The production of plant cell wall polysaccharide-degrading enzymes by hemicellulolytic rumen bacterial isolates grown on a range of carbohydrate substrates

Effect of barley straw and Egyptian clover hay on the rumen fermentation and structure and fibrolytic activities of rumen bacteria in dromedary camel

Background and Aim: Understanding the regulations of rumen microbiota and their fibrolytic capabilities under different forages are essential to improve rumen fermentation and animal feed efficiency. This study aimed to evaluate the changes in the rumen fermentation and the structure and fibrolytic activities of rumen bacteria in camels fed barley straw and Egyptian clover hay. Materials and Methods: Three fistulated camels were fed a diet containing barley straw for 30 days; then transitioned to a diet containing Egyptian clover hay for 30 days. In addition, bacterial media enriched with xylan and different cellulose sources, namely, filter paper, wheat straw, and alfalfa hay, were used to evaluate the ability of camel rumen bacteria to produce xylanase and cellulase enzymes. Results: The camel group fed Egyptian clover hay showed higher crude protein intake, rumen ammonia, total volatile fatty acids, and acetic acid. Moreover, the camel group fed barley straw showed higher neutral detergent fiber intake, rumen pH, and propionic and butyric acids. Principal component analysis showed that bacterial communities were separated based on the forage type. Forage type affected the composition of rumen bacteria and most of the bacterial community was assigned to phylum Bacteroidetes and Firmicutes. Egyptian clover hay diet increased the proportions of genus Prevotella and Ruminococcus; while fed barley straw diet increased the Butyrivibrio, RC9_gut_group, and Fibrobacteres. The bacterial culture of the Egyptian clover hay fed group produced the greatest xylanase and the bacterial culture of the barley straw fed group produced the maximum cellulase. Conclusion: Egyptian clover hay is recommended to feed camels in intensive production. Moreover, the bacterial community in the camel rumen is a promising source of lignocellulolytic enzymes.

Lignocelluloytic activities and composition of bacterial community in the camel rumen

The camel is well-adapted to utilize the poor-quality forages in the harsh desert conditions as the camel rumen sustains fibrolytic microorganisms, mainly bacteria that are capable of breaking down the lignocellulosic biomass efficiently. Exploring the composition of the bacterial community in the rumen of the camel and quantifying their cellulolytic and xylanolytic activities could lead to understanding and improving fiber fermentation and discovering novel sources of cellulases and xylanases. In this study, Illumina MiSeq sequencing of the V4 region on 16S rRNA was applied to identify the bacterial and archaeal communities in the rumen of three camels fed wheat straw and broom corn. Furthermore, rumen samples were inoculated into bacterial media enriched with xylan and different cellulose sources, including filter paper (FP), wheat straw (WS), and alfalfa hay (AH) to assess the ability of rumen bacteria to produce endo-cellulase and endo-xylanase at different fermentation intervals. The results revealed that the phylum Bacteroidetes dominated the bacterial community and Candidatus Methanomethylophilus dominated the archaeal community. Also, most of the bacterial community has fibrolytic potential and the dominant bacterial genera were Prevotella, RC9_gut_group, Butyrivibrio, Ruminococcus, Fibrobacteres, and Treponema. The highest xylanase production (884.8 mU/mL) was observed at 7 days. The highest cellulase production (1049.5 mU/mL) was observed when rumen samples were incubated with Alfalfa hay for 7 days.

