Comparative proteomics insights into the degradation of ethoxylated surfactants by Pseudomonas nitroreducens TX1

Abstract

The bacterium Pseudomonas nitroreducens TX1 (ATCC PTA-6168) is especially interested due to its capability to efficiently remove octylphenol polyethoxylates (OPEO_n), which belong to non-ionic surfactants and commonly used in industrial, agricultural and domestic applications. Although the biodegradation pathways of OPEO_n were studied, the variations at the level of expression of the key enzymes during catabolism are still not quantitatively understood. In this study, we used comparative proteomics analysis approach to determine differential expression and regulation of key enzymes in strain TX1 during octylphenol polyethoxylates utilization as sole carbon source. 43 protein spots (2D gel) and 25 protein bands (SDS-PAGE followed by activity-guided sub-proteomes) significantly up-regulated in OPEO_n-grown cells were identified, whereas 20 protein spots and 11 protein bands were significantly down-regulated. Based on the proteomic results, OPEO_n and its intermediates were proposed in pathways to take up through membrane transport systems, mainly ABC transporters and outer membrane proteins. Key oxidoreductases such as dihydrolipoamide dehydrogenase and NADPH:quinone reductase may drive oxidative degradation of OPEO_n. Elevated levels of FAD/FMN-containing dehydrogenases and NAD-dependent aldehyde dehydrogenases indicate that oxidative reactions were involved in ethoxylate side chains and transferring electrons to the respiratory chain. Our proteomic data also revealed increased expression of glycolate dehydrogenase, isocitrate lyase, and malate synthase, supporting our previous finding of the integration of OPEO_n-derived intermediates into the glyoxylate cycle. Thus, this study provides the first quantitative proteomic insight into OPEOn catabolism in P. nitroreducens TX1.