Effects of metabolic flux on stress response pathways in
Lactococcus lactis
Patrick Duwat,1* S. Dusko Ehrlich2 and Alexandra
Gruss1
1Génétique Appliquée, URLGA, Institut National de la
Recherche Agronomique, Domaine de Vilvert, 78352
Jouy en Josas Cedex, France.
2Génétique Microbienne, Institut National de la
Recherche Agronomique, Domaine de Vilvert, 78352
Jouy en Josas Cedex, France.
Summary
Studies of cellular responses to stress conditions such
as heat, oxygen or starvation have revealed the exis-
tence of numerous specific or interactive response
pathways. We previously observed in Lactococcus
lactis that inactivation of the recA gene renders the
lactococcal strain sensitive not only to DNA-damag-
ing agents but also to oxygen and heat. To further
examine the stress response pathways in L. lactis,
we isolated thermoresistant insertional mutants (Trm)
of the recA strain. Eighteen independent trm mutations
were identified and characterized. We found that muta-
tions map in only seven genes, implicated in purine
metabolism (deoB, guaA and tktA), phosphate uptake
(pstB and pstS), mRNA stability (pnpA) and in one
uncharacterized gene (trmA). All the trm mutations,
with the exception of trmA, confer multiple stress
resistance to the cell. Some of the mutations confer
improved heat stress resistance not only in the recA
but also in the wild-type context. Our results reveal
that cellular metabolic pathways are intimately related
to stress response and that the flux of particular meta-
bolites, notably guanine and phosphate, may be impli-
cated in stress response in lactococci.
Introduction
Growth and survival of a living cell depend on its ability to
perceive and respond to a changing environment. Data
accumulated in the last 10 years indicate that bacteria
have evolved specific functions in response to environ-
mental signals during rapid growth (exponential phase)
and other specific functions for the period of nutrient star-
vation (stationary phase). In both phases, the responses
improve the ability of the c