Use of Operon Fusions to Examine the Regulation of the L-1,2-Propanediol Oxidoreductase Gene of the Fucose System in Escherichia coli K12

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Abstract
E. coli K12 growing anaerobically on L-fucose excretes L-1,2-propanediol as a fermentation product whose formation is catalyzed by an inducible NAD-linked oxidoreductase. The activity of this enzyme is highly induced only during anaerobic growth. Three bacterial strains bearing a hybrid operon with the structural genes for lactose utilization (lacZYA) fused to the promoter of the propanediol oxidoreductase gene (fucO) were constructed to test whether transcriptional control was involved. In contrast to propanediol oxidoreductase of wild-type cells, .beta.-galactosidase in the .PHI.(fuc-lac) strains was induced by fucose to high levels both aerobically and anaerobically. These data agree with the previous report that the enzyme protein (assayed by specific antibodies) was induced both aerobically and anaerobically, but that only in anaerobically grown cells was the oxidoreductase catalytically active. In the present study, the oxidoreductase induced anaerobically in wild-type cells remained enzymically active during aerobic growth in the absence of fucose. Wild-type cells grown aerobically in the presence of fucose and then allowed limited anaerobic growth on glucose did not gain any oxidoreductase activity. The mechanism of this post-transcriptional control remains to be discovered.