| dc.description.abstract | Alkylphenol polyethoxylates (APEOn), one kind of non-ionic surfactants, was extensively used in the industrial, agricultural and household activities. These compounds were frequently discharged into natural environment and transformed to alkylphenol (AP) and APEOn (n=1-2), which was more recalcitrant and has been demonstrated as the environmental hormone with estrogenic-like activity to aquatic organisms, wildlife and humans. Only a few of microorganism that can degrade alkylphenol polyethoxylates or alkylphenol were isolated. The biodegradation pathway of these compounds still remains unproven in previous study. The objectives of this study were aimed to isolate and characterize novel bacterial isolates able to grow on both APEOn and AP in order to elucidate the mechanism of disruption of estrogenic-like metabolites.
In this study, 28 bacterial strains are found to be able to degrade alkylphenol and/or from different topsoil samples. All of these isolates were Gram-negative bacteria. They were identified by three methods, Biolog breathprinting, fatty acid fingerprinting and 16S rDNA sequence analysis. 64% of them was belonged to Pseudomonas genus. Other species included Alcaligenes defragrans, Bordetella brochiseptica, Zoogloea ramigera and Inquilinus limosus. Among them, a strain Pseudomonas putida TX2 was shown to have a novel activity to grow on alkylphenol polyethoxylates (0.05~20%) or alkyphenol (<0.02%) as the sole carbon source, which is the first pure culture showing the feature. The strain TX2 reveals an oxygen uptake activity of 192.6, 4.2 and 4.2 nmole/min for a 5 ml cell suspension at OD600 = 0.3 using octylphenol polyethoxylates, octylphenol and octylcatechol as substrates, respectively. Moreover, the oxygen uptake rate of strain TX2 decreased with the increase of carbon numbers in alkyl-chain in bulk alkylphenol and alkylcatechol. In addition, Western blotting further demonstrated an catechol 2, 3-dioxygenase-like aromatic ring-cleavage enzyme that was inducible when strain TX2 was grown on octylphenol polyethoxylates, octylphenol, or octylcatechol as the sole carbon source. Furthermore, LC/MS analysis of the TX2 transformed metabolites from OPEOn and AEO8 showed that octylphenol polyethoxylates could be degraded as a sequential cleavage of the polyethoxylate chain and then produced octylphenol, which was further transformed to form octylcatechol followed by generating a metabolite with a molecular weight of 206. It was suggested as a aromatic ring-cleavage product. These results suggested that strain TX2 was able to shorten the alky chain followed by the cleavage of aromatic ring in the degradation of octylcatechol. | en_US |