초록
<P><I>Salmonella enteric</I> serovar Typhimurium, a major cause of food-borne illness, is capable of using a variety of carbon and nitrogen sources. Fructoselysine and glucoselysine are Maillard reaction products formed by the reaction of glucose or fructose, respectively, with the ε-amine group of lysine. We report here that <I>S</I>. Typhimurium utilizes fructoselysine and glucoselysine as carbon and nitrogen sources via a mannose family phosphotransferase (PTS) encoded by <I>gfrABCD</I> (glucoselysine/fructoselysine PTS components EIIA, EIIB, EIIC, and EIID; locus numbers STM14_5449 to STM14_5454 in <I>S</I>. Typhimurium 14028s). Genes coding for two predicted deglycases within the <I>gfr</I> operon, <I>gfrE</I> and <I>gfrF</I>, were required for growth with glucoselysine and fructoselysine, respectively. GfrF demonstrated fructoselysine-6-phosphate deglycase activity in a coupled enzyme assay. The biochemical and genetic analyses were consistent with a pathway in which fructoselysine and glucoselysine are phosphorylated at the C-6 position of the sugar by the GfrABCD PTS as they are transported across the membrane. The resulting fructoselysine-6-phosphate and glucoselysine-6-phosphate subsequently are cleaved by GfrF and GfrE to form lysine and glucose-6-phosphate or fructose-6-phosphate. Interestingly, although <I>S</I>. Typhimurium can use lysine derived from fructoselysine or glucoselysine as a sole nitrogen source, it cannot use exogenous lysine as a nitrogen source to support growth. Expression of <I>gfrABCDEF</I> was dependent on the alternative sigma factor RpoN (σ<SUP>54</SUP>) and an RpoN-dependent LevR-like activator, which we designated GfrR.</P><P><B>IMPORTANCE</B> <I>Salmonella</I> physiology has been studied intensively, but there is much we do not know regarding the repertoire of nutrients these bacteria are able to use for growth. This study shows that a previously uncharacterized PTS and associated enzymes function together to transport and catabolize fructoselysine and glucoselysine. Knowledge of the range of nutrients that <I>Salmonella</I> utilizes is important, as it could lead to the development of new strategies for reducing the load of <I>Salmonella</I> in food animals, thereby mitigating its entry into the human food supply.</P>