A luxAB transcriptional fusion to the cryptic celF gene of Escherichia coli displays increased luminescence in the presence of nickel.

From a library of 3000 Escherichia coli clones, each containing a single, chromosomally located luxAB transcriptional gene fusion, one clone was found in which luminescence increased in the presence of 1 to 50 ppm of NiSO4. A molecular analysis revealed that the insertion occurred within the celF gene of E. coli. This gene encodes the phospho-beta-glucosidase involved in cleavage of the sugars cellobiose, salicin and arbutin. Cloning and sequencing of DNA downstream of the celF gene revealed three open reading frames (potentially encoding polypeptides of 9.9, 14.1 and 28.5 kDa) that could be co-expressed with the celF gene and that may underlie the observed induction of the celF gene by nickel. A polypeptide of 26 kDa was produced when this region was placed under the control of the Ptac promoter. Moreover, this region was found to be directly adjacent to, and transcribed in the opposite orientation from, the katE gene of E. coli.