Bd. Wei et al., Global regulatory mutations in csrA and rpoS cause severe central carbon stress in Escherichia coli in the presence of acetate, J BACT, 182(6), 2000, pp. 1632-1640
The csrA gene encodes a small RNA-binding protein, which acts as a global r
egulator in Escherichia coli and other bacteria (T. Romeo, Mel. Microbiol.
29:1321-1330, 1998). Its key regulatory role in central carbon metabolism,
both as an activator of glycolysis and as a potent repressor of glycogen bi
osynthesis and gluconeogenesis, prompted us to examine the involvement of c
ad in acetate metabolism and the tricarboxylic acid (TCA) cycle; We found t
hat growth of csrA rpoS mutant strains was very poor on acetate as a sole c
arbon source. Surprisingly, growth also was inhibited specifically by the a
ddition of modest amounts of acetate to rich media (e.g., tryptone broth).
Cultures grown in the presence of greater than or equal to 25 mM acetate co
nsisted substantially of glycogen biosynthesis (glg) mutants, which were no
longer inhibited by acetate. Several classes of glg mutations were mapped
to known and novel loci. Several hypotheses were examined to provide furthe
r insight into the effects of acetate on growth and metabolism in these str
ains. We determined that csrA positively regulates acs (acetyl-coenzyme A s
ynthetase; Acs) expression and isocitrate lyase activity without affecting
key TCA cycle enzymes or phosphotransacetylase. TCA cycle intermediates or
pyruvate, but not glucose, galactose, or glycerol, restored growth and prev
ented the gig mutations in the presence of acetate. Furthermore, amino acid
uptake was inhibited by acetate specifically in the csrA rpoS strain. We c
onclude that central carbon flux imbalance, inhibition of amino acid uptake
, and a deficiency in acetate metabolism apparently are combined to cause m
etabolic stress by depleting the TCA cycle.