Identification of Rickettsia-Like Organism (RLO) in the Oyster Crassostrea rivularis Gould - Abstract
The oyster Crassostrea rivularis Gould (also known as Crassostrea ariakensisis) an important bivalve species cultured in southeastern China. Since 1992, these oysters have suffered high mortality during winter and spring. An intracellular rickettsia-like organism (RLOs) was proposed as the causative agent. In this study, RLOs were purified from the gill and digestive gland of dying oyster (C. rivularis Gould), and their 16S rDNA was amplified from the purified products. To eliminate non-specific bacterial 16S rDNA contamination, the cloned products of bacterial 16S rDNA from gill RLO were screened by the probes of bacterial 16S rDNA amplified from the digestive gland RLO. Finally, the five strongest hybridized dots were picked out and sequenced. The RLO’s 16S rDNA sequence was reconfirmed and the pathogen was found only in epithelia cells by in situ hybridization (ISH) using specific probes. Sequence alignment and phylogenetic analysis indicated the RLO bacterium found in oyster C. rivularis Gould was most similar to Piscirickettsia salmonis, and might be classified into the family of gamma proteobacteria.