Studies On The Bioactivity And Culture Of Bacterial Symbiont Of Entomopathogenic Nematodes

The symbiotic bacteria associated with insect pathogenic nematodes are placed in thefamily Enterobacteriaceae. Xenorhabdus and Photorhabdus are two bacterial generamutualistically associated with infective juveniles of entomopathogenic nematodes from thegenera Steinernema and Heterorhabditis, respectively. More than 30 bioactive secondarymetabolites, belonging to diverse chemical classes,have been reported from cultures ofXenorhabdus and Photorhabdus. These metabolites not only have diverse chemicalstructures,but also a wide range of bioactivities of medicinal and agricultural interest, such asantibiotic, antimycotic, insecticidal, nematicidal, antiulcer, antineoplastic andantiviral.especially, an important breakthrough was the discovery of a large-molecule,insecticidal toxin and gene from cultures of Photorhabdus. It offer some new insecticidalmicrobial resources and insecticidal geng for exploiting new types micro-insecticidal agentand anti-insect gene engineer. The symbionts have the potential of exploitation and theprospect of application. There has been a steady flow of publications reporting on thechemical nature and bioactivity of the products derived from both Xenorhabdus andPhotorhabdus species,but up to date, there are no reports about relation between metabolitesbioactivities and fermentation of the symbiotic bacteria. In this paper, the symbiotic bacteriaassociated with Steinernema sp YL001 and Steinernema sp YL002 from Shanxi provincewere separated and identified,and the relation between metabolites bioactivities andfermentation of the symbiotic bacteria were studied. The primary results are as follows: 1. The phenotypes and biochemical characteristics of the symbiotic bacteria associatedwith Steinernema sp YL001 and Steinernema sp YL002 were studied to determine thetaxonomic classification. These characteristics of both symbiotic bacteria were consistent withother strains of X.nematophilus and X.bovienii in morphological and biochemical properties,respectively. On the basis of the phenotypes and biochemical characteristics analysis, bothsymbiotic bacteria should belong to the species of X. nematophilus and X.bovienii, so namedXenorhabdus nematophilus YL001 and Xenorhabdus bovienii YL002 by this study. 2. Studies on bioactivity of metabolites of X. nematophilus YL001 and X. bovieniiYL002 shown that both symbiotic bacteria have highly injectable toxicity for Galleriamellonella, with the mortality of 100% after 48h when injected the cell-free aqueous filtratesof fermented liquid of different culture time ,but the mortality of Mythimna separatedecreased with prolonged culture time. Both symbiotic bacteria were lower oral toxicity forPlutella xylostella and H.armigera.The injectable toxin were possible proteins. Both symbiotic bacteria had different antimicrobial activity against 14 species of plantpathogenic fungi and 5 species of bacteria . The plant pathogenic fungi were almostlyinhibited by the fermented liquid , and the inhition rate was 75-100% . Phytophthora capsiciwas only completely inhibited by cell-free aqueous filtrates of fermented liquid . After diluted10 fold , the cell-free aqueous filtrates of fermented liquid had highly antimicrobial activityagainst Phytophthora capsici , and the EC50 was 16.3 ml/L and 13.0 ml/Lrespectively .When capsicum seeds were soaked into the cell-free aqueous filtrates offermented liquid for 6h prior to planting,the disease reduction reached 60.6% and 73.2% after12days planting.When disease soil treated with 100ml/L the cell-free aqueous filtrates offermented liquid and metalaxl, the disease reduction reached by 48.72% , 74.34% and 64.1%.YL001 and YL002 had higher antibacterial activity against Xanthomonas campestris andStaphylococcus aureus, but lower antibacterial activity against E.coli.and Salmonella typhi .The cell-free aqueous filtrates of fermented liquid had higher stability for heat , and higherantimicrobial activity at alkalesce...