Valio Finnish Co-operative Dairies' Association, Research and Development Centre, P.O. Box 176, SF-00181 Helsinki, Finland.
Appl Environ Microbiol. 1989 Oct;55(10):2690-5. doi: 10.1128/aem.55.10.2690-2695.1989.
A cloned chromosomal fragment of Lactococcus lactis subsp. lactis SSL135 on plasmid p VS8 in an L. lactis subsp. lactis MG1614 background enabled proteinase-negative strain MG1614 to grow in autoclaved milk. The strain (VS230) did not, however, degrade milk proteins and did not grow in pasteurized milk. In contrast, a strain (VS150) carrying p VS9, the proteinase plasmid of SSL135, in an MG1614 background degraded beta-casein but did not grow in milk. VS230 was shown to utilize peptides produced by VS150 in growth experiments in pasteurized milk preincubated with the latter strain. The peptide utilization phenotype linked with p VS8 was further confirmed by growth of VS230 on tryptic peptide fractions, on which the plasmid-free but otherwise isogenic strain MG1614 failed to grow. Plasmid p VS8 produced 69-, 42-, 38-, and 36-kilodalton proteins, as determined by in vitro transcription-translation. At least three of these proteins affected the peptide utilization phenotype. We suggest that there could be a coupled peptidase-peptide transport system encoded by the chromosomal fragment.
在乳球菌乳亚种 MG1614 背景下，质粒 pVS8 上的乳球菌乳亚种 SSL135 的克隆染色体片段使蛋白酶阴性菌株 MG1614 能够在巴氏消毒奶中生长。然而，该菌株（VS230）不会降解牛奶蛋白，也不会在巴氏杀菌奶中生长。相比之下，携带 SSL135 的蛋白酶质粒 pVS9 的菌株（VS150）在 MG1614 背景下可以降解β-酪蛋白，但不能在牛奶中生长。在与后者菌株预孵育的巴氏杀菌奶中进行生长实验表明，VS230 可以利用 VS150 产生的肽。通过在胰酶肽馏分上生长，进一步证实了与 pVS8 相关的肽利用表型，而没有质粒的但其他方面同基因的菌株 MG1614 则无法在其上生长。质粒 pVS8 通过体外转录-翻译产生 69、42、38 和 36 千道尔顿的蛋白质。这些蛋白质中至少有三种影响肽利用表型。我们推测，该染色体片段可能编码一个偶联的肽酶-肽转运系统。
