| Abstract: | A quantitative capillary assay was used to show that aromatic acids, compounds that are chemorepellents for Escherichia coli and Salmonella sp., are chemoattractants for Pseudomonas putida PRS2000. The most effective attractants were benzoate; p-hydroxybenzoate; the methylbenzoates; m-, p-, and o-toluate; salicylate; DL-mandelate; beta-phenylpyruvate; and benzoylformate. The chemotactic responses to these compounds were inducible. Taxis to benzoate and m-toluate was induced by beta-ketoadipate, a metabolic intermediate formed when benzoate is dissimilated via enzymes specified by chromosomal genes. Benzoylformate taxis was induced by benzoylformate and L(+)-mandelate. Taxis to mandelate, benzoylformate, and beta-phenylpyruvate was exhibited by cells grown on mandelate, but not by cells grown on benzoate. Cells grown on benzoate were chemotactic to benzoate, the toluates, p-hydroxybenzoate, and salicylate. These results show that P. putida synthesizes at least two distinct chemoreceptors for aromatic acids. Although DL-mandelate was an effective attractant in capillary assays, additional experiments indicated that the cells were actually responding to benzoylformate, a metabolite formed from mandelate. With the exception of mandelate taxis, chemotaxis to aromatic acids was not dependent on the expression of pathways for aromatic degradation. Therefore, the tactic responses exhibited by cells cannot be attributed to an effect of the oxidation of aromatic acids on the energy metabolism of cells. |
