Identification of PTS(Fru) 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, PTS(Fru), PTS(ManI), and PTS(ManII). 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 PTS(Fru) as primary uptake system for fructose, whereas growth with fructose was not impaired in PTS(ManI) and slightly altered in PTS(ManII)-deficient strains of C. acetobutylicum. The inactivation of PTS(ManI) resulted in slower growth on mannose whereas the loss of PTS(ManII) revealed no phenotype during growth on mannose. This is the first time that it has been shown that PTS(Fru) and PTS(ManI) of C. acetobutylicum are directly involved in fructose and mannose uptake, respectively. Moreover, comprehensive comparison of the fermentation products revealed that the loss of PTS(Fru) prevents the solvent shift as no butanol and only basic levels of acetone and ethanol could be determined.