Partitioning of phenanthrene into surfactant hemi-micelles on the bacterial cell surface and implications for surfactant-enhanced biodegradation

Recent studies have suggested that the ability of a surfactant to enhance the bioavailability of hydrophobic organic compounds (HOC) requires the formation of surfactant hemi-micelles on the bacterial cell surface and subsequent partitioning of HOC into the hemi-micelles. However, the studies did not provide direct evidence of HOC partitioning into surfactant hemi-micelles on the bacterial cell surface. In this study, direct evidence is provided to demonstrate that the nonionic surfactant Brij 30 forms hemi-micelles on the bacterial cell surface and that phenanthrene sorption at the bacterial surface is enhanced by the surfactant. These results are in agreement with the current theory describing surfactant-enhanced HOC bioavailability. This enhanced bioavailability is put into context with microbial kinetics and system partitioning processes, and it is demonstrated that the addition of surfactant can enhance, have no effect, or inhibit HOC biodegradation depending upon surfactant concentration and microbial growth rate. Understanding these non-linear relationships between surfactant-enhanced HOC bioavailability, biodegradation kinetics, and system partitioning will assist in the design and implementation of surfactant-enhanced bioremediation programs.

Antibacterial activity of a lectin-like Burkholderia cenocepacia protein

Bacteriocins of the LlpA family have previously been characterized in the γ-proteobacteria Pseudomonas and Xanthomonas. These proteins are composed of two MMBL (monocot mannose-binding lectin) domains, a module predominantly and abundantly found in lectins from monocot plants. Genes encoding four different types of LlpA-like proteins were identified in genomes from strains belonging to the Burkholderia cepacia complex (Bcc) and the Burkholderia pseudomallei group. A selected recombinant LlpA-like protein from the human isolate Burkholderia cenocepacia AU1054 displayed narrow-spectrum genus-specific antibacterial activity, thus representing the first functionally characterized bacteriocin within this β-proteobacterial genus. Strain-specific killing was confined to other members of the Bcc, with mostly Burkholderia ambifaria strains being susceptible. In addition to killing planktonic cells, this bacteriocin also acted as an antibiofilm agent.

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.

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.

Mannitol promotes adherence of an outbreak strain of Burkholderia multivorans via an exopolysaccharide-independent mechanism that is associated with upregulation of newly identified fimbrial and afimbrial adhesins

Burkholderia multivorans, a member of the Burkholderia cepacia complex (Bcc), is an important pathogen of the cystic fibrosis (CF) lung. Mannitol, approved as an inhaled osmolyte therapy for use in CF patients, promotes exopolysaccharide (EPS) production by the Bcc. In the present study, we investigated the role of mannitol-induced EPS in the adherence of B. multivorans. We report that mannitol promoted adherence of two representative B. multivorans strains. However, whilst this enhanced adherence was largely EPS-dependent in an environmental isolate, it was EPS-independent within a CF outbreak strain, suggesting strain-to-strain variation in adhesins. Genome sequencing of the outbreak strain enabled the identification of two distinct loci encoding putative fimbrial and afimbrial adhesins. The putative fimbriae-encoding locus was found to be widely distributed amongst clinical and environmental B. multivorans. In contrast, the locus encoding the putative afimbrial adhesin (of the filamentous haemagglutinin family, FHA) was restricted to clinical isolates. Both loci contributed to biofilm formation and mucin adherence. Furthermore, we report that mannitol promoted expression of both loci, and that the locus encoding the putative FHA-family adhesin is a key determinant of the enhanced adherence observed following growth in mannitol. Our studies provide the first characterization, to our knowledge, of B. multivorans adhesins, and in so doing highlight the strain-dependent role of EPS in the Bcc and the difficulties in assigning phenotypic traits to Bcc EPS due to the wider response to mannitol. Our observations also highlight the need to monitor the microbiological effects of inhaled mannitol therapy in Bcc-infected CF patients.

