Methylcellulose inhibition of exo-beta-1,4-glucanase A from Ruminococcus flavefaciens FD-1

Effects of Methylcellulose on Cellulolytic Bacteria Attachment and Rice Straw Degradation in the In vitro Rumen Fermentation

An in vitro experiment was conducted to evaluate the effect of methylcellulose on the attachment of major cellulolytic bacteria on rice straw and its digestibility. Rice straw was incubated with ruminal mixture with or without 0.1% methylcellulose (MC). The attachment of F. succinogenes, R. flavefaciens and R. albus populations on rice straw was measured using real-time PCR with specific primer sets. Methylcellulose at the level of 0.1% decreased the attachment of all three major cellulolytic bacteria. In particular, MC treatment reduced (p<0.05) attachment of F. succinogenes on rice straw after 10 min of incubation while a significant reduction (p<0.05) in attachment was not observed until 4 h incubation in the case of R. flavefaciens and R. albus. This result indicated F. succinogenes responded to MC more sensitively and earlier than R. flavefaciens and R. albus. Dry matter digestibility of rice straw was subsequently inhibited by 0.1% MC, and there was a significant difference between control and MC treatment (p<0.05). Incubated cultures containing MC had higher pH and lower gas production than controls. Current data clearly indicated that the attachment of F. succinogenes, R. flavefaciens and R. albus on rice straw was inhibited by MC, which apparently reduced rice straw digestion.

Adhesion of cellulolytic ruminal bacteria to barley straw

Adhesion of the cellulolytic ruminal bacteria Ruminococcus flavefaciens and Fibrobacter succinogenes to barley straw was measured by incubating bacterial suspensions with hammer-milled straw for 30 min, filtering the mixtures through sintered glass filters, and measuring the optical densities of the filtrates. Maximum adhesion of both species occurred at pH 6.0 and during mid- to late-exponential phase. Adhesion was saturable at 33 and 23 mg (dry weight) g of straw for R. flavefaciens and F. succinogenes, respectively. Methyl cellulose and carboxymethyl cellulose inhibited adhesion by 24 to 33%. Competition between species was determined by measuring characteristic cell-associated enzyme activities in filtrates of mixtures incubated with straw; p-nitrophenyl-beta-d-lactopyranoside hydrolysis was used as a marker for F. succinogenes, while either beta-xylosidase or carboxymethyl cellulase was used for R. flavefaciens, depending on the other species present. R. flavefaciens had no influence on F. succinogenes adhesion, and F. succinogenes had only a minor (<20%) effect on R. flavefaciens adhesion. The noncellulolytic ruminal bacteria Bacteroides ruminicola and Selenomonas ruminantium had no influence on adhesion of either cellulolytic species, although these organisms also adhered to the straw. We concluded that R. flavefaciens and F. succinogenes have separate, specific adhesion sites on barley straw that are not obscured by competition with non-cellulolytic species.

Effects of Tween 60 and Tween 80 on protease activity, thiol group reactivity, protein adsorption, and cellulose degradation by rumen microbial enzymes

Microbial enzymes extracted from mixed ruminal microorganisms were incubated for 2 h with casein and Tween 60 or Tween 80 at 10 concentrations ranging from 0 to 2.0% (vol/vol) to determine the effects of these nonionic surfactants on protease activation and thiol reactivity (unmasking of thiol groups). Rate and extent of protein adsorption to cellulosic substrate (barley straw) was measured in the presence of 0, 0.05, 0.10, 0.25, and 0.50% (vol/vol) Tween 80. Degradation of cellulose by a rumen bacterial fraction was measured over 48 h of incubation with and without Tween 60 or Tween 80 at 0.25% (vol/vol). Maximum accelerations of protease activity achievable with Tween 60 and Tween 80 (calculated from a Michaelis-Menten kinetics model) were 99.2 and 166.8%, respectively. Concentrations of Tween 60 and Tween 80 at which half the maximal velocities were attained were 0.28 and 0.20% (vol/vol), respectively. Tween 80 increased (P < 0.05) the rate and extent of adsorption of microbial protein to barley straw, and the effect was related to concentration of Tween 80 up to 0.10% (vol/vol). Initial rates of cellulose degradation with no surfactant, 0.25% Tween 60, or 0.25% Tween 80 were 0.60, 0.87, and 1.04 micrograms/ml per h, respectively. These nonionic surfactants were effective for enhancing rumen microbial protease and cellulase activities. Thus, further study is warranted to determine their potential for improving ruminant feeding.

Effects of Physicochemical Factors on the Adhesion to Cellulose Avicel of the Ruminal Bacteria Ruminococcus flavefaciens and Fibrobacter succinogenes subsp. succinogenes

Ruminococcus flavefaciens adhered instantly to cellulose, while Fibrobacter succinogenes had the highest percentage of adherent cells after about 25 min of contact between bacteria and cellulose. Adhesion of R. flavefaciens was unaffected by high concentrations of sugars (5%), temperature, pH, oxygen, metabolic inhibitors, and lack of Na + . In contrast, the attachment was affected by the removal of divalent cations (Mg 2+ and Ca 2+ ), the presence of cellulose derivatives (methylcellulose and hydroxyethylcellulose), and cystine. Adhesion of F. succinogenes was sensitive to low and high temperatures, high concentrations of glucose and cellobiose (5%), hydroxyethylcellulose (0.1%), redox potential, pH, lack of monovalent cations, and the presence of an inhibitor of membrane ATPases or lasalocid and monensin. Cells of F. succinogenes heated at 100°C no longer were adherent. On the other hand, adhesion was insensitive to the lack of divalent cations (Mg 2+ and Ca 2+ ), the presence of 2,4-dinitrophenol, tetrachlorosalicylanilide, or inhibitors of the electron transfer chains. Adhesion of F. succinogenes seems to be related to the metabolic functions of the cell. External proteins and/or cellulases themselves might play a part in the attachment process. Several mechanisms are probably involved in the adhesion of R. flavefaciens , the main one being the interaction between the large glycocalyx and the divalent cations Ca 2+ and Mg 2+ . Hydrophobic bonds and enzymes may also be involved.

Improved assay for quantitating adherence of ruminal bacteria to cellulose

A quantitative technique suitable for the determination of adherence of ruminal bacteria to cellulose was developed. This technique employs adherence of cells to cellulose disks and alleviates the problem of nonspecific cell entrapment within cellulose particles. By using this technique, it was demonstrated that the adherence of Ruminococcus flavefaciens FD1 to cellulose was inhibited by formaldehyde, methylcellulose, and carboxymethyl cellulose. Adherence was unaffected by acid hydrolysates of methylcellulose, glucose, and cellobiose.