Reduced infectivity and environmental resistance of microsporidian Nosema bombycis after spore wall proteins-removal treatment

Abstract

Nosema bombycis is a highly virulent causative agent of the pebrine disease in sericulture. The only infective stage of the parasite is the environmentally resistant spore, on which the protein-rich spore wall supposedly contributes to their infection and resistance. In this study, we explore the potential roles of spore wall proteins (SWPs) of mature N. bombycis spores by evaluation of their performances on staining, infectivity, and resistance, following SWPs-removal treatment. Although no significant structural change is discerned by ultrastructural micrographs, the treated spores showed enhanced eosin B staining with strong shades of reddish purple or violet. Moreover, their infectivity to silkworms was significantly affected, resulting in 38.89% compared to 61.11% for the untreated control. Further infectivity bioassays show clearly that they are more susceptible to sodium chloride and heating pretreatment. In all, the enhanced permeability, decreased infectivity and environmental resistance of the SWPs-removal spores indicated thatSWPs play multiple roles in the infection and resistance for N. bombycis. These results have significant implication for controlling the pebrine disease in sericultrue. Key words: Nosema bombycis, microsporidia, spore wall proteins, infectivity, resistance.