Relative Contributions Of Rumen Microorganisms To Degradation Of Plant Cell Walls And The Relationship Between Their Adhesion And Degradation

Four experiments were conducted to study the relative contributions to the degradation of rumen microorganisms of plant cell walls with different particle sizes. The relationship between cellulolytic bacterial adhesion and subsequent degradation was also investigated. Furthermore, modification of bacterial cell surface was adopted with various enzymes and chemicals to determine the mechanism of adhesion of cellulolytic bacteria to plant cell walls.Exp. 1 was conducted to study the relative contributions and interactions of various ruminal microbial fractions to the degradation of ball-milled or ground com stalk cell walls using gas production and dry matter degradation in vitro procedure. Various chemicals and antibiotics were used to differentiate bacteria, protozoa, and fungi in the rumen fluid, and the following ruminal microbial fractions were formed: the whole rumen fluid (WRF) as positive control, the bacterial fraction (B), the protozoal fraction (P), the fungal fraction (F), bacterial plus protozoa! fraction (B+P), bacterial plus fungal fraction (B+F), protozoal plus fungal fraction (P+F), and a negative control fraction (CON). The gas production and degradation rate were significantly enhanced by the treatment of cell walls with ball mill (P<0.01); but the pattern of fermentation was not changed. There were significant differences in gas production and degradation rates among the various ruminal microbial fractions (P<0.01). The WRF fraction had the highest gas production and degradation rates of the cell wall of corn stover, followed by the co-cultures (B+P, P+F, and B+F), whereas monocultures (bacteria, protozoa, and fungi) showed a very low gas production and degradation rates. These results suggested that the digestion of plant cell wall in the rumen be achieved by the interaction of the ruminal bacteria, protozoa, and fungi. Either of them or each two combinations could not reach the same level of degradation of WRF. While the bacteria and protozoa be the main players to the degradation of cell walls of corn stover in the rumen. The contribution of rumen fungi to the ruminal degradation of plant cell walls be very small.Exp. 2 was conducted to study the adhesion ability of the cellulolytic bacterial strains Ruminococcus albus -7 to either ball milled or regular ground com stalk cell walls, or crystalline cellulose by incubating bacterial suspensions with each of three substrates for 60 min at 39#, allowing the substrates to precipitate for 60 min, centrifuging the mixtures at 1500 rpm for 5 min, and measuring the optical densities of the supernatants. There was no significant difference between the adhesion of R. albus -7 to ball milled com stalks cell wall and to crystalline cellulose, but both of them were significantly higher than the ground corn stalks cell wall (P<0.01). This result indicated that the increase of surface areas of substrates could enhance the extent of adhesion to substrates. The adhesion ability of R. albus -7 to ball milled corn stalks cell walls or crystalline cellulose was significantly decreased by the modifications with enzymes (trypsin or protease) or periodate (P<0.01), but the modifications with formalin and glutaraldehyde on adhesion of R. albus -7 to both of the substrates had no statistical difference compared with the control (P>0.05), indicating that both the protein and carbohydrate existing on the bacterial cell surface involved the mechanism of adhesion. The adhesion ability of R.albus -7 was greatly decreased by the modification with LiCl, strongly suggesting that the S-layer protein may take an important role in the adhesion process of R. albus -7.Exp. 3 was conducted to study the adhesion abilities and adhesive mechanisms of the ruminal cellulolytic bacterial strains of Rwninococcus jlavefaciens FD-1 and Fibrobacter succinogenes S85 to either ball milled or regular ground com stalks cell walls, or crystalline cellulose by the method of Exp. 2. There was no significant difference among the adhesion to the three substrates of R. flavefacie...