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1990 Lactobacilli isolated from sugary kefir grains capable of polysaccharide production and minicell formation. Journal of Applied Bacferiology 69, 31 1-320. Homoand heterofermentative species of Luctobacillus have been isolated from sugary kefir grains. Most of the homofermentative strains fermented tagatosc and aldonitol and presented 48-54% of homology with Lactobacillus paracasei ssp. paracasei NCDO 151 (ex Lactobacillus casei). The two variants of a heterofermentative species, although fermenting arabinose, were related to Lactobacillus hilgardii NCDO 264 (type strain) with 88% of homology. One of them produced plysaccharide from sucrose at pH 4.8 and 30°C; the best glucose conversion into plysaccharide was obtained from 3% of sucrose (81.8%), and the maximum production occurred about 35 hours after the end of the log phase of growth, in MRS sucrose broth. Polysaccharide formation did not occur above 40°C. a temperature at which no growth was observed. The two variants were forming minicells by abnormal divisions.

F. L E R O I A N D M . PIDOUX. 1993. Stimulation of the growth of Lactobacillus hilgardii and production of lactic acid in the presence of SaccharomycesJEorentinus have already been observed in a poor glucose medium. I n this study we showed that CO, , pyruvate, propionate, acetate and succinate excreted by the yeast were responsible for this phenomenon, whereas ethanol, fumarate and a cocktail of vitamins had no effect. Fermentation by the yeast did not enrich the total nitrogen or free amino acid content of the medium. T h e use of proteases confirmed that it was improbable that any nitrogenous compound could be responsible for the bacterial activation. Between values of 0.1 and 5%, the initial yeast : bacteria ratio had no effect on the stimulation of Lact. hilgardii, even though yeast fermentation was drastically affected by a low initial value. T h e interactions differed greatly according to the sugar source. With monosaccharides, stimulation began after 48 h of culture, and was higher on glucose than on fructose. With sucrose, stimulation appeared at the beginning of fermentation. Different mechanisms seemed to be involved.