The potential of bacteria isolated from ruminal contents of seaweed-eating North Ronaldsay sheep to hydrolyse seaweed components and produce methane by anaerobic digestion in vitro

The production of methane biofuel from seaweeds is limited by the hydrolysis of polysaccharides. The rumen microbiota of seaweed-eating North Ronaldsay sheep was studied for polysaccharidic bacterial isolates degrading brown-seaweed polysaccharides. Only nine isolates out of 65 utilized > 90% of the polysaccharide they were isolated on. The nine isolates (eight Prevotella spp. and one Clostridium butyricum) utilized whole Laminaria hyperborea extract and a range of seaweed polysaccharides, including alginate (seven out of nine isolates), laminarin and carboxymethylcellulose (eight out of nine isolates); while two out of nine isolates additionally hydrolysed fucoidan to some extent. Crude enzyme extracts from three of the isolates studied further had diverse glycosidases and polysaccharidase activities; particularly against laminarin and alginate (two isolates were shown to have alginate lyase activity) and notably fucoidan and carageenan (one isolate). In serial culture rumen microbiota hydrolysed a range of seaweed polysaccharides (fucoidan to a notably lesser degree) and homogenates of L. hyperborea, mixed Fucus spp. and Ascophyllum nodosum to produce methane and acetate. The rumen microbiota and isolates represent potential adjunct organisms or enzymes which may improve hydrolysis of seaweed components and thus improve the efficiency of seaweed anaerobic digestion for methane biofuel production.

Interactions between rumen bacterial strains during the degradation and utilization of the monosaccharides of barley straw cell-walls

Pure cultures and pair-combinations of strains representative of the rumen cellulolytic species Ruminococcus flavefaciens, Fibrobacter succinogenes and Butyrivibrio fibrisolvens were grown on cell-wall materials from barley straw. Of the pure cultures, R. flavefaciens solubilized straw most rapidly. The presence of B. fibrisolvens, which was unable to degrade straw extensively in pure culture, increased the solubilization of dry matter by R. flavefaciens and the solubilization of cell-wall carbohydrates by both R. flavefaciens and F. succinogenes. During fermentation, both R. flavefaciens and F. succinogenes released bound glucose and free and bound arabinose and xylose into solution. The accumulation of these sugars, especially arabinose and xylose, was greatly reduced in co-cultures containing B. fibrisolvens, suggesting that significant interspecies cross feeding of the products of hemicellulose hydrolysis (particularly soluble bound xylose released by F. succinogenes) occurs during straw degradation by mixed cultures containing this species.

Esterases of xylan-degrading microorganisms: production, properties, and significance

This review focuses on the description of recently discovered esterase enzymes involved in xylan degradation (acetyl xylan, feruloyl, and p-coumaroyl esterases). The occurrence of these enzymes in various microorganisms, assays used for determination of their activity, induction and production on different substrates, interaction with other xylanolytic enzymes, mode of action, substrate specificity, and biochemical characteristics are presented. The nature of substrates on which acetyl xylan esterase, feruloyl, and p-coumaroyl esterase are active and their role in xylan hydrolysis is emphasized. The potential applications of xylan-debranching esterases are outlined and their significance to applied microbiology is discussed.

Degradation of galactomannan by a Clostridium butyricum strain

An anaerobic, sporeforming, galactomannan-degrading bacterium was isolated from methanogenic granular sludge of an UASB reactor used for treatment of wastewater from a sugar refinery. The isolate degraded the polymer rapidly (doubling time was 55 min) and completely in mineral media. The bacterium was classified as Clostridium butyricum; the main products were acetate, butyrate, hydrogen, formate, and presumably CO2. The strain produced extracellular endo-mannanase, cell-associated exo-mannanase and intracellular alpha-galactosidase activity. The mannanases were present when grown on galactomannan, but not after growth on glucose, galactose, or mannose.

