Bacterial intracellular nanoparticles exhibiting antioxidant properties and the significance of their formation in ROS detoxification.

Biogenic magnetic nanoparticles (BMNPs) can be formed by numerous microorganisms. However, the significance of their formation and their possible functions have not been explored in detail. To explore a possible function of Fe3 O4 NPs in Burkholderia sp. strain YN01, we investigated their catalytic abilities in the elimination of intracellular reactive oxygen species (ROS). Changes in ROS content under different conditions were assessed and showed that low oxygen and high iron concentrations in the growth medium promoted ROS production. However, the levels of ROS gradually decreased with BMNP formation, suggesting that these particles possess intrinsic superoxide dismutase (SOD)-like activity and catalase (CAT)-like activity, as proven in this study. To ensure that the observed ROS decrease was not due to antioxidase overexpression caused by the oxidative stress response, SOD and CAT were inhibited in vivo to analyse the ROS variation and BMNP yield under microoxic and high-iron conditions respectively. The results demonstrated that the formation of these intracellular iron nanoparticles was required for the efficient scavenging of excess ROS, which was dependent on their antioxidase-like properties. This result reveals a novel physiological function of biogenic intracellular Fe3 O4 nanoparticles.

Enhancing methyl parathion degradation by the immobilization of Burkholderia sp. isolated from agricultural soils.

Organophosphate pesticides are of great interest for research because they are currently the most commonly used pesticides. In this study, a bacterial strain capable of completely degrading methyl parathion (MP) was isolated from agricultural soils in central Mexico. This strain was designated strain S5-2 and was identified as Burkholderia cenocepacia. To increase degradation yields, cells were immobilized on three different supports: powdered zeolite and Opuntia sp. and Agave sp. fibers. The results indicated a significant increase in MP hydrolysis and p-nitrophenol (PNP) degradation with immobilized cells compared to free cell cultures. Furthermore, immobilized cells were capable of withstanding and degrading higher concentrations of PNP compared to cell suspension cultures. The cell viability in the free cell cultures, as well as PNP degradation, was affected at concentrations greater than 25 mg/L. In contrast, cells immobilized on Opuntia sp. and Agave sp. fibers completely degraded PNP at concentrations of 100 mg/L. To verify that MP solution toxicity was decreased by B. cenocepacia strain S5-2 via pesticide degradation, we measured the acetylcholinesterase activity, both before and after treatment with bacteria. The results demonstrate that the activity of acetylcholinesterase was unaffected after MP degradation by bacteria.

Insights into selenite reduction and biogenesis of elemental selenium nanoparticles by two environmental isolates of Burkholderia fungorum.

Microorganisms capable of transforming toxic selenium oxyanions into non-toxic elemental selenium (Se°) may be considered as biocatalysts for the production of selenium nanoparticles (SeNPs), eventually exploitable in different biotechnological applications. Two Burkholderia fungorum strains (B. fungorum DBT1 and B. fungorum 95) were monitored during their growth for both capacity and efficiency of selenite (SeO32-) reduction and elemental selenium formation. Both strains are environmental isolates in origin: B. fungorum DBT1 was previously isolated from an oil refinery drainage, while B. fungorum 95 has been enriched from inner tissues of hybrid poplars grown in a soil contaminated by polycyclic aromatic hydrocarbons. Our results showed that B. fungorum DBT1 is able to reduce 0.5mM SeO32- to Se° when cultured aerobically in liquid medium at 27°C, while B. fungorum 95 can reduce more than 1mM SeO32- to Se° within 96h under the same growth conditions, with the appearance of SeNPs in cultures of both bacterial strains. Biogenic SeNPs were spherical, with pH-dependent charge and an average hydrodynamic diameter of 170nm and 200nm depending on whether they were produced by B. fungorum 95 or B. fungorum DBT1, respectively. Electron microscopy analyses evidenced that Se nanoparticles occurred intracellularly and extracellularly. The mechanism of SeNPs formation can be tentatively attributed to cytoplasmic enzymatic activation mediated by electron donors. Biogenic nanoparticles were then probably released outside the bacterial cells as a consequence of a secretory process or cell lysis. Nevertheless, formation of elemental selenium nanoparticles under aerobic conditions by B. fungorum DBT1 and B. fungorum 95 is likely due to intracellular reduction mechanisms. Biomedical and other high tech sectors might exploit these biogenic nanoparticles in the near future, once fully characterized and tested for their multiple properties.

