The effect of the carbohydrate growth substrate on the glycosidase activity of hemicellulose-degrading rumen bacterial isolates

Forages and pastures symposium: forage biodegradation: advances in ruminal microbial ecology

The rumen microbial ecosystem provides ruminants a selective advantage, the ability to utilize forages, allowing them to flourish worldwide in various environments. For many years, our understanding of the ruminal microbial ecosystem was limited to understanding the microbes (usually only laboratory-amenable bacteria) grown in pure culture, meaning that much of our understanding of ruminal function remained a "black box." However, the ruminal degradation of plant cell walls is performed by a consortium of bacteria, archaea, protozoa, and fungi that produces a wide variety of carbohydrate-active enzymes (CAZymes) that are responsible for the catabolism of cellulose, hemicellulose, and pectin. The past 15 years have seen the development and implementation of numerous next-generation sequencing (NGS) approaches (e.g., pyrosequencing, Illumina, and shotgun sequencing), which have contributed significantly to a greater level of insight regarding the microbial ecology of ruminants fed a variety of forages. There has also been an increase in the utilization of liquid chromatography and mass spectrometry that revolutionized transcriptomic approaches, and further improvements in the measurement of fermentation intermediates and end products have advanced with metabolomics. These advanced NGS techniques along with other analytic approaches, such as metaproteomics, have been utilized to elucidate the specific role of microbial CAZymes in forage degradation. Other methods have provided new insights into dynamic changes in the ruminal microbial population fed different diets and how these changes impact the assortment of products presented to the host animal. As more omics-based data has accumulated on forage-fed ruminants, the sequence of events that occur during fiber colonization by the microbial consortium has become more apparent, with fungal populations and fibrolytic bacterial populations working in conjunction, as well as expanding understanding of the individual microbial contributions to degradation of plant cell walls and polysaccharide components. In the future, the ability to predict microbial population and enzymatic activity and end products will be able to support the development of dynamic predictive models of rumen forage degradation and fermentation. Consequently, it is imperative to understand the rumen's microbial population better to improve fiber degradation in ruminants and, thus, stimulate more sustainable production systems.

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.

Cellulolytic enzymes of rumen anaerobic fungi Orpinomyces joyonii and Caecomyces communis

The rumen anaerobic fungi Orpinomyces joyonii A4 and Caecomyces communis JB1 were grown on microcrystalline cellulose (MC) and alfalfa hay. The cellular distribution of cellulases produced by these organisms was monitored. Fungal cultures were separated into extracellular, intracellular and cell wall fractions and assayed for endoglucanase (EG) and beta-glucosidase activity. In both fungal isolates, EG activity was the highest in the extracellular fraction regardless of the substrate used. The beta-glucosidase activity produced by O. joyonii was mainly found in the cell wall fraction. On the contrary, the same enzyme activity in C. communis predominated in the extracellular fraction. The polycentric isolate A4 more efficiently utilized both substrates, produced more short chain fatty acids (up to 31 mmol/l) and showed higher total levels of EG (2744 nmol glucose/h/ml) than the monocentric strain JB1. On the other hand, beta-glucosidase (9033 nmol glucose/h/ml) activity was the highest in cultures of C. communis grown on cellulose. In cultures of O. joyonii grown on MC, the production of yellow affinity substance (YAS) with similar properties compared with yellow substance from Clostridium thermocellum was observed. This compound increased the adsorption of fungal cellulases to MC the temperature and pH range tested.

Glycoside hydrolase production by an anaerobic rumen fungus Caecomyces communis

The ruminal fungus Caecomyces communis was grown anaerobically either in a discontinuous cultivation system or in a fermentor with daily withdrawal and addition of fresh medium. Lowe and Orpin media were tested. The best culture conditions for glycoside hydrolase production were obtained in Lowe medium with daily fresh medium addition, whereas the Orpin medium with ruminal fluid was favourable to fungal growth and to the enzyme export process. Among glycoside hydrolases assessed in both culture fluid and cellular homogenate, beta-D-fucosidase activity was preponderant. Most studied enzymes were mainly associated with cells (from 50% to 99%). Glycoside hydrolase activities were constitutive, but their level was regulated by a carbon source. beta-D-fucosidase and beta-D-xylosidase activity production was activated by the association of glucose plus cellobiose, whereas beta-D-glucosidase activity production was stimulated by cellobiose alone. Enzyme release could be favoured by glucose alone or by Ray grass hay added to glucose plus cellobiose.

