Diversity Analysis Of Pasteuria Penetrans, An Obligate Parasite Of Root-knot Nematode

Root-knot nematodes (Meloidogyne spp.), which are widely distributed all over the world, are seriously harmful pathogens for agricultural industry. Although the chemical nematicides had high efficiency in managing these pests, they were prohibited for their heavily environmental pollution in recent years. Nowadays, biological control attracted more attention as a possible and environmental friendly way. Hainan Island, the southernmost of China, is located in the north margin of tropical zone. Its tropical monsoon climate causes severe root-knot disease. As one of the most important economical crops in Hainan Island, pepper particularly infested with root-knot diseases. Pasteuria penetrans is a kind of obligate bacteria parasite of root-knot nematodes, which could efficiently reduce the amount of root-knot nematodes.In the study, the pathogenic nematodes sampled in Huangzhu, Dingan were identified as M. incognita and M. javanica by using universal primers and specific markers. Combined with morphological and16S rRNA gene sequence analysis, the Pasteuria endospores isolated from single M. incognita and M. javanica were identified as P. penetrans.Phylogenetic and diversity analysis of P. penetrans obtained from single M. incognita and M. javanica were studied at the16S rRNA, gyrB and sigE gene level. It suggested that, the16S rRNA gene sequences were sustained to form three main groups, and16parsimony informative sites were located in the first250bp fragment of the5’terminal sequence, mostly within Ⅵ and V2variable regions. P. penetrans gyrB gene sequences were separated into two groups and the distinctions were derived from P. penetrans infested M. javanica. P. penetrans sigE gene sequences were mostly identical and no parsimony informative sites were found. It revealed that the genetic diversities presented within P. penetrans population infected a single nematode, but no obvious host specificity was identified between single M. incognita and M. javanica identified in the study. Diverse strains of P. penetrans existed in one field but no obvious regional specificity was identified.Twelve pepper root samples contained Pasteuria-like endospores were collected in the sampling from six counties in Hainan Island. Thirty characterized Pasteuria16S rRNA gene sequences which were most similar to P. penetrans were obtained after eliminating repeats. Cluster analysis of16S rRNA gene revealed that the30sequences were separated into3main groups. Sixteen parsimony informative sites which were identical with the former study of P. penetrans infested single nematode were found in the29sequences; combining with the morphological characteristics, the strains corresponding to the29sequences were identified to be P. penetrans; however, clone tf-1only shared97.7%highest similarities with Pasteuria penetransT (AF077672), with most SNP sites located within the downstream sequence. It was suggested that sample tf contained potentially novel species of genus Pasteuria.