We have studied trehalose uptake in Salmonella typhimurium and the possible involvement of the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) in this process. Two transport systems could recognize and transport trehalose, the mannose PTS and the galactose permease. Uptake of trehalose via the latter system required that it be expressed constitutively (due to a galR or gaiC mutation). Introduction of a ptsM mutation, resulting in a defective IIManjIIIjIi system, in S. typhimurium strains that grew on trehalose abolished growth on trehalose. A ptsG mutation, eliminating IIGIc of the glucose PTS, had no effect. In contrast, a crr mutation that resulted in the absence of 111GIc of the glucose PTS prevented growth on trehalose. The inability of crr and also cya mutants to grow on trehalose was due to lowered intracellular cyclic AMP synthesis, since addition of extracellular cyclic AMP restored growth. Subsequent trehalose metabolism could be via a trehalose phosphate hydrolase, if trehalose phosphate was formed via the PTS, or trehalase. Trehalose-grown cells contained trehalase activity, but we could not detect phosphoenolpyruvate-dependent phosphorylation of trehalose in toluenized cells.The phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PT$) catalyzes the transport and concomitant phosphorylation of a large number of carbohydrates in a variety of bacteria. The system has been studied in most detail in the members of the family Enterobacteriaceae, e.g., Escherichia coli and Salmonella typhimurium. More than 10 different sugar-specific, membrane-bound enzymes II pf the PTS have been identified. Together with the general, cytoplasmic proteins enzyme I and HPr and (in a number of cases) sugar-specific enzymes III, the enzymes II catalyze carbohydrate uptake and phosphorylation. For instance, glucose (Glc) is taken up and phosphorylated to glucose 6-phosphate via enzyme IIG1c and its associated IIIGIc. Mannitol (Mtl), on the other hand, requires only an enzyme lIMtl (for a review, see reference 14).