Salhi B, Mendelson N H
Department of Microbiology and Immunology, University of Arizona, Tucson 85721.
J Bacteriol. 1993 Aug;175(16):5000-8. doi: 10.1128/jb.175.16.5000-5008.1993.
Bacillus subtilis 5:7, a derivative of macrofiber-producing strain FJ7, carries the lacZ reporter gene within Tn917 at an unknown location in the host genome. Expression of the host gene carrying lacZ within colonies of 5:7 was observed by examining growth under different conditions in the presence of 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal). At a high plating density small colonies arose that expressed the host gene early and throughout the colony, whereas at a low density large colonies were produced that expressed the host gene late in development and only in cells forming a ring pattern close to the colony periphery. A highly regulated spatial and temporal gene expression pattern was observed in growth from cross-streaks, suggesting that gene expression is responsive to concentration gradient fields established by neighboring growth. Colonies cultured on agar blocks revealed that expression was governed by depletion of a medium component and also by the geometry of the substrate upon which the colonies grew. At least three factors influenced the control of expression: (i) the concentration of a diffusible component of the medium exhausted by cell growth, (ii) a spatial-temporal factor related to growth within the colony, and (iii) the geometry of the growth substrate.
枯草芽孢杆菌5:7是产生大纤维菌株FJ7的衍生物，其在宿主基因组中未知位置的Tn917内携带lacZ报告基因。通过在5-溴-4-氯-3-吲哚基-β-D-吡喃半乳糖苷（X-Gal）存在下于不同条件下检查生长情况，观察了5:7菌落内携带lacZ的宿主基因的表达。在高接种密度下，出现了小菌落，这些小菌落在整个菌落中早期就表达宿主基因；而在低密度下，产生了大菌落，这些大菌落在发育后期才表达宿主基因，且仅在靠近菌落周边形成环状图案的细胞中表达。在交叉划线生长过程中观察到了高度调控的时空基因表达模式，这表明基因表达对相邻生长建立的浓度梯度场有反应。在琼脂块上培养的菌落表明，表达受培养基成分的消耗以及菌落生长所依托底物的几何形状的控制。至少有三个因素影响表达的控制：（i）细胞生长耗尽的培养基中可扩散成分的浓度，（ii）与菌落内生长相关的时空因素，以及（iii）生长底物的几何形状。
