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Applied and Environmental Microbiology, October 2001, p. 4594-4602, Vol. 67, No. 10
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.10.4594-4602.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Survival Response and Rearrangement of Plasmid DNA of Lactococcus lactis during Long-Term Starvation

Woojin S. Kim,* Ji Hyeon Park, Jun Ren, Ping Su, and Noel W. Dunn

Department of Biotechnology, University of New South Wales, Sydney, NSW 2052, Australia

Received 20 April 2001/Accepted 30 July 2001

The survival response of Lactococcus lactis during long-term starvation was investigated. The cells were cultured with different levels of glucose (the sole energy source) and either were kept in the resultant spent medium or transferred to fresh medium (without glucose) for up to 2 years. The survival of the cells during starvation was not dependent on the nature of transition phase, as expected, but on the nature of medium in which the cells were kept. The proliferation of cells, despite the apparent lack of glucose, could have been due to some cells being able to utilize the small amounts of peptides still present in the spent medium or to use energy sources provided by the breakup of dead cells. The 1- and 2-year-old cultures contained cells with vastly changed morphotypes. When these isolates were examined, it was revealed that the original plasmids present in the parent were rearranged in a certain way, and an entirely new plasmid was generated. Changes were also evident in the chromosomal DNA and in gene expression. Furthermore, all of the isolates exhibited a growth advantage relative to the parent cells when grown in energy-limiting media. When they were tested against different types of stresses, they exhibited a higher resistance against the bile salt and hydrogen peroxide stresses compared to the parent. Because of the similar changes observed in the 2-year-old isolates, a similar survival strategy may be operational in those cells that survive for that length of time.


* Corresponding author. Mailing address: Department of Biotechnology, University of New South Wales, Sydney, NSW 2052, Australia. Phone: 61 2 9385 1299. Fax: 61 2 9385 1015. E-mail: w.kim{at}unsw.edu.au.


Applied and Environmental Microbiology, October 2001, p. 4594-4602, Vol. 67, No. 10
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.10.4594-4602.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



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Copyright © 2001 by the American Society for Microbiology. All rights reserved.