STUDIES OF TRANSCRIPTIONAL STATE HETEROGENEITY IN SPORULATING CULTURES OF BACILLUS-SUBTILIS

Using a flow cytometry-based technique for detecting beta-galactosidas e, lacZ fusions have been used to study the pattern of gene expression exhibited by stationary phase cultures of Bacillus subtilis that have initiated the developmental pathway of spore formation. We have found that within such cultures there exist two distinct cell types: one th at has induced the developmental program of gene expression and one th at has not. This heterogeneity among transcriptional states is shown t o be established early during the stationary phase and plays a signifi cant role in influencing later stationary phase events. Additionally, when this technique is used to study gene expression in mutants that d isplay altered patterns of gene expression, we are able to conclude th at the cellular apparatus responsible for sensing and transducing stat ionary phase developmental signals represents a bottleneck that contro ls the expression of certain early stationary phase genes. These findi ngs provide a demonstration of the utility of single cell measurements of gene expression and indicate that unless culture heterogeneity is properly taken into account, standard measurements of gene expression may not provide information suitable for the analysis of events occurr ing at the cellular level. (C) 1995 John Wiley and Sons, Inc.