Use of green fluorescent protein for detection of cell-specific gene expression and subcellular protein localization during sporulation in Bacillus subtilis

Wild-type and mutant forms of the gene encoding green fluorescent protein (GFP) from Aequorea victoria have been introduced into Bacillus subtilis as translational fusions to the prespore-specific and mother-cell-specific genes dacF and spoIVA. In both cases, the protein was readily detected by fluorescence microscopy, and its synthesis was correctly localized. The S65T substitution, which improves the quantum yield and rate of development of fluorescence, also produced a spectral shift that allowed the protein to be colocalized with DNA, after staining with 4',6-diamidino-2-phenylindole. Three different translational fusions to the N-terminal region of GFP all produced active protein. Moreover, a full-length SpoIVA-GFP fusion showed proper targeting to the surface of the spore, albeit at low temperature and in the presence of wild-type SpoIVA protein. A mutation in the gfp gene which changes the light emitted by the protein from green to blue was found not to be useful because of the intrinsic autofluorescence of a. subtilis in the blue part of the spectrum.