Physiology and genetics of xylan degradation by gastrointestinal tract bacteria

Hemicelluloses or xylans are major components (35%) of plant materials. For ruminant animals, about 50% of the dietary xylans are degraded, but only small amounts of xylans are degraded in the lower gut of nonruminant animals and humans. In the rumen, the major xylanolytic species are Butyrivibrio fibrisolvens and Bacteroides ruminicola. In the human colon, Bacteroides ovatus and Bacteroides fragilis subspecies "a" are major xylanolytic bacteria. Xylans are chemically complex, and their degradation requires multiple enzymes. Expression of these enzymes by gut bacteria varies greatly among species. Butyrivibrio fibrisolvens makes extracellular xylanases but Bacteroides species have cell-bound xylanase activity. Biochemical characterization of xylanolytic enzymes from gut bacteria has not been done. A xylosidase gene has been cloned from B. fibrosolvens 113. The data from DNA hybridizations using a xylanase gene cloned from B. fibrisolvens 49 indicate this gene may be present in other B. fibrisolvens strains. A cloned xylanase from Bact. ruminicola was transferred to and highly expressed in Bact. fragilis and Bact. uniformis. Arabinosidase and xylosidase genes from Bact. ovatus have been cloned and both activities appear to be catalyzed by a single, bifunctional, novel enzyme. Continued research in genetic and biochemical areas will provide knowledge and insights for manipulation of digestion at the gut level and improved understanding of colonic fiber digestion.

Molecular cloning of genes from Ruminococcus flavefaciens encoding xylanase and beta(1-3,1-4)glucanase activities

Clones expressing activity against xylan or beta(1-3,1-4)glucan (lichenan) were isolated from a library of Ruminococcus flavefaciens 17 DNA made in bacteriophage lambda EMBL3. Hybridization analyses indicated the recovery of four separate genes encoding xylanases that showed no detectable associated carboxylmethylcellulase activity. One of these genes was associated with clones that also expressed beta(1-3,1-4)glucanase and beta-xylosidase activities.

Synergism of rumen microbial hydrolases during degradation of plant polymers

In isolated mixture of exocellular enzymes of rumen bacteria Ruminococcus flavefaciens, Butyrivibrio fibrisolvens and rumen fungus Neocallimastix frontalis, specific activities of cellulases, hemicellulases and glycosidases were determined. The highest specific activities were shown mostly for proteins of N. frontalis.

Bacteroides xylanolyticus sp. nov., a xylanolytic bacterium from methane producing cattle manure

As part of a study of the biogas production from cattle waste, xylanolytic bacteria were isolated from enrichments of fermenting cattle manure. From 34 isolates, mostly Gram-negative rods, a typical strain was investigated in more detail. It was an anaerobic non-sporeforming, Gram-negative rod, which was motile with peritrichous flagella. This organism fermented xylan and many soluble sugars (glucose, cellobiose, mannose, xylose, arabinose). Other hemicelluloses such as gum xanthan, laminaran, locust bean gum, and gum arabic were not utilized. It also could not use cellulose. Fermentation products were carbon dioxide, hydrogen, acetate and ethanol. The bacterium produced carboxymethylcellulase and xylanase, especially when growing on xylan. Growth was optimal between 25 degrees C and 40 degrees C and between pH 6.5 and 7.5. The guanine plus cytosine content of the DNA was 34.8 +/- 0.8%. The isolate was identified as a member of the genus Bacteroides, and a new species is proposed: Bacteroides xylanolyticus (xylan dissolving). The type strain of B. xylanolyticus is strain X5-1 (DSM 3808).

Intracellular glycosidases of human colon Bacteroides ovatus B4-11

Activity of various glycosidases in the intracellular enzyme fraction of Bacteroides ovatus B4-11 was investigated. During 120 h of incubation at 37 degrees C, ca. 30% of the crude hemicellulose was hydrolyzed by an intracellular enzyme fraction of strain B4-11. Xylose was the major sugar released from crude hemicellulose. Glycosidases (alpha-1,6-glucosidase, alpha-1,4-glucosidase, beta-1,4-glucosidase, and beta-1,4-xylosidase) were induced in B. ovatus B4-11 by crude hemicellulose and heteroxylan. When B. ovatus B4-11 was grown on either crude hemicellulose or heteroxylan, the predominant enzyme in the intracellular enzyme fraction was beta-1,4-xylosidase.