Lactate dehydrogenase catalyses the production of lactate from pyruvate. It is the first target for many researches on lactic acid producer microorganisms like Rhizopus oryzae. In the present study based on the known sequences of R. oryzae ldhA and ldhB genes Skory (2000), they were cloned and expressed in a citric acid producer fungus Aspergillus niger. The Aspergillus niger strains expressing ldhA or ldhB gene resulted in increased production of lactate in Aspergillus niger. Among 50 transformants tested 4 ldhA and 5 ldhB expressing strains were found to have higher lactate dehydrogenase activity compared to wild type in the conditions tested. The highest specific activity obtained with ldhA transformants was only 2.5 times of the wild type while this was 10 times for one of the transformants expressing ldhB. In addition to increased lactate production citric acid production was also increased. However, gluconic acid production ceased in the ldhAor ldhB expressing A. niger strains. The production of lactic acid in A. niger transformants and lactate dehydrogenase A and lactate dehydrogenase B enzymes are being investigated in the chosen strains.
|Journal||Journal of Biotechnology|
|Issue number||1, Suppl.|
|Publication status||Published - 2005|