Identification of PTSFru as the major fructose uptake system of Clostridium acetobutylicum

As a member of the saccharolytic clostridia, a variety of different carbohydrates like glucose, fructose, or mannose can be used as carbon and energy source by Clostridium acetobutylicum ATCC 824. Thirteen phosphoenolpyruvate-dependent phosphotransferase systems (PTS) have been identified in C. acetobutylicum, which are likely to be responsible for the uptake of hexoses, hexitols, or disaccharides. Here, we focus on three PTS which are expected to be involved in the uptake of fructose, PTSFru, PTSManI, and PTSManII. To analyze their individual functions, each PTS was inactivated via homologous recombination or insertional mutagenesis. Standardized comparative batch fermentations in a synthetic medium with glucose, fructose, or mannose as sole carbon source identified PTSFru as primary uptake system for fructose, whereas growth with fructose was not impaired in PTSManI and slightly altered in PTSManII-deficient strains of C. acetobutylicum. The inactivation of PTSManI resulted in slower growth on mannose whereas the loss of PTSManII revealed no phenotype during growth on mannose. This is the first time that it has been shown that PTSFru and PTSManI of C. acetobutylicum are directly involved in fructose and mannose uptake, respectively. Moreover, comprehensive comparison of the fermentation products revealed that the loss of PTSFru prevents the solvent shift as no butanol and only basic levels of acetone and ethanol could be determined.