In recent years, a novel aquaculture pathogen Spiroplasma eriocheiris has been found in many crustaceans including Procambarus clarkii, Eriocheir sinensis, Penaeus vannamei, Macrobrachium rosenbergii and Macrobrachium nipponense.This Spiroplasma has caused serious diseases and catastrophic economic losses in aquaculture.Transmission electron micrographs of the spiroplasmas indicated the organisms had a single cell surface membrane and lacked a cell wall.Prior research showed that the infectious cycle of the spiroplasma begins by invasion of host hemocytes and subsequent invasion to other organs and tissues in the Chinese mitten crab E.sinensis.Until now, little was known about the molecular and cellular interactions contributing to the crossing of physical barriers.For human and animal pathogenic mollicutes, it is well established that successful colonization of the host cells requires adhesion as the first step.This event is mediated by surface proteins, and among these proteins adhesins play an important role.