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

本研究的主要目的是通过系统的比较检查表型特征的差异来阐明乳酸乳球菌物种的多样性。我们从几种商业混合奶酪发酵剂中分离出在CVT琼脂（含1ppm结晶紫）上形成菌落的乳球菌菌株。虽然这些菌株（CVT菌株）在含有1%色氨酸，0.5%酵母提取物，1%葡萄糖，pH 7.0的TYG培养液中成对或短链生长，但在含有30 mM柠檬酸盐的TYGC培养液中培养时，它们形成了极长的链，并表现出特殊的生长行为，即聚集形成。大多数CVT菌株利用存在可发酵糖的柠檬酸，产生大量乙酰酶，部分CVT菌株表现出较强的胰蛋白酶样活性。这些CVT菌株属于乳酸乳杆菌亚种。乳酸菌/二乙酰乳酸菌，但保持了乳酸菌的一些特征。结果表明，乳酸菌/二乙酰化乳酸菌的特征较为统一，而乳酸菌的特征则具有多样性。我们证实了CVT菌株共有的质粒DNA的存在。当这些质粒被固化后，CVT菌株失去了上述特有的生长特性和柠檬酸的发酵能力。用蒸馏水、1%和3% NaCl溶液提取骨料，并对75%乙醇沉淀的馏分进行分析。结果表明，该馏分由甘露糖为主要成分的多糖组成。

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.