Production of D-lactate from glucose using Klebsiella pneumoniae mutants

Background: D-Lactate is a valued chemical which can be produced by some bacteria including Klebsiella pneumoniae. However, only a few studies have focused on K. pneumoniae for D-lactate production with a significant amount of by-products, which complicated the purification process and decreased the yield of D-lactate. Results: Based on the redirection of carbon towards by-product formation, the effects of single-gene and multiple-gene deletions in K. pneumoniae on D-lactate production from glucose via acetolactate synthase (budB), acetate kinase (ackA), and alcohol dehydrogenase (adhE) were tested. Klebsiella pneumoniae mutants had different production behaviours. The accumulation of the main by-products was decreased in the mutants. The triple mutant strain had the most powerful ability to produce optically pure D-lactate from glucose, and was tested with xylose and arabinose as carbon sources. Fed-batch fermentation was also carried out under various aeration rates, and the strain accumulated 125.1 g/L D-lactate with a yield of 0.91 g/g glucose at 2.5 vvm. Conclusions: Knocking out by-product synthesis genes had a remarkable influence on the production and yield of D-lactate. This study demonstrated, for the first time, that K. pneumoniae has great potential to convert monosaccharides into D-lactate. The results provide new insights for industrial production of D-lactate by K. pneumoniae.