Acid-adapted strains of Escherichia coli K-12 obtained by experimental evolution.

Autor:	Harden MM; Department of Biology, Kenyon College, Gambier, Ohio, USA., He A; Department of Biology, Kenyon College, Gambier, Ohio, USA., Creamer K; Department of Biology, Kenyon College, Gambier, Ohio, USA., Clark MW; Department of Biology, Kenyon College, Gambier, Ohio, USA., Hamdallah I; Department of Biology, Kenyon College, Gambier, Ohio, USA., Martinez KA 2nd; Department of Biology, Kenyon College, Gambier, Ohio, USA., Kresslein RL; Department of Biology, Kenyon College, Gambier, Ohio, USA., Bush SP; Department of Biology, Kenyon College, Gambier, Ohio, USA., Slonczewski JL; Department of Biology, Kenyon College, Gambier, Ohio, USA slonczewski@kenyon.edu.
Jazyk:	angličtina
Zdroj:	Applied and environmental microbiology [Appl Environ Microbiol] 2015 Mar; Vol. 81 (6), pp. 1932-41. Date of Electronic Publication: 2015 Jan 02.
DOI:	10.1128/AEM.03494-14
Abstrakt:	Enteric bacteria encounter a wide range of pHs throughout the human intestinal tract. We conducted experimental evolution of Escherichia coli K-12 to isolate clones with increased fitness during growth under acidic conditions (pH 4.5 to 4.8). Twenty-four independent populations of E. coli K-12 W3110 were evolved in LBK medium (10 g/liter tryptone, 5 g/liter yeast extract, 7.45 g/liter KCl) buffered with homopiperazine-N,N'-bis-2-(ethanosulfonic acid) and malate at pH 4.8. At generation 730, the pH was decreased to 4.6 with HCl. By 2,000 generations, all populations had achieved higher endpoint growth than the ancestor at pH 4.6 but not at pH 7.0. All evolving populations showed a progressive loss of activity of lysine decarboxylase (CadA), a major acid stress enzyme. This finding suggests a surprising association between acid adaptation and moderation of an acid stress response. At generation 2,000, eight clones were isolated from four populations, and their genomes were sequenced. Each clone showed between three and eight missense mutations, including one in a subunit of the RNA polymerase holoenzyme (rpoB, rpoC, or rpoD). Missense mutations were found in adiY, the activator of the acid-inducible arginine decarboxylase (adiA), and in gcvP (glycine decarboxylase), a possible acid stress component. For tests of fitness relative to that of the ancestor, lacZ::kan was transduced into each strain. All acid-evolved clones showed a high fitness advantage at pH 4.6. With the cytoplasmic pH depressed by benzoate (at external pH 6.5), acid-evolved clones showed decreased fitness; thus, there was no adaptation to cytoplasmic pH depression. At pH 9.0, acid-evolved clones showed no fitness advantage. Thus, our acid-evolved clones showed a fitness increase specific to low external pH. (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)
Databáze:	MEDLINE
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