Characterization of plant-growth-promoting effects and concurrent promotion of heavy metal accumulation in the tissues of the plants grown in the polluted soil by Burkholderia strain LD-11

Plant-growth-promoting (PGP) bacteria especially with the resistance to multiple heavy metals are helpful to phytoremediation. Further development of PGP bacteria is very necessary because of the extreme diversity of plants, soils, and heavy metal pollution. A Burkholderia sp. strain, numbered LD-11, was isolated, which showed resistances to multiple heavy metals and antibiotics. It can produce indole-3-acetic acid, 1-aminocyclopropane-1-carboxylic acid deaminase and siderophores. Inoculation with the LD-11 improved germination of seeds of the investigated vegetable plants in the presence of Cu, promoted elongation of roots and hypocotyledonary axes, enhanced the dry weights of the plants grown in the soils polluted with Cu and/or Pb, and increased activity of the soil urease and the rhizobacteria diversity. Inoculation with the LD-11 significantly enhanced Cu and/or Pb accumulation especially in the roots of the plants grown in the polluted soils. Notably, LD-11 could produce siderophores in the presence of Cu. Conclusively, the PGP effects and concurrent heavy metal accumulation in the plant tissues results from combined effects of the above-mentioned multiple factors. Cu is an important element that represses production of the siderophore by the bacteria. Phytoremediation by synergistic use of the investigated plants and the bacterial strain LD-11 is a phytoextraction process.

Optimization of lipase production by Burkholderia sp. using response surface methodology

Response surface methodology (RSM) was employed to optimize the extracellular lipase production by Burkholderia sp. HL-10. Preliminary tests showed that olive oil, tryptone and Tween-80 exhibited significant effects on the lipase production. The optimum concentrations of these three components were determined using a faced-centered central composite design (FCCCD). The analysis of variance revealed that the established model was significant (p < 0.01). The optimized medium containing 0.65% olive oil (v/v), 2.42% tryptone (w/v) and 0.15% Tween-80 (v/v) resulted in a maximum activity of 122.3 U/mL, about three fold higher than that in basal medium. Approximately 99% of validity of the predicted value was achieved.

Identification of elongation factor G as the conserved cellular target of argyrin B

Argyrins, produced by myxobacteria and actinomycetes, are cyclic octapeptides with antibacterial and antitumor activity. Here, we identify elongation factor G (EF-G) as the cellular target of argyrin B in bacteria, via resistant mutant selection and whole genome sequencing, biophysical binding studies and crystallography. Argyrin B binds a novel allosteric pocket in EF-G, distinct from the known EF-G inhibitor antibiotic fusidic acid, revealing a new mode of protein synthesis inhibition. In eukaryotic cells, argyrin B was found to target mitochondrial elongation factor G1 (EF-G1), the closest homologue of bacterial EF-G. By blocking mitochondrial translation, argyrin B depletes electron transport components and inhibits the growth of yeast and tumor cells. Further supporting direct inhibition of EF-G1, expression of an argyrin B-binding deficient EF-G1 L693Q variant partially rescued argyrin B-sensitivity in tumor cells. In summary, we show that argyrin B is an antibacterial and cytotoxic agent that inhibits the evolutionarily conserved target EF-G, blocking protein synthesis in bacteria and mitochondrial translation in yeast and mammalian cells.

Inhibition of Burkholderia multivorans adhesion to lung epithelial cells by bivalent lactosides

Burkholderia cepacia complex (Bcc) is an opportunistic pathogen in cystic fibrosis patients which is inherently resistant to antimicrobial agents. The mechanisms of attachment and pathogenesis of Bcc, a group of 17 species, are poorly understood. The most commonly identified Bcc species in newly colonised patients, Burkholderia multivorans, continues to be acquired from the environment. Development of therapies which can prevent or reduce the risk of colonization on exposure to Bcc in the environment would be a better alternative to antimicrobial agents. Previously, it has been shown that Bcc strains bound to many glycolipid receptors on lung epithelia. Using a real-time PCR method to quantify the levels of binding of B. multivorans to the lung epithelial cells, we have examined glycoconjugate derivatives for their potential to inhibit host cell attachment. Bivalent lactosides previously shown to inhibit galectin binding significantly reduced the attachment of B. multivorans to CF lung epithelial cells at micromolar concentrations. This was in contrast to monosaccharides and lactose, which were only effective in the millimolar range. Development of glycoconjugate therapies such as these, which inhibit attachment to lung epithelial cells, represent an alternative means of preventing infection with inherently antimicrobially resistant pathogens such as B. multivorans.

