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Applied and Environmental Microbiology, June 2001, p. 2677-2682, Vol. 67, No. 6
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.6.2677-2682.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Metabolic Behavior of Lactococcus lactis MG1363 in Microaerobic Continuous Cultivation at a Low Dilution Rate

Niels Bang Siemsen Jensen,dagger Claus Rix Melchiorsen,Dagger Kirsten Væver Jokumsen,Dagger and John Villadsen*

Center for Process Biotechnology, Department of Biotechnology, Technical University of Denmark, DK-2800 Lyngby, Denmark

Received 7 November 2000/Accepted 20 March 2001

Minute amounts of oxygen were supplied to a continuous cultivation of Lactococcus lactis subsp. cremoris MG1363 grown on a defined glucose-limited medium at a dilution rate of 0.1 h-1. More than 80% of the carbon supplied with glucose ended up in fermentation products other than lactate. Addition of even minute amounts of oxygen increased the yield of biomass on glucose by more than 10% compared to that obtained under anaerobic conditions and had a dramatic impact on catabolic enzyme activities and hence on the distribution of carbon at the pyruvate branch point. Increasing aeration caused carbon dioxide and acetate to replace formate and ethanol as catabolic end products while hardly affecting the production of either acetoin or lactate. The negative impact of oxygen on the synthesis of pyruvate formate lyase was confirmed. Moreover, oxygen was shown to down regulate the protein level of alcohol dehydrogenase while increasing the enzyme activity levels of the pyruvate dehydrogenase complex, alpha -acetolactate synthase, and the NADH oxidases. Lactate dehydrogenase and glyceraldehyde dehydrogenase enzyme activity levels were unaffected by aeration.

* Corresponding author. Mailing address: Center for Process Biotechnology, Department of Biotechnology, Building 223, Technical University of Denmark, DK-2800 Lyngby, Denmark. Phone: (45) 45252668. Fax: (45) 45884148. E-mail: john.villadsen{at}biocentrum.dtu.dk.

dagger Present address: Chr. Hansen AS, DK-2970 Hørsholm, Denmark.

Dagger Present address: Novo Nordisk AS, DK-2880 Bagsværd, Denmark.

Applied and Environmental Microbiology, June 2001, p. 2677-2682, Vol. 67, No. 6
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.6.2677-2682.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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