Comparative transcriptomics of the response of Escherichia coli to the disinfectant monochloramine and to growth conditions inducing monochloramine resistance.

Escherichia coli growth in biofilms and growth at a suboptimal temperature of 20 °C have been shown to decrease sensitivity to monochloramine (Berry, D., C. Xi, L. Raskin. 2009. Environ. Sci. Technol. 43, 884-889). In order to better understand why growth conditions affect sensitivity to monochloramine, a comparative transcriptomic approach was used to identify common patterns of differentially-expressed genes under these growth conditions and during monochloramine exposure. This approach revealed a set of differentially-expressed genes shared under multiple conditions (planktonic growth at 20 °C, biofilm growth, and exposure of planktonic cells to monochloramine), with nine genes shared under all three conditions. Functional gene categories enriched in the shared gene sets included: general metabolic inhibition, redox and oxidoreductase response, cell envelope integrity response, control of iron and sulfur transport metabolism and several genes of unknown function. Single gene deletion mutant analyses verified that loss of 15 of the 24 genes up-regulated during monochloramine exposure as well as during other tested conditions increased E. coli sensitivity to monochloramine up to two fold. Constitutive expression of down-regulated genes in single gene mutants yielded mixed results, indicating that the expression of some down-regulated genes actually decreases sensitivity to monochloramine. These results contribute to the understanding of the bacterial response to disinfectants by characterizing the overlap between growth condition associated stress responses and monochloramine-associated stress responses. This characterization highlights the bacterial responses responsible for decreased sensitivity to monochloramine under different growth conditions.