Abstract Almost all methods for transformation of the social ameba Dictyostelium discoideumrely on axenic growth, that is, growth in a synthetic medium, for at least part of the procedure. Axenic growth requires several mutations. Here we describe a procedure that can be used to transform wild-type strains which are able to grow only on the natural food source, bacteria. The method relies on a new selection cassette driven by the V18 promoter, a promoter that we show is substantially more active during growth on bacteria than the actin-6 promoter, which is widely used for axenic transformation. The procedure gives transformation frequencies of about 10 −5with both strains Ax2 (capable of axenic growth) and NC4 (capable of growth only on bacteria). Using this vector, we have obtained NC4 strains carrying several β-galactosidase reporter cassettes. Our vector can also be used in axenic transformations.