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 rRNA sequence studies has shown in three cases that endosymbiotic methanogenic bacteria differ from free-living species. Frequently, endosymbiotic methanogens are localized in anaerobic protozoa near hydrogenosomes - organelles that produce H-2, CO2 and acetate, all of which are substrates for methanogenesis. Hydrogenosomes are also present in anaerobic fungi. The current view is that the organelles are endosymbiont-derived and were probably acquired on several distinct occasions during evolution.