Salmonella typhimurium possesses at least three inducible transport systems for the tricarboxylic acids (citric, isocitric, cis -aconitic, and tricarballylic). The first system was induced by citrate, isocitrate, or cis -aconitate, and transported citric acid and isocitric acid. The second system was also induced by the same acids as in the first system and transported cis -aconitic acid. This system required Mg 2+ ions and was stable at pH 8.4 but unstable at pH 7.0. The metal ion was replaced with Sr 2+ or Ca 2+ ions but not with Ba 2+ ions. The third system was induced by tricarballylate and transported citric acid, cis -aconitic acid, and tricarballylic acid.

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