Expression of the transposable lac operon Tn951 in Rhodopseudomonas sphaeroides.

The transposon Tn951 (lac) was introduced into the photosynthetic bacterium Rhodopseudomonas sphaeroides 2.4.1, which is normally Lac-, via the P-group plasmid RP1. beta-Galactosidase was produced constitutively in both chemotrophically and phototrophically grown cells, and the levels were found to be the same but low. Mutants were isolated, however, that were able to grow on lactose minimal medium and which expressed different levels of beta-galactosidase when grown chemotrophically or phototrophically. The beta-galactosidase levels found in all R. sphaeroides strains were much less than those found in Escherichia coli.