Mechanical resistance of wheat straw after incubation in cultures of ruminal cellulolytic microorganisms

The mechanical properties of wheat straw fragments were measured using tensile and shear tests before and after incubation in pure cultures of the rumen fungus Neocallimastix frontalis MCH3, in pure cultures of the rumen cellulolytic bacteria Fibrobacter succinogenes S85 and Ruminococcus flavefaciens 007 and in co-cultures associating the fungus with each of the two bacterial species.

N. frontalis considerably reduced the tensile strength of the straw; on the contrary R. flavefaciens increased it and F. succinogenes did not affect it. In co-cultures, F. succinogenes and N. frontalis interacted synergistically to weaken straw resistance, whereas R. flavefaciens inhibited the fungal action. The shear test also revealed that physical and mechanical properties were strongly affected by the action of the three microorganisms. After six days of incubation the straws resistance to shearing was lower after incubation with N. frontalis or R. flavefaciens than in the presence of F. succinogenes. No synergism or antagonism between microorganisms was observed in the shear test.

These results thus clearly demonstrate a specific action of the three rumen microorganisms in physical degradation of plant material.