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Medium- and long-chain fatty acid uptake and utilization by Streptomyces coelicolor A3(2): first characterization of a Gram-positive bacterial system

Programa Multidisciplinario de Biología Experimental (PROMUBIE-CONICET) and Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmaceúticas, Universidad Nacional de Rosario, Suipacha 531, 2000-Rosario, Argentina

*Author for correspondence: Hugo C. Gramajo. Tel: +54 41 350661. Fax: +54 41 390465. e-mail: gramajo@unromb.edu.ar

ABSTRACT

Summary: The first characterization of fatty acid uptake in a Gram-positive bacterium is reported. Streptomyces coelicolor A3(2) utilizes fatty acids of different chain length (C₄-C₁₈) as sole carbon and energy sources. In vivo -oxidation studies and the assay of two enzymes of the -oxidation cycle proved that fatty acid degradation is constitutive in this micro-organism. Uptake of the medium-chain fatty acid octanoate showed the characteristics of simple diffusion, whereas the uptake of palmitate, a long-chain fatty acid, occurred by both simple diffusion and active transport. After correcting for non-mediated transport, palmitate uptake measured over a wide range of concentrations followed Michaelis-Menten kinetics. The apparent K_m for palmitate was 97.8 µM and the V_max was 19.3 nmol min^-1 (mg protein)^-1. Competition experiments showed specificity of the mediated transport component for long-chain fatty acids (> C₁₀). Metabolic inhibitors such as oligomycin, NaF and vanadate, and the ionophores gramicidin and carbonyl cyanide m-chlorophenylhydrazone (CCCP) inhibited palmitate uptake to different degrees, consistent with the existence of an active transport mechanism. Uptake rates measured at different pH values indicated that both the ionized and the unionized forms of octanoate crossed the cytoplasmic membrane by simple diffusion. Palmitate in its ionized form appears to be transported by an active mechanism, whereas the unionized molecule diffuses through the membrane. When present in the medium, glucose stimulated the degradation of long-chain fatty acids by increasing the rate of uptake and the level of acyl-CoA synthetase.

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