Twelve positions in a β-lactamase that can expand its substrate spectrum with a single amino acid substitution

The continuous evolution of β-lactamases resulting in bacterial resistance to β-lactam antibiotics is a major concern in public health, and yet the underlying molecular basis or the pattern of such evolution is largely unknown. We investigated the mechanics of the substrate fspectrum expansion of the class A β-lactamase using PenA of Burkholderia thailandensis as a model. By analyzing 516 mutated enzymes that acquired the ceftazidime-hydrolyzing activity, we found twelve positions with single amino acid substitutions (altogether twenty-nine different substitutions), co-localized at the active-site pocket area. The ceftazidime MIC (minimum inhibitory concentration) levels and the relative frequency in the occurrence of substitutions did not correlate well with each other, and the latter appeared be largely influenced by the intrinsic mutational biases present in bacteria. Simulation studies suggested that all substitutions caused a congruent effect, expanding the space in a conserved structure called the omega loop, which in turn increased flexibility at the active site. A second phase of selection, in which the mutants were placed under increased antibiotic pressure, did not result in a second mutation in the coding region, but a mutation that increased gene expression arose in the promoter. This result suggests that the twelve amino acid positions and their specific substitutions in PenA may represent a comprehensive repertoire of the enzyme's adaptability to a new substrate. These mapped substitutions represent a comprehensive set of general mechanical paths to substrate spectrum expansion in class A β-lactamases that all share a functional evolutionary mechanism using common conserved residues.

In vitro antibacterial activity of sphaeropsidins and chemical derivatives toward Xanthomonas oryzae pv. oryzae, the causal agent of rice bacterial blight

Sphaeropsidin A, the main phytotoxin produced by Diplodia cupressi, as well as the two natural analogues sphaeropsidins B and C and 14 derivatives obtained by chemical modifications were assayed for antibacterial activity against Xanthomonas oryzae pv. oryzae, Pseudomonas fuscovaginae, and Burkholderia glumae, the causal agents of severe bacterial rice diseases. The results showed a strong and specific activity of sphaeropsidin A against X. oryzae pv. oryzae, while no activity was observed against the other two pathogens. The results of structure-activity relationship studies showed that structural features important to impart this antibacterial activity are the presence of the C-7 carbonyl group and the hemiketalic lactone functionality. The C-13 vinyl group, the double bond of ring C, and/or the tertiary C-9 hydroxy group, as well as the pimarane arrangement of the tricylic carbon skeleton, were also important for the antibacterial activity. These findings may be useful in designing novel compounds for practical applications in agriculture.

Alteration in cell surface properties of Burkholderia spp. during surfactant-aided biodegradation of petroleum hydrocarbons

Chemical surfactants may impact microbial cell surface properties, i.e., cell surface hydrophobicity (CSH) and cell surface charge, and may thus affect the uptake of components from non-aqueous phase liquids (NAPLs). This work explored the impact of Triton X-100, Igepal CA 630, and Tween 80 (at twice the critical micelle concentration, CMC) on the cell surface characteristics of Burkholderia cultures, Burkholderia cepacia (ES1, aliphatic degrader) and Burkholderia multivorans (NG1, aromatic degrader), when grown on a six-component model NAPL. In the presence of Triton X-100, NAPL biodegradation was enhanced from 21% to 60% in B. cepacia and from 18% to 53% in B. multivorans. CSH based on water contact angle (50-52°) was in the same range for both strains while zeta potential at neutral pH was -38 and -31 mV for B. cepacia and B. multivorans, respectively. In the presence of Triton X-100, their CSH increased to greater than 75° and the zeta potential decreased. This induced a change in the mode of uptake and initiated aliphatic hydrocarbon degradation by B. multivorans and increased the rate of aliphatic hydrocarbon degradation in B. cepacia. Igepal CA 630 and Tween 80 also altered the cell surface properties. For B. cepacia grown in the presence of Triton X-100 at two and five times its CMC, CSH increased significantly in the log growth phase. Growth in the presence of the chemical surfactants also affected the abundance of chemical functional groups on the cell surface. Cell surface changes had maximum impact on NAPL degradation in the presence of emulsifying surfactants, Triton X-100 and Igepal CA630.

