Studies on the diversity of phenotypic characteristics of Lactococcus lactis and the technological significance in milk industry

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The main purpose of this study was to elucidate the diversity of species Lactococcus lactis by means of systematic comparative examinations of the difference of the phenotypic characteristics.1. We isolated lactococcal strains that formed colonies on CVT agar (containing 1 ppm crystal violet) from several commercial mixed cheese starters. Although these strains (CVT strains) grew in pairs or short chains in TYG broth (1 % tryptone, 0.5 % yeast extract, 1 % glucose, pH 7.0), they formed extremely long chains and showed peculiar growth behavior i.e., aggregate formation when they were cultivated in TYGC broth containing 30 mM citrate. The majority of CVT strains utilized citric acid in existence of fermentable sugars and produced a large quantity of acetoin and some CVT strains exhibited a rather strong trypsin-like activity. These CVT strains were found to belong to L.lactis subsp.lactis / diacetylactis but they maintained a few characteristics of L.cremoris.2. Using 26 test strains, it was shown that the characteristics of L.cremoris was full of diversity, whereas those of L.lactis / diacetylactis were comparatively uniform.3. We confirmed the existence of plasmid DNA common to CVT strains.CVT strains lost above peculiar growth characteristics and the fermentability of citric acid when these plasmids were cured.4. We extracted the aggregate with distillled water and 1 % and 3 % NaCl solutions, and analyzed the fraction precipitated with 75 % ethanol. It was suggested that the fraction was constituted by polysaccharide, in which mannose was the main component.