Structure Analysis And Antibacterial Mechanism Of Extracellular Polymers Produced By Bacillus Amyloliquefaciens SQ-2

Aspergillus spp.could cause a complex disease named summer bunch rot which is responsible for the most significant decline in production and quality of table grapes worldwide.Bacillus amyloliquefaciens SQ-2 which has antagonistic effects on a variety of pathogenic fungi especially Stemphylium solani(ACCC 36456),Fusarium moniliforme(ACCC 36127),Fusarium graminearum(ACCC 38067),Aspergillus tubingensis(ACCC32407)was used in this study.Some important antagonistic properties were observed.Under vitro conditions,observed by SEM,B.amyloliquefaciens SQ-2 showed a significant inhibitory effect on the mycelial growth and spore germination of four fungi species.The complete genome of Bacillus amyloliquefaciens SQ-2 was sequenced,and multiple genes related to the synthesis of antibiotics were detected.The results showed that strain SQ-2had a total of 11 secondary metabolite gene clusters,including 6 classes of substances with antibacterial activity: bacillaene,bacillibactin,fengycin,bacilysin,surfactin and butirosin.Effect of SQ-2 in vivo was evaluated using berries from Shine-Muscat Grape,Kyoho Grape,Crimson Seedless cultivars,the results showed that the inhibition rate of SQ-2 against Aspergillus tubingensis in different grape varieties was greater than 40%.The sequencing data from this article were submitted to the NCBI and were available in the Gen Bank database(Login No.JAHXSB000000000).UPLC/MS showed that strain SQ-2 produced two lipopeptides(bacillibactin and surfactin),and a polyketide(bacillaene)to inhibit fungal growth.In addition to this,SQ-2 not only produced diffusible compounds,but also volatile organic compounds(VOCs),and showed good antifungal activity.GC/MS showed that strain SQ-2 produces some alkanes including dodecane,tetradecane,hexadecane,octadecane and eicosane.The genetic mechanism of the SQ-2 biocontrol trait was analyzed by using the whole genome sequence of SQ-2.SQ-2 produced diffusible and volatile organic compounds(VOCs)and showed good antifungal properties.Transcriptome studies showed that SQ-2 crude extract and VOCs significantly induced different expression of numerous genes in Aspergillus tubingensis.The up-regulated genes of Aspergillus tubingensis synthesize proteins through other pathways to maintain their basic growth,and downregulated genes may affect ribosome assembly and protein synthesis,resulting in inhibited growth and reduced aflatoxin biosynthesis.In addition,this paper also analyzed the structure of exopolysaccharides produced by Bacillus amyloliquefaciens SQ-2,and the results of methylation and nuclear magnetic resonance show that EPS-3 is fructan.