Abstract
The biocontrol process mediated by plant growth-promoting rhizobacteria (PGPR) relies on multiple mechanisms. Biofilm formation plays an important role in the ability of PGPR to control plant diseases. Bacillus pumilus HR10, one such PGPR, promotes the growth of Pinus thunbergii. This study showed that the wild-type strain B. pumilus HR10 produces a stable and mature biofilm in vitro. Biofilm-deficient mutants of B. pumilus HR10 with different phenotypes were screened by mutagenesis. The contents of extracellular polysaccharides (EPS) and proteins produced by the mutant strains were significantly reduced, and the biofilms of the mutants were weakened to varying degrees. The swarming abilities of the wild-type and mutant strains were positively correlated with biofilm formation. A colonization assay demonstrated that B. pumilus HR10 could colonize the roots of Pinus massoniana seedlings in a large population and persist, while biofilm-deficient mutants showed weak colonization ability. Furthermore, a biocontrol assay showed that biocontrol efficacy of the mutants was reduced to a certain degree. We determined the inhibitory activity of B. pumilus HR10 and its ability to induce systemic resistance against Rhizoctonia solani of plants. The synthesis of lipopeptide antibiotics is probably involved in biofilm formation by B. pumilus HR10. These observations not only provide a reference for further research about the coordinated action between biofilm formation and the multiple biocontrol mechanisms of B. pumilus HR10 but also improve the understanding of the regulatory pathway of biofilm formation by B. pumilus HR10.
Highlights
Plant growth-promoting rhizobacteria (PGPR) have been reported to exhibit biocontrol processes including competition, antibiosis, growth promotion, and the induction of systemic resistance in plants [1,2,3,4,5,6]
We propose that the biocontrol efficacy of B. pumilus HR10 depends on the coordinated action of inhibitory activity, induced systemic resistance and excellent colonization
The results of this study demonstrated that B. pumilus HR10 produces a mature biofilm structure, which contributes to its colonization on the roots of pine seedlings
Summary
Plant growth-promoting rhizobacteria (PGPR) have been reported to exhibit biocontrol processes including competition, antibiosis, growth promotion, and the induction of systemic resistance in plants [1,2,3,4,5,6]. The Bacillus genus is one of the most frequently reported and promising PGPR with various biocontrol mechanisms. Bacillus velezensis FZB42, a model strain for excellent plant growth promoting and biocontrol rhizobacteria, has been studied on its genes and expression involved in biocontrol process and the bacteria-plant interaction [8,9,10]. Due to colonizing the root of plants persistently, PGPR can effectively promote the growth of plants and inhibit the pathogens [10,11,12]. Persistent colonization of PGPR on roots is essential for suppressing different plant diseases, and biofilm formation is considered a key factor for efficient root
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