Project description:Burkholderia vietnamiensis strain G4, representative of a species routinely encountered as a contaminant of industrial product, was exposed to a proprietary preservative agent for 24 hours and gene expression analysed by RNA-seq.
Project description:Burkholderia species have environmental, industrial and medical significance, and are important opportunistic pathogens in individuals with cystic fibrosis (CF). Using a combination of existing and newly determined genome sequences, this study investigated prophage carriage across the species B. vietnamiensis, and also isolated spontaneously inducible prophages from a reference strain, G4. Eighty-one B. vietnamiensis genomes were bioinformatically screened for prophages using PHASTER (Phage Search Tool Enhanced Release) and prophage regions were found to comprise up to 3.4% of total genetic material. Overall, 115 intact prophages were identified and there was evidence of polylysogeny in 32 strains. A novel, inducible Mu-like phage (vB_BvM-G4P1) was isolated from B. vietnamiensis G4 that had lytic activity against strains of five Burkholderia species prevalent in CF infections, including the Boston epidemic B. dolosa strain SLC6. The cognate prophage to vB_BvM-G4P1 was identified in the lysogen genome and was almost identical (>93.5% tblastx identity) to prophages found in 13 other B. vietnamiensis strains (17% of the strain collection). Phylogenomic analysis determined that the G4P1-like prophages were widely distributed across the population structure of B. vietnamiensis. This study highlights how genomic characterization of Burkholderia prophages can lead to the discovery of novel bacteriophages with potential therapeutic or biotechnological applications.
Project description:Bacteria of the Burkholderia cepacia complex consist of five discrete genomic species, including genomovars I and III and three new species: Burkholderia multivorans (formerly genomovar II), Burkholderia stabilis (formerly genomovar IV), and Burkholderia vietnamiensis (formerly genomovar V). Strains of all five genomovars are capable of causing opportunistic human infection, and microbiological identification of these closely related species is difficult. The 16S rRNA gene (16S rDNA) and recA gene of these bacteria were examined in order to develop rapid tests for genomovar identification. Restriction fragment length polymorphism (RFLP) analysis of PCR-amplified 16S rDNA revealed sequence polymorphisms capable of identifying B. multivorans and B. vietnamiensis but insufficient to discriminate strains of B. cepacia genomovars I and III and B. stabilis. RFLP analysis of PCR-amplified recA demonstrated sufficient nucleotide sequence variation to enable separation of strains of all five B. cepacia complex genomovars. Complete recA nucleotide sequences were obtained for 20 strains representative of the diversity of the B. cepacia complex. Construction of a recA phylogenetic tree identified six distinct clusters (recA groups): B. multivorans, B. vietnamiensis, B. stabilis, genomovar I, and the subdivision of genomovar III isolates into two recA groups, III-A and III-B. Alignment of recA sequences enabled the design of PCR primers for the specific detection of each of the six latter recA groups. The recA gene was found on the largest chromosome within the genome of B. cepacia complex strains and, in contrast to the findings of a previous study, only a single copy of the gene was present. In conclusion, analysis of the recA gene of the B. cepacia complex provides a rapid and robust nucleotide sequence-based approach to identify and classify this taxonomically complex group of opportunistic pathogens.
Project description:When a combination of hydrogen peroxide and hypochlorite was used to surface sterilize rice seeds, a 10(2)- to 10(4)-fold decrease in CFU was observed during the first 15 h after inoculation of the rice rhizosphere organism Burkholderia vietnamiensis TVV75. This artifact could not be eliminated simply by rinsing the seeds, even thoroughly, with sterile distilled water. When growth resumed, a significant increase in the frequency of rifampin- and nalidixic acid-resistant mutants in the population was observed compared to the control without seeds. This phenomenon was a specific effect of hypochlorite; it was not observed with hydrogen peroxide alone. It was also not observed when the effect of hypochlorite was counteracted by sodium thiosulfate. We hypothesized that the hypochlorite used for disinfection reacted with the rice seed surface, forming a chlorine cover which was not removed by rinsing and generated mutagenic chloramines. We studied a set of rifampin- and nalidixic acid-resistant mutants obtained after seed surface sterilization. The corresponding rpoB and gyrA genes were amplified and sequenced to characterize the induced mutations. The mutations in five of seven nalidixic acid-resistant mutants and all of the rifampin-resistant mutants studied were found to correspond to single amino acid substitutions. Hypochlorite surface sterilization can thus be a source of artifacts when the initial bacterial colonization of a plant is studied.
Project description:Burkholderia vietnamiensis has both the cepIR quorum-sensing system that is widely distributed among the Burkholderia cepacia complex (BCC) and the bviIR system. Comparison of the expression of cepI, cepR, bviI, and bviR-luxCDABE fusions in B. vietnamiensis G4 and the G4 cepR and bviR mutants determined that the expression of bviI requires both a functional cognate regulator, BviR, and functional CepR. The cepIR system, however, is not regulated by BviR. Unlike the cepIR genes in other BCC species, the cepIR genes are not autoregulated in G4. N-Acyl-homoserine lactone (AHL) production profiles in G4 cepI, cepR, bviI, and bviR mutants confirmed the regulatory organization of the G4 quorum-sensing systems. The regulatory network in strain PC259 is similar to that in G4, except that CepR positively regulates cepI and negatively regulates cepR. AHL production and the bviI expression levels in seven B. vietnamiensis isolates were compared. All strains produced N-octanoyl-homoserine lactone and N-hexanoyl-homoserine lactone; however, only one of four clinical strains but all three environmental strains produced the BviI synthase product, N-decanoyl-homoserine lactone (DHL). The three strains that did not produce DHL expressed bviR but not bviI. Heterologous expression of bviR restored DHL production in these strains. The bviIR loci of the non-DHL-producing strains were sequenced to confirm that bviR encodes a functional transcriptional regulator. Lack of expression of G4 bviI in these three strains indicated that an additional regulatory element may be involved in the regulation of bviIR expression in certain strains of B. vietnamiensis.