Interrelationships of cytoplasmic structures in Bonamia sp. (Haplosporidia) infecting oysters Tiostrea chilensis: An interpretation

Abstract

Reticular structures, confronting cisternae (CC), including cylindrical confronting cisternae (CCC), an unusual surface projection, formation of haplosporosome-like bodies (H-LB) and haplosporogenesis are described from Bonamia sp. infecting oysters Tiostrea chilensis from New Zealand. Formation of H-LB began when balls of putative nuclear material derived from indentations in the nuclear surface were encircled by cisternae of Golgi bearing a layer of dense material on their inner, concave surface. Also. H-LB were formed when CC split longitudinally and putative nuclear material filled the lumen of the resultant tubular structure, which subsequently pinched off H-LB. Haplosporogenesis began with the formation of cytoplasmic multi-vesicular bodies (MVB), which filled with dark osmiophilic material derived from nearby Golgi. The characteristic membranes of haplosporosomes appeared to form within these MVBs. It is suggested that H-LB are unusual structures in haplosporidans and that their core is formed from nuclear material. The CC from which they may form are also unusual, and in mammals CC occur in rapidly divid~ngo r diseased cells. As CCC can only be induced in virally infected, transformed or neoplastic mammalian cells, it is considered that in Bonamia sp. CCC may be overt signs of an underlying disease. The significance of this is discussed in relation to the sudden appearance and pathogenicity of Bonamia sp. and, possibly, Haplosporidium nelsonj (MSX).