Project description:Glucose-lysine based Maillard reaction products (MRPs) are introduced to the human body via food ingestion or are synthesized in vivo. Depending on reaction conditions, they represent a mixture of compounds with diverse chemical structures and physiological properties. MRPs may also be a potential nutrient source for Salmonella, a major foodborne gastrointestinal pathogen. This study was designed to determine the growth and transcriptional responses of S. Typhimurium LT2 to MRPs generated at low water activity to simulate the reaction occurring during food processing and storage. Maillard reactions between N-α-acetyl-lysine and glucose were varied in time (4, 23, and 143 h) to generate sub-samples with prevailing Amadori compound, advanced glycation end products (AGEs), or melanoidines respectively. The addition of MRP up to 5 mg mL-1 to defined media with 0.4% glucose had no effect on S. Typhimurium LT2 growth. In media, where the MRP sub-samples (4 and 23 h) served as the only carbon source, MRP assimilation by S. Typhimurium LT2 was observed as secondary logarithmic growth phases (0.063 h-1 and 0.072 h-1) after the growth on glucose available in the MRP reaction mixtures (0.479 h-1). The MRPs sub-sample with the highest concentration of melanoidines (143 h) also supported S. Typhimurium LT2 growth (0.368 h-1). Of the three MRPs sub-samples, the Amadori compound was the preferred carbon source for S. Typhimurium LT2 as evidenced by its almost complete disappearance (98%). Decreases in AGEs (37%) and melanoidines (15%), when incubated with S. Typhimurium LT2, also occurred. Transcription profiles of the cells grown on the MRPs fractions revealed predominant up-regulation of genes associated with the functional groups of energy metabolism, fatty and phospholipid metabolism, cellular process, and regulatory functions, and general down-regulation of the genes in the groups of amino acid biosynthesis, protein synthesis and transcription, transport and binding proteins, and DNA metabolism. The carbon flow in tricarboxylic acid (TCA) cycle partitioned by the glyoxylate cycle appeared to play an essential role in the assimilation of glucose-lysine-derived MRPs. The high expression level of numerous genes encoding hypothetical proteins or proteins with unknown function suggested the presence of genes whose role in glucose-lysine MRPs catabolism in Salmonella remains to be determined.
Project description:To explore the mechanisms of Salmonella desiccation resistance, we studied the transcriptomic responses in Salmonella Tennessee (Tennessee), using S. Typhimurium LT2 (LT2), a strain weakly resistant to desiccation, as a reference strain. In response to 2 h air-drying at 11% equilibrated relative humidity, approximately one-fourth of the ORFs in the Tennessee genome and one-fifth in LT2 were differentially expressed (> 2-fold). Among all differentially expressed functional groups (>5-fold) in both strains, the expression fold change associated with fatty acid metabolism was the highest, and constituted 51 and 35% of the total expression fold change in Tennessee and LT2, respectively. Tennessee showed greater changes in expression of genes associated with stress response and envelope modification than LT2, while showing lesser changes in protein biosynthesis expression. Expression of flagella genes was significantly more inhibited in stationary phase cells of Tennessee than LT2 both before and after desiccation.
Project description:Investigation of gene expression level changes in Salmonella typhimurium LT2 TA100 upon exposure to C60, compared to unexposed controls. The mutations engineered into this strain make it susceptile to mutagenic compounds. The Salmonella typhimurium TA100 strain used in this study is further described in Pedersen P, Thomsen E, Stern RM. 1983. Detection by Replica Plating of False Revertant Colonies Induced in the Salmonella Mammalian Microsome Assay by Hexavalent Chromium. Environmental health perspectives 51: 227-230. A 4 x 72K array study using total RNA recovered from triplicate cultures of Salmonella typhimurium LT2 TA100 exposed to C60 and triplicate cultures of controls that were not exposed to C60. Each 72K array measures the expression level of 4,504 genes from Salmonella typhimurium LT2 with seven 45 to 60-mer probe pairs per gene.