Molecular identification of a novel intracellular proteobacteria from scallop Chlamys farreri

Abstract

The scallop Chlamys farreri is an important bivalve species cultured in the north of China. With the large expansion of culturing, mass mortalities have occurred persistently and caused great economic loss since 1996. An intracellular Rickettsiales-like prokaryote (RLP) was proposed as the causative agent. To identify the RLP, a partial 16S rDNA sequence of 1319 base pairs was amplified, cloned and sequenced. Phylogenetic analysis indicates that the prokaryote is a member of the α subclass of the proteobacteria. In the phylogenetic tree, it forms an independent and novel clade, which shares an evolutionary line of descent with a group of uniquely obligate intracellular organism comprised of Caedibacter caryophilus, an endosymbiont of Acanthamoeba sp., and the necrotizing hepatopancreatitis (NHP) bacterium of shrimp. Based on the obtained 16S rDNA sequence, three specific RNA targeted oligonucleotide DNA probes were designed, synthesized and labeled with digoxigenin for in situ hybridization detection. Results showed that the probes specifically bonded to the RLP inclusion in infected C. farreri tissues, indicating the amplified, cloned and sequenced 16S rDNA originated from the intracellular RLP parasitizing the C. farreri. We propose the name Sinorickettsia chlamys sp.nov. to C. farreri RLP.