Crosstalk between sugarcane and a plant-growth promoting Burkholderia species.

Bacterial species in the plant-beneficial-environmental clade of Burkholderia represent a substantial component of rhizosphere microbes in many plant species. To better understand the molecular mechanisms of the interaction, we combined functional studies with high-resolution dual transcriptome analysis of sugarcane and root-associated diazotrophic Burkholderia strain Q208. We show that Burkholderia Q208 forms a biofilm at the root surface and suppresses the virulence factors that typically trigger immune response in plants. Up-regulation of bd-type cytochromes in Burkholderia Q208 suggests an increased energy production and creates the microaerobic conditions suitable for BNF. In this environment, a series of metabolic pathways are activated in Burkholderia Q208 implicated in oxalotrophy, microaerobic respiration, and formation of PHB granules, enabling energy production under microaerobic conditions. In the plant, genes involved in hypoxia survival are up-regulated and through increased ethylene production, larger aerenchyma is produced in roots which in turn facilitates diffusion of oxygen within the cortex. The detected changes in gene expression, physiology and morphology in the partnership are evidence of a sophisticated interplay between sugarcane and a plant-growth promoting Burkholderia species that advance our understanding of the mutually beneficial processes occurring in the rhizosphere.

Bacteria belonging to the genus Burkholderia are obligatory symbionts of the eriococcids Acanthococcus aceris Signoret, 1875 and Gossyparia spuria (Modeer, 1778) (Insecta, Hemiptera, Coccoidea).

In the fat body cells of the scale insects, Gossyparia spuria and Acanthococcus aceris, numerous rod-shaped symbiotic bacteria occur. Molecular analyses have revealed that these microorganisms are closely related to the widely distributed bacterium Burkholderia. Ultrastructural observations have revealed that the bacteria are transovarially (vertically) transmitted from the mother to offspring. The microorganisms leave the fat body cells and invade ovarioles containing vitellogenic oocytes. They pass through the follicular epithelium in the neck region of the ovariole and enter the perivitelline space. Next, the symbionts infest the anterior region of the oocyte.

Activity of Tobramycin against Cystic Fibrosis Isolates of Burkholderia cepacia Complex Grown as Biofilms.

Pulmonary infection with Burkholderia cepacia complex in cystic fibrosis (CF) patients is associated with more-rapid lung function decline and earlier death than in CF patients without this infection. In this study, we used confocal microscopy to visualize the effects of various concentrations of tobramycin, achievable with systemic and aerosolized drug administration, on mature B. cepacia complex biofilms, both in the presence and absence of CF sputum. After 24 h of growth, biofilm thickness was significantly reduced by exposure to 2,000 µg/ml of tobramycin for Burkholderia cepacia, Burkholderia multivorans, and Burkholderia vietnamiensis; 200 µg/ml of tobramycin was sufficient to reduce the thickness of Burkholderia dolosa biofilm. With a more mature 48-h biofilm, significant reductions in thickness were seen with tobramycin at concentrations of ≥100 µg/ml for all Burkholderia species. In addition, an increased ratio of dead to live cells was observed in comparison to control with tobramycin concentrations of ≥200 µg/ml for B. cepacia and B. dolosa (24 h) and ≥100 µg/ml for Burkholderia cenocepacia and B. dolosa (48 h). Although sputum significantly increased biofilm thickness, tobramycin concentrations of 1,000 µg/ml were still able to significantly reduce biofilm thickness of all B. cepacia complex species with the exception of B. vietnamiensis. In the presence of sputum, 1,000 µg/ml of tobramycin significantly increased the dead-to-live ratio only for B. multivorans compared to control. In summary, although killing is attenuated, high-dose tobramycin can effectively decrease the thickness of B. cepacia complex biofilms, even in the presence of sputum, suggesting a possible role as a suppressive therapy in CF.

Competition between Burkholderia pseudomallei and B. thailandensis.

