Two intracellular and cell type-specific bacterial symbionts in the placozoan Trichoplax H2

摘要: Placozoa is an enigmatic phylum of simple, microscopic, marine metazoans1,2. Although intracellular bacteria have been found in all members this phylum, almost nothing known about their identity, location and interactions with host3-6. We used metagenomic metatranscriptomic sequencing single host individuals, plus metaproteomic imaging analyses, to show that the placozoan Trichoplax sp. H2 lives symbiosis two bacteria. One symbiont forms undescribed genus Midichloriaceae (Rickettsiales)7,8 has a genomic repertoire similar rickettsial parasites9,10, but does not seem express key genes for energy parasitism. Correlative image analyses three-dimensional electron tomography revealed resides rough endoplasmic reticulum its host's internal fibre cells. The second belongs Margulisbacteria, without cultured representatives form associations11-13. This ventral epithelial cells Trichoplax, probably metabolizes algal lipids digested by capacity supplement placozoan's nutrition. Our study shows one simplest animals evolved highly specific intimate associations symbiotic, highlights symbioses can provide access otherwise elusive microbial dark matter.