Xiangsheng Zhang, Jonathan G. Hughes, Gabriel A. Subuyuj, Jayna L. Ditty, Rebecca E. Parales

Although alcohols are toxic to many microorganisms, they are good carbon and energy sources for some bacteria, including many pseudomonads. However, most studies that have examined chemosensory responses to alcohols have reported that alcohols are sensed as repellents, which is consistent with their toxic properties. In this study, we examined the chemotaxis of Pseudomonas putida F1 to n-alcohols with chain lengths of one to twelve carbons. P. putida F1 was attracted to all n-alcohols that served as growth substrates (C2-C12) for the strain, and the responses were induced when cells were grown in the presence of alcohols. By assaying mutant strains lacking single or multiple methyl-accepting chemotaxis proteins, the receptor mediating the response to C2-C12 alcohols was identified to be McfP, the ortholog of the P. putida KT2440 receptor for C2 and C3 carboxylic acids. Besides n-alcohols, McfP was required for the response of P. putida F1 to pyruvate, L-lactate, acetate, and propionate,which are detected by the KT2440 receptor, and the medium and long chain carboxylic acids hexanoic acid and dodecanoic acid. β-Galactosidase assays of P. putida F1 carrying a mcfP-lacZ transcriptional fusion showed that the mcfP gene is not induced in response to alcohols. Together, our results are consistent with the idea that the carboxylic acids generated from the oxidation of alcohols are the actual attractants sensed by McfP in P. putida F1, rather than the alcohols themselves.IMPORTANCEAlcohols, released as fermentation products and produced as intermediates in the catabolism of many organic compounds including hydrocarbons and fatty acids, are common components of the microbial food web in soil and sediments. Although they serve as good carbon and energy sources for many soil bacteria, alcohols have primarily been reported to be repellents rather than attractants for motile bacteria. Little is known about how alcohols are sensed by microbes in the environment. We report here that catabolizable n-alcohols with linear chains of up to twelve carbons serve as attractants for the soil bacterium Pseudomonas putida, and rather than being detected directly, alcohols appear to be catabolized to acetate, which is then sensed by a specific cell-surface chemoreceptor protein.