Palumbo Emmanuelle, Favier Christine F, Deghorain Marie, Cocconcelli Pier Sandro, Grangette Corinne, Mercenier Annick, Vaughan Elaine E, Hols Pascal
Université catholique de Louvain, Institut des Sciences de la Vie (ISV), Unité de Génétique, B-1348 Louvain-La-Neuve, Belgium.
FEMS Microbiol Lett. 2004 Apr 1;233(1):131-8. doi: 10.1016/j.femsle.2004.02.001.
A stable mutant of Lactobacillus plantarum deficient in alanine racemase (Alr) was constructed by two successive homologous recombination steps. When the mutant was supplemented with D-alanine, growth and viability were unaffected. Surprisingly, deprivation of d-alanine during exponential growth did not result in a rapid and extensive lysis as observed in Alr-deficient strains of Escherichia coli or Bacillus subtilis. Rather, the starved mutant cells underwent a growth arrest and were gradually affected in viability with a decrease in colony forming units over 99% in less than 24 h. Additionally, fluorescent techniques demonstrated a loss of cell envelope integrity in the starved cells. Prolonged d-alanine starvation resulted in cells with an aberrant morphology. Scanning and transmission electron microscopy analyses revealed an increase in cell length, deficiencies in septum formation, thinning of the cell envelope and perforation of the cell wall in the septum region. We discuss the involvement of peptidoglycan hydrolases in these phenotypic defects in the context of the crucial role played by D-alanine in peptidoglycan biosynthesis and teichoic acids substitution.
通过两个连续的同源重组步骤构建了一株缺乏丙氨酸消旋酶（Alr）的植物乳杆菌稳定突变体。当向该突变体补充D-丙氨酸时，其生长和活力不受影响。令人惊讶的是，在指数生长期剥夺D-丙氨酸并不会像在缺乏Alr的大肠杆菌或枯草芽孢杆菌菌株中观察到的那样导致快速而广泛的细胞裂解。相反，饥饿的突变体细胞会停止生长，并逐渐影响其活力，在不到24小时内菌落形成单位减少超过99%。此外，荧光技术表明饥饿细胞的细胞膜完整性丧失。长时间的D-丙氨酸饥饿导致细胞形态异常。扫描和透射电子显微镜分析显示细胞长度增加、隔膜形成缺陷、细胞膜变薄以及隔膜区域细胞壁穿孔。我们在D-丙氨酸在肽聚糖生物合成和磷壁酸取代中所起的关键作用的背景下，讨论了肽聚糖水解酶在这些表型缺陷中的作用。
