SYMBIONTS AND ORGANELLES IN ANAEROBIC PROTOZOA AND FUNGI

The discovery of methanogenic bacteria as endosymbionts of free-living anaerobic protozoa opened new fields of research in microbial ecology , cell physiology and molecular biology. Recent information from 16S r RNA sequence studies has shown in three cases that endosymbiotic metha nogenic bacteria differ from free-living species. Frequently, endosymb iotic methanogens are localized in anaerobic protozoa near hydrogenoso mes - organelles that produce H-2, CO2 and acetate, all of which are s ubstrates for methanogenesis. Hydrogenosomes are also present in anaer obic fungi. The current view is that the organelles are endosymbiont-d erived and were probably acquired on several distinct occasions during evolution.