BACKGROUND: Burkholderia pseudomallei is a Gram-negative bacterium that causes melioidosis, an often fatal disease in tropical countries. Burkholderia thailandensis is a non-virulent but closely related species. Both species are soil saprophytes but are almost never isolated together. RESULTS: We identified two mechanisms by which B. pseudomallei affects the growth of B. thailandensis. First, we found that six different isolates of B. pseudomallei inhibited the growth of B. thailandensis on LB agar plates. Second, our results indicated that 55% of isolated strains of B. pseudomallei produced a secreted compound that inhibited the motility but not the viability of B. thailandensis. Analysis showed that the active compound was a pH-sensitive and heat-labile compound, likely a protein, which may affect flagella processing or facilitate their degradation. Analysis of bacterial sequence types (STs) demonstrated an association between this and motility inhibition. The active compound was produced from B. pseudomallei during the stationary growth phase. CONCLUSION: Taken together, our results indicate that B. pseudomallei inhibits both the growth and motility of its close relative B. thailandensis. The latter phenomenon appears to occur via a previously unreported mechanism involving flagellar processing or degradation.

Active invasion of bacteria into living fungal cells.

The rice seedling blight fungus Rhizopus microsporus and its endosymbiont Burkholderia rhizoxinica form an unusual, highly specific alliance to produce the highly potent antimitotic phytotoxin rhizoxin. Yet, it has remained a riddle how bacteria invade the fungal cells. Genome mining for potential symbiosis factors and functional analyses revealed that a type 2 secretion system (T2SS) of the bacterial endosymbiont is required for the formation of the endosymbiosis. Comparative proteome analyses show that the T2SS releases chitinolytic enzymes (chitinase, chitosanase) and chitin-binding proteins. The genes responsible for chitinolytic proteins and T2SS components are highly expressed during infection. Through targeted gene knock-outs, sporulation assays and microscopic investigations we found that chitinase is essential for bacteria to enter hyphae. Unprecedented snapshots of the traceless bacterial intrusion were obtained using cryo-electron microscopy. Beyond unveiling the pivotal role of chitinolytic enzymes in the active invasion of a fungus by bacteria, these findings grant unprecedented insight into the fungal cell wall penetration and symbiosis formation.

Membrane-active mechanism of LFchimera against Burkholderia pseudomallei and Burkholderia thailandensis.

LFchimera, a construct combining two antimicrobial domains of bovine lactoferrin, lactoferrampin265-284 and lactoferricin17-30, possesses strong bactericidal activity. As yet, no experimental evidence was presented to evaluate the mechanisms of LFchimera against Burkholderia isolates. In this study we analyzed the killing activity of LFchimera on the category B pathogen Burkholderia pseudomallei in comparison to the lesser virulent Burkholderia thailandensis often used as a model for the highly virulent B. pseudomallei. Killing kinetics showed that B. thailandensis E264 was more susceptible for LFchimera than B. pseudomallei 1026b. Interestingly the bactericidal activity of LFchimera appeared highly pH dependent; B. thailandensis killing was completely abolished at and below pH 6.4. FITC-labeled LFchimera caused a rapid accumulation within 15 min in the cytoplasm of both bacterial species. Moreover, freeze-fracture electron microscopy demonstrated extreme effects on the membrane morphology of both bacterial species within 1 h of incubation, accompanied by altered membrane permeability monitored as leakage of nucleotides. These data indicate that the mechanism of action of LFchimera is similar for both species and encompasses disruption of the plasma membrane and subsequently leakage of intracellular nucleotides leading to cell dead.

A single-cell imaging screen reveals multiple effects of secreted small molecules on bacteria.

Bacteria cells exist in close proximity to other cells of both the same and different species. Bacteria secrete a large number of different chemical species, and the local concentrations of these compounds at the surfaces of nearby cells may reach very high levels. It is fascinating to imagine how individual cells might sense and respond to the complex mix of signals at their surface. However, it is difficult to measure exactly what the local environmental composition looks like, or what the effects of individual compounds on nearby cells are. Here, an electron microscopy imaging screen was designed that would detect morphological changes induced by secreted small molecules. This differs from conventional approaches by detecting structural changes in individual cells rather than gene expression or growth rate changes at the population level. For example, one of the changes detected here was an increase in outer membrane vesicle production, which does not necessarily correspond to a change in gene expression. This initial study focussed on Pseudomonas aeruginosa, Escherichia coli, and Burkholderia dolosa, and revealed an intriguing range of effects of secreted small molecules on cells both within and between species.

Gene and protein expression in response to different growth temperatures and oxygen availability in Burkholderia thailandensis.

