Burkholderia cepacia complex bacteria comprise opportunistic pathogens causing chronic respiratory infections in cystic fibrosis (CF) patients. These microorganisms produce exopolysaccharides which are considered virulence determinants. Here, we report the isolation of an evolved nonmucoid variant (17616nmv) after the ancestor, Burkholderia multivorans ATCC 17616, was subjected to prolonged stationary phase. Lack of exopolysaccharide cepacian biosynthesis in the variant was correlated with downregulation of bce genes expression. Furthermore, genome sequence of the variant identified the transposition of a mobile element of the IS406 family into the promoter region of an hns-like gene (Bmul_0158) encoding a histone-like nucleoid structuring protein, a known global transcriptional repressor. This IS element upregulated the expression of Bmul_0158 gene. Transcriptome analysis identified the global effects of this mutation on gene expression, with major changes in motility, pili synthesis, type VI secretion, and chromosome associated functions. Concomitant with these differences, the nonmucoid variant displays reduced adherence to a CF lung bronchial cell line, reduced surface hydrophobicity, forms smaller cellular aggregates, but has an increase in swimming and swarming motilities. Finally, bioinformatic analysis led to the identification of various genomic regions, possibly acquired by horizontal gene transfer, which were transcriptionally repressed by the increased expression of hns gene in the nonmucoid variant. Taken together, our results revealed a significant role for this H-NS protein in the regulation of B. multivorans persistence- and virulence-associated genes.
Overall design: For expression profiling, overnight cultures of the Burkholderia multivorans ATCC 17616 and its nonmucoid variant 17616nmv were grown in SM medium and diluted to an initial OD640 nm of 0.1 into the same medium. Triplicate samples were cultured at 37ºC with 250 r.p.m. agitation for 10 h and RNA extracted.
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