumulated transiently at a high level using Pz1-ETBE (74 mg L(-1)). An on-site pilot plant (2m(3)) filled with polluted groundwater and inoculated by MC-IFP, successfully degraded four successive additions of ETBE and gasoline. However, an insignificant ETBE isotopic fractionation was also accompanying this decrease which suggested the involvement of low fractionating-strains using EthB enzymes, but required of additional proofs. The ethB gene encoding a cytochrome P450 involved in ETBE biodegradation (present in R. aetherivorans IFP 2017) was monitored by quantitative real-time polymerase chain reaction (q-PCR) on DNA extracted from water sampled in the pilot plant which yield up to 5×10(6) copies of ethB gene per L(-1).

Optimization of 2,3-dihydroxybiphenyl 1,2-dioxygenase expression and its application for biosensor

In this study, two statistical experimental designs, Plackett-Burman design (PBD) and response surface methodology (RSM), were employed to enhance the expression of 2,3-dihydroxybiphenyl 1,2-dioxygenase (BphC_LA-4), which was subsequently used for the construction of catechol biosensor. Ten important factors were evaluated by PBD, and four significant parameters were then optimized by RSM. Under the favorable fermentation conditions, the maximal specific activity of BphC_LA-4 was about 0.58U/mg with catechol as substrate. Meanwhile, homology modeling and molecular docking were utilized to help understand the interaction between BphC_LA-4 and catecholic substrates, which illustrated that BphC_LA-4 presented lower binding affinity towards 4-methylcatechol in comparison with 3-methylcatechol and catechol. Interestingly, the BphC_LA-4 enzyme electrode prepared by SiO2 sol-gel showed good response to all these three catecholic compounds. The differences of selectivity to 4-methylcatechol between free and immobilized enzyme implied that the introduction of electro-catalysis might have an effect on the enzyme-catalysis process.

Sources of diversity in bactobolin biosynthesis by Burkholderia thailandensis E264

A series of deletion mutants in the recently identified bactobolin biosynthetic pathway defined the roles of several key biosynthetic enzymes and showed how promiscuity in three enzyme systems allows this cluster to produce multiple products. Studies on the deletion mutants also led to four new bactobolin analogs that provide additional structure-activity relationships for this interesting antibiotic family.

The homogentisate and homoprotocatechuate central pathways are involved in 3- and 4-hydroxyphenylacetate degradation by Burkholderia xenovorans LB400

Background

Genome characterization of the model PCB-degrading bacterium Burkholderia xenovorans LB400 revealed the presence of eleven central pathways for aromatic compounds degradation, among them, the homogentisate and the homoprotocatechuate pathways. However, the functionality of these central pathways in strain LB400 has not been assessed and related peripheral pathways has not been described.

Methodology/Principal Findings

The aims of this study were to determine the functionality of the homogentisate and homoprotocatechuate central pathways in B. xenovorans LB400 and to establish their role in 3-hydroxyphenylacetate (3-HPA) and 4-hydroxyphenylacetate (4-HPA) catabolism. Strain LB400 was able to grow using 3-HPA and 4-HPA as sole carbon source. A genomic search in LB400 suggested the presence of mhaAB and hpaBC genes clusters encoding proteins of the 3-hydroxyphenylacetate and 4-hydroxyphenylacetate peripheral pathways. LB400 cells grown with 3-HPA and 4-HPA degraded homogentisate and homoprotocatechuate and showed homogentisate 1,2-dioxygenase and homoprotocatechuate 2,3-dioxygenase activities. Transcriptional analyses by RT-PCR showed the expression of two chromosomally-encoded homogentisate dioxygenases (BxeA2725 and BxeA3900) and the hpaD gene encoding the homoprotocatechuate 2,3-dioxygenase during 3-HPA and 4-HPA degradation. The proteome analyses by two-dimensional polyacrilamide gel electrophoresis of B. xenovorans LB400 grown in 3-HPA and 4-HPA showed the induction of fumarylacetoacetate hydrolase HmgB (BxeA3899).

Conclusions/Significance

This study revealed that strain LB400 used both homogentisate and homoprotocatechuate ring-cleavage pathways for 3- hydroxyphenylacetate and 4-hydroxyphenylacetate catabolism and that these four catabolic routes are functional, confirming the metabolic versatility of B. xenovorans LB400.

