The nature of anaerobic fungi and their polysaccharide degrading enzymes

The discovery of anaerobic fungi has added a new member to the indigenous microorganisms that inhabit the rumen ecosystem. Anaerobic fungi do not appear essential for the survival of ruminants due to their presence in very low numbers, and sometimes absence, in ruminants fed low fiber diets, but their presence may likely be very important in the digestion of fibrous diets. The anaerobic fungi have adapted well to the rumen environment. They are able to ferment a large array of soluble carbohydrates and can synthesize cellular components in an anaerobic environment. The fungi posses hydrogenosomes for the removal of reducing equivalents in the form of molecular hydrogen and the removal of trace oxygen is a accomplished via removal by NADH oxidase. Their positive synergistic interaction with methanogenic bacteria eludes to their highly evolved role in the rumen environment. The fungi also produce resistant sporangia that allows for transfer of species to a new host in an oxygen environment. The anaerobic fungi posses a highly active array of polysaccharide degrading enzymes that may provide an advantage in the highly competitive rumen ecosystem. The production of specific enzymes that hydrolyze the lignocellulosic fraction of plant walls is unique in rumen microorganisms and allows for their attachment and growth on fibrous plant particles that are not available to the rumen bacteria.