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Appl Environ Microbiol, May 1998, p. 1673-1679, Vol. 64, No. 5
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

A Deficiency in Aspartate Biosynthesis in Lactococcus lactis subsp. lactis C2 Causes Slow Milk Coagulationdagger

Hua Wang,1 Weizhu Yu,1,Dagger Tim Coolbear,2 Dan O'Sullivan,1 and Larry L. McKay1,*

Department of Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota 55108,1 and New Zealand Dairy Research Institute, Palmerston North, New Zealand2

Received 8 September 1997/Accepted 24 February 1998

A mutant of fast milk-coagulating (Fmc+) Lactococcus lactis subsp. lactis C2, designated L. lactis KB4, was identified. Although possessing the known components essential for utilizing casein as a nitrogen source, which include functional proteinase (PrtP) activity and oligopeptide, di- and tripeptide, and amino acid transport systems, KB4 exhibited a slow milk coagulation (Fmc-) phenotype. When the amino acid requirements of L. lactis C2 were compared with those of KB4 by use of a chemically defined medium, it was found that KB4 was unable to grow in the absence of aspartic acid. This aspartic acid requirement could also be met by aspartate-containing peptides. The addition of aspartic acid to milk restored the Fmc+ phenotype of KB4. KB4 was found to be defective in pyruvate carboxylase and thus was deficient in the ability to form oxaloacetate and hence aspartic acid from pyruvate and carbon dioxide. The results suggest that when lactococci are propagated in milk, aspartate derived from casein is unable to meet fully the nutritional demands of the lactococci, and they become dependent upon aspartate biosynthesis.

* Corresponding author. Mailing address: Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Ave., St. Paul, MN 55108. Phone: (612) 624-3090. Fax: (612) 625-5272. E-mail: lmckay{at}che2.che.umn.edu.

dagger Published as paper no. 971180027 of the contribution series of the Minnesota Agricultural Experimental Station and based on research conducted under project 18-62.

Dagger Present address: Nabisco Foods Group, East Hanover, NJ 07936.

Appl Environ Microbiol, May 1998, p. 1673-1679, Vol. 64, No. 5
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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