Switching metabolic status by activating a silent glycerol catabolism pathway for acetoin production from glycerol

The physiological roles of silent genes are still unsolved puzzles and their application potentials are unexplored. Herein, a silent glycerol catabolism pathway encoded by 1 These authors contributed equally to this work glp system was activated in a Klebsiella pneumoniae mutant, of which the acetoin degradation pathway was blocked. Surprisingly, the activation produced significant effects on cellular metabolism and over 90% of the carbon flux was redirected to acetoin biosynthesis, which was formerly a minor product in this mutant. Transcription analyses suggest that the genes involved in acetoin, 1,3-propanediol and adenosyl-cobalamin biosynthesis were differentially regulated upon the glp system activation, demonstrating the cross-talk between silent and active pathways. Through pathway, cofactor and bioprocess engineering, high-level acetoin production from glycerol (32.2 g L -1 , 90.8% of the theoretical value) was achieved. Our findings suggest that some silent genes represent unexplored switches of cellular metabolic status and activating them may be an easy strategy for reprogramming microorganisms into efficient cell factories.