Buist G, Karsens H, Nauta A, van Sinderen D, Venema G, Kok J
Department of Genetics, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Haren, The Netherlands.
Appl Environ Microbiol. 1997 Jul;63(7):2722-8. doi: 10.1128/aem.63.7.2722-2728.1997.
The optical density of a culture of lactococcus lactis MG1363 was reduced more than 60% during prolonged stationary phase. Reduction in optical density (autolysis) was almost absent in a culture of an isogenic mutant containing a deletion in the major autolysin gene, acmA. An acmA mutant carrying multiple coples of a plasmid encoding AcmA lysed to a greater extent than the wild-type strain did. Intercellular action of AcmA was shown by mixing end-exponential-phase cultures of an acmA deletion mutant and a tripeptidase (pepT) deletion mutant. PepT, produced by the acmA mutant, was detected in the supernatant of the mixed culture, but no PepT was present in the culture supernatant of the acmA mutant. A plasmid was constructed in which acmA, lacking its own promoter, was placed downstream of the inducible promoter/operator region of the temperate lactococcal bacteriophage r1t. After mitomycin induction of an exponential-phase culture of L. lactis LL302 carrying this plasmid, the cells became subject to autolysis, resulting in the release of intracellular proteins.
在延长的稳定期，乳酸乳球菌MG1363培养物的光密度降低了60%以上。在主要自溶素基因acmA缺失的同基因突变体培养物中，几乎没有光密度降低（自溶）的情况。携带编码AcmA质粒多个拷贝的acmA突变体比野生型菌株裂解程度更大。通过混合acmA缺失突变体和三肽酶（pepT）缺失突变体的指数末期培养物，显示了AcmA的细胞间作用。在混合培养物的上清液中检测到由acmA突变体产生的PepT，但在acmA突变体的培养上清液中没有PepT。构建了一个质粒，其中缺乏自身启动子的acmA被置于温和乳球菌噬菌体r1t的可诱导启动子/操纵子区域下游。在用丝裂霉素诱导携带该质粒的乳酸乳球菌LL302指数期培养物后，细胞开始自溶，导致细胞内蛋白质释放。
