Structure of Nitrosocystis oceanus and Comparison with Nitrosomonas and Nitrobacter

Abstract

Murray , R. G. E. (University of Western Ontario, London, Ont., Canada), and S. W. Watson . Structure of Nitrosocystis oceanus and comparison with Nitrosomonas and Nitrobacter . J. Bacteriol. 89: 1594–1609. 1965.— Nitrosocystis oceanus has distinctive features: the cell wall (overall thickness, 250 A) has an inner triplet structure and a dense enveloping layer; between these lie the “cell-wall organelles” (two or more per cell; plaques about 0.5 μ in diameter and 0.1 μ thick) of unknown function and genesis. The plasma membrane (ca. 80 A) shows rare intrusions that form irregular peripheral vesicles, which appear to form the component lamellae of the “membranous organelle” and probably detach from the periphery. The membranous organelles consist of about 20 vesicles so flattened that the lumen is only 100 A thick. The outer surfaces are in contact and form a triplet structure with an accentuated center line; these lamellae almost traverse the cell, displace the cytoplasm and the nucleoplasms, and form the prominent, seemingly permanent, feature of the cell. Division is constrictive without trace of a septum, and the act of division divides the membranous organelle. No mesosomes appear to be formed. Nitrosomonas europaea shows no sign of a cell-wall organelle or of the outer enveloping layer of wall. The cytoplasm contains intrusive paired lamellae, which might or might not remain connected to the periphery, and they do not fuse or form regular associations. These are thought to be the equivalent of the vesicles in Nitrosocystis but remaining almost parallel and close to the plasma membrane. Nitrobacter agilis has a unique plasma membrane with a (50 A) dense layer applied to the inside of the usual unit membrane. All of the components are represented in the intrusions, which are arranged over and shape the poles of the cells, with close and regular spacing. Each nitrifier was distinctive; in common they have membrane systems which, it is considered, must relate to the specialized mechanisms for acquiring energy adopted by these organisms.