The effects of nutrient amendment on biodegradation and cytochrome P450 activity of an n-alkane degrading strain of Burkholderia sp. GS3C

The promotion of hexadecane biodegradation activity by an n-alkane degrading strain of Burkholderia cepacia (GS3C) with yeast extract amendment was studied using various carbon, nitrogen, vitamin, and amino acid amendments. Cytochrome P450 monooxygenase enzymes play a very important role and are especially required to introduce oxygen in n-alkane degradation. These enzymes from GS3C were located and detected using amino acid amendments. It was shown that biodegradation activity was promoted with amino acids amendments. However, only specific amino acids (L-phenylalanine, L-glutamic acid, L-proline, L-lysine, L-valine and L-leucine) have biodegradation promoting ability for GS3C. Cell protein concentration and cytochrome P450 activity were promoted significantly with the addition of L-phenylalanine and yeast extract. Furthermore, a significant positive linear relationship between cytochrome P450 activity and biodegradation efficiency of GS3C was observed. The results indicate that amino acid is the primary factor of nutrient amendment in promoting hexadecane biodegradation by influencing cytochrome P450 activity in GS3C.

A product analog bound form of 3-oxoadipate-enol-lactonase (PcaD) reveals a multifunctional role for the divergent cap domain

Lactones are a class of structurally diverse molecules that serve essential roles in biological processes ranging from quorum sensing to the aerobic catabolism of aromatic compounds. Not surprisingly, enzymes involved in the bioprocessing of lactones are often targeted for protein engineering studies with the potential, for example, of optimized bioremediation of aromatic pollutants. The enol-lactone hydrolase (ELH) represents one such class of targeted enzymes and catalyzes the conversion of 3-oxoadipate-enol-lactone into the linear β-ketoadipate. To define the structural details that govern ELH catalysis and assess the impact of divergent features predicted by sequence analysis, we report the first structural characterization of an ELH (PcaD) from Burkholderia xenovorans LB400 in complex with the product analog levulinic acid. The overall dimeric structure of PcaD reveals an α-helical cap domain positioned atop a core α/β-hydrolase domain. Despite the localization of the conserved catalytic triad to the core domain, levulinic acid is bound largely within the region of the active site defined by the cap domain, suggesting a key role for this divergent substructure in mediating product release. Furthermore, the architecture of the cap domain results in an unusually deep active-site pocket with topological features to restrict binding to small or kinked substrates. The evolutionary basis for this substrate selectivity is discussed with respect to the homologous dienelactone hydrolase. Overall, the PcaD costructure provides a detailed insight into the intimate role of the cap domain in influencing all aspects of substrate binding, turnover, and product release.

Expression, purification, crystallization and preliminary X-ray analysis of maleylacetate reductase from Burkholderia sp. strain SJ98

Maleylacetate reductase (EC 1.3.1.32) is an important enzyme that is involved in the degradation pathway of aromatic compounds and catalyzes the reduction of maleylacetate to 3-oxoadipate. The gene pnpD encoding maleylacetate reductase in Burkholderia sp. strain SJ98 was cloned, expressed in Escherichia coli and purified by affinity chromatography. The enzyme was crystallized in both native and SeMet-derivative forms by the sitting-drop vapour-diffusion method using PEG 3350 as a precipitant at 293 K. The crystals belonged to space group P2(1)2(1)2, with unit-cell parameters a = 72.91, b = 85.94, c = 53.07 A. X-ray diffraction data for the native and SeMet-derivative crystal were collected to 2.7 and 2.9 A resolution, respectively.

ACC (1-aminocyclopropane-1-carboxylate) deaminase activity, a widespread trait in Burkholderia species, and its growth-promoting effect on tomato plants

The genus Burkholderia includes pathogens of plants and animals and some human opportunistic pathogens, such as the Burkholderia cepacia complex (Bcc), but most species are nonpathogenic, plant associated, and rhizospheric or endophytic. Since rhizobacteria expressing ACC (1-aminocyclopropane-1-carboxylate) deaminase may enhance plant growth by lowering plant ethylene levels, in this work we investigated the presence of ACC deaminase activity and the acdS gene in 45 strains, most of which are plant associated, representing 20 well-known Burkholderia species. The results demonstrated that ACC deaminase activity is a widespread feature in the genus Burkholderia, since 18 species exhibited ACC deaminase activities in the range from 2 to 15 mumol of alpha-ketobutyrate/h/mg protein, which suggests that these species may be able to modulate ethylene levels and enhance plant growth. In these 18 Burkholderia species the acdS gene sequences were highly conserved (76 to 99% identity). Phylogenetic analysis of acdS gene sequences in Burkholderia showed tight clustering of the Bcc species, which were clearly distinct from diazotrophic plant-associated Burkholderia species. In addition, an acdS knockout mutant of the N(2)-fixing bacterium Burkholderia unamae MTl-641(T) and a transcriptional acdSp-gusA fusion constructed in this strain showed that ACC deaminase could play an important role in promotion of the growth of tomato plants. The widespread ACC deaminase activity in Burkholderia species and the common association of these species with plants suggest that this genus could be a major contributor to plant growth under natural conditions.

