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

The mechanical properties of wheat straw fragments were measured using tens ile and shear tests before and after incubation in pure cultures of the rum en fungus Neocallimastix frontalis MCH3, in pure cultures of the rumen cell ulolytic bacteria Fibrobacter succinogenes S85 and Ruminococcus flavefacien s 007 and in co-cultures associating the fungus with each of the two bacter ial species. N. frontalis considerably reduced the tensile strength of the straw; on the contrary R. flavefaciens increased it and F: succinogenes did not affect i t. In co-cultures, F. succinogenes and N. frontalis interacted synergistica lly to weaken straw resistance, whereas R. flavefaciens inhibited the funga l action. The shear test also revealed that physical and mechanical propert ies were strongly affected by the action of the three microorganisms. After six days of incubation the straws resistance to shearing was lower after i ncubation with N. frontalis or R. flavefaciens than in the presence of F. s uccinogenes. 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. (C) 1999 Elsevie r Science B.V. All rights reserved.