Effect of cellulose fine structure on kinetics of its digestion by mixed ruminal microorganisms in vitro (original) (raw)
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Initial pH as a determinant of cellulose digestion rate by mixed ruminal microorganisms in vitro
Journal of dairy science, 2001
In vitro fermentations of pure cellulose by mixed ruminal microorganisms were conducted under conditions in which pH declined within ranges similar to those observed in the rumen. At low cellulose concentrations (12.5 g/L), the first-order rate constants (k) of cellulose disappearance were successively lower at initial pH values of 6.86, 6.56, and 6.02, but in each case the value of k was maintained over a pH range of 0.3 to 1.2 units, as the fermentation progressed. Plots of k versus initial pH were linear, and k displayed a relative decrease of approximately 7% per 0.1 unit decrease in pH. At high cellulose concentration (50 g/L) and an initial pH of 6.8, cellulose digestion was initially zero order, the absolute rate of digestion declined with pH and digestion essentially ceased at pH 5.3 after only 30% of the added cellulose was digested. Further incubation resulted in a loss of bound N and P, suggesting that at low pH cells lysed or detached from the undigested fibers. Pure cul...
Quantitative analysis of cellulose degradation and growth of cellulolytic bacteria in the rumen
FEMS Microbiology Ecology, 2000
Ruminant animals digest cellulose via a symbiotic relationship with ruminal microorganisms. Because feedstuffs only remain in the rumen for a short time, the rate of cellulose digestion must be very rapid. This speed is facilitated by rumination, a process that returns food to the mouth to be rechewed. By decreasing particle size, the cellulose surface area can be increased by up to 10 6fold. The amount of cellulose digested is then a function of two competing rates, namely the digestion rate (K d) and the rate of passage of solids from the rumen (K p). Estimation of bacterial growth on cellulose is complicated by several factors: (1) energy must be expended for maintenance and growth of the cells, (2) only adherent cells are capable of degrading cellulose and (3) adherent cells can provide nonadherent cells with cellodextrins. Additionally, when ruminants are fed large amounts of cereal grain along with fiber, ruminal pH can decrease to a point where cellulolytic bacteria no longer grow. A dynamic model based on STELLA s software is presented. This model evaluates all of the major aspects of ruminal cellulose degradation: (1) ingestion, digestion and passage of feed particles, (2) maintenance and growth of cellulolytic bacteria and (3) pH effects.
Differential fermentation of cellulose allomorphs by ruminal cellulolytic bacteria
Applied and environmental microbiology, 1991
In addition to its usual native crystalline form (cellulose I), cellulose can exist in a variety of alternative crystalline forms (allomorphs) which differ in their unit cell dimensions, chain packing schemes, and hydrogen bonding relationships. We prepared, by various chemical treatments, four different alternative allomorphs, along with an amorphous (noncrystalline) cellulose which retained its original molecular weight. We then examined the kinetics of degradation of these materials by two species of ruminal bacteria and by inocula from two bovine rumens. Ruminococcus flavefaciens FD-1 and Fibrobacter succinogenes S85 were similar to one another in their relative rates of digestion of the different celluloses, which proceeded in the following order: amorphous > III(I) > IV(I) > III(II) > I > II. Unlike F. succinogenes, R. flavefaciens did not degrade cellulose II, even after an incubation of 3 weeks. Comparisons of the structural features of these allomorphs with t...
Degradation of Cellulose and Hemicellulose by Ruminal Microorganisms
Microorganisms
As major structural components of plant cell walls, cellulose and hemicellulose are degraded and fermented by anaerobic microbes in the rumen to produce volatile fatty acids, the main nutrient source for the host. Cellulose degradation is carried out primarily by specialist bacteria, with additional contributions from protists and fungi, via a variety of mechanisms. Hemicelluloses are hydrolyzed by cellulolytic bacteria and by generalist, non-cellulolytic microbes, largely via extracellular enzymes. Cellulose hydrolysis follows first-order kinetics and its rate is limited by available substrate surface area. Nevertheless, its rate is at least an order of magnitude more rapid than in anaerobic digesters, due to near-obligatory adherence of microbial cells to the cellulose surface, and a lack of downstream inhibitory effects; in the host animal, fiber degradation rate is also enhanced by the unique process of rumination. Cellulolytic and hemicellulolytic microbes exhibit intense compe...
Journal of Dairy Science, 1968
Per cent cellulose digestion values for twelve different forages~ under limiting substrafe conditions, were obtained with seven strains of cellulolytic rlnnen bacteria and correlated with various in vivo parameters of forage digestibility. When the forages were considered by type (eight samples of grasses and four samples of alfalfa)~ correlations with all seven strains were very high. On the other hand, when all twelve forages were combined, cellulose digestion by four of the seven strains was highly correlated with in vivo dry matter digestibility (D~.ID) and cellulose digestibility (CD), and quite low correlation coefficients were obtained with the criteria of relative intake (RI) and nutritive value index (NVI). Considerably better correlation coefficients with NVI and RI were obtained with eellulose digestibility data from the three remaining strains. Combining the cellulose digestibility data with the chemical measurement of dry matter solubility (DMS) markedly improved the correlations with both NVI and RI. On the basis of these results, one organlsm from each of the two groups was selected, and cellulose digestion was measured on a seNes of 64 forages. Correlation eoefficients were calculated for the different types of forages (22 grasses~ 17 alfalfa and 25 mixed forages) and all forages combined. In addition, DMS values were combined with the di~'estibility data and similar correlations determined. For all 64 forages combined, the best correlation coefficients obtained were: RI, 0.76; NVI, 0.88; DMD, 0.89; CD, 0.90~ energy digestion (ED), 0.90. These correlations are similar to or somewhat higher than those obtained on this series of forages by ehemieaI and in vitro mixed culture fermen-
Why don't ruminal bacteria digest cellulose faster?
