3.3. Excretion of 1-octanol
We noted that during the early to late stationary phases of cell cultivation with TPC3-Ahr, a strong perfume-like fragrance emanated from the cell cultures which suggested the extracellular presence of product(s). After separation of the cells from the media, GC–MS analysis confirmed that 73±3% of the total 1-octanol in the culture was present in the media while the remainder was found to be localised within the cellular fraction (Fig. 1c). E. coli harbours a large range of efflux pumps ( Segura et al., 2012). Among them, the AcrAB–TolC complex is the most well-studied and has been implicated in tolerance to exogenously added solvents (Tsukagoshi and Aono, 2000 and White et al., 1997). We constructed an ΔacrA deletion strain of E. coliBL21(DE3) in order to test whether AcrAB–TolC was responsible for the efflux of internally produced 1-octanol. The mutant strain displayed a ~3-fold decrease in excreted 1-octanol along with a similar drop in total 1-octanol production levels ( Fig. 1c). The ratio of external to internal 1-octanol, however, was slightly lower for the ΔacrA deletion strain (2.0) compared to the wild-type strain (2.8). The marked reduction in both excretion and production suggested that the AcrAB–TolC complex is most likely responsible for the majority of 1-octanol efflux.