PATTERNS OF GENE-EXPRESSION IN BACILLUS-SUBTILIS COLONIES

Bacillus subtilis 5:7, a derivative of macrofiber-producing strain FJ7 , carries the lacZ reporter gene within Tn917 at an unknown location i n the host genome. Expression of the host gene carrying lacZ within co lonies of 5:7 was observed by examining growth under different conditi ons in the presence of bromo-4-chloro-3-indolyl-beta-D-galactopyrranos ide (X-Gal). At a high plating density small colonies arose that expre ssed the host gene early and throughout the colony, whereas at a low d ensity large colonies were produced that expressed the host gene late in development and only in cells forming a ring pattern close to the c olony periphery. A highly regulated spatial and temporal gene expressi on pattern was observed in growth from cross-streaks, suggesting that gene expression is responsive to concentration gradient fields establi shed by neighboring growth. Colonies cultured on agar blocks revealed that expression was governed by depletion of a medium component and al so by the geometry of the substrate upon which the colonies grew. At l east three factors influenced the control of expression: (i) the conce ntration of a diffusible component of the medium exhausted by cell gro wth, (ii) a spatial-temporal factor related to growth within the colon y, and (iii) the geometry of the growth substrate.