Abstract
AimsThis study examined the contribution of GltB on biofilm formation and biocontrol efficiency of B. subtilis Bs916.Methods and ResultsThe gltB gene was identified through a biofilm phenotype screen and a bioinformatics analysis of serious biofilm formation defects, and then a gltB single knockout mutant was constructed using homologous recombination. This mutant demonstrated severe deficits in biofilm formation and colonisation along with significantly altered production ofγ-polyglutamate (γ-PGA) and three lipopeptide antibiotics (LPs) as measured by a transcriptional analysis of both the wild type B. subtilis Bs916 and the gltB mutant. Consequently, the mutant strain retained almost no antifungal activity against Rhizoctonia solani and exhibited decreased biocontrol efficiency against rice sheath blight. Very few gltB mutant cells colonised the rice stem, and they exhibited no significant nutrient chemotaxis compared to the wild type B. subtilis Bs916. The mechanism underlying these deficits in the gltB mutant appears to be decreased significantly in production of γ-PGA and a reduction in the production of both bacillomycin L and fengycin. Biofilm restoration of gltB mutant by additionγ-PGA in the EM medium demonstrated that biofilm formation was able to restore significantly at 20 g/L.ConclusionsGltB regulates biofilm formation by altering the production ofγ-PGA, the LPs bacillomycin L and fengcin and influences bacterial colonisation on the rice stem, which consequently leads to poor biocontrol efficiency against rice sheath blight.Significance and Impact of StudyThis is the first report of a key regulatory protein (GltB) that is involved in biofilm regulation and its regulation mechanism and biocontrol efficiency by B. subtilis.
Highlights
Bacillus biofilms consist of a highly structured extracellular matrix attached to the surface of cells [1,2,3,4,5] that play an important role in the biological control of multiple pathogens [6,7,8]; for example, the presence of a biofilm can significantly improve the colonisation of Bacillus amyloliquefaciens SQR9, and its biocontrol efficiency towards other microbes
GltB regulates biofilm formation by altering the production ofγ-PGA, the lipopeptide antibiotics (LPs) bacillomycin L and fengcin and influences bacterial colonisation on the rice stem, which leads to poor biocontrol efficiency against rice sheath blight
This is the first report of a key regulatory protein (GltB) that is involved in biofilm regulation and its regulation mechanism and biocontrol efficiency by B. subtilis
Summary
Bacillus biofilms consist of a highly structured extracellular matrix attached to the surface of cells [1,2,3,4,5] that play an important role in the biological control of multiple pathogens [6,7,8]; for example, the presence of a biofilm can significantly improve the colonisation of Bacillus amyloliquefaciens SQR9, and its biocontrol efficiency towards other microbes. In addition to TasA and EPS, γ-polyglutamate (γ-PGA) plays an intricate role in biofilm formation by different B. subtilis strains. A mutant strain of B. amyloliquefaciens C06 defective in γ-PGA production was unable to form biofilms effectively [17]. Previous studies showed that many genes are involved in regulating the biofilms of Bacillus, including spo0A, spo0H, and abrB, which are needed for EPS and surfactin expression during early sporulation [19]. spo0A mutants demonstrate defective cell–cell interactions and cannot form a multicellular biofilm; abrB negatively regulates biofilm formation; sipW and yoaW, which are regulated by AbrB, are required for normal biofilm formation [20,21]; and degQ regulates the production of fengycins and is necessary for normal biofilm formation [22]
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