Isolation And Identification Of Marine Bacteria With Nematicidal Activity Against Barsaphelenchus Xylophilus

Pine wilt disease(PWD), caused by the pine wood nematode (PWN)(Bursaphelenchus xylophilus) and transmitted by the pine sawyer(Monochamus alternatus), is one of the most devastating disease of pine trees and causes major losses in coniferous forests in Japan, China, South Korea and Portugal. As such, the PWN is among the most important pests included in the quarantine lists of many countries around the world. Because there has been no effective means to control PWD, the use of synthetic pesticides including chemical insecticides against the PWN vector, Monochamus alternatus, and the chemical nematicides killing PWNs have been the most common strategy for controlling PWD in the past few years. However, increasing concerns by the public about pesticide resistance, environmental and human health problems associated with pesticides, the application of some pesticides has been restricted and biocontrol of PWD has attracted a lot of attention in recent years. The reseaches on biocontrol aimed at the PWNs were mainly focused on the plants and the microbes with nematicidal activities. Nematicidal microbes included trapping fungi, endoparasitic fungi, toxigenic fungi, nematicidal actinomycetes and nematicidal bacteria. A few of the microbes with nematicidal activities have been isolated from freshwater habitats, but most of them were isolated from terrestrial environments. In order to search for new microbial strains with high nematicidal activities against PWNs from marine environments as sources of biological nematicides, in this study, fourteen marine bacterial strains were isolated from the marine samples of seawater, sediment, seaweeds and marine animals collected from the Yellow Sea near Qingdao, Shandong and their cultural filtrates were assayed in vitro for nematicidal activity against PWNs using immersion test. It was found that the cultural filtrates of strain PX3-1and strain PX3-2displayed stronger nematicidal activity to the tested nematodes and the revised mortalities of PWNs treated for8h were89.1%and91.6%, respectively. Based on the observation of morphology, the determination of physiological and biochemical characteristics, the analysis of16S rDNA sequence and phylogenetic tree, PX3-1and PX3-2were identified as the strains of Bacillus megaterium. This study provides the theoretical basis for the resource utilization of marine microbes and the biocontrol of pine wilt disease.