Departamento de Microbiología y Bioquímica, Instituto de Productos Lácteos de Asturias (CSIC), Carretera de Infiesto s/n, 33300-Villaviciosa, Spain.
Appl Environ Microbiol. 2011 Aug;77(15):5324-35. doi: 10.1128/AEM.02991-10. Epub 2011 Jun 10.
Twenty Lactococcus lactis strains with an L. lactis subsp. lactis phenotype isolated from five traditional cheeses made of raw milk with no added starters belonging to the L. lactis subsp. lactis and L. lactis subsp. cremoris genotypes (lactis and cremoris genotypes, respectively; 10 strains each) were subjected to a series of phenotypic and genetic typing methods, with the aims of determining their phylogenetic relationships and suitability as starters. Pulsed-field gel electrophoresis (PFGE) analysis of intact genomes digested with SalI and SmaI proved that all strains were different except for three isolates of the cremoris genotype, which showed identical PFGE profiles. Multilocus sequence typing (MLST) analysis using internal sequences of seven loci (namely, atpA, rpoA, pheS, pepN, bcaT, pepX, and 16S rRNA gene) revealed considerable intergenotype nucleotide polymorphism, although deduced amino acid changes were scarce. Analysis of the MLST data for the present strains and others from other dairy and nondairy sources showed that all of them clustered into the cremoris or lactis genotype group, by using both independent and combined gene sequences. These two groups of strains also showed distinctive carbohydrate fermentation and enzyme activity profiles, with the strains in the cremoris group showing broader profiles. However, the profiles of resistance/susceptibility to 16 antibiotics were very similar, showing no atypical resistance, except for tetracycline resistance in three identical cremoris genotype isolates. The numbers and concentrations of volatile compounds produced in milk by the strains belonging to these two groups were clearly different, with the cremoris genotype strains producing higher concentrations of more branched-chain, derived compounds. Together, the present results support the idea that the lactis and cremoris genotypes of phenotypic Lactococcus lactis subsp. lactis actually represent true subspecies. Some strains of the two subspecies in this study appear to be good starter candidates.
从五个由未经巴氏杀菌奶制成的传统奶酪中分离出的 20 株乳球菌属菌株（乳亚种和乳亚种分别属于 10 株）具有乳亚种乳亚种表型，属于乳亚种和乳亚种基因型（分别为基因型；基因型）。凝固酶基因型（乳亚种和乳亚种分别属于 10 株）分别属于乳亚种和乳亚种基因型）用一系列表型和遗传分型方法进行了处理，目的是确定它们的系统发育关系和作为起始剂的适用性。用 SalI 和 SmaI 消化完整基因组的脉冲场凝胶电泳（PFGE）分析证明，除 3 株凝固酶基因型分离株外，所有菌株均不同，这 3 株分离株具有相同的 PFGE 图谱。使用 7 个内部序列的多位序列分型（MLST）分析（即 atpA、rpoA、pheS、pepN、bcaT、pepX 和 16S rRNA 基因）显示出相当大的基因型间核苷酸多态性，尽管推导的氨基酸变化很少。对本研究菌株和其他来自其他乳制品和非乳制品来源的菌株的 MLST 数据分析表明，所有菌株均聚类到乳亚种或乳亚种基因型组，使用独立和组合基因序列。这两组菌株还显示出不同的碳水化合物发酵和酶活性谱，而乳亚种组的菌株显示出更广泛的谱。然而，对 16 种抗生素的耐药/敏感性谱非常相似，除了 3 株相同的乳亚种基因型分离株对四环素的耐药性外，没有非典型耐药性。这两组菌株在牛奶中产生的挥发性化合物的数量和浓度明显不同，乳亚种菌株产生的浓度更高，具有更多的支链衍生化合物。总之，目前的结果支持乳亚种和乳亚种的乳球菌属表型实际上代表真正的亚种的观点。本研究中的两个亚种的一些菌株似乎是很好的起始候选物。
