Pseudomonas sp. C27 is a facultative autotrophic bacterium that can effectively conduct mixotrophic and heterotrophic denitrification reactions using organic matters and sulfide as electron donors. There is no experimental confirmation on proteomic levels the pure C27 strain can have the capability to simultaneous removal of sulfide, nitrate and organic carbon from waters. The proteome in total C27 cell extracts was observed by two-dimensional gel electrophoresis. The 160 mg/L sulfide upregulated or specifically expressed succinate dehydrogenase, iron-sulfur protein, oxidoreductase, serine hydroxymethyltransferase, and iron superoxide dismutase for sulfide metabolism, 2-oxoglutarate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, NAD(+)-dependent aldehyde dehydrogenase, malate dehydrogenase and succinate dehydrogenase for carbon metabolism, and nitrous-oxide reductase and respiratory nitrate reductase for nitrogen metabolism. The study confirmed that the C27 strain has an effective enzyme system to conduct denitrifying sulfide removal reactions. Also, sulfide stress can enhance energy consumption rate and rates of nitrate reduction and sulfide oxidation by C27. Conversely, sulfide stress repressed the sulfate-reducing power of C27, evidenced by down-regulation or specific un-expression of sulfate ABC transporter, periplasmic sulfate-binding protein in the (C+ N + S) sample. (C) 2013 Elsevier Inc. All rights reserved.