抄録
Additional, intracytoplasmic membrane-stacked bacterial symbionts were found to colonize the same bacteriocytes of a hydrothermal vent snail, Alviniconcha hessleri, along with previously found slender rod-shaped symbionts. These membrane-stacked bacteria (MSB) were observed only in a part of the bacteriocytes in gill sections examined. Electron microscopy revealed that the bacteriocytes of A. hessleri possessed phagocytic activity. The phagocytic incorporation of MSB by bacteriocytes, in addition to uneven distribution of these bacteria among gill filaments, strongly suggest that MSB were acquired by the bacteriocyte as guests from the external environment. Electron micrographs revealed an intermediate phase of intracellular and extracellular existence of both types of bacteria. This mode of occurrence can be explained by the compromise between the avoidance of self defense mechanisms of host cell and keeping intimate contact with their host. Phage-like particles (PLPs) were found in the slender rod-shaped symbionts of A. hessleri. This is the first observation of PLPs inside symbiotic chemoautotrophic bacteria.
