ANALYSIS BY FLUORESCENCE MICROSCOPY OF THE DEVELOPMENT OF COMPARTMENT-SPECIFIC GENE-EXPRESSION DURING SPORULATION OF BACILLUS-SUBTILIS

The use of a fluorogenic substrate, anoylaminofluorescein-di-beta-D-ga lactopyranoside, for beta-galactosidase has made it possible to visual ize enzyme activity in individual cells of sporulating populations of Bacillus subtilis by fluorescence microscopy. lacZ fusions to differen t sporulation-associated genes have been used to investigate the cell compartmentalization of gene expression during sporulation. A strain w ith a lacZ fusion to sspA, a gene which is transcribed by E sigma(G) a t a late stage of sporulation, displayed predominantly compartment-spe cific fluorescence. Expression of the early-expressed spolIA locus, wh ich includes the structural gene for sigma(F), was seen not to be comp artmentalized. Populations of strains with lacZ fusions to gpr and dac F, genes which are transcribed by E sigma(F) at intermediate stages of sporulation, included some organisms showing uncompartmentalized fluo rescence and others showing compartment-specific fluorescence; the pro portion showing compartment-specific fluorescence increased in samples taken later in sporulation. Several possible explanations of the resu lts obtained with gpr and dacF are considered. A plausible interpretat ion is that sigma(F) activity is initially not compartmentalized and b ecomes compartmentalized as sporulation progresses. The progression to compartmentalization does not require the activities of the sporulati on-specific factor sigma(E) or sigma(G) but may require some product o f sigma(F) activity.