Transcriptional regulation of lux genes transferred into Vibrio harveyi

Past work has shown that transformed Escherichia coli is not a suitable vehicle for studying the expression and regulation of the cloned luminescence (lux) genes of Vibrio harveyi. Therefore, we have used a conjugative system to transfer lux genes cloned into E. coli back into V. harveyi, where they can be studied in the parental organism. To do this, lux DNA was inserted into a broad-spectrum vector, pKT230, cloned in E. coli, and then mobilized into V. harveyi by mating aided by the conjugative plasmid pRK2013, also contained in E. coli. Transfer of the wild-type luxD gene into the V. harveyi M17 mutant by this means resulted in complementation of the luxD mutation and full restoration of luminescence in the mutant; expression of transferase activity was induced if DNA upstream of luxC preceded the luxD gene on the plasmid, indicating the presence of a strong inducible promoter. To extend the usefulness of the transfer system, the gene for chloramphenicol acetyltransferase was inserted into the pKT230 vector as a reporter. The promoter upstream of luxC was verified to be cell density regulated and, in addition, glucose repressible. It is suggested that this promoter may be the primary autoregulated promoter of the V. harveyi luminescence system. Strong termination signals on both DNA strands were recognized and are located downstream from luxE at a point complementary to the longest mRNA from the lux operon. Structural lux genes transferred back into V. harveyi under control of the luxC promoter are expressed at very high levels in V. harveyi as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis: the gene transfer system is thus useful for expression of proteins as well as for studying the regulation of lux genes in their native environment.