Malic Enzyme Facilitates d-Lactate Production through Increased Pyruvate Supply during Anoxic Dark Fermentation in
Ryota Hidese1, Mami Matsuda1,2, Takashi Osanai3
1Graduate School of Science, Innovation and Technology , Kobe University , 1-1 Rokkodai , Nada, Kobe 657-8501 , Japan.
Abstract:
d-Lactate is one of the most valuable compounds for manufacturing biobased polymers. Here, we have investigated the significance of endogenous malate dehydrogenase (decarboxylating) (malic enzyme, ME), which catalyzes the oxidative decarboxylation of malate to pyruvate, in d-lactate biosynthesis in the cyanobacterium Synechocystis sp. PCC6803. d-Lactate levels were increased by 2-fold in ME-overexpressing strains, while levels in ME-deficient strains were almost equivalent to those in the host strain. Dynamic metabolomics revealed that overexpression of ME led to increased turnover rates in malate and pyruvate metabolism; in contrast, deletion of ME resulted in increased pool sizes of glycolytic intermediates, probably due to sequential feedback inhibition, initially triggered by malate accumulation. Finally, both the loss of the acetate kinase gene and overexpression of endogenous d-lactate dehydrogenase, concurrent with ME overexpression, resulted in the highest production of d-lactate (26.6 g/L) with an initial cell concentration of 75 g-DCW/L after 72 h fermentation.
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