Abstract
Bacillus nematocida B16 has been shown to use “Trojan horse” mechanism in pathogenesis that has characteristics of “social” behavior. The ComP-ComA system, a conserved quorum sensing system in the genus Bacillus, functions in many physiological processes including competence development, lipopeptide antibiotic surfactin production, degradative enzyme production and even some unknown functions. Here we investigated the requirement of ComP-ComA system in B. nematocida B16 for its pathogenicity against nematodes. The ΔcomP mutant displayed deficiencies in attracting and killing nematodes, due to the absence of attractive signal molecules and the decreased expressions of virulence factors, respectively. Contrarily, a complemented comP mutant at least partially resumed its pathogenicity. Our data from transcriptional analysis further confirmed that this signaling system directly or indirectly regulated the expressions of two major virulence proteases in the infection of B. nematocida B16. Bioinformatics analyses from comparative genomics also suggested that the potential target genes of transcription factor ComA were involved in the processes such as the synthesis of attractants, production of extracellular degradative enzymes and sortase, secondary metabolites biosynthesis, regulation of transcription factors, mobility, as well as transporters, most of which were different from a saprophytic relative B. subtilis 168. Therefore, our investigation firstly revealed that the participation and necessity of ComP-ComA signaling system in bacterial pathogenesis.
Highlights
Bacillus nematocida strain B16 has been isolated from a soil sample in Yunnan province in China, and is pathogenic to freeliving nematode Panagrellus redivius as well as the plant parasite nematode Bursaphelenchus xylophilus [1]
At least three quorum sensing (QS) signaling systems have been identified based on the different types of signal molecules, including N-acylhomoserine lactone (AHL) in Gram-negative signaling systems [4], autoinducing peptides (AIPs) in Gram-positive signaling systems [5], and AI-2-type interspecies signaling systems [6]
The QS systems that depend on the signal molecules of oligopeptides to trigger two component phosphorelay is only used by Grampositive bacteria, and requires further elucidated [7]
Summary
Bacillus nematocida strain B16 has been isolated from a soil sample in Yunnan province in China, and is pathogenic to freeliving nematode Panagrellus redivius as well as the plant parasite nematode Bursaphelenchus xylophilus [1]. Bioinformatics analyses demonstrate that the candidate target genes regulated by ComP-ComA in B. nematocida B16 were quite different from those predicted in a saprophytic bacterium B. subtilis 168, one of the closest relatives of B. nematocida in the Bacillus genus but with almost no nematocidal activity (Figure S1 in File S1). Those potential target genes in B. nematocida B16 included a variety of pathogenic genes. Our investigation is the first report about the roles of signaling system ComP-ComA in the infection of bacterial pathogens
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