Characterization of Enterobacter cloacae under phoxim stress by two-dimensional gel electrophoresis

Phoxim, an organophosphorus pesticide, was widely used in agriculture but was banned because of its associated toxic runoff, which accumulated in surrounding water outlets. Here, Enterobacter cloacae was isolated from water outlets adjacent to industrial, agricultural and residential sewage having high organic phosphorus contents. To investigate the ability of E. cloacae to respond and survive under phoxim stress, both at the proteomic and transcriptional level, two-dimensional gel electrophoresis (2-DE), matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS/MS) and quantitative real-time PCR (qPCR) were used. A 2-DE analysis showed that 12 h post phoxim exposure, 46 proteins were differentially expressed and 21 protein spots were selected for MALDI-TOF-MS/MS identification. This resulted in the successful identification of 16 spots, nine up-regulated and seven down-regulated. Of these, stress response proteins, including the chaperone protein DnaK, GroEL, F₀F₁ ATP synthase subunit beta, phosphoenolpyruvate carboxykinase and outer membrane channel protein, were only expressed in the phoxim-treated experimental group. To validate these findings, seven genes were selected and positively confirmed using qPCR. The results suggest that the identified expression patterns relate to E. cloacae resistance and tolerance to high phoxim concentrations.