Production of optically pure d-lactate from glycerol by engineered Klebsiella pneumoniae strain

• K. pneumoniae was engineered to produce optically pure d-lactate from glycerol.
• The aeration rate played a critical role in d-lactate production.
• The strain produced 142 g/L d-lactate under microaerobic conditions.
• The highest d-lactate production and yield from glycerol were achieved.

In this study, glycerol was used to produce optically pure d-lactate by engineered Klebsiella pneumoniae strain. In the recombinant strain, d-lactate dehydrogenase LdhA was overexpressed, and two genes, dhaT and yqhD for biosynthesis of main byproduct 1,3-propanediol, were knocked out. To further improve d-lactate production, the culture condition was optimized and the results demonstrated that aeration rate played an important role in d-lactate production. In microaerobic fed-batch fermentation, the engineered strain accumulated 142.1 g/L optically pure d-lactate with a yield of 0.82 g/g glycerol, which represented the highest d-lactate production from glycerol so far. This study showed that K. pneumoniae strain has high efficiency to convert glycerol into d-lactate and high potentiality in utilization of crude glycerol from biodiesel industry.