Biomolecular Response By Escherichia Coli Under Triclocarban Stress

The phenylurea compound,triclocarban,is an antibacterial agent that has been widely used in personal care products for decades.Triclocarban enters the environment through the discharge of domestic sewage and the disposal of sludge,promoting the expression of bacterial resistance genes and causing a public health risk.The toxic mechanism of triclocarban on microbes are still needed to be explored at the molecular level.The typical Gram-negative model organism,Escherichia.coli was selected to investigate the metabolic regulation network related to triclocarban at the system level using the proteomics and metabolomics approaches.Furthermore,the key enzymes were verified.After the exposure,cells were separated and cultured to determine whether cells would inherit the molecular responses to pollutant stress.Results of proteomics showed that Escherichia.coli transformed to a phenotype of carbon saving and adapting to nutritional restrictions via regulating protein expressions.Phosphotransferase system,glycolysis,pentose phosphate pathway and fatty acid metabolism were upregulated.The adaptive pathway glyoxylate shunt was activated,allowing cells to use acetyl-Co A produced by the ?-oxidation of fatty acids.In addition,triclocarban interfered with the first step of the non-mevalonate pathway via inhibiting 1-deoxy-D-xylulose-5-phosphate synthase(Dxs).The non-mevalonate pathway is responsible for the biosynthesis of isoprenoids.The effect of triclocarban on the pool of isoprenoid could leave a negative effect on the transport of peptidoglycan precursors.In response to this,proteins involved in multi-drug efflux system,Tol-Pal system,cell division and lipopolysaccharide biosynthesis were upregulated,enhancing the bacterial resistance,membrane adaptability and the connection between envelope structure.Intracellular metabolomics identified a decrease in the abundance of leucine and isoleucine.This result is consistent with the upregulation of leucine-responsive regulatory protein(Lrp)and leucine-specific-binding protein(Liv K)which is a response to nutritional restriction.The identification of the downstream metabolites of glyoxylate proved that glyoxylate was stably converted into malate,ensuring the carbon mass required for the growth of the organism.The consumption of ethanolamine was used for lipopolysaccharides biosynthesis.In addition,the measurement of enzyme activity verified that under triclocarban stress,1-deoxy-D-xylulose-5-phosphate synthase of Escherichia.coli was downregulated,and isocitratelyase was upregulated.After withdrawal of triclocarban and recovery culture for 12 h,the disturbed pathways and most of the adaptation mechanisms were regulated to the normal level,which indicated that triclocarban did not trigger irreversible effects under the experimental conditions.