Inactivating NADH:quinone oxidoreductases affects the growth and metabolism of Klebsiella pneumoniae

NADH:quinone oxidoreductases (NQOs) act as the electron entry sites in bacterial respiration and oxidize intracellular NADH that is essential for the synthesis of numerous molecules. Klebsiella pneumoniae contains three NQOs (NDH‐1, NDH‐2, and NQR). The effects of inactivating these NQOs, separately and together, on cell metabolism were investigated under different culture conditions. Defective growth was evident in NDH‐1‐NDH‐2 double and NDH‐1‐NDH‐2‐NQR triple deficient mutants, which was probably due to damage to the respiratory chain. The results also showed that K. pneumoniae can flexibly use NQOs to maintain normal growth in single NQO‐deficient mutants. And more interestingly, under aerobic conditions, inactivating NDH‐1 resulted in a high intracellular NADH:NAD+ ratio, which was proven to be beneficial for 2,3‐butanediol production. Compared with the parent strain, 2,3‐butanediol production by the NDH‐1‐deficient mutant was increased by 46% and 62% in glycerol‐ and glucose‐based media, respectively. Thus, our findings provide a practical strategy for metabolic engineering of respiratory chains to promote the biosynthesis of 2,3‐butanediol in K. pneumoniae.