MEMBRANE-BOUNDED NUCLEOIDS IN MICROBIAL SYMBIONTS OF MARINE SPONGES

In thin sections of resin-embedded samples of glutaraldehyde- and osmi um tetroxide-fixed tissue from five genera of marine sponges, Stromato spongia, Astrosclera, Jaspis, Pseudoceratina and Axinyssa, cells of a bacteria-like symbiont microorganism which exhibit a membrane-bounded nuclear region encompassing the fibrillar nucleoid have been observed within the sponge mesohyl. The nuclear region in these cells is bounde d by a single bilayer membrane, so that the cell cytoplasm is divided into two distinct regions. The cell wall consists of subunits analogou s to those in walls of some Archaea. Cells of the sponge symbionts obs erved here are similar to those of the archaeal sponge symbiont Cenarc haeum symbiosum. (C) 1998 Federation of European Microbiological Socie ties. Published by Elsevier Science B.V. All rights reserved.