Composition of Bacterial Communities Associated with a Plant-Parasitic Nematode Bursaphelenchus mucronatus

Bursaphelenchus mucronatus is a plant-parasitic nematode widely existing in Eurasian pine forests. To analyze the diversity and role of bacteria associated with the nematode, culture-dependent and culture-independent methods were used to identify and characterize the composition of bacterial community. A total of 13 bacterial isolates were obtained from B. mucronatus by the culture-dependent method. Sixty-four species of bacteria were identified from two 16S rDNA clone libraries constructed from the nematodes of a Chinese and a Japanese population. These bacteria were clustered into four groups: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Bacteroidetes. Comparison of the two libraries showed that the Chinese library had a higher diversity than that of the Japanese library, and the dominant group and species in each library were also different. In the Japanese library, Alphaproteobacteria group was obviously dominant (60.3%), and Rhizobium sp. was the most dominant species. Whereas in the Chinese library the proportion of each group was similar (from 19.4 to 23.6%), and Pedobacter sp. was a slightly dominant species. Moreover, 18 operational taxonomic units (OTUs) were obtained from each of the two libraries according to a 97% sequence similarity. Metabolic analysis showed that 61.5 and 38.5% of the bacterial isolates could have protease and lipase activities, respectively. But only one had cellulase activity. Testing of reproductive parameter showed that the wild-type nematodes (bacteria carried) could produce more progeny than the bacterium-free nematodes did. So, we speculated that bacteria could promote the propagation and development of the nematode B. mucronatus.