Xylanolytic enzymes from fungi and bacteria

The development of new analytical techniques and the commercial availability of new substrates have led to the purification and characterization of a large number of xylan-degrading enzymes. Furthermore, the introduction of recombinant DNA technology has resulted in the selection of xylanolytic enzymes that are more suitable for industrial applications. For a successful integration of xylanases in industrial processes, a detailed understanding of the mechanism of enzyme action is, however, required. This review gives an overview of various xylanolytic enzyme systems from bacteria and fungi that have been described recently in more detail.

Polysaccharide hydrolase production by the rumen fungus Caecomyces communis

The anaerobic fungus Caecomyces communis was grown in a fermentor in either a discontinuous cultivation system or in a culture system with daily withdrawal and addition of fresh medium. Lowe and Orpin media were tested. The Lowe medium was best for the stimulation of enzyme production, the Orpin medium, for the stimulation of fungal growth and enzyme release. Xylanase activity was predominant among the polysaccharide hydrolases. Most of the enzymes studied were associated with cells except when the culture medium contained glucose or Ray grass hay. Enzymatic activities were constitutive, but their level was regulated by a carbon source. Cellulase production in both the cellular and extracellular fractions and the extracellular xylanase activity were stimulated by the presence of glucose. Cell-associated xylanase activity, however, was stimulated by glucose plus cellobiose. The presence of glucose enhanced enzyme release.

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.

Degradation and utilization of cellulose and straw by three different anaerobic fungi from the ovine rumen

Three different ruminal fungi, a Neocallimastix sp. (strain LM-1), a Piromonas sp. (strain SM-1), and a Sphaeromonas sp. (strain NM-1), were grown anaerobically in liquid media which contained a suspension of either 1% (wt/vol) purified cellulose or finely milled wheat straw as the source of fermentable carbon. Fungal biomass was estimated by using cell wall chitin or cellular protein in cellulose cultures and chitin in straw cultures. Both strains LM-1 and SM-1 degraded cellulose with a concomitant increase in fungal biomass. Maximum growth of both fungi occurred after incubation for 4 days, and the final yield of protein was the same for both fungi. Cellulose degradation continued after growth ceased. Strain NM-1 failed to grow in the cellulose medium. All three anaerobic fungi grew in the straw-containing medium, and loss of dry weight from the cultures indicated degradation of straw to various degrees (LM-1 greater than SM-1 greater than NM-1). The total fiber component and the cellulose component of the straw were degraded in similar proportions, but the lignin component remained undegraded by any of the fungi. Maximum growth yield on straw occurred after 4 days for strain LM-1 and after 5 days for strains SM-1 and NM-1. The calculated yield of cellular protein for strain LM-1 was twice that of both strains SM-1 and NM-1. The cellular protein yield of strain SM-1 was the same in both cellulose and straw cultures. In contrast to cellulose, straw degradation ceased after the end of the growth phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of mucin on glycosidase, protease and arylamidase activities of human gut bacteria grown in a 3-stage continuous culture system

Human intestinal bacteria were grown in a 3-stage continuous culture system on a medium containing complex polysaccharides and proteins as carbon and nitrogen sources. Selected bacterial populations were enumerated and glycosidase, protease and arylamidase activities measured. Comparison of arylamidase and glycosidase activities in the multichamber system (MCS) and faeces showed that the predominant faecal enzymes were also produced by bacteria growing in the MCS. After 48 d operation, porcine gastric mucin (5.8 g/d) was independently fed to vessel 1. Elevated levels of volatile fatty acid (VFA) formation showed that the glycoprotein was actively fermented. The increase in carbohydrate availability as a result of breakdown of the mucin oligosaccharides stimulated bacterial growth and activities. The enzymological measurements showed that mucin increased production of both cell-bound and extracellular glycosidases, such as beta-galactosidase, alpha-glucosidase and N-acetyl-beta-glucosaminidase. Protease activities were profoundly influenced by mucin. These were largely cell-bound in non-mucin cultures but were predominantly extracellular and collagenolytic when mucin was present. Experiments with protease inhibitors showed that cysteine proteases were the major cell-bound and extracellular enzymes in both mucin and non-mucin cultures, but that serine and metalloproteases were also present. The effect of mucin on arylamidase formation was less marked, although there was increased production of these enzymes in vessels 1 and 2 of the MCS. These results suggest that host-produced substances such as mucin glycoprotein may play a role in modulating the growth and activity of bacteria growing in the human large intestine.

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.