Grossman A D, Losick R
Department of Cellular and Developmental Biology, Harvard University, Cambridge, MA 02138.
Proc Natl Acad Sci U S A. 1988 Jun;85(12):4369-73. doi: 10.1073/pnas.85.12.4369.
Spore formation in the Gram-positive bacterium Bacillus subtilis has been classically viewed as an example of unicellular differentiation that occurs in response to nutritional starvation. We present evidence that B. subtilis produces an extracellular factor(s) that is required, in addition to starvation conditions, for efficient sporulation. This factor is secreted and accumulates in a cell density-dependent fashion such that cells at a low density sporulate poorly under conditions in which cells at a high density sporulate efficiently. Conditioned medium (sterile filtrate) from cells grown to a high density contains this extracellular differentiation factor (EDF-A) and stimulates spore formation of cells at low density under normal starvation conditions. EDF-A is heat-resistant, protease-sensitive, and dialyzable, indicating that it is at least in part an oligopeptide. Production of EDF-A is reduced or eliminated in spoOA and spoOB mutants, which are defective in many processes associated with the end of vegetative growth. Mutations in abrB, which suppress many of the pleiotropic phenotypes of spoOA mutants, restore production of EDF-A.
革兰氏阳性细菌枯草芽孢杆菌中的孢子形成传统上被视为单细胞分化的一个例子，它是在营养饥饿的情况下发生的。我们提供的证据表明，除饥饿条件外，枯草芽孢杆菌还产生一种细胞外因子，这种因子对于高效产孢是必需的。这种因子以细胞密度依赖性方式分泌并积累，以至于低密度细胞在高密度细胞能高效产孢的条件下产孢很差。来自高密度生长细胞的条件培养基（无菌滤液）含有这种细胞外分化因子（EDF-A），并能在正常饥饿条件下刺激低密度细胞的孢子形成。EDF-A耐热、对蛋白酶敏感且可透析，这表明它至少部分是一种寡肽。在spoOA和spoOB突变体中，EDF-A的产生减少或消除，这两种突变体在许多与营养生长末期相关的过程中存在缺陷。abrB基因的突变抑制了spoOA突变体的许多多效性表型，恢复了EDF-A的产生。
