Genome-scale analysis of the genes that contribute to Burkholderia pseudomallei biofilm formation identifies a crucial exopolysaccharide biosynthesis gene cluster.
PLoS Negl Trop Dis 2017;
11:e0005689. [PMID:
28658258 PMCID:
PMC5507470 DOI:
10.1371/journal.pntd.0005689]
[Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2017] [Revised: 07/11/2017] [Accepted: 06/08/2017] [Indexed: 11/19/2022] Open
Abstract
Burkholderia pseudomallei, the causative agent of melioidosis, is an important public health threat due to limited therapeutic options for treatment. Efforts to improve therapeutics for B. pseudomallei infections are dependent on the need to understand the role of B. pseudomallei biofilm formation and its contribution to antibiotic tolerance and persistence as these are bacterial traits that prevent effective therapy. In order to reveal the genes that regulate and/or contribute to B. pseudomallei 1026b biofilm formation, we screened a sequence defined two-allele transposon library and identified 118 transposon insertion mutants that were deficient in biofilm formation. These mutants include transposon insertions in genes predicted to encode flagella, fimbriae, transcriptional regulators, polysaccharides, and hypothetical proteins. Polysaccharides are key constituents of biofilms and B. pseudomallei has the capacity to produce a diversity of polysaccharides, thus there is a critical need to link these biosynthetic genes with the polysaccharides they produce to better understand their biological role during infection. An allelic exchange deletion mutant of the entire B. pseudomallei biofilm-associated exopolysaccharide biosynthetic cluster was decreased in biofilm formation and produced a smooth colony morphology suggestive of the loss of exopolysaccharide production. Conversely, deletion of the previously defined capsule I polysaccharide biosynthesis gene cluster increased biofilm formation. Bioinformatics analyses combined with immunoblot analysis and glycosyl composition studies of the partially purified exopolysaccharide indicate that the biofilm-associated exopolysaccharide is neither cepacian nor the previously described acidic exopolysaccharide. The biofilm-associated exopolysaccharide described here is also specific to the B. pseudomallei complex of bacteria. Since this novel exopolysaccharide biosynthesis cluster is retained in B. mallei, it is predicted to have a role in colonization and infection of the host. These findings will facilitate further advances in understanding the pathogenesis of B. pseudomallei and improve diagnostics and therapeutic treatment strategies.
B. pseudomallei, the etiological agent of melioidosis, is an emerging pathogen with limited therapeutic options and no available vaccines. A better understanding of the role of biofilm formation during pathogenesis will aid in melioidosis diagnosis and the development of new therapeutics and vaccines. Melioidosis has both acute and chronic disease manifestations in addition to a highly variable period of latency, which contributes to complications in diagnosis and treatment of the disease. Relapsing melioidosis is correlated with biofilm formation and the role of biofilm growth during chronic human infections has been widely accepted. We utilized a two-allele sequence defined transposon mutant library of B. pseudomallei 1026b to identify genes involved in biofilm formation. This study identified factors that contribute to biofilm formation and included a previously undescribed exopolysaccharide and the genes underlying its biosynthesis. Since antibiotic tolerance in B. pseudomallei has been associated with biofilm formation, the genes identified in this study that contribute to biofilm production are potential targets for therapeutic development. Additionally, the products of these biofilm genes could be used for the development of diagnostics and vaccines.
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