Decrease in cell surface galactose residues of Schizosaccharomyces pombe enhances its coflocculation with Pediococcus damnosus.

Pediococcus damnosus can coflocculate with Saccharomyces cerevisiae and cause beer acidification that may or may not be desired. Similar coflocculations occur with other yeasts except for Schizosaccharomyces pombe which has galactose-rich cell walls. We compared coflocculation rates of S. pombe wild-type species TP4-1D, having a mannose-to-galactose ratio (Man:Gal) of 5 to 6 in the cell wall, with its glycosylation mutants gms1-1 (Man:Gal = 5:1) and gms1Delta (Man:Gal = 1:0). These mutants coflocculated at a much higher level (30 to 45%) than that of the wild type (5%). Coflocculation of the mutants was inhibited by exogenous mannose but not by galactose. The S. cerevisiae mnn2 mutant, with a mannan content similar to that of gms1Delta, also showed high coflocculation (35%) and was sensitive to mannose inhibition. Coflocculation of P. damnosus and gms1Delta (or mnn2) also could be inhibited by gms1Delta mannan (with unbranched alpha-1,6-linked mannose residues), concanavalin A (mannose and glucose specific), or NPA lectin (specific for alpha-1,6-linked mannosyl units). Protease treatment of the bacterial cells completely abolished coflocculation. From these results we conclude that mannose residues on the cell surface of S. pombe serve as receptors for a P. damnosus lectin but that these receptors are shielded by galactose residues in wild-type strains. Such interactions are important in the production of Belgian acid types of beers in which mixed cultures are used to improve flavor.