New Perspective On The Haplosporidian Parasites Of Molluscs

The protist phylum Haplosporidia comprises over 40 described species with representatives infecting a range of mollusc hosts, including several ecologically and economically significant pathogens. Continuing exploration of haplosporidian diversity has added ten new species in recent years and brought the phylogenetics of the group into somewhat clearer focus, with monophyletic Bonamia and Minchinia lineages continuing to be supported. However, the addition of new sequences to phylogenetic analyses has left the paraphyletic genus Haplosporidium’s picture less resolved. It is not clear that even two genera will be enough to accommodate the species presently drawn to the Haplosporidium regions of the haplosporidian tree. In this review, we summarize recent findings in haplosporidian diversity and phylogenetics, and provide a synthesis of our understanding of the life cycles and environmental influences on haplosporidians, with particular emphasis on the important pathogens Haplosporidium nelsoni and Bonamia ostreae. Additionally, we consider the evolution of the “microcell haplosporidian” lifestyle of Bonamia parasites, and suggest that colonization of high-density oyster host populations in relatively stable euhaline marine environments may have been an important development favoring the evolution of the microcell haplosporidian life strategy.

Crassaminicella profunda gen. nov., sp nov., an anaerobic marine bacterium isolated from deep-sea sediments

A novel, anaerobic, chemo-organotrophic bacterium, designated strain Ra1766HT, was isolated from sediments of the Guaymas basin (Gulf of California, Mexico) taken from a depth of 2002 m. Cells were thin, motile, Gram-stain-positive, flexible rods forming terminal endospores. Strain Ra1766H(T) grew at temperatures of 25-45 degrees C (optimum 30 degrees C), pH 6.7-8.1 (optimum 7.5) and in a salinity of 5-60 g l(-1) NaCl (optimum 30 g l(-1)). It was an obligate heterotrophic bacterium fermenting carbohydrates (glucose and mannose) and organic acids (pyruvate and succinate). Casamino acids and amino acids (glutamate, aspartate and glycine) were also fermented. The main end products from glucose fermentation were acetate, butyrate, ethanol, H-2 and CO2. Sulfate, sulfite, thiosulfate, elemental sulfur, fumarate, nitrate, nitrite and Fe(III) were not used as terminal electron acceptors. The predominant cellular fatty acids were C-14 : 0, C-16:1 omega 7, C-16:1 omega 7 DMA and C-16:0. The main polar lipids consisted of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine and phospholipids. The G +C content of the genomic DNA was 33.7 molo/o. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain Ra1766H(T) was affiliated to cluster XI of the order Clostridia les, phylum Firmicutes. The closest phylogenetic relative of Ra1766H(T) was Geosporobacter subterraneus (94.2% 16S rRNA gene sequence similarity). On the basis of phylogenetic inference and phenotypic properties, strain Ra1766H(T) (=DSM 27501(T)=JCM 19377(T)) is proposed to be the type strain of a novel species of a novel genus, named Crassaminicella pro funda.