Effect of anaerobic fungi on glycoside hydrolase and polysaccharide depolymerase activities, in sacco straw degradation and volatile fatty acid concentrations in the rumen of gnotobiotically reared lambs.

Four naturally born lambs were placed in sterile isolators 24 h after birth, before the natural establishment of the cellulolytic microorganisms. At the age of 4 weeks, a cellulolytic bacterial population of approximately 10(8) cells g-1 of rumen contents was established by inoculation with a 10(-6) dilution of ruminal contents taken from an adult sheep. A pure culture of Neocallimastix frontalis MCH3 and Piromyces communis FL was inoculated into the rumen 5 months after birth and a stable population of 10(3)-10(4) zoospores g-1 developed; the cellulolytic bacteria and fungi established populations in the 4 lambs that were similar to those observed in conventional animals. The presence of fungi led to an increase in the activity of most of the glycoside and polysaccharide hydrolases of the particle-associated microbial populations. However, this effect was not accompanied by an increase in the in sacco degradation of wheat straw or an increase in the volatile fatty acid concentration in the rumen contents.