Neutral sugar composition and gravimetric yield of plant and bacterial fractions of feces.

Separating dietary fiber from other polysaccharides in digesta and feces is necessary to understand its mechanisms of action. A gravimetric method that separates fecal plant and bacterial matter based on size and density was evaluated and modified to determine the plant and bacterial mass of lyophilized whole and blended rat and human feces. Three screen mech combinations (150 and 75 microns, 150 and 35 microns, 35 microns) were used with rat feces. Filtration of a homogenized rat fecal slurry sequentially through 150- and 35-microns-mesh screens versus 150- and 75-microns-mesh screens decreased the gravimetric recovery of bacteria from congruent to 35 to congruent to 25% of fecal dry weight and increased the plant fraction weight. Neutral sugar composition, determined by gas chromatography of alditol acetates, and bacterial counts of the fractions suggested that the decreased yield of bacterial fraction represented removal of plant material and not a loss of bacteria. Rat excreta contained 29.5% (dry weight) total neutral sugar, 88% of which was recovered in the plant material. Human feces containing wheat bran, fractionated with the 150- and 35-microns-mesh screens, was 21% neutral sugar, congruent to 65% of which was in the plant fraction. The plant fractions had more xylose and arabinose and less glucose than the bacterial fractions. Processing samples in a Waring blender had no adverse effect on the rat or human fecal bacterial counts. The use of this gravimetric method in combination with the sugar analysis of the fractions provided a better measure of plant and bacteria than only gravimetric yield

Mucin-bacterial interactions in the human oral cavity and digestive tract

Mucins are a family of heavily glycosylated proteins that are the major organic components of the mucus layer, the protective layer covering the epithelial cells in many human and animal organs, including the entire gastro-intestinal tract. Microbes that can associate with mucins benefit from this interaction since they can get available nutrients, experience physico-chemical protection and adhere, resulting in increased residence time. Mucin-degrading microorganisms, which often are found in consortia, have not been extensively characterized as mucins are high molecular weight glycoproteins that are hard to study because of their size, complexity and heterogeneity. The purpose of this review is to discuss how advances in mucus and mucin research, and insight in the microbial ecology promoted our understanding of mucin degradation. Recent insight is presented in mucin structure and organization, the microorganisms known to use mucin as growth substrate, with a specific attention on Akkermansia muciniphila, and the molecular basis of microbial mucin degradation owing to availability of genome sequences