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Applied and Environmental Microbiology, October 2001, p. 4594-4602, Vol. 67, No. 10
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.
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
*
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.
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