Relative contributions of bacteria, protozoa, and fungi to in vitro degradation of orchard grass cell walls and their interactions

To assess the relative contributions of microbial groups (bacteria, protozo a, and fungi) in rumen fluids to the overall process of plant cell wall dig estion in the rumen, representatives of these groups were selected by physi cal and chemical treatments of whole rumen fluid and used to construct an a rtificial rumen ecosystem, Physical treatments involved homogenization, cen trifugation, filtration, and heat sterilization, Chemical treatments involv ed the addition of antibiotics and various chemicals to rumen fluid, To eva luate the potential activity and relative contribution to degradation of ce ll walls by specific microbial groups, the following fractions were prepare d: a positive system (whole ruminal fluid), a bacterial (B) system, a proto zoal (P) system, a fungal (F) system, and a negative system (cell-free rume n fluid), To assess the interactions between specific microbial fractions, mixed cultures (B+P, B+F, and P+F systems) were also assigned, Patterns of degradation due to the various treatments resulted in three distinct groups of data based on the degradation rate of cell wall material and on cell wa ll-degrading enzyme activities. The order of degradation was as follows: po sitive and F systems > B system > negative and P systems. Therefore, fungal activity was responsible for most of the cell wall degradation. Cell wall degradation by the anaerobic bacterial fraction was significantly less than by the fungal fraction, and the protozoal fraction failed to grow under th e conditions used. In general, in the mixed culture systems the coculture s ystems demonstrated a decrease in cellulolysis compared,vith that of the mo noculture systems. When one microbial fraction was associated with another microbial fraction, two types of results were obtained. The protozoal fract ion inhibited cellulolysis of cell wall material by both the bacterial and the fungal fractions, while in the coculture between the bacterial fraction and the fungal fraction a a synergistic interaction was detected.