Effects of low concentrations of fatty acids on Escherichia coli depend on the kind of culture medium and incubation temperature

Fatty acids play important, yet different roles in bacterial physiology, specifically their growth, either stimulating or inhibiting this parameter which are of biotechnological importance. Here, we present results showing to what degree short- and medium-chain fatty acids (butyric acid (butanoic acid, C4:0); caproic acid (hexanoic acid, C6:0); caprylic acid (octanoic acid, C8:0)), used at relatively low concentrations (in a range of μg/mL, contrary to previously reported mg/mL which revealed inhibitory effects on bacterial growth) affect growth of Escherichia coli K-12 (MG1655 laboratory strain) depending on various conditions. In rich medium (LB) positive effects of all tested fatty acids on E. coli growth were observed, while temperature of incubation (growth at 25 °C and 37 °C was assessed) modulated these effects. In contrast, a slight but significant growth inhibition by fatty acids was observed in a minimal medium (M9) supplemented with glucose. Nonetheless, in minimal medium containing acetate, the effects of these compounds varied, being either positive or negative depending on their concentrations. No measurable bacterial growth was observed in the case of the presence of any tested fatty acids when primary carbon source (glucose or acetate) was removed from a minimal medium before addition of butyric acid, caproic acid or caprylic acid. Our results indicated that effects of low concentrations of fatty acids on E. coli cells depend on growth conditions of bacterial cultures. This may be of biotechnological importance, especially for modulating E. coli growth by using different compositions of media and incubation temperatures.