dc.description.abstract | Octylphenol polyethoxylates (OPEOn) belongs to a nonionic surfactant family, alkylphenol polyethoxylates, which are difficult be to completely degrade in the environment. Nevertheless, the mechanism for degradation remains unclear. A Gram-nagative rod, Pseudomonas nitroreducens TX1, was previously isolated from contaminated sediment. The bacterium was able to grow on 0.05% ~20% OPEOn (Triton X-100, average n=9.5) as sole carbon source and energy. This study was aimed to investigate how P. nitroreducens TX1 metabolizes surfactant by a functional proteomics approach. OPEOn-dependent oxygen consumption activity was induced by the bacterium when grown on OPEOn as sole carbon source compared to grown on succinate. Oxygen consumption sub-proteomes were obtained from the bacterial crude extract separated by DEAE-Sepharose chromatography. Three sub-proteomes were subjected to protein by both 1D- and 2D-PAGE, and the protein spots with different expression between OPEOn- and succinate-grown sub-protemes were focused. Eighty-five up-regulated proteins and thirty-five down-regulated proteins were identified by MALDI-Q-TOF or ESI-MS/MS. The expression of outer membrane protein (porin), OrpF and OmpH, were up-regulated. Two type of transpoters, periplasmic binding proteins in ATP binding cassette transporters for transportation of polar and branch amino acids and TolB for transporting of biopolymer, were up-regulated as well. Another two periplasmic enzymes, quinoprotein ethanol dehydrogenase and aldehyde dehydrogenase, were up-regulated. The two enzymes might be related to the carboxylation of the hydroxyl terminus of the OPEOn, which was previously observed in the transformation products by strain TX1. The catabolism of OPEOn by strain TX1 was proposed by a sequential cleavage of two-carbon unit from the carboxylated ethoxylate chain to form acetate or glyoxylate. Three enzymes participated in TCA cycle, 2-oxo-glutarate dehydrogenase (E1), dihydrolipoamide dehydrogenase (E3) and succinyl-CoA synthetase, were up-regulation. In addition, three enzymes in nitrogen metabolism, ornithine carbamoyltransferase, argininosuccinate lyase and ornithine decarboxylase, were up-regulated to form furmarate in TCA cycle. The enzymes related to the synthesis of fatty acids and some amino acids (cystein, serine, and lysine) from acetyl-CoA were down-regulation. Therefore, the increased acetyl-CoA was proposed to be driven into TCA cycle to produce reducing power. Proteins in respiratory chain, such as NADH oxidoreductase (including FMN oxidoreductase), electron transfer flavoprotein, Azurin, and ATP synthase, were also up-regulated for ATP synthesis. In our previous result, the oxygen consumption activity was induced correlating to the concentration of OPEOn (0.005~0.5%) in the growth media. Therefore, from our proteomics study, the surfactant up-regulated proteins might explain the induced OPEOn-dependent oxygen consumption in whole-cell grown on OPEOn. The enzymes in glyoxylate cycle, isocitrate lyase and malate synthase, were up-regulated, indicating the gluconeogenesis might be from glyoxlate via glycerate pathway. Generally, the increased concentration of acetyl-CoA and NADH will negatively feedback to inhibit pyruvate dehydrogenase. Therefore, we also found that the enzymes in Entner-Doudoff pathway, phosphoenolpyruvate synthase and pyruvate dehydrogenase, were observed to be down-regulated. In addition, surfactant also induced stress responsive proteins such as oxidative stress proteins, alkyl hydroperoxide reductase (AhpC), tellurium resistance protein (TerZ, TerE), peroxidase and superoxide dismutase (SodB). Other stress responsive proteins such as chaperones to mediate protein folding, heat-Shock protein (GroEL, IbpA, and DnaK), and ATP-dependent Clp protease binding protein (ClpB) were also induced. The up regulated stress responsive proteins might indicate important roles on anti-surfactant stresses. The two componet response regulator (KdpE) was up-regulated, which was proposed to be involved in the osmosis regulation. In conclusion, while OPEOn was provided to P. nitreducens TX1 as sole source of carbon and energy, the bacterium increases the expression of enzymes in catabolism and reduced those in anabolism to respond. The energy was much increased through such pathway changes. In addition, a series of anti-stress proteins were up-regulated for the survival in such a stress environment. | en_US |