Identification and isolation of a spiroplasma pathogen from diseased oriental river prawn, Macrobrachium nipponense, in China: A new freshwater crustacean host

Spiroplasmas are small, wall-less, helical, and motile bacteria classified within the class Mollicutes. Spiroplasma has been identified as a lethal pathogen of four freshwater crustaceans in previous studies. Here, the fifth crustacean host of spiroplasma was found. A novel disease of oriental river prawn Macrobrachium nipponense appeared in the summer of 2012 in Jiangsu province of China. Morphological observation, molecular biological methods and infection experiments identified the pathogen as a spiroplasma. The agent isolated from diseased prawns was able to pass through membrane filters with pores 220 nm in diameter and cultivated by R2 medium. A 16S rRNA complete sequence was cloned from the isolation and alignment results revealed that the spiroplasmas from freshwater crustaceans were highly related. Phylogenetic analysis of these sequences showed that the five freshwater crustacean spiroplasma strains had a close relationship with Spiroplasma mirum. The pathogenicity of the agent, evaluated by the mortalities, was determined to be 65% through a challenge experiment. The above results indicated that M. nipponense is another new spiroplasma host in aquatic crustaceans, thus further indicating that more attention should be paid to this pathogen.