ANAEROBIC FUNGI IN HERBIVOROUS ANIMALS

The conviction that all fungi required oxygen for growth was summarize d in 1949 by J. N. Foster when he wrote, 'One of the major metabolic d ifferences between moulds and bacteria is that there are no anaerobic moulds, either obligate or facultative'. For obligate anaerobes, this view held until 1975, when C. G. Orpin demonstrated that certain motil e cells in the rumen of sheep, previously believed to be protozoan fla gellates, were in fact zoospores of an obligately anaerobic fungus. Pr ior to this discovery it was assumed that only anaerobic bacteria and protozoa were involved in the hydrolysis of plant biomass in the rumen , but now it is acknowledged that anaerobic fungi participate in this process both in ruminants such as sheep and hindgut-fermenting herbivo res such as horses. This review describes the life-cycles and physiolo gy of anaerobic fungi, details their interactions with other rumen mic ro-organisms and assesses their contribution to the digestion of plant material in herbivores.