Transcript amplification from single bacterium for transcriptome analysis

Total transcript amplification (TTA) from single eukaryotic cells for transcriptome analysis is established, but TTA from a single prokaryotic cell presents additional challenges with much less starting material, the lack of poly(A)-tails, and the fact that the messages can be polycistronic. Here, we describe a novel method for single-bacterium TTA using a model organism, Burkholderia thailandensis, exposed to a subinhibitory concentration of the antibacterial agent, glyphosate. Utilizing a B. thailandensis microarray to assess the TTA method showed low fold-change bias (less than twofold difference and Pearson correlation coefficient R ≈ 0.87-0.89) and drop-outs (4%-6% of 2842 detectable genes), compared with data obtained from the larger-scale nonamplified RNA samples. Further analysis of the microarray data suggests that B. thailandensis, when exposed to the aromatic amino acid biosynthesis inhibitor glyphosate, induces (or represses) genes to possibly recuperate and balance the intracellular amino acid pool. We validated our single-cell microarray data at the multi-cell and single-cell levels with lacZ and gfp reporter-gene fusions, respectively. Sanger sequencing of 192 clones generated from the TTA product of a single cell, with and without enrichment by elimination of rRNA and tRNA, detected only B. thailandensis sequences with no contamination. These data indicate that RNA-seq of TTA from a single cell is possible using this novel method.

Evolution of an endofungal lifestyle: Deductions from the Burkholderia rhizoxinica genome

BACKGROUND

Burkholderia rhizoxinica is an intracellular symbiont of the phytopathogenic zygomycete Rhizopus microsporus, the causative agent of rice seedling blight. The endosymbiont produces the antimitotic macrolide rhizoxin for its host. It is vertically transmitted within vegetative spores and is essential for spore formation of the fungus. To shed light on the evolution and genetic potential of this model organism, we analysed the whole genome of B. rhizoxinica HKI 0454 - a type strain of endofungal Burkholderia species.

RESULTS

The genome consists of a structurally conserved chromosome and two plasmids. Compared to free-living Burkholderia species, the genome is smaller in size and harbors less transcriptional regulator genes. Instead, we observed accumulation of transposons over the genome. Prediction of primary metabolic pathways and transporters suggests that endosymbionts consume host metabolites like citrate, but might deliver some amino acids and cofactors to the host. The rhizoxin biosynthesis gene cluster shows evolutionary traces of horizontal gene transfer. Furthermore, we analysed gene clusters coding for nonribosomal peptide synthetases (NRPS). Notably, B. rhizoxinica lacks common genes which are dedicated to quorum sensing systems, but is equipped with a large number of virulence-related factors and putative type III effectors.

CONCLUSIONS

B. rhizoxinica is the first endofungal bacterium, whose genome has been sequenced. Here, we present models of evolution, metabolism and tools for host-symbiont interaction of the endofungal bacterium deduced from whole genome analyses. Genome size and structure suggest that B. rhizoxinica is in an early phase of adaptation to the intracellular lifestyle (genome in transition). By analysis of tranporters and metabolic pathways we predict how metabolites might be exchanged between the symbiont and its host. Gene clusters for biosynthesis of secondary metabolites represent novel targets for genomic mining of cryptic natural products. In silico analyses of virulence-associated genes, secreted proteins and effectors might inspire future studies on molecular mechanisms underlying bacterial-fungal interaction.

In vitro susceptibility of Burkholderia vietnamiensis to aminoglycosides

Burkholderia cepacia complex (BCC) bacteria are opportunistic pathogens that can cause severe disease in cystic fibrosis (CF) patients and other immunocompromised individuals and are typically multidrug resistant. Here we observed that unlike other BCC species, most environmental and clinical Burkholderia vietnamiensis isolates were intrinsically susceptible to aminoglycosides but not to cationic antimicrobial peptides or polymyxin B. Furthermore, strains acquired aminoglycoside resistance during chronic CF infection, a phenomenon that could be induced under tobramycin or azithromycin pressure in vitro. In comparing susceptible and resistant B. vietnamiensis isolates, no gross differences in lipopolysaccharide structure were observed, all had lipid A-associated 4-amino-4-deoxy-L-arabinose residues, and all were resistant to the permeabilizing effects of aminoglycosides, a measure of drug entry via self-promoted uptake. However, susceptible isolates accumulated 5 to 6 times more gentamicin than a resistant isolate, and aminoglycoside susceptibility increased in the presence of an efflux pump inhibitor. B. vietnamiensis is therefore unusual among BCC bacteria in its susceptibility to aminoglycosides and capacity to acquire resistance. Aminoglycoside resistance appears to be due to decreased cellular accumulation as a result of active efflux.