Burkholderia thailandensis, although normally avirulent for mammals, can infect macrophages in vitro and has occasionally been reported to cause pneumonia in humans. It is therefore used as a model organism for the human pathogen B. pseudomallei, to which it is closely related phylogenetically. We characterized the B. thailandensis clinical isolate CDC2721121 (BtCDC272) at the genome level and studied its response to environmental cues associated with human host colonization, namely, temperature and oxygen limitation. Effects of the different growth conditions on BtCDC272 were studied through whole genome transcription studies and analysis of proteins associated with the bacterial cell surface. We found that growth at 37°C, compared to 28°C, negatively affected cell motility and flagella production through a mechanism involving regulation of the flagellin-encoding fliC gene at the mRNA stability level. Growth in oxygen-limiting conditions, in contrast, stimulated various processes linked to virulence, such as lipopolysaccharide production and expression of genes encoding protein secretion systems. Consistent with these observations, BtCDC272 grown in oxygen limitation was more resistant to phagocytosis and strongly induced the production of inflammatory cytokines from murine macrophages. Our results suggest that, while temperature sensing is important for regulation of B. thailandensis cell motility, oxygen limitation has a deeper impact on its physiology and constitutes a crucial environmental signal for the production of virulence factors.

Symbiotic ß-proteobacteria beyond legumes: Burkholderia in Rubiaceae.

Symbiotic ß-proteobacteria not only occur in root nodules of legumes but are also found in leaves of certain Rubiaceae. The discovery of bacteria in plants formerly not implicated in endosymbiosis suggests a wider occurrence of plant-microbe interactions. Several ß-proteobacteria of the genus Burkholderia are detected in close association with tropical plants. This interaction has occurred three times independently, which suggest a recent and open plant-bacteria association. The presence or absence of Burkholderia endophytes is consistent on genus level and therefore implies a predictive value for the discovery of bacteria. Only a single Burkholderia species is found in association with a given plant species. However, the endophyte species are promiscuous and can be found in association with several plant species. Most of the endophytes are part of the plant-associated beneficial and environmental group, but others are closely related to B. glathei. This soil bacteria, together with related nodulating and non-nodulating endophytes, is therefore transferred to a newly defined and larger PBE group within the genus Burkholderia.

Burkholderia dabaoshanensis sp. nov., a heavy-metal-tolerant bacteria isolated from Dabaoshan mining area soil in China.

Heavy-metal-tolerant bacteria, GIMN1.004(T), was isolated from mine soils of Dabaoshan in South China, which were acidic (pH 2-4) and polluted with heavy metals. The isolation was Gram-negative, aerobic, non-spore-forming, and rod-shaped bacteria having a cellular width of 0.5-0.6 µm and a length of 1.3-1.8 µm. They showed a normal growth pattern at pH 4.0-9.0 in a temperature ranging from 5 °C to 40 °C.The organism contained ubiquinone Q-8 as the predominant isoprenoid quinine, and C(16:0), summed feature 8 (C(18:1)ω7c and C(18:1)ω6c), C(18:0), summed feature 3 (C(16:1)ω7c or iso-C(15:0) 2-OH), C(17:0) cyclo, C(18:1)ω9c, C(19:0) cyclo ω8c, C(14:0) as major fatty acid. These profiles were similar to those reported for Burkholderia species. The DNA G+C % of this strain was 61.6%. Based on the similarity to 16S rRNA gene sequence, GIMN1.004(T) was considered to be in the genus Burkholderia. The similarities of 16S rRNA gene sequence between strain GIMN1.004(T) and members of the genus Burkholderia were 96-99.4%, indicating that this novel strain was phylogenetically related to members of that genus. The novel strain showed the highest sequence similarities to Burkholderia soli DSM 18235(T) (99.4%); Levels of DNA-DNA hybridization with DSM 18235(T) was 25%. Physiological and biochemical tests including cell wall composition analysis, differentiated phenotype of this strain from that closely related Burkholderia species. The isolation had great tolerance to cadmium with MIC of 22 mmol/L, and adsorbability of 144.94 mg/g cadmium,and it was found to exhibit antibiotic resistance characteristics. The adsorptive mechanism of GIMN1.004(T) for cadmium depended on the action of the amide,carboxy and phosphate of cell surface and producing low-molecular-weight (LMW) organic acids to complex or chelated Cd(2+).Therefore, the strain GIMN1.004(T) represented a new cadmium resistance species, which was tentatively named as Burkholderia dabaoshanensis sp. nov. The strain type is GIMN1.004(T) (= CCTCC M 209109(T) = NRRL B-59553(T)).