Production, partial purification and characterization of organic solvent tolerant lipase from Burkholderia multivorans V2 and its application for ester synthesis

Burkholderia multivorans V2 (BMV2) isolated from soil was found to produce an extracellular solvent tolerant lipase (6.477 U/mL). This lipase exhibited maximum stability in n-hexane retaining about 97.8% activity for 24h. After performing statistical optimization of medium components for lipase production, a 2.2-fold (14 U/mL) enhancement in the lipase production was observed. The crude lipase from BMV2 was partially purified by ultrafiltration and gel permeation chromatography with 24.64-fold purification. The K(m) and V(max) values for partially purified BMV2 lipase were found to be 1.56 mM and 5.62 micromoles/mg min. The metal ions Ca(2+), Mg(2+) and Mn(2+) had stimulatory effect on lipase activity, whereas Cu(2+), Fe(2+) and Zn(2+) strongly inhibited the lipase activity. EDTA and PMSF at 10mM concentration strongly inhibited the lipase activity. Non-ionic and anionic surfactants stimulated the lipase activity. BMV2 lipase was proved to be efficient in synthesis of ethyl butyrate ester under non-aqueous environment.

Purification, crystallization and X-ray diffraction analysis of a novel ring-cleaving enzyme (BoxC(C)) from Burkholderia xenovorans LB400

The assimilation of aromatic compounds by microbial species requires specialized enzymes to cleave the thermodynamically stable ring. In the recently discovered benzoate-oxidation (box) pathway in Burkholderia xenovorans LB400, this is accomplished by a novel dihydrodiol lyase (BoxC(C)). Sequence analysis suggests that BoxC(C) is part of the crotonase superfamily but includes an additional uncharacterized region of approximately 115 residues that is predicted to mediate ring cleavage. Processing of X-ray diffraction data to 1.5 A resolution revealed that BoxC(C) crystallized with two molecules in the asymmetric unit of the P2(1)2(1)2(1) space group, with a solvent content of 47% and a Matthews coefficient of 2.32 A(3) Da(-1). Selenomethionine BoxC(C) has been purified and crystals are currently being refined for anomalous dispersion studies.

Lipolytic activity of suspended and membrane immobilized lipase originating from indigenous Burkholderia sp. C20

In this work, a simple, inexpensive, and efficient method of preparing immobilized lipase is presented. The lipase originating from a newly isolated indigenous strain Burkholderia sp. C20 was immobilized onto cellulose nitrate (CN) membrane via filtration. The CN-immobilized lipase was able to retain 60% of its original activity after repeated uses for nine times. The thermal stability of the lipase was also slightly improved after immobilization. The optimal reaction conditions of CN-lipase were pH 9.0 and 55 degrees C, which are similar to those for the suspended lipase. Both suspended and immobilized lipase could hydrolyze the six oil substrates examined, while immobilized lipase displayed less specificity over the oil substrates. Kinetic analysis shows that the dependence of lipolytic activity of both suspended and immobilized lipase on oil substrate concentration can be described by Michaelis-Menten model with good agreement. The estimated kinetic constants for suspended lipase (v(max)=243.9 U/mg, K(m)=0.024 mM) and immobilized lipase (v(max)=32.8 U/mg, K(m)=5.61 mM) were quite different. Employment of immobilization seemed to result in a decrease in v(max) and an increase in K(m), most likely due to the mass transfer resistance arising from formation of micelles during the lipase immobilization process.

Cloning and expression of a parathion hydrolase gene from a soil bacterium, Burkholderia sp. JBA3

A bacterium, Burkholderia sp. JBA3, which can mineralize the pesticide parathion, was isolated from an agricultural soil. The strain JBA3 hydrolyzed parathion to p-nitrophenol, which was further utilized as the carbon and energy sources. The parathion hydrolase was encoded by a gene on a plasmid that strain JBA3 harbored, and it was cloned into pUC19 as a 3.7-kbp Sau3AI fragment. The ORF2 (ophB) in the cloned fragment encoded the parathion hydrolase composed of 526 amino acids, which was expressed in E. coli DH10B. The ophB gene showed no significant sequence similarity to most of other reported parathion hydrolase genes.