| An enormous range of insects exists in nature.They have a wide symbiotic association with diverse species of microorganisms.Based on the diversity and complexity of the living habitat and food species,the symbiotic association of insects with microbiota has the diversity of the species.It gives a resource to discover and isolate novel species and bioactive compounds from insect symbionts.In this paper,the bacteria associated with Armadillidium vulgare and termite symbiotic Streptomyces sp.BYC-18 was studied.The diversity of bacteria from A.vulgare was studied using the methods of dilution culture,morphology,and molecular biology.In addition,the antimicrobial activity of bacteria of A.vulgare and Streptomyces sp.BYC-18 from Odontotermes formosanus was investigated by the filter paper diffusion method.Four monomer compounds were isolated from the A.vulgare-associated Streptomyces sp.N-12 and O-17,and termite symbiotic Streptomyces sp.BYC-18 and the structures of three compounds were determined by using various chromatographic separation techniques and spectral analysis techniques.The details are as follows:1.The diversity of bacteria of A.vulgare was investigated using dilution culture,morphology,and molecular biological identification based on the 16 S r RNA sequence analysis.The results showed that 30 strains of bacteria belonged to 4 genera,18 of which were from Streptomyces,9 were from Pseudomonas,2 from Advenella,and 1 from Cedecea.2.The antagonistic activity of bacteria associated with A.vulgare against plant pathogenic fungi was tested.The results showed that 17 strains had antifungal activities.Among them,N-12 had moderate antifungal activities against Fusarium oxysporum and Alternaria alternate with the inhibitory rates of 46.30 mm and 53.64 mm,respectively.Besides,the antibacterial activities of ethyl acetate extracts of bacteria associated with A.vulgare against three pathogenic bacteria were further tested.The results showed that N-12 crude extract had weak activity against Staphylococcus aureus and Micrococcus tetragenus,and no inhibitory activity against Escherichia coli.However,O-17 crude extract had significant inhibitory activity against all three pathogens S.aureus,M.tetragenus,and E.coli,with the inhibition zone diameter(IZD,mm)of 20.6 mm,19.3 mm,and 18.6 mm,respectively,which were slightly higher than those of positive gentamicin sulfate(20.0 mm,13.8 mm,and 12.1 mm,respectively).3.Three monomer compounds were isolated from the ethyl acetate extracts of A.vulgare associated Streptomyces sp.N-12 and O-17.Two compounds actiphenol(N-12.1)and 3,5-dihydroxyacetophenone(O-17.2)were identified.The structure of the O-17.3compound was still to be further identified.The antibacterial activity showed that compounds N-12.1 and O-17.2 had no inhibitory activity against all tested bacteria at the concentration of 30 μg/ filter paper.However,O-17.3 showed potent antibacterial activity against E.coli with an IZD of 8.3 mm,which was comparable to the positive gentamycin sulfate(IZD =12.1 mm).O-17.3 also presented moderate antibacterial activity against S.aureus with an IZD of 8.0 mm.4.One monomer compound BYC-18.1 was isolated and purified from ethyl acetate extract of Streptomyces sp.BYC-18 and identified as β-rubromycin.The compound had antimicrobial activity against E.coli,S.aureus,Bacillus subtilis,and Candida albicans.In particular,it had strong antibacterial activity against S.aureus(IZD = 13.2 mm),which was equivalent to that of positive gentamicin sulfate(IZD = 16.6 mm)The above research results show that insect-related bacteria,as a kind of special microorganisms with less research,are an important resource bank of antimicrobial natural substances.These kinds of special microorganisms and their metabolites have important research value. |
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