Abstract
Bacillus amyloliquefaciens is a plant-beneficial Gram-positive bacterium involved in suppressing soil-borne pathogens through the secretion of secondary metabolites and high rhizosphere competence. Biofilm formation is regarded as a prerequisite for high rhizosphere competence. In this work, we show that plant extracts affect the chemotaxis and biofilm formation of B. amyloliquefaciens SQY 162 (SQY 162). All carbohydrates tested induced the chemotaxis and biofilm formation of the SQY 162 strain; however, the bacterial growth rate was not influenced by the addition of carbohydrates. A strong chemotactic response and biofilm formation of SQY 162 were both induced by pectin through stimulation of surfactin synthesis and transcriptional expression of biofilm formation related matrix genes. These results suggested that pectin might serve as an environmental factor in the stimulation of the biofilm formation of SQY 162. Furthermore, in pot experiments the surfactin production and the population of SQY 162 in the rhizosphere significantly increased with the addition of sucrose or pectin, whereas the abundance of the bacterial pathogen Ralstonia decreased. With increased production of secondary metabolites in the rhizosphere of tobacco by SQY 162 and improved colonization density of SQY 162 in the pectin treatment, the disease incidences of bacterial wilt were efficiently suppressed. The present study revealed that certain plant extracts might serve as energy sources or environmental cues for SQY 162 to enhance the population density on tobacco root and bio-control efficacy of tobacco bacterial wilt.
Highlights
The use of plant growth promoting rhizobacteria (PGPR) to bio-control soil-borne diseases and promote plant growth is a promising way to improve agriculture sustainability [1,2]
The present study revealed that certain plant extracts might serve as energy sources or environmental cues for SQY 162 to enhance the population density on tobacco root and bio-control efficacy of tobacco bacterial wilt
SQY 162 was strongly attracted by sucrose, with as many as 6.62 log cfu/ml observed in the syringe
Summary
The use of plant growth promoting rhizobacteria (PGPR) to bio-control soil-borne diseases and promote plant growth is a promising way to improve agriculture sustainability [1,2]. Bacillus amyloliquefaciens produces lipopeptides (LPs) to protect the plant from pathogens [6]. B. amyloliquefaciens induces the systemic resistance in plants against pathogens [7,8,9]. Successful root colonization of bio-control agents in the rhizosphere was essential for biocontrol efficacy [4,9,10]. Chowdhury et al [10] demonstrated that successful control of lettuce bottom rot was achieved through high rhizosphere competence of B. amyloliquefaciens FZB42 in the field. The bio-control of Fusarium oxysporum on cucumber was facilitated by the biofilm formation of B. amyloliquefaciens on cucumber roots [11]. When appropriate environmental cues are present, the kinases are active and induce biofilm formation and root colonization
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