Transcriptomic approach and membrane fatty acid analysis to study the response mechanisms of Escherichia coli to thyme essential oil, carvacrol, 2-(E)-hexanal and citral exposure

AIMS: The application of essential oils and their components as food preservatives is promising but requires a deeper understanding of their mechanisms of action. This study aims to evaluate the effects of thyme essential oil, carvacrol, citral and 2-(E)-hexenal, on whole-genome gene expression (the transcriptome), as well as the fatty acids composition of the cell membranes of Escherichia coli K12. METHODS AND RESULTS: Therefore, we studied the response against 1 hour of exposure to sublethal concentrations of natural antimicrobials, of exponentially growing Escherichia coli K12, using DNA microarray technology and a gas chromatographic method. The results show that treatment with a sublethal concentration of the antimicrobials strongly affects global gene expression in E. coli for all antimicrobials used. Major changes in the expression of genes involved in metabolic pathways as well as in fatty acid biosynthesis and protection against oxidative stress were evidenced. Moreover, the sub-lethal treatments resulted in increased levels of unsaturated and cyclic fatty acids as well as an increase of the chain length compare to the controls. CONCLUSIONS: The down-regulation of genes involved in aerobic metabolism indicate a shift from respiration to fermentative growth. Moreover, the results obtained suggest that the cytoplasmic membrane of E. coli is the major cellular target of essential oils and their components. In addition, the key role of membrane unsaturated fatty acids in the response mechanisms of E. coli to natural antimicrobials has been confirmed in this study. SIGNIFICANCE AND IMPACT OF THE STUDY: The transcriptomic data obtained signify a further step to understand the mechanisms of action of natural antimicrobials also when sub-lethal concentrations and short term exposure. In addition, this research goes in deep correlating the transcriptomic modification with the changes of E. coli fatty acid composition of cell membrane identified as the main target of the natural antimicrobials. This article is protected by copyright. All rights reserved