Acclimation of the Escherichia coli transcriptome after 10 hours of incubation in the presence of silver nitrate at sublethal levels.

Silver nitrate has been explored as an FDA-approved alternative to treat antibiotic-resistant bacterial strains. Questions remain as it relates to the full-systems response elicited to counteract its toxic effects, especially in the context of a non-lethal exposure. We explored the transcriptomic response profile of Escherichia coli K12 BW25113 when challenged to grow planktonically for 10 hours in M9-glucose minimal media spiked with a sublethal concentration of silver nitrate (7 µM, 1.18 µg/mL). Our results yielded significant changes in gene expresson levels: 131 genes were up-regulated, while 558 were down-regulated in our silver nitrate treatment. Some biological processes became dysregulated to cope with the presence of this metal stressor, including iron metabolism and protein folding at the inner membrane and periplasm. Altogether, this work provides a valuable snapshot of how our indicator strain adapts to metal-induced stress. This is a significant step in understanding how bacteria can adjust their physiology to coexist with sublethal concentrations of metal-based antimicrobials. Overall design: Two treatment groups were set up: a non-metal control with M9-glucose minimal media, and a metal challenge using the same culture media but spiked with a sublethal concentration of silver nitrate (7 µM, 1.18 µg/mL). Both treatments were inoculated with Escherichia coli K12 BW25113, with three biological trials each. RNA extraction took place after an incubation time of 10 hours at 37 ºC 150 rpm. Differential gene expression was identified by contrasting both treatments, using p-adj value < 0.05 and absolute fold-change (FC) of at least 2 (|log2 FC| > 1) as significance thresholds.