Binding and degradation of lectins by components of rumen liquor

Benefits and Challenges of Jatropha Meal as Novel Biofeed for Animal Production

Jatropha curcas L. has gained importance as a source of seed oil for biodiesel production. The meal contained about 60% protein with a good balance of essential amino acids, containing various bioactive compounds, including saponins, phytic acids, trypsin inhibitors, lectins, phenolics, and flavonoids, which render it as a potential biofeed for animal production. The Jatropha meal demonstrated various biological activities, including antioxidant, antibacterial, and anti-inflammatory effects which enhance its property as a bio-feed. The levels of these bioactive compounds in the seeds are dependent on the genotypes. The J. curcas possessed different varieties which are either toxic or non-toxic according to the presence of phorbol esters. The presence of phorbol esters in the meal confirmed the toxic variety of Jatropha resulting in the limited application of meal as a biofeed. The Jatropha meal devoid of phorbol esters could be applied as a biofeed in the animal production industry, and for the toxic varieties, various techniques such as physicochemical and biological treatments have been introduced to the industry to remove the phorbol esters from Jatropha meal. Several studies employing various cells and animals confirmed the toxicity of the phorbol esters. The molecular mechanism of action of phorbol esters is through up-regulation of PKC-β II gene, overexpression of down-stream proto-oncogenes resulted in inflammation and oxidative stress ending by apoptotic cell death. Despite the presence of valuable bioactive compounds in the Jatropha meal, its nutritional application is not recommended unless the phorbol esters are completely removed.

Interaction of concanavalin a with bacterial lipopolysaccharides in agarose gel

Binding of fluorescein isothiocyanate-labeled concanavalin A to a series of molecular species of lipopolysaccharide (LPS), purified from pathogenic bacteria, was studied via agarose gel precipitation experiments and the results were compared with available structural data.The LPS species could be divided into ConA-reactive and non-reactive ones. Reactivity resided in the O-specific chain of LPS, and binding to the lipid A or core moieties of LPS could not be demonstrated by the present methods. The α-D-glucose or α-D-mannose residues of the repeating O-specific oligosaccharide units appeared to be recognized by ConA, except when blocked by steric hindrance. Specificity of the reaction was verified by inhibition with 2% D-glucose. Binding by bacterium-specific sugar-residues could not be demonstrated.For precipitation to occur, polyvalency was required both for LPS and ConA, and the resulting precipitation appeared to be promoted by hydrophobic interactions between the lipid A moieties of LPS molecules. The LPS species were differently retained by the agarose gel, which can be explained by differences in their micellar structure in aqueous solution. E. coli O83 LPS did not readily diffused in 1% agarose gel, but its precipitation with ConA could be demonstrated either at elevated temperature or mixing it previously with molten agarose (Mancini's arrangement).

Sucrose co-administration reduces the toxic effect of lectin on gut permeability and intestinal bacterial colonization

INTRODUCTION

Legume lectins can have toxic effects when consumed without adequate cooking, occasionally leading to an acute gastroenteritis. Lectins are sugar binging proteins and may use this property to execute their toxic effects; these toxic effects may be secondary to increased gut bacteria and intestinal permeability. However, whether or not sucrose rescues these toxic effects by decreasing gut bacterial concentration and intestinal permeability is unknown.

AIM

Our aim was to test the hypothesis that sucrose may reduce toxic effects of legume lectins by protecting barrier function, bacterial overgrowth and bacterial translocation.

METHODS

Twenty-four rats were randomized to an ad libitum diet of either standard rat chow, a chow containing 26% crude red kidney beans or a chow containing 26% crude red kidney beans supplemented with 1 mM sucrose in drinking water for 24 h. After 12-h fast, rats were gavaged with sugar probes; breath gas and urine were collected for 5 h. Intestine and liver tissues were then collected. Mucosa-associated total bacterial count were measured by targeting the 16s rRNA gene. Four groups of in vitro Caco-2 cell lines were treated with PBS, 200 μg/ml phytohemagglutinin (PHA), 1 mM sucrose and both 200 μg/ml PHA and 1 mM sucrose, respectively, and trans-epithelial resistance was measured.

RESULTS

Rats fed crude red kidney beans for 24 h showed significant weight loss when compared to controls (P < 0.05), as well as increased intestinal permeability (P < 0.05), increased bacterial load (P < 0.05) and increased bacterial translocation to the liver (P < 0.05). Sucrose rescues the drop in trans-epithelial resistance due to PHA in CaCO2-cells (P < 0.05).

CONCLUSIONS

Sucrose reduced crude red kidney beans induced increase in intestinal permeability, bacterial load and translocation. Since red kidney beans are an important source of dietary protein in the world, their potential toxicity when inadequately cooked may be rescued by a suitable complementary diet.

