Pectin Enhances Bio-Control Efficacy by Inducing Colonization and Secretion of Secondary Metabolites by Bacillus amyloliquefaciens SQY 162 in the Rhizosphere of Tobacco

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.

Should the biofilm mode of life be taken into consideration for microbial biocontrol agents?

“…These reports demonstrate that many biocontrol agents can form biofilms on crops and in the rhizosphere. It has also been shown that biofilm formation by biopesticides can be stimulated by plant root exudates (Espinosa‐Urgel et al ., ; Timmusk et al ., ; Haggag and Timmusk, ; Khezri et al ., ; Chen et al ., ; Sang and Kim, ; Zhang et al ., ), or by exposure of the microorganisms to antimicrobial products or stress (Bais et al ., ; Selin et al ., ; Fan et al ., ; Xu et al ., ; Chi et al ., ; Wu et al ., ; Zhou et al ., ), but only a few studies have focused on biocontrol mechanisms that may be related to the properties of the mature biofilm itself, rather than the secretion of antimicrobials. Bacillus are ubiquitous spore forming bacteria predominantly found in soil.…”

Pectin-Rich Amendment Enhances Soybean Growth Promotion and Nodulation Mediated by Bacillus Velezensis Strains

“…While a slow rate of growth was observed when purified pectin was added to a minimal medium, the B. velezensis growth observed in the presence of orange peel powder was significantly greater, suggesting that additional nutritional requirements for Bv growth were supplied from the orange peel powder. A previous study [27] assessed the effects of adding different carbohydrates to the complex medium Lysogeny broth (LB) on the growth of B. amyloliquefaciens SQY 162 (a strain that may now be affiliated with B. velezensis ), and did not observe any significant differences in growth for any added carbohydrate; however, due to the use of the nutrient-rich LB medium in these experiments, this precluded any assessment of Bacillus growth due to the use of any of these carbohydrates as a sole carbon and energy source. Hence, our study is therefore the first demonstration of the growth of B. velezensis strains using pectin or a pectin-rich organic source such as orange peel powder as a substrate.…”

“…While Bv strain AP193 was one of the strains observed to grow very well in a minimal medium containing either pectin or orange peel powder, other Bv strains showed comparable in vitro growth and yet did not perform as well in plant trials, suggesting that other bacterial functions such as secondary metabolite biosynthesis might explain these strain differences. A previous study [27] demonstrated that pectin increased biofilm formation, chemotactic activity, and extracellular polymeric substance (EPS) production by B. amyloliquefaciens SQY 162, resulting in the enhanced root colonization of tobacco. In our study, there were no significant increases in Bv populations in plant rhizospheres despite significant effects observed on plant physiology.…”

“…There are currently only three commercially available sources of pectin extracts in the United States (U.S.): sugar beet [24], apple pomace [25], and citrus peel [26]. A recent study conducted by Wu et al [27] demonstrated that exogenous pectin or other carbohydrate amendments induced B. amyloliquefaciens SQY 162 to increase biofilm formation and secretion of the secondary metabolite surfactin, resulting in enhanced biocontrol activity against Ralstonia solanacearum in tobacco. However, this study did not investigate the potential synergy between pectin and PGPR-mediated plant growth-promotion.…”

Mecanismos de acción de <i>Bacillus</i> spp. (Bacillaceae) contra microorganismos fitopatógenos durante su interacción con plantas

“…La relación de la formación de biopelículas con la colonización de bacterias del género Bacillus tiene gran importancia en el control biológico de microorganismos de fitopatógenos. Como bien lo plantean Pandin et al, (2017), dicha relación esta mediada por varios aspectos que pueden resumirse en cuatro aspectos fundamentales: i) antagonismo directo por exclusión de nicho, debido a competencia por espacio y nutrientes, ii) comunicación microbiana en términos de cooperación e interferencia, la primera entre benéficos y la segunda entre benéficos y patógenos (Chen et al, 2015), iii) producción de compuestos antimicrobianos por las células componentes de la biopelícula (Wu et al, 2015c) y iv) la fitoestimulación de la planta.…”