Ultrastructure of a haplosporidian containing Rickettsiae, associated with mortalities among cultured paua Haliotis iris

Abstract

Uninucleate and multinucleate stages of a protozoan parasite are described from cultured abalone Haliotis iris Martyn, 1784 in New Zealand. The parasite is identified as a haplosporidian by the occurrence of multinucleate plasmodia, mitochondria with tubular cristae, lipid droplets, anastomosing endoplasmic reticulum (aER), multivesicular bodies (MVBs), haplosporogenesis by the production of haplosporosome-like bodies from nuclear membrane-bound Golgi, and their maturation to haplosporosomes. Coated pits occurred in the plasma membrane and coated vesicles were scattered in the cytoplasm, particularly in association with the Golgi face away from the nucleus, and aER. It is concluded that the outward face of the Golgi may be the trans face, and that aER is the trans-Golgi network. Coated pits and bristle-coated vesicles are reported from a haplosporidian for the first time. The vesicles in the MVBs resembled the cores and inner membranes of haplosporosomes, without the outer layer. The possible inter-relationships of these features are discussed. The abalone parasite differs from previously described haplosporidians in the apparent absence of a persistent mitotic spindle, and the presence of intracytoplasmic coccoid to rod-shaped bacteria resembling Rickettsiales-like prokaryotes. Phylogenetic analysis of the 16S rRNA gene sequence of the Rickettsiales-like prokaryotes indicated that these organisms belong to the Rickettsia cluster. The prokaryotes have a high (7%) sequence divergence from known Rickettsieae, with Rickettsia sp. and R. massiliae being the closest relatives. The lack of non-molecular evidence prevents us from proposing a new rickettsial genus at this time.

‘Candidatus Megaira polyxenophila’ gen. nov., sp. nov.: Considerations on Evolutionary History, Host Range and Shift of Early Divergent Rickettsiae

“…1; [9]). Second, these bacteria display a broad host range, including arthropods (reviewed by [11]), protists [12]–[19], cnidarians [20], leeches [21] and even plants [22], [23], while medically relevant rickettsiae are typically confined to ticks or lice [2] with vertebrates as alternate hosts. Third, some “neglected Rickettsiaceae ”, e.g.…”

Molecular Identification of Rickettsial Endosymbionts in the Non-Phagotrophic Volvocalean Green Algae

“…Recently, several Rickettsiaceae species associated with non-arthropod hosts have been reported in the cells of various organisms, such as leeches [6], [7], hydras [8], amoebas [9], haplosporidians [10], and ciliates [11]–[13]. These rickettsias are phylogenetically placed in separate positions within the Rickettsiaceae [13], [14].…”

“Candidatus Finniella” (Rickettsiales, Alphaproteobacteria), Novel Endosymbionts of Viridiraptorid Amoeboflagellates (Cercozoa, Rhizaria)

“…There is also one report on "Ca. Megaira" in Haplosporidium, an intracellular, osmotrophic parasite of molluscs that belongs to the phylum Cercozoa (Rhizaria) (77). In light of the large diversity of phagotrophic (often bacterivorous) Cercozoa with flagellate or amoeboid morphology (78)(79)(80)(81), it is remarkable that the only evidence for a rickettsial endosymbiont in a rhizarian host so far comes from a plasmodial parasite, which lost its ability to feed by phagocytosis and lives inside other eukaryotic cells.…”