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Transcriptional Characterization of Salmonella TAl00 in Growth and Stationary Phase: Mutagenesis of MX in Both Types of Cells
Citation:
WARD, W. O., C. D. Swarz, N. M. HANLEY, AND D. M. DEMARINI. Transcriptional Characterization of Salmonella TAl00 in Growth and Stationary Phase: Mutagenesis of MX in Both Types of Cells. MUTAGENESIS. Oxford University Press, Cary, NC, 692(1-2):19-25, (2010).
Impact/Purpose:
This study assesses global gene expresion in the Ames mutagenicity assay using cells in different growth phases to determine the basis for how cells respond to mutagenic treatment.
Description:
The Salmonella (Ames) mutagenicity assay can be performed using cells that are in different growth phases. Thus, the plate-incorporation assay involves plating stationary-phase cells with the mutagen, after which the cells undergo a brief lag phase and, consequently, are exposed to the mutagen and undergo mutagenesis while in the growth (log) phase. In contrast, a liquid-suspension assay involves exposure ofeither growth-or stationary-phase cells to the mutagen for a specified period oftime, sometimes followed by a wash, resulting in the cells growing in medium in the absence ofthe mutagen. To explore global gene expression in Salmonella in both growth and stationary phase cells, and to see the influence ofthe transcriptional status ofthe cell on mutagenesis, we performed microarray analysis on strain TAIOOofSalmonella that were exposed to the drinking-water mutagen MX while in the growth or stationary phase. The genes in functional pathways involving amino acid transport and metabolism and energy metabolism were expressed differentially in growth-phase cells, whereas genes in functional pathways involving protein trafficking, cell envelope,and two-component systems using common signal transduction were expressed differentially in stationary-phase cells. More than 90% ofthe ribosomal-protein biosynthesis genes were up-regulated in stationary-versus growth-phase cells. When expressed as mutant frequency (revertants/survivors/IlM), MX was equally mutagenic in both phases, but it was 2.5 times more mutagenic in stationary-phase cells when the results were expressed as mutant yield (revertants/nmole). After MX treatment, stationary-phase cells up-regulated sulA to inhibit cell division and umuC/D to increase error-prone repair. This resulted in an increase in survival and mutant yield in MX-treated stationary-phase cells relative to growth-phase cells. Knowledge of 3 ofthe transcriptionalstate ofcells atthetime ofmutagentreatment andafterwardsmayhelp explain the response of cells to mutagen treatment.
