Antimicrobial Activity And Complete Genome Sequence Analysis Of Biocontrol Strain Asaia Bogorensis CSR-2

Plant diseases and insect pests which cause crop reduction,quality decline,is an important threat in agricultural production.At present,the control of plant diseases mainly depends on chemical fungicides,but they pose serious threat to human health and ecological environment.Microbial strains and their secondary metabolites with biocontrol effect are harmless and environmentally friendly to humans and animals,and are safe and effective control methods with more development potential.In this study,bacterial strain CSR-2 was isolated from maize rhizosphere soil with good biocontrol effect,and its antibacterial effect was studied.The whole genome of CSR-2 strain was sequenced and bioinformatics analysis was performed using the third generation PacBio sequencing technology.It provides a theoretical basis for further exploiting microbial resources for agricultural biological control.The results are as follows:1.Isolation and identification of biocontrol strainsSeventy-eight strains were isolated from maize rhizosphere soil,including 62strains of bacteria,13 strains of filamentous fungi and 3 strains of actinomycetes.Common plant pathogenic fungi were used as the indicator bacteria to conduct primary screening and rescreening of the isolated strains,and finally a strain CSR-2with significant inhibitory effect was obtained.The strain CSR-2 was identified by morphological and molecular biological methods,and the biocontrol strain CSR-2was identified as Asaia bogorensis.2.Inhibitory effect of biocontrol strain CSR-2Biocontrol CSR-2 had significant bacteriostatic effect.Inhibition spectrum analysis showed that CSR-2 had significant effects on Fusarium graminearum,Cochliobolus heterostrophus,Magnaporthe oryzae,Botrytis cinerea,Sclerotinia sclerotiorum,Cercospora zeae-maydi and Rhizoctonia solani all showed significant inhibitory effects.The inhibition rate was 63.3%-71.3%.The growth of F.graminearum,R.solani and C.zeae-maydi was significantly inhibited by CSR-2fermentation broth.The surface of F.graminearum mycelia treated with CSR-2fermentation broth was wrinkled and uneven in thickness.The mycelia of R.solani and C.zeae-maydi showed uneven distribution of inclusions and extravasation.The conidial surface of F.graminearum treated with CSR-2 fermentation liquid was constricted and its permeability was abnormal,so it could not germinate normally.The germination rates of conidia of F.graminearum were reduced by 25.09%,75.98%and 77.17%in CSR-2 fermentation broth with OD₆₀₀=0.15,0.3 and 0.6,respectively.CSR-2 fermentation broth also had certain inhibitory effect on plant pathogens on corn seeds.In addition,CSR-2 also has the ability to fix nitrogen,dissolve phosphorus and produce indole acetic acid.3.Sequencing results of the whole genome of biocontrol CSR-2The whole genome of STRAIN CSR-2 was sequenced using the third-generation PacBio sequencing technology.A total of 198,692 high-quality reading fragments were obtained.The assembled genome length was 3,202,366 bp,and the average GC content was 59.11%.The complete genome sequence of CSR-2 contains 3007 coding genes,97 tandem repeats,5 gene islands and 2 prophage structures in the whole genome of CSR-2.The basic functions of the whole CSR-2 genome were annotated using basic databases NR,COG/KOG,Swiss Prot,KEGG and GO.The results showed that 2743,2317,1937,1522 and 1493 genes were annotated in NR,COG/KOG,Swiss Prot,KEGG and GO databases respectively,accounting for 91.22%,77.05%,64.42%,50.62%and 49.65%of the total number of genes.Specific functional genes were annotated by CAZy database and VIRulence factor（VFDB）database.71 genes encoded protein domains belonging to CAZy family and 436genes belonging to virulence factor were found in CSR-2 genome.The whole genome sequencing results have been logged in to Genbank,with the inclusion number CP081941.These results indicated that CSR-2 had significant bacteriostasis and antagonistic activity against a variety of plant pathogenic fungi.By annotating the structure,basic functions and specific functions of the whole genome of A.bogorensis CSR-2,the genomic information of A.bogorensis CSR-2 was improved,which laid a foundation for further exploring its biocontrol potential.