Burkholderia contaminans MS14 shows excellent antimicrobial activities against a wide range of pathogens. Complete sequence analysis reveals that the MS14 genome harbors multiple gene loci that contribute to its antimicrobial activities and lacks key virulence features commonly found in pathogenic Burkholderia species. A mutagenesis study identified the genes required for MS14 antibacterial activities and gene expression profiling targeted a polyketide synthase (PKS) gene cluster. Site-specific mutagenesis confirmed the PKS gene cluster is directly related to MS14 antibacterial activities and the PKS gene product is predicted to be the MS14 antibacterial compound. Strain UFB2 isolated from Mississippi shows significant antifungal and antibacterial activities. UFB2 was classified to be Pseudomonas chlororaphis and its complete genome sequence was reported in this study. Green house trails showed P. chlororaphis strain UFB2 could efficiently reduce the disease severity of bacterial canker of tomato, by significantly inhibiting the growth of the pathogen Clavibacter michiganensis subsp. michiganensis. The research findings of B. contaminans MS14 and P. chlororaphis UFB2 have provided insights into the development of MS14 antibacterial compound for agricultural application and potential use of strain UFB2 as a biocontrol agent.

Strains MS455 and MS389, endophytic bacteria, were isolated from healthy soybean plant growing adjacent to a patch of plants affected by charcoal rot disease, caused by the fungal pathogen Macrophomina phaseolina. The complete genomes of both strains were sequenced and identified as Burkholderia species Strain MS455 exhibits broad-spectrum antifungal activities against economically important pathogens, including Aspergillus flavus. Random and site-specific mutations were employed in discovery of the genes that share high homology to the ocf gene cluster of Burkholderia contaminans strain MS14, which is responsible for production of the antifungal compound occidiofungin. RNA-seq analysis demonstrated ORF1, a homolog to the ambR1 LuxR-type regulatory gene, not only regulates occidiofungin biosynthesis in MS455, but also involved in expression of multiple genes, especially those involved in ornibactin biosynthesis. Plate and corn kernel assays showed that growth of A. flavus and aflatoxin production were reduced significantly by MS455 as compared with buffer control and the ORF1 mutant. Strain MS389 shows significant antifungal and antibacterial activities as well. Mutagenesis study identified that the TatC gene, an important unit of twin-arginine translocase (Tat) secretion system, and the LysR-type transcriptional regulatory gene were essential for the antifungal activity of strain MS389. RNA-seq analysis implied that the pyrrolnitrin biosynthesis gene cluster and an uncharacterized NRPS / PKS gene cluster were involved in antifungal activity. By comparing several endophytic bacteria of Burkholderia, including MS455 and MS389, to pathogenic Burkholderia species, endophytic bacteria were observed to harbor multiple antimicrobial biosynthesis genes but lack certain pathogenic or virulence genes. The potential endophytic behavior related genes and characteristics related to antibiotic resistance, secretion system, and CRISPR-Cas profiles were well established. The research findings on strains MS455 and MS389 have provided important genetic clues for understanding their molecular mechanism of antimicrobial activities and exhibited their potential possibility as biocontrol agents.

No / To investigate whether there are differences between members of the Burkholderia cepacia complex in their ability to invade human respiratory epithelial cells, 11 strains belonging to genomovars I-V were studied in an antibiotic protection assay using the A549 cell line. Strains belonging to genomovars II and III were more invasive than those of genomovars I, IV and V. There was also intra-genomovar variation in invasiveness. No correlation between invasiveness and other putative virulence factors of importance in B. cepacia infection in individuals with cystic fibrosis, cable pilus and B. cepacia epidemic strain marker was identified.

Cystic Fibrosis (CF) is a common autosomal genetic disorder in Caucasian populations. CF is caused by mutations in the cftr gene, which encodes the CF transmembrane conductance regulator (CFTR). CFTR regulates chloride and sodium ion transport across the epithelial cells lining the exocrine organs. Mutations in the cftr result in a failure to mediate chloride transport, which leads to dehydration of the mucus layer surrounding the epithelial cells. The mucus coating in the lung epithelia provides a favorable environment for invasion and growth of several opportunistic bacterial pathogens resulting in life threatening respiratory infections in CF patients. Pseudomonas aeruginosa(Pa) and Burkholderia cepacia complex (Bcc) are associated with chronic lung infections and are responsible for much of the mortality in CF. Little is known about interactions between these two, often co-infecting, species. When in competition, it is not known whether Bcc replaces the resident Pa or if the two species co-exist in the CF lung. Bacteriocins are potent toxins produced by bacteria. They have a quite narrow killing range in comparison to antibiotics and have been implicated in intra-specific and inter-specific bacterial competition brought on by limited nutrients or niche space. Both Pa and Bcc produce bacteriocins known as pyocins and cepaciacins, respectively. More than 90% of Pa strains examined to date produce one or more of three pyocin types: R, F, and S. A limited number of phenotypic surveys suggest that approximately 30% of Bcc also produce bacteriocins. The goals of my thesis study were to determine if clinical strains of Pa and Bcc produce bacteriocins and to determine whether these toxins play a role in mediating intra- and inter-specific bacterial interactions in the CF lung. The final goal was to identify novel bacteriocins from clinical Pa and Bcc strains. First, I designed a phenotypic bacteriocin survey to evaluate bacteriocin production in 66 clinical Pa (38) and Bcc (28) strains procured from CF patients. This study revealed that 97% of Pa strains and 68% of Bcc strains produce bacteriocin-like inhibitory activity. Further phenotypic and molecular based assays showed that the source of inhibition is different for Pa and Bcc. In Pa, much of the inhibitory activity is due to the well known S- and RF-type pyocins. S-and RF pyocins were the source of within species inhibitory activity while RF pyocins were primarily implicated in the between species inhibitory activity of Pa strains. In contrast, Bcc inhibition appeared to be due to novel inhibitory agents. Finally, I constructed genome libraries of B. multivorans, B. dolosa, and B. cenocepacia to screen for genes responsible for the inhibitory activity previously described in Bcc. ~10,000 clones/genome were screened, resulting in fifteen clones with the anticipated inhibition phenotype. Of these fifteen, only five clones had stable inhibitory activity. These clones encoded proteins involved in various metabolic pathways including bacterial apoptosis, amino acid biosynthesis, sugar metabolism, and degradation of aromatic compounds. Surprisingly, none of Bcc clones possessed typical bacteriocin-like genes. These data suggest that, in contrast to all bacterial species examined in a similar fashion to date, Bcc may not produce bacteriocins. Instead, Bcc may be using novel molecular strategies to mediate intra- and inter-specific bacterial interactions.

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