BETA-GALACTOSIDASE ACTIVITY IN SINGLE DIFFERENTIATING BACTERIAL-CELLS

Myxoccus xanthus strains containing transcriptional fusions to lacZ we re analyzed and fractionated by differences in their levels of beta-ga lactosidase expression. The fluorogenic substrate for beta-galactosida se, fluorescein di-beta-galactopyranoside, was introduced into M. xant hus cells during a rapid decrease in osmolarity of the medium followed by a return to isoosmolarity. Fluorescein, the product of hydrolysis, was retained within the cells and their viability was preserved. Fluo rescence increased linearly with time and was proportional to beta-gal actosidase activity. Beta-galactosidase expression in most fusion stra ins, though beginning at different phases of growth or development, wa s distributed unimodally amongst cells. However, fusion strain Tn5 lac OMEGA4473 was shown to be heterogeneous at 9 hr of development. It wa s possible to separate physically cells that expressed beta-galactosid ase at a high level from other, still viable, cells with no expression . The approach described here could be adapted to study differentiatio n in plants and animals as well, where transcriptional fusions and flu orogenic substrates for enzyme probes of gene expression also can be u sed.