Molecular basis for different levels of tet(M) expression in Streptococcus pneumoniae clinical isolates.

Seventy-four unrelated clinical isolates of Streptococcus pneumoniae harboring the tet(M) gene were studied. Seven strains with low tetracycline (Tc) MICs (0.25 to 0.5 µg/ml) were found to harbor truncated tet(M) alleles that were inactivated by different frameshift mutations. In contrast, five strains bore deletions in the tet(M) promoter region, among which four displayed increased Tc MICs (16 to 64 µg/ml). The same promoter mutations were detected in Tc-resistant mutants selected in vitro from various susceptible strains. Sequence analysis revealed that these deletions might impede the formation of the transcriptional attenuator located immediately upstream of tet(M). Expression in Enterococcus faecalis of a tet(M) reporter gene transcribed from these promoter mutants conferred a level of Tc resistance similar to that observed in the parental S. pneumoniae strains. These results show that different levels of Tc susceptibility found in clinical isolates of S. pneumoniae can be explained by frameshift mutations within tet(M) and by alterations of the upstream transcriptional attenuator.

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.

Antioxidant compounds improved PCB-degradation by Burkholderia xenovorans strain LB400.

Polychlorobiphenyls (PCBs) are toxic and persistent organic pollutants that are widely distributed in the environment. Burkholderia xenovorans LB400 is capable of degrading aerobically an unusually wide range of PCBs. However, during PCB-degradation B. xenovorans LB400 generates reactive oxygen species (ROS) that affect its viability. The aim of this study was to increase the efficiency of PCB-degradation of B. xenovorans LB400 by adding antioxidant compounds that could increase tolerance to oxidative stress. The effect of antioxidant compounds on the growth, morphology and PCB-degradation by B. xenovorans LB400 was evaluated. α-Tocopherol or vitamin E (vitE) and berry extract (BE) increased slightly the growth of strain LB400 on biphenyl, whereas in presence of ascorbic acid or vitamin C (vitC) an inhibition of growth was observed. The growth of B. xenovorans LB400 in glucose was inhibited by the addition of 4-chlorobiphenyl (4-CB). Interestingly, in presence of α-tocopherol the growth of strain LB400 was less affected by 4-CB. By transmission electronic microscopy it was observed that α-tocopherol preserved the cell membranes and improved cell integrity of glucose-grown LB400 cells exposed to 4-CB, suggesting a protective effect of α-tocopherol. Notably, α-tocopherol increased biphenyl and 4-CB degradation by B. xenovorans LB400 in an aqueous solution. The effect of antioxidants compounds on PCB-bioremediation was evaluated in agricultural soil spiked with 2-chlorobiphenyl (2-CB), 4-CB and 2,4'-chlorobiphenyl (2,4'-CB). For bioaugmentation, LB400 cells grown on biphenyl and subsequently incubated with pyruvate were added to the soil. Native soil microbiota was able to remove PCBs. Bioaugmentation with strain LB400 increased strongly the PCB-degradation rate. Bioaugmentation with strain LB400 and biostimulation with α-tocopherol or berry extract increased further the PCB degradation. Half-life of 2,4'-CB decreased by bioaugmentation from 24 days to 4 days and by bioaugmentation in presence of α-tocopherol and berry extract to 2 days. By bioaugmentation with strain LB400, 85% of 2,4'-CB was degraded in 20 days, whereas bioaugmentation with strain LB400 and biostimulation with α-tocopherol or berry extract reduced the time to less than 13 days. This indicates that antioxidant compounds stimulated PCB-degradation in soil. Therefore, the addition of antioxidant compounds constitutes an attractive strategy for the scale-up of aerobic PCB-bioremediation processes.

Antibacterial activity and mechanism of action of chitosan solutions against apricot fruit rot pathogen Burkholderia seminalis.

