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Appl. Environ. Microbiol., 12 1995, 4147-4151, Vol 61, No. 12
U Rinas, K Hellmuth, R Kang, A Seeger and H Schlieker
Endogenous and exogenous accumulation of nucleobases was observed when
Escherichia coli entered the stationary phase. The onset of the stationary
phase was accompanied by excretion of uracil and xanthine. Except for
uracil and xanthine, other nucleobases (except for minor amounts of
hypoxanthine), nucleosides, and nucleotides (except for cyclic AMP) were
not detected in significant amounts in the culture medium. In addition to
exogenous accumulation of nucleobases, stationary-phase cells increased the
endogenous concentrations of free nucleobases. In contrast to extracellular
nucleobases, hypoxanthine was the dominating intracellular nucleobase and
xanthine was present only in minor concentrations inside the cells.
Excretion of nucleobases was always connected to declining growth rates. It
was observed in response to entry into the stationary phase independent of
the initial cause of the cessation of cell growth (e.g., starvation for
essential nutrients). In addition, transient accumulation of exogenous
nucleobases was observed during perturbations of balanced growth conditions
such as energy source downshifts. The nucleobases uracil and xanthine are
the final breakdown products of pyrimidine (uracil and cytosine) and purine
(adenine and guanine) bases, respectively. Hypoxanthine is the primary
degradation product of adenine, which is further oxidized to xanthine. The
endogenous and exogenous accumulation of these nucleobases in response to
entry into the stationary phase is attributed to degradation of rRNA.
Copyright © 1995, American Society for Microbiology
Entry of Escherichia coli into stationary phase is indicated by endogenous and exogenous accumulation of nucleobases
Biochemical Engineering Division, GBF National Research Center for Biotechnology, Braunschweig, Germany.
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