Analogues of peptide SMAP-29 with comparable antimicrobial potency and reduced cytotoxicity

SMAP-29 (sheep myeloid antimicrobial peptide-29) is a peptide with potent antibacterial properties. However, it is also highly cytotoxic both to human red blood cells (hRBCs) and human embryonic kidney (HEK) cells. In this study, some of the amino acids of SMAP-29 were changed in an attempt to reduce haemolytic activity whilst maintaining high antibacterial efficacy. These analogues, plus other analogues described in the literature with potent antimicrobial activity against Gram-positive bacteria coupled with no or low haemolytic activity, were evaluated for their cytotoxicity (hRBCs and HEK cells) as well as antimicrobial efficacy against two Gram-positive (Bacillus anthracis and Bacillus globigii) and two Gram-negative bacteria (Escherichia coli and Burkholderia thailandensis). The analogues previously described in the literature were found to have low antibacterial and haemolytic activity. Two of the designed analogues had comparable antibacterial efficacy with SMAP-29 against B. anthracis but reduced haemolytic activity and therefore had a therapeutic index that was enhanced 2.3-2.6-fold over that of SMAP-29.

Efficacy of various chemical disinfectants on biofilms formed in spacecraft potable water system components

As the provision of potable water is critical for successful habitation of the International Space Station (ISS), life support systems were installed in December 2008 to recycle both humidity from the atmosphere and urine to conserve available water in the Station. In-flight pre-consumption testing from the dispensing needle at the Potable Water Dispenser (PWD) indicated that bacterial concentrations exceeded the current ISS specifications of 50 colony-forming units (CFU) ml(-1). Subsequent investigations revealed that a corrugated stainless steel flex hose upstream of the dispensing needle in the PWD was filled with nonsterile water and left at room temperature for more than 1 month before launch. To simulate biofilm formation that was suspected in the flight system, sterile flex hoses were seeded with a consortium of bacterial isolates previously recovered from other ISS water systems, including Ralstonia pickettii, Burkholderia multivorans, Caulobacter vibrioides, and Cupriavidus pauculus. After incubation for 5 days, the hoses were challenged with various chemical disinfectants including hydrogen peroxide (H2O2), colloidal silver, and buffered pH solutions to determine the ability of the disinfectants to decrease and maintain bacterial concentrations below ISS specifications. The disinfection efficacy over time was measured by collecting daily heterotrophic plate counts after exposure to the disinfectants. A single flush with either 6% H2O2 solution or a mixture of 3% H2O2 and 400 ppb colloidal silver effectively reduced the bacterial concentrations to <1 CFU ml(-1) for a period of up to 3 months.

Effects of pesticides on the bacterial production of pyrrolnitrin

Pyrrolnitrin is a halogenated bacterial metabolite with antifungal and antibacterial activities which served as a lead structure of synthetic fungicides. Several pyrrolnitrin-producing bacteria are considered to be promising biopesticides. However, the application of these microorganisms is not straightforward since many synthetic pesticides usually coexist in agricultural fields and inevitably affect the efficacy of biocontrol agents. In this regard, effects of 25 xenobiotics, including 18 pesticides, were investigated for pyrrolnitrin biosynthesis by Burkholderia sp. O33 and Pseudomonas fluorescens Pf-5. Strong inhibition of pyrrolnitrin synthesis was observed in 9 chemicals, including 6 pesticides, while glyphosate and validamycin enhance biosynthesis. Fenpiclonil and fludioxonil strongly inhibit the oxidative transformation of aminopyrrolnitrin to pyrrolnitrin. Halogenation reaction to aminopyrrolnitrin was reduced by methimazole, a well-known flavin-dependent monooxygenase inhibitor. Most pesticides gave moderate growth inhibitory effects. The results suggested that synthetic chemicals can modulate the efficacy of pyrrolnitrin producing bacteria, through the inhibition of cell growth or pyrrolnitrin biosynthesis. Pathway specific inhibition by fenpiclonil, fludioxonil, and methimazole will give structural insights of corresponding enzymes.

p-Nitrophenol degradation via 4-nitrocatechol in Burkholderia sp. SJ98 and cloning of some of the lower pathway genes

