Growth of Escherichia coli on Short-Chain Fatty Acids: Growth Characteristics of Mutants

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The parent Escherichia coli K-12 is constitutive for the enzymes of the glyoxylate bypass and adapts to growth on long-chain fatty acids (C12 to C18). It does not utilize medium-chain (C6 to C11) or short-chain (C4, C5) n-monocarboxylic acids. Several mutants of this strain which grow using short- or medium-chain acids, or both, as the sole carbon source were selected and characterized. One mutant (D1) synthesizes the β-oxidation enzymes constitutively and grows on medium-chain but not on short-chain acids. A second (N3) is partially derepressed for synthesis of these enzymes and grows both on medium-chain and on short-chain acids. Secondary mutants (N3V−, N3B−, N3OL−) were derived from N3. N3V− grows on even-chain but not on odd-chain acids and exhibits a lesion in propionate oxidation. N3B− grows on odd-chain but not on even-chain acids and exhibits no crotonase activity as assayed by hydration of crotonyl-CoA. N3OL− grows on acetate and propionate but does not utilize fatty acids C4 to C18; it exhibits multiple deficiencies in the β-oxidation pathway. Growth on acetate of N3, but not of the parent strain, is inhibited by 4-pentenoate. Revertants of N3 which are resistant to growth inhibition by 4-pentenoate (N3PR) exhibit loss of ability to grow on short-chain acids but retain the ability to grow on medium-chain and long-chain acids. The growth characteristics of these mutants suggest that in order to grow at the expense of butyrate and valerate, E. coli must be (i) derepressed for synthesis of the β-oxidation enzymes and (ii) derepressed for synthesis of a short-chain fatty acid uptake system.

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