Effect of live-yeast culture and lasalocid supplementation on performance of growing–finishing steers fed alfalfa-silage, corn-silage and high-grain diets sequentially

Trials were conducted to determine the effect of supplementing feedlot diets with live-yeast culture (YC), lasalocid (LAS) or YC + LAS on intake, growth and carcass characteristics of steers. Dietary additives in either 96% corn-silage or 75% dry-rolled barley-based diets increased (P < 0.05) final weights and carcass weights of steers. Key words: Yeast, lasalocid, steers, carcass quality, growth

Flocculation of Saccharomyces cerevisiae: inhibition by sugars

Flocculation is governed by the competition between electrostatic repulsion (nonspecific interactions) and polysaccharide–protein bonds (specific interactions). In our study, the inhibition of flocculation by sugars for 12 strains of Saccharomyces cerevisiae leads us to extend the classification described in the literature and to define three groups of yeasts: flocculation mannose sensitive (MS), flocculation glucose–mannose sensitive (GMS), and flocculation mannose insensitive (MI). Only the first two groups showed specific interactions between proteins and mannans. In the MI group, the sugars tested did not inhibit flocculation. To characterize the particularities of the stereochemistry of the cell-wall proteic receptors of strains belonging to the MS and GMS groups, 31 sugars were used as inhibitor probes on two representative strains. The results show that the lectin specificity of strains belonging to the GMS group is less restricted regarding C-1 and C-2 hydroxyl groups than the lectin from strains belonging to the MS group, which interacts with all of the hydroxyl groups of mannopyranose. The two groups also differ with respect to inhibition by sugars: strains belonging to the MS group are partially inhibited whereas strains of the GMS group are completely inhibited. We observed that the presence of ethanol increases sugar fixation by strains from the MS group, but not from the GMS group. Moreover, both receptors interact with disaccharides, provided the two monomers are linked by an α(1 → 4), α(1 → 3), or α(1 → 2) bond. Key words: yeast flocculation, proteic receptors, sugars, lectins.

Interaction between flocculent and nonflocculent cells of Saccharomyces cerevisiae

Interaction between nonflocculent and flocculent cells of Saccharomyces cerevisiae was studied. Adhesion experiments were done using three types of nonflocculent cells and a flocculent one. Two types of nonflocculent cells were obtained from the flocculent strain by changing environmental growth conditions. The integration of nonflocculent cells in the flocs was observed by two different methods: measurement of the sedimentation capacity of mixtures and microscopic observation of stained nonflocculent cells blended with flocculent cells. It was possible to verify that cell–cell interaction corresponds to a true stable binding and not to a simple entrapment inside the floe matrix. Key words: yeast, Saccharomyces cerevisiae, flocculation, adhesion.