Microbial degradation studies have pointed toward the occurrence of two distinct PNP catabolic pathways in Gram positive and Gram negative bacteria. The former involves 4-nitrocatechol (4-NC), 1,2,4-benzenetriol (BT), and maleylacetate (MA) as major degradation intermediates, whereas the later proceeds via formation of 1,4-benzoquinone (BQ) and hydroquinone (HQ). In the present study we identified a Gram negative organism viz. Burkholderia sp. strain SJ98 that degrades PNP via 4NC, BT, and MA. A 6.89 Kb genomic DNA fragment of strain SJ98 that encompasses seven putatively identified ORFs (orfA, pnpD, pnpC, orfB, orfC, orfD, and orfE) was cloned. PnpC is benzenetriol dioxygenase belonging to the intradiol dioxygenase superfamily, whereas PnpD is identified as maleylacetate reductase, a member of the Fe-ADH superfamily showing NADH dependent reductase activity. The in vitro activity assays carried out with purified pnpC and pnpD (btd and mar) gene products transformed BT to MA and MA to beta-ketoadipate, respectively. The cloning, sequencing, and characterization of these genes along with the functional PNP degradation studies ascertained the involvement of 4-NC, BT, and MA as degradation intermediates of PNP pathway in this strain. This is one of the first conclusive reports for 4-NC and BT mediated degradation of PNP in a Gram negative organism.

Carboxymethyl-beta-cyclodextrin mitigates toxicity of cadmium, cobalt, and copper during naphthalene biodegradation

Hazardous waste sites are commonly contaminated with both organic and metal pollutants. Many metal pollutants have been shown to inhibit organic pollutant biodegradation. We investigated the ability of a modified, polydentate cyclodextrin (carboxymethyl-beta-cyclodextrin, CMCD) to reduce the toxicity of 33.4 microM cadmium, cobalt or copper during naphthalene degradation by a Burkholderia sp. in 120 h aerobic, batch studies. The highest investigated concentration of CMCD, 3340 microM, reduced cadmium, cobalt, and copper toxicity. With each metal, the length of the lag phase was reduced (by as much as 108 h with cobalt or copper), the cell yield was increased (by as much as a factor of 16 with cobalt), and the growth rate was increased (by as much as a factor of 31 with cobalt). The degrader was unable to use CMCD as the sole source of carbon and energy. Our data suggest that the ability of CMCD to complex metals plays an important role in its ability to mitigate metal toxicity and that CMCD has the potential to enhance biodegradation in organic and metal co-contaminated environments.

Transgenic tomato plants alter quorum sensing in plant growth-promoting rhizobacteria

Two Gram-negative, plant growth-promoting rhizobacteria (PGPRs), denominated as M12 and M14, were classified by 16S rDNA sequencing as Burkholderia graminis species. Both strains were shown to produce a variety of N-acyl-homoserine lactone (AHL) quorum sensing (QS) signalling molecules. The involvement of these molecules in plant growth promotion and the induction of protection against salt stress was examined. AHL production was evaluated in vitro by thin-layer chromatography using AHL biosensors, and the identity of the AHLs produced was determined by liquid chromatography-tandem mass spectrometry. The in situ production of AHLs by M12 and M14 in the rhizosphere of Arabidopsis thaliana plants was detected by co-inoculation with green fluorescent protein-based biosensor strains and confocal laser scanning microscopy. To determine whether plant growth promotion and protection against salt stress were mediated by QS, these PGPRs were assayed on wild-type tomato plants, as well as their corresponding transgenics expressing YenI (short-chain AHL producers) and LasI (long-chain AHL producers). In wild-type tomato plants, only M12 promoted plant growth, and this effect disappeared in both transgenic lines. In contrast, M14 did not promote growth in wild-type tomatoes, but did so in the LasI transgenic line. Resistance to salt stress was induced by M14 in wild-type tomato, but this effect disappeared in both transgenic lines. The strain M12, however, did not induce salt resistance in wild-type tomato, but did so in LasI tomato plants. These results reveal that AHL QS signalling molecules mediate the ability of both PGPR strains M12 and M14 to promote plant growth and to induce protection against salt stress.

