Expression of levansucrase- -galactosidase hybrids inhibits secretion and is lethal in Bacillus subtilis

The lacZ gene of Escherichia coli was fused to several positions downstream from the 5' end of the Bacillus subtilis sacB gene, which encodes levansucrase (LS), a sucrose-inducible extracellular enzyme. Effects of hybrid protein expression in B. subtilis were studied. Several fusions were tested, and two significantly interfered with growth of cells and with LS secretion when induced with sucrose. Chromosomal amplification of the fusions, leading to strong expression of the hybrid proteins, completely blocked LS secretion and was lethal for B. subtilis when expression was induced.