The in vitro antibacterial activity and mechanism of action of two kinds of acid-soluble chitosan and one water-soluble chitosan against apricot fruit rot pathogen Burkholderia seminalis was examined in this study. Results showed that water-soluble chitosan displayed limited antibacterial activity at four tested concentrations. However, two kinds of acid-soluble chitosan solution at 2.0 mg/mL had strong antibacterial activity against B. seminalis although weak antibacterial activity was observed at a concentration lower than 1 mg/mL. The antibacterial activity of acid-soluble chitosan may be due to membrane disruption, cell lysis, abnormal osmotic pressure, and additional chitosan coating around the bacteria based on integrity of cell membranes test, out membrane permeability assays and transmission electron microscopy observation. In addition, biofilm biomass were markedly reduced after treating with two kinds of acid-soluble chitosan at concentrations of 2.0 and 1.0 mg/mL for 3 and 12 h, indicating the importance of biofilm formation in the antibacterial mechanism of chitosan. Overall, the results clearly indicated that two kinds of acid-soluble chitosan had a potential to control the contamination of apricot fruits caused by B. seminalis.

Subsurface examination of a foliar biofilm using scanning electron- and focused-ion-beam microscopy.

The dual beam scanning electron microscope, equipped with both a focused ion- and scanning electron-beam (FIB SEM) is a novel tool for the exploration of the subsurface structure of biological tissues. The FIB can remove a predetermined amount of material from a selected site to allow for subsurface exploration and when coupled with SEM or scanning ion-beam microscopy (SIM) could be suitable to examine the subsurface structure of bacterial biofilms on the leaf surface. The suitability of chemical and cryofixation was examined for use with the FIB SEM to examine bacterial biofilms on leaf surfaces. The biological control agent, Burkholderia pyroccinia FP62, that rapidly colonizes the leaf surface and forms biofilms, was inoculated onto geranium leaves and incubated in a greenhouse for 7 or 14 days. Cryofixation was not suitable for examination of leaf biofilms because it created a frozen layer over the leaf surface that cracked when exposed to the electron beam and the protective cap required for FIB milling could not be accurately deposited. With chemically fixed samples, it was possible to precisely FIB mill a single cross section (5µm) or sequential cross sections from a single site without any damage to the surrounding surface. Biofilms, 7 days post-inoculation (DPI), were composed of 2-5 bacterial cell layers while biofilms 14 DPI ranged from 5 to greater than 30 cell layers. Empty spaces between bacteria cells in the subsurface structure were observed in biofilms 7- and 14-DPI. Sequential cross sections inferred that the empty spaces were often continuous between FP62 cells and could possibly make up a network of channels throughout the biofilm. FIB SEM was a useful tool to observe the subsurface composition of a foliar biofilm.

Perchlorate degradation using an indigenous microbial consortium predominantly Burkholderia sp.

An acclimatized mixed microbial consortium, predominantly Burkholderia sp., was isolated from an activated sludge and investigated for its potential to degrade perchlorate in batch shake flasks. The 16S rDNA analysis of the predominant strain in the mixed culture showed the closest homology (98%) with Burkholderia sp. ATSB16. For the first time mixed culture with predominantly Burkholderia sp., has been reported to be involved in perchlorate degradation. The substrate perchlorate was completely utilized within 10 days even at a high concentration of 1000 mg L(-1) utilizing succinate as the sole carbon-source. Compared to other carbon-sources tested in this study, succinate proved to be better for perchlorate degradation by the mixed consortium. The optimum conditions for perchlorate degradation by the enriched mixed culture were found to be 30 °C and pH 7.0. The effect of co-pollutants on perchlorate removal by the mixed culture was also investigated at a mixed perchlorate concentration of 500 mg L(-1). Results showed that the degradation of perchlorate was affected to different extent due to the presence of an equal concentration (500 mg L(-1)of each) of co-pollutants such as nitrate, nitrite, chlorate and phosphate.

Antimicrobial activities of LL-37 and its truncated variants against Burkholderia thailandensis.

Antimicrobial peptides (AMPs) are essential host defence molecules found in a wide variety of species and are promising antibacterial therapeutic candidates. Focusing on the human cathelicidin peptide LL-37, the aim of the present study was to explore the mechanisms of action and antimicrobial activities of a library of LL-37 fragments using Burkholderia thailandensis E264 as a model. The results revealed that IG-19 was the shortest fragment within LL-37 that exhibited antibacterial activity. LL-31, missing six residues at the C-terminus of LL-37, exhibited the strongest killing effect. Freeze-fracture electron microscopy of bacterial cells treated with either LL-37 or LL-31 revealed irregular bacterial surfaces with bleb projections, indicating that these peptides disrupted the integrity of the membrane. In addition, these peptides induced leakage of cell components, including nucleotides and even proteins. Altogether, the results obtained indicate the potential of using LL-31 as a new AMP to combat Burkholderia spp.