Isolation and characterization of a heavy metal-resistant Burkholderia sp. from heavy metal-contaminated paddy field soil and its potential in promoting plant growth and heavy metal accumulation in metal-polluted soil

A heavy metal-resistant bacterial strain was isolated from heavy metal-contaminated soils and identified as Burkholderia sp. J62 based on the 16S rDNA gene sequence analysis. The heavy metal- and antibiotic resistance, heavy metal solubilization of the isolate were investigated. The isolate was also evaluated for promoting plant growth and Pb and Cd uptakes of the plants from heavy metal-contaminated soils in pot experiments. The isolate was found to exhibit different multiple heavy metal and antibiotic resistance characteristics. Atomic absorption spectrometer analysis showed increased bacterial solubilization of lead and cadmium in solution culture and in soils. The isolate produced indole acetic acid, siderophore and 1-aminocyclopropane-1-carboxylate deaminase. The isolate also solubilized inorganic phosphate. Inoculation with the isolate was found to significantly (p<0.05) increase the biomass of maize and tomato plants. Increase in tissue Pb and Cd contents varied from 38% to 192% and from 5% to 191% in inoculated plants growing in heavy metal-contaminated soils compared to the uninoculated control, respectively. These results show that heavy metal-solubilizing and plant growth promoting bacteria are important for plant growth and heavy metal uptake which may provide a new microbial enhanced-phytoremediation of metal-polluted soils.

Physiological and toxicological characterization of an engineered whole-cell biosensor

Bioluminescence-based bacterial biosensors are often reported as reliable and efficient tools for risk assessment and environmental monitoring. However, there are few data comparing the metabolism of genetically engineered strains to the corresponding wild type. A pollutant-degrading bacterium capable of mineralising 2,4-dichlorophenoxyacetic acid (2,4-D), Burkholderia sp. strain RASC c2, was genetically engineered to produce light constitutively and tested for assessing the main causes of biodegradation constraint affected by growth rates, toxicity, bioavailability and metal speciation in complex environments. This research focuses on such aspects by characterizing two pollutant-degrading isolates, the wild type and the genetically engineered biosensor (lux-marked). Degradation and growth rates of both isolates were assessed with different concentrations of 2,4-D as the sole carbon source. Kinetic rates were affected by initial concentration of substrate and isolates showed distinct growth rates at different 2,4-D concentrations. Toxic effects of zinc and copper were also comparatively assessed using a dehydrogenase assay and light output. The isolates were sensitive to both metals and at similar EC(50) values. Therefore, bioluminescence response of the lux-marked isolate accurately reflected the toxic response of the parental organism towards zinc and copper, making it an ideal test-organism for assessing toxicity in the context of pollutant mineralization.

Bacterial diversity in soil enrichment cultures amended with 2 (2-methyl-4-chlorophenoxy) propionic acid (mecoprop)

Summary The tfdA gene encodes for an alpha-ketoglutarate-dependent dioxygenase enzyme which catalyses the first step of the degradation of phenoxyalkanoic acid herbicides such as 2 (2-methyl-4-chlorophenoxy) propionic acid (mecoprop). The bacterial diversity of soil enrichment cultures containing mecoprop was examined by Denaturing Gradient Gel Electrophoresis (DGGE) and clone libraries of both 16S rRNA genes and tfdA genes. The 16S rRNA gene sequences were diverse and clustered with either the Beta- or Gammaproteobacteria. The 16S rRNA gene sequence from a bacterial strain isolated from an enrichment culture, grown on R-mecoprop, which represented a dominant band in the DGGE profiles, had a high 16S rRNA sequence identity (100%) to Burkholderia glathei. This is the first report that B. glathei is implicated in mecoprop degradation. PCR amplification of the tfdA genes detected class III tfdA genes only, and no class I or class II tfdA sequences were detected. To understand the genes involved the degradation of specific mecoprop (R-) and (S-) enantiomers, oligonucleotide probes targeting the tfdA, rdpA, sdpA and cadA genes were hybridized to DNA extracted from enrichment cultures grown on either R-mecoprop or (R/S) racemic mecoprop. Strong hybridization signals were obtained with sdpA and tfdA probes using DNA extracted from cultures grown on racemic mecoprop. A strong hybridization signal was also obtained with the rdpA probe with DNA extracted from the cultures grown on R-mecoprop. This suggests the rdpA gene is involved in R-mecoprop degradation while tfdA, sdpA and cadA genes are involved in the degradation of both R- and S-mecoprop.