The effect of heavy metals on soluble microbial products (SMPs) have been widely studied in the activated sludge system. However, their impact on the biofunctions of SMPs remain unclear, which could reflect state of cellular metabolism. In present work, we investigated toxic impact of Cd2+ and Cu2+ on properties of soluble microbial products (SMPs) and cellular metabolism activities via proteomics analysis and genotoxicity. The results indicated all sized fractions in SMPs have been increased by addition of Cd2+ or Cu2+ through altering several cellular metabolic pathways; especially for the appearance of Cu2+. The toxicity of Cd2+ impacted cellular substrate consumption, energy generation, and electron transport activities via changing metabolism and/or degradation of amino acid, while the addition of Cu2+ threated transfer of genetic information and cellular signals, energy generation and storage, and activity of enzymes via affecting metabolic activities of ribonucleic acid, purine, and pyrimidine. Meanwhile, ribosomes played essential roles in toxic resistance under Cd2+ shock, ATP-binding cassette (ABC) transporters functioned in toxic resistance under Cu2+ shock. In addition, the expression of functional genes grpE, dnaJ, ibpB, and ytfE were specially regulated by Cd2+ shock, and the expression of functional genes grxA, grxB, gst, ahpF, marC, dacB, and pbpG are particularly sensitive to the Cu2+ stress; which confirmed differences in cellular response activities under stressful conditions of toxic Cd2+ and Cu2+. Those findings provided key insights into how toxic metals change cellular metabolism at the molecular level, which would be meaningful to operational control and optimization of biological wastewater treatment.
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