McKay L L, Baldwin K A, Walsh P M
Appl Environ Microbiol. 1980 Jul;40(1):84-9. doi: 10.1128/aem.40.1.84-91.1980.
Streptococcus lactis strains ML3 and C(2)O and S. lactis subsp. diacetylactis strains DRC3, 11007, and WM(4) were found to transfer lactose-fermenting ability to LM0230, an S. lactis C2 lactose-negative (Lac(-)) derivative which is devoid of plasmid deoxyribonucleic acid (DNA). Lactose-positive streptomycin-resistant (Lac(+) Str(r)) recombinants were found when the Lac(+) Str(s) donor was mixed with Lac(-) Str(r) LM0230 in solid-surface matings. Transduction and transformation were ruled out as the mechanism of genetic exchange in strains ML3, DRC3, 11007, and WM(4), nor was reversion responsible for the high number of Lac(+) Str(r) recombinants. Furthermore, chloroform treatment of the donor prevented the appearance of recombinants, indicating that transfer of lactose-fermenting ability required viable cell-to-cell contact. Strain C(2)O demonstrated transduction as well as conjugation. Transfer of plasmid DNA during conjugation for all strains was confirmed by demonstrating the presence of plasmid DNA in the transconjugants by using agarose gel electrophoresis. In some instances, a cryptic plasmid was transferred in conjunction with the lactose plasmid by using strains DRC3, 11007, and WM(4). In S. lactis C2 x LM0230 matings, the Str(r) marker was transferred from LM0230 to C2, suggesting conjugal transfer of chromosomal DNA. The results confirm conjugation as another mechanism of genetic exchange occurring in dairy starter cultures.
已发现乳酸乳球菌菌株ML3和C(2)O以及乳酸乳球菌亚种双乙酰乳酸乳球菌菌株DRC3、11007和WM(4)能够将乳糖发酵能力转移至LM0230，LM0230是乳酸乳球菌C2的乳糖阴性（Lac(-)）衍生物，不含质粒脱氧核糖核酸（DNA）。当Lac(+) Str(s)供体与Lac(-) Str(r)的LM0230在固体表面交配中混合时，发现了乳糖阳性链霉素抗性（Lac(+) Str(r)）重组体。转导和转化被排除为菌株ML3、DRC3、11007和WM(4)中基因交换的机制，回复突变也不是大量Lac(+) Str(r)重组体产生的原因。此外，对供体进行氯仿处理可阻止重组体出现，这表明乳糖发酵能力的转移需要活细胞间的接触。菌株C(2)O表现出转导以及接合现象。通过琼脂糖凝胶电泳证明转接合子中存在质粒DNA，从而证实了所有菌株在接合过程中质粒DNA的转移。在某些情况下，使用菌株DRC3、11007和WM(4)时，一种隐蔽质粒与乳糖质粒一起被转移。在乳酸乳球菌C2与LM0230的交配中，Str(r)标记从LM0230转移至C2，这表明染色体DNA发生了接合转移。这些结果证实接合是发生在乳制品发酵剂培养物中的另一种基因交换机制。
