Prokaryotic endosymbionts in the chloroplast stroma of the dinoflagellateWoloszynskia pascheri

Abstract

Chloroplasts of the freshwater dinoflagellate,Woloszynskia pascheri, were found to contain small, double membrane-bound bodies that appear to be modified bacteria existing in this organelle as endosymbionts. These “chloroplast endosymbionts” (CESs) contain thin filaments, which observations on thin-sectioned and Feulgen-stained material indicate to be strands of “naked” DNA. They also possess putative prokaryotic-sized ribosomes. The outer of the two membranes that surround a CES may be expanded to form cisternae or tubules, which frequently connect with the outer membrane of adjacent CESs. Considering their appearance in relation to free-living bacteria, and their apparently benign presence in the dinoflagellate host, it is suggested that the CESs have been involved in a symbiotic relationship withW. pascheri for some time.