Molecular Cloning, Expression and Characterization of a Novel L-lactate Dehydrogenase from Aspergillus oryzae

Lactic acid is the building block of poly-lactic acid (PLA), a biopolymer that could be set to replace petroleum-based plastics. To make lactic acid production cost-effective, the production process should be carried out at low pH, in low-nutrient media, and with a low-cost carbon source. Aspergillus oryzae is an important fermentation microorganism, which are versatile microbial cell factories able to naturally produce large amounts of organic acids. Neither a functional lactate dehydrogenase (LDH) nor lactate production by A. oryzae is reported. A novel L-lactate dehydrogenase from Aspergillus oryzae (AoLDH) was cloned with 1107 bp in length and encoded a protein of 368 amino acids with a 6.27 isoelectric point. In silico analyses revealed that no signal peptide sequences and transmembrane domains were contained in AoLDH. Further, AoLDH displayed relatively narrow temperature adaptability and exhibited optimum temperature at 40°C, which was close to the growth environment. Also, the purified AoLDH exhibited the maximum activity at pH 8 while AoLDH deactivatd the enzymatic activity at pH 5. Moreover, the enzymatic activity of AoLDH was stimulated by Zn2+ and Ca2+, but inhibited in the presence of Mg2+, Mn2+ and Fe2+. In addition, high concentrations of metal ions caused more obvious effects. These results provided a better understanding of L-lactate dehydrogenase from Aspergillus oryzae.