Submitted to: Society of Industrial Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: August 2, 2001
Publication Date: N/A
Technical Abstract: Recent ecological interests have fueled the demand of lactic acid for the manufacture of the plastic, polylactic acid (PLA), and the "green-solvent," ethyl lactate. However, fermentation efficiency must be improved to ensure the economic feasibility of these anticipated market expansions. The fungus Rhizopus oryzae produces significant quantities of lactic acid when grown aerobically, but shifts to ethanolic fermentation with anaerobically stressed conditions. To better understand this regulation, we cloned two pyruvate decarboxylase, pdcA and pdcB, genes from R. oryzae and compared expression levels during growth with varying oxygen availability. Both pdc transcripts and PDC (EC 18.104.22.168) activity were detected within 2 h of transfer to a glucose containing medium, but were approximately 10-times higher for the oxygen-limited cultures. Over the next 4 h, both transcripts continued to increase under aerobic conditions. With limited oxygen availability, pdcA further increased, while pdcB transcript levels remained fairly constant. Total PDC activity more than doubled with oxygen limited growth. However, PDC activity under aerobic conditions was not detected after 6 h, even though both transcript levels were increasing.