Journal of dairy science, 1996
The bacteria Fibrobacter succinogenes, Ruminococcus flavefaciens, and Ruminococcus albus generally are regarded as the predominant cellulolytic microbes in the rumen. Comparison of available data from the literature reveals that these bacteria are the most actively cellulolytic of all mesophilic organisms described to date from any habitat. In light of numerous proposals to improve microbial cellulose digestion in ruminants, it is instructive to examine the characteristics of these species that contribute to their superior cellulolytic capabilities and to identify the factors that prevent them from digesting cellulose even more rapidly. As a group, these species have extreme nutritional specialization. They are able to utilize cellulose (or in some cases xylan) and its hydrolytic products as their nearly sole energy sources for growth. Moreover, each species apparently has evolved to similar maximum rates of cellulose digestion (first-order rate constants of 0.05 to 0.08 h-1). Activ...
Enhancement of solubilization rate of cellulose in anaerobic digestion and its drawbacks
Process Biochemistry, 2011
Hydrolysis is widely acknowledged as the rate-limiting step in anaerobic digestion of solid cellulose to biogas (methane), and pretreatment is generally considered to facilitate the process. However, few studies have investigated how such pretreatment may affect the rest of this complex process. The present study compared the solubilization rate in anaerobic digestion of cotton linter (high crystalline cellulose), with that of regenerated cellulose (amorphous cellulose), using pretreatment with NMMO. Batch digestions were performed, with the initial cellulose concentrations ranging between 5 and 40 g/l, and during 30 days of incubation, biogas and VFAs production as well as pH and COD changes were measured. The lag time before digestion started was longer for the high crystalline cellulose than for the amorphous one. The maximum solubilization rates of treated cellulose were 842 and 517 mg sCOD/g cCOD/day at the initial cellulose concentration of 5 and 30 g/l, respectively, while the solubilization rate of untreated cellulose never exceeded 417 mg sCOD/g cCOD/day. The difference between the two cellulose types was a direct result of the high rate of hydrolysis inhibiting the acetogenesis/methanogenesis microorganisms, a drawback to the rest of the process.
Applied and environmental microbiology, 1992
The ruminal cellulolytic bacterium Ruminococcus flavefaciens FD-1 was grown in cellulose-fed continuous culture with 20 different combinations of pH and dilution rate (D); the combinations were selected according to the physiological pH range of the organism (6.0 to 7.1) and growth rate of the organism on cellulose (0.017 to 0.10 h-1). A response surface analysis was used to characterize the effects of pH and D on the extent of cellulose consumption, growth yield, soluble sugar concentration, and yields of fermentation products. The response surfaces indicate that pH and D coordinately affect cellulose digestion and growth yield in this organism. As expected, the net cellulose consumption increased with increasing D while the fraction of added cellulose that was utilized decreased with increasing D. The effect of changes in pH within the physiological range on cellulose consumption was smaller than that of changes in D. Cellulose degradation was less sensitive to low pH than to high...
Journal of Animal Science, 2003
A series of in vitro studies was conducted to determine the effects of adding a commercial enzyme product on the hydrolysis and fermentation of cellulose, xylan, and a mixture (1:1 wt/wt) of both. The enzyme product (Liquicell 2500, Specialty Enzymes and Biochemicals, Fresno, CA) was derived from Trichoderma reesei and contained mainly xylanase and cellulase activities. Addition of enzyme (0.5, 2.55 and 5.1 L/g of DM) in the absence of ruminal fluid increased (P < 0.001) the release of reducing sugars from xylan and the mixture after 20 h of incubation at 20°C. Incubations with ruminal fluid showed that enzyme (0.5 and 2.55 L/g of DM) increased (P < 0.05) the initial (up to 6 h) xylanase, endoglucanase, and β-D-glucosidase activities in the liquid fraction by an average of 85%. Xylanase and endoglucanase activities in the solid fraction also were increased (P < 0.05) by enzyme addition,
Studies on cellulose degrading microorganisms associated with rumen of ruminant animals
Studies on cellulose degrading microorganisms associated with rumen of ruminants was carried out from ruminants (ram, cow, and goat), through culture, microscopic identification, Biochemical test and cellulose degrading methods. In the rumen content of ram four bacteria were isolated Bacteriodes and Staphylococcus had the highest percentage (33.3%) each while Veillonella and Bacillus had 16.6% each. Seven bacteria were isolated from cow with Streptococcus having (22.2%) Staphylococcus (22.2%), while Bacteroides, Yersinia, Peptococcus, Nesseria and Bacillus had equal distribution. Goat had eight bacteria including Bacteroides, Clostridium, Yersinia, Staphylococcus, Homofermentative Lactobacillus Alcaligens and Bacillus all of which had equal distribution. Bacteroides and Bacillus are common in all rumens, with Bacteroides, being more prevalent in the ram. study revealed that ruminants harbors various organisms that are active cellulose degraders, out of which Bacteroides specie grow best on cellulose agar. For fungi, Aspergillus flavus and Aspergillus fumigatus highly degrades cellulose, Scopulariopsis candida degrades minimally. The study revealed that ruminants harbors various organisms that are active cellulose degraders, out of which Bacteroides specie grow best on cellulose agar. Therefore, Rumen should be used as a site for isolation of micro organisms capable of cellulose hydrolysis in order to reduce the coast of purchasing commercial enzymes