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Applied and Environmental Microbiology, November 2002, p. 5249-5257, Vol. 68, No. 11
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.11.5249-5257.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Increasing Acidification of Nonreplicating Lactococcus lactis {Delta}thyA Mutants by Incorporating ATPase Activity

Martin B. Pedersen,1,2* Brian J. Koebmann,2 Peter R. Jensen,2 and Dan Nilsson3

Department of Genomics and Strain Development,1 Research, Development, and Application, Chr. Hansen A/S, DK-2970 Hørsholm,3 Section of Molecular Microbiology, BioCentrum, Technical University of Denmark, DK-2800 Lyngby, Denmark2

Received 1 March 2002/ Accepted 5 August 2002

Lactococcus lactis MBP71 {Delta}thyA (thymidylate synthase) cannot synthesize dTTP de novo, and DNA replication is dependent on thymidine in the growth medium. In the nonreplicating state acidification by MBP71 was completely insensitive to bacteriophages (M. B. Pedersen, P. R. Jensen, T. Janzen, and D. Nilsson, Appl. Environ. Microbiol. 68:3010-3023, 2002). For nonreplicating MBP71 the biomass increased 3.3-fold over the first 3.5 h, and then the increase stopped. The rate of acidification increased 2.3-fold and then started to decrease. Shortly after inoculation the lactic acid flux was 60% of that of exponentially growing MBP71. However, when nonspecific ATPase activity was incorporated into MBP71, the lactic acid flux was restored to 100% but not above that point, indicating that control over the flux switched from ATP demand to ATP supply (i.e., to sugar transport and glycolysis). As determined by growing nonreplicating cells with high ATPase activity on various sugar sources, it appeared that glycolysis exerted the majority of the control. ATPase activity also stimulated the rate of acidification by nonreplicating MBP71 growing in milk, and pH 5.2 was reached 40% faster than it was without ATPase activity. We concluded that ATPase activity is a functional means of increasing acidification by nonreplicating L. lactis.

* Corresponding author. Mailing address: Department of Genomics and Strain Development, Chr. Hansen A/S, Bøge Allé 10-12, DK-2970 Hørsholm, Denmark. Phone: 45 45 74 84 79. Fax: 45 45 74 88 16. E-mail: MartinB.Pedersen{at}dk.chr-hansen.com.

Applied and Environmental Microbiology, November 2002, p. 5249-5257, Vol. 68, No. 11
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.11.5249-5257.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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