Genome-Wide RNA Sequencing Analysis of Quorum Sensing-Controlled Regulons in the Plant-Associated Burkholderia glumae PG1 Strain

Abstract

dBurkholderia glumae PG1 is a soil-associated motile plant-pathogenic bacterium possessing a cell density-dependent regulation system called quorum sensing (QS). Its genome contains three genes, here designated bgaI1 to bgaI3, encoding distinct autoinducer-1 (AI-1) synthases, which are capable of synthesizing QS signaling molecules. Here, we report on the construction of B. glumae PG1 ⌬bgaI1, ⌬bgaI2, and ⌬bgaI3 mutants, their phenotypic characterization, and genome-wide transcriptome analysis using RNA sequencing (RNA-seq) technology. Knockout of each of these bgaI genes resulted in strongly decreased motility, reduced extracellular lipase activity, a reduced ability to cause plant tissue maceration, and decreased pathogenicity. RNA-seq analysis of all three B. glumae PG1 AI-1 synthase mutants performed in the transition from exponential to stationary growth phase revealed differential expression of a significant number of predicted genes. In comparison with the levels of gene expression by wild-type strain B. glumae PG1, 481 genes were differentially expressed in the ⌬bgaI1 mutant, 213 were differentially expressed in the ⌬bgaI2 mutant, and 367 were differentially expressed in the ⌬bgaI3 mutant. Interestingly, only a minor set of 78 genes was coregulated in all three mutants. The majority of the QS-regulated genes were linked to metabolic activities, and the most pronounced regulation was observed for genes involved in rhamnolipid and Flp pilus biosynthesis and the type VI secretion system and genes linked to a clustered regularly interspaced short palindromic repeat (CRISPR)-cas gene cluster. Q uorum sensing (QS) is a cell density-dependent gene regulation system in bacteria (1) in which the population density is sensed through the accumulation of bacterially produced signaling molecules called autoinducers (AIs). This cell-to-cell signaling process allows the microbial population to synchronize group behavior and alter its gene expression accordingly. QS is involved in a wide array of regulatory circuits, among which are pathogenicity, secretion of extracellular proteins, secondary metabolite production, and others (2). Key QS signaling molecules in many Gram-negative bacteria are N-acyl-homoserine lactones (AHLs) (3-5), synthesized mainly through LuxI homologs (EC 2.3.1.184) using S-adenosylmethionine (SAM), and an acyl-acyl carrier protein (acyl-ACP) from the fatty acid biosynthesis pathway (6). LuxR-type receptor/regulator proteins are involved in AHL signal perception. Together with LuxR, other proteins may be part of this regulatory circuit.The motile, rod-shaped Gram-negative soil bacterium Burkholderia glumae is considered to be a seed-borne pathogen that causes panicle blight of rice (7). B. glumae has also been reported to infect other plant species, like tomato, sunflower, and pepper (8, 9). Although it is not classified as a human pathogen, a single case of the isolation of B. glumae from a clinical sample was reported (10), indicating that at least some strains of this pathogen may be associated w...

Quorum sensing controls the Pseudomonas aeruginosa CRISPR-Cas adaptive immune system

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N‐acylhomoserine lactone‐regulation of genes mediating motility and pathogenicity in Pseudomonas syringae pathovar tabaci 11528

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