Interaction betweenLactobacillus kefirandSaccharomyces lipolyticaisolated from kefir grains: evidence for lectin-like activity of bacterial surface proteins

Abstract

Several microbial interactions involving yeast and lactobacilli have been suggested in fermented products. Co-aggregation betweenLactobacillus kefirand yeastSaccharomyces lipolyticaisolated from kefir grains was studied by scanning electron microscopy and aggregation assays. Six out of twentyLb. kefirstrains were able to co-aggregate withSacch. lipolyticaCIDCA 812 and showed thermolabile non-covalently bound surface molecules involved in this interaction. Co-aggregation inhibition afterLb. kefirpre-treatment with 5m-LiCl or 20 g SDS/l showed that bacterial S-layer proteins play an important role in this interaction. Presence of different sugar (mannose, sucrose and fructose) or yeast pre-treatment with sodium periodate inhibited co-aggregation betweenLb. kefirandSacch. lipolytica. Co-aggregatingLb. kefirstrains were also able to agglutinate with human red blood cells and they lost this ability after treatment with 5m-LiCl. These results and the capacity of purified S-layer proteins ofLb. kefirto haemagglutinate, strongly suggest that a lectin-like activity of bacterial surface proteins (S-layer) mediates the aggregation with yeast cells.