ENDOSYMBIOTIC INTERACTIONS IN ANAEROBIC PROTOZOA

Several aspects of the endosymbiosis of methanogenic archaea with anae robic protozoa are reviewed. Special attention is payed to the role of hydrogenosomes and plastid-like organelles that seem to provide the s ubstrates for the methanogenic endosymbionts. Evidence is presented th at hydrogenosomes evolved several times in the various protoctistan ta xa. Hydrogenosomes are seemingly different, and their common denominat or is the production of hydrogen. The absence of nucleic acids and a p rotein-synthesizing machinery hampers the analysis of their divergent evolutionary history, and molecular genetic data argue not only for di fferent but even a chimeric origin of the hydrogenosomes.