Opportunities to improve fiber degradation in the rumen: microbiology, ecology, and genomics

The degradation of plant cell walls by ruminants is of major economic importance in the developed as well as developing world. Rumen fermentation is unique in that efficient plant cell wall degradation relies on the cooperation between microorganisms that produce fibrolytic enzymes and the host animal that provides an anaerobic fermentation chamber. Increasing the efficiency with which the rumen microbiota degrades fiber has been the subject of extensive research for at least the last 100 years. Fiber digestion in the rumen is not optimal, as is supported by the fact that fiber recovered from feces is fermentable. This view is confirmed by the knowledge that mechanical and chemical pretreatments improve fiber degradation, as well as more recent research, which has demonstrated increased fiber digestion by rumen microorganisms when plant lignin composition is modified by genetic manipulation. Rumen microbiologists have sought to improve fiber digestion by genetic and ecological manipulation of rumen fermentation. This has been difficult and a number of constraints have limited progress, including: (a) a lack of reliable transformation systems for major fibrolytic rumen bacteria, (b) a poor understanding of ecological factors that govern persistence of fibrolytic bacteria and fungi in the rumen, (c) a poor understanding of which glycolyl hydrolases need to be manipulated, and (d) a lack of knowledge of the functional genomic framework within which fiber degradation operates. In this review the major fibrolytic organisms are briefly discussed. A more extensive discussion of the enzymes involved in fiber degradation is included. We also discuss the use of plant genetic manipulation, application of free-living lignolytic fungi and the use of exogenous enzymes. Lastly, we will discuss how newer technologies such as genomic and metagenomic approaches can be used to improve our knowledge of the functional genomic framework of plant cell wall degradation in the rumen.

Invited review: adhesion mechanisms of rumen cellulolytic bacteria

We divided the adhesion process of the predominant cellulolytic rumen bacteria Fibrobacter succinogenes, Ruminococcus flavefaciens, and Ruminococcus albus into four phases: 1) transport of the nonmotile bacteria to the substrate; 2) initial nonspecific adhesion of bacteria to unprotected sites of the substrate that is dominated by constitutive elements of bacterial glycocalyx; 3) specific adhesion via adhesins or ligands formation with the substrate, which can be dominated by several bacterial organelles including cellulosome complexes, fimbriae connections, glycosylated epitopes of cellulose-binding protein (CBP) or glycocalyx, and cellulose-binding domain (CBD) of enzymes; 4) proliferation of the attached bacteria on potentially digestible tissues of the substrate. Each of the phases and its significance in the adhesion process are described. Factors affecting bacterial adhesion are described including: 1) factors related to bacterial age, glycocalyx condition, and microbial competition; 2) factors related to the nature of substrate including, cuticle protection, surface area, hydration, and ionic charge; and 3) environmental factors including pH, temperature, and presence of cations and soluble carbohydrate. Based on the information available from the literature, it appears that each of the predominant rumen bacteria--F. succinogenes, R. flavefaciens, and R. albus--has a specific mechanism of adhesion to cellulose. In F. succinogenes, both the glycosidic residues of the outer membrane CBP and especially of the 180-kDa CBP, and the distinct CBD of EG2 EGF and Cl-stimulated cellobiosidase, may play a role in the adhesion to cellulose. No direct evidence, except scanning electron microscopy observations, yet supports the existence of either cellulosome complex or fimbriae structures involved in the adhesion mechanism of F. succinogenes. At least two mechanisms, cellulosome-like complexes and carbohydrate epitopes of the glycocalyx layer are involved in the specific adhesion of R. flavefaciens to cellulose. Ruminococcus albus possesses at least two mechanisms for specific adhesion to cellulose: a cellulosomal-like mechanism, and a CbpC (Pil)-protein mechanism that probably involves the production of fimbrial-like structures. Indirect and direct studies suggested that carbohydrate epitopes of CBPs and CBD epitope of cellulases may also be involved mostly in the nonspecific phase of adhesion of R. albus.

Kidney bean lectin-induced Escherichia coli overgrowth in the small intestine is blocked by GNA, a mannose-specific lectin

The reversible and dose-dependent hyperplastic growth of the small intestine and accelerated epithelial cell turnover caused by feeding rats with diets containing kidney bean lectin (PHA) increased the proportion of immature cells on the villi whose membrane and/or cytoplasm contained mainly simple, polymannosylated glycans. These new alpha-linked mannosyl terminals, particularly of the damaged epithelium, facilitated the preferential adherence of opportunistic Escherichia coli with mannose-sensitive Type 1 fimbriae, and other coliforms, to the glycocalyx. Accordingly, the growth of the gut was accompanied by a reversible and PHA dose-dependent overgrowth with E. coli. As expected from their common carbohydrate specificity, the inclusion in the diet of the mannose-specific agglutinin from snowdrop (Galanthus nivalis) bulbs (GNA) significantly reduced the extent of E. coli overgrowth, but abolished neither the growth nor the damage caused by PHA to the small intestine. Thus, GNA and perhaps other mannose-specific lectins, especially when used in a preventive mode, can be used to specifically block the proliferation of Type 1 E. coli in the small intestine.

Fate of the antinutritive proteins of soyabean in the ovine gut

Defatted raw soyabean flour was administered intraruminally at a level of 10 g/kg body weight to a sheep fitted with ruminal, duodenal, and ileal cannulas. Soyabean lectin and trypsin inhibitor appeared in the duodenum within one hour, both reached the terminal ileum and disappeared within 24 hours. The passage of the lectin along the gut progressively lagged behind that of the inhibitor, which indicates that the lectin binds to the intestinal surface. The effect of the inhibitors was neutralized by a marked pancreatic hypersecretion. Contrary to earlier assumptions, the antinutritional proteins were not effectively degraded in the forestomachs.