Diversity And Antimicrobial Activity Of Rhizosphere Actinomycetes From Two Fagopyrum Species

As the main antibiotic-producing bacteria,actinomycetes have tremendous potential and play a huge role in medical and other industries.Existing studies have confirmed that the rhizosphere actinomycetes of medicinal plants show good potential in producing bioactive secondary metabolites.In the past,there were few reports on the rhizosphere actinomycetes of genus Fagopyrum.However,our recent studies on pure culture studies show that the diversity of rhizosphere actinomycetes of Fagopyrum tataricum and Fagopyrum dibotrys is abundant.Therefore,it is of great practical significance to explore the rhizosphere actinomycetes resources of genus Fagopyrum.The diversity of rhizosphere soil actinomycetes of Fagopyrum tataricum was analyzed by using the high-throughput sequencing technology for preliminary understanding the dominant species,rare species and some unknown species in the samples,in order to provide theoretical support for the isolation and screening of the rhizosphere actinomycetes resources of genus Fagopyrum.Then,the diversity of culturable actinomycetes of Fagopyrum dibotrys and Fagopyrum tataricum was explored by pure culture technique.And the potential novel species were identified by polyphasic taxonomic approach.Finally,the antagonistic activities of isolated strains were tested.The main results are as follows.(1)The results of high-throughput sequencing showed that actinobacteria accounted for13.0%of the total number of colonies at the class level,which was one of the dominant bacterial population.12 populations actinomycetes were detected at the order level,including Propionibacteriales(31.80%),Micrococcales(24.60%),Streptomycetales(7.4%),Frankiales(17.20%),Pseudonocardiales(6.40%),Mircomonosporales(7.70%),Corynebacteriales(2.70%),Streptosporangiales(0.80%),Kineosporiales(0.80%),Bifidobacteriales(0.40%),Glycomycetales(0.05%)and Other(0.04%).Propionibacteriales,Micrococcales and Frankiales are rich.And the average abundance of Streptomycetales was7.40%in all samples.The results showed that the diversity of actinomycetes of Fagopyrum tataricum was abundant,which had high exploration value in discovering novel species and mining new secondary metabolites or other active substances.(2)More than 350 strains of actinomycetes were isolated from the samples.They were integrated into 50 strains of different actinomycetes based on morphological characteristics and 16S r RNA gene sequence analysis.The 50 strains of actinomycetes represented 4different genera of actinomycetes,include 47 strains of Streptomyces,1 strain of Sacc Charomyces,1 strain of Methylarum and 1 strain of Micromonospora.The evolutionary statuses of these 50 strains of actinomycetes were preliminary ly determined by morphological,cultural,physiological and biochemical characteristics and the phylogenetic tree based on 16S r RNA gene sequence analysis.Strain QMT-12?QMT-28?QMT-37?QMT-45?QMT-48 and QMT-49 were identified as potential novel species.(3)The strain QMT-28 and QMT-12 was identified by polyphasic taxonomic approach.All morphological,cultural,chemical,physiological and biochemical characteristics,phylogenetic and whole genome sequence analysis indicated strain QMT-28 and QMT-12represented as two novel species of Streptomyces,for which the name Streptomyces fagopyri sp.nov.and Streptomyces liangshanensis sp.nov.were proposed,respectively.The type strain QMT-28^T=CICC 24808^T=JCM 33796^T and QMT-12^T=CICC 11056^T=JCM 33963^T.(4)Antagonistic test showed that 18 of 50 strains of actinomycetes had certain inhibitory effect on Aspergillus niger,Penicillium,Rhizoctonia solani,Escherichia coli or Staphylococcus aureus.Strains QMT-10?QMT-11?QMT-34 and QMT-46 could inhibit the growth of A.niger.Strains QMT-01?QMT-05?QMT-07?QMT-08?QMT-09?QMT-10?QMT-11?QMT-13 and QMT-22 showed a certain degree of inhibition on Penicillium.Among them,QMT-09 and QMT-10 had the best inhibition effect on Penicillium,and the width of inhibition ring was 1.7 and 1.3 cm respectively.In the resistance test of Rhizoctonia solani,most of the strains could had inhibition effect on the target bacteria,including strains QMT-07?QMT-10?QMT-11?QMT-12?QMT-13?QMT-24 and QMT-45.The inhibition ring width of strains QMT-10?QMT-11 and QMT-13 was 1.0 cm.Strains QMT-05?QMT-07?QMT-15?QMT-25?QMT-27 and QMT-35 had obvious effect on E.coli.The results showed that there were strains with antibacterial activity in the genus Fagopyrum and its rhizosphere soil,which could be used as potential sources of antibiotics.