| Summary: | 碩士 === 國立中央大學 === 生命科學研究所 === 98 === Alkylphenols and alkylphenol polyethoxylates (APEOn) are used in the formulation and production of mainly plastics, paints, pesticides and detergents, and they are omnipresent in the environment. Nonylphenol and octylphenol are the primary members in the alkylphenol, and are also the major metabolites from APEOn. The prior studies have demonstrated that octylphenol is 10 to 20 folds higher in the estrogenic effect than nonylphenol. In this study, 4-t-octylphenol was used as the sole carbon source for the isolation of octylphenol-degrading bacteria in Taiwan. Seventeen octylphenol-degrading bacteria were isolated from paddy farm topsoil, soil microcosm and 4-t-octylphenol reagent bottle by previous works. The topsoil had been intermittently polluted by agricultural surfactants. These bacteria were identified by 16S rDNA gene sequencing, BioLog substrate profiling and fatty acid methyl ester fingerprinting. All the bacterial strains belong to α, β and γ-proteobacteria. In the past, most of the akylphenol degrading bacteria were found to belong to α and γ-proteobacteria. In this article, we propose the octylphenol degrading mechanism of the soil microcosm isolated Alcaligenes sp. SH542. which is belongs to β-proteobacteria. For the substrate utilization, strain SH542 can grow on MSB plate containing OPEOn, OPEO1, OPEO2, octylcatechol and phenol as sole carbon source.
For a time-course study of octylphenol degradation, 100% of octylphenol was removed after 22 days of incubation. In metabolite analysis, the data shows that the 1,2,4-trihydroxybenzene increase coincides with the obvious decrease of octylphenol in bacteria log phase at the first four days. After 12 days of incubation, the intermediate hydroquinone was found to accumulate and was further completely degraded after 22 days. For analysis of genes which related to degrade aromatic compounds, our lab member Tuan et al. (2010) shows that Alcaligenes sp. SH542 has multiple component phenol hydroxylase gene. We assumed that oxygen is involved in the degradation of octylphenol. Strain SH542 shows the oxygen was uptaked during octylphenol degradation, the oxygen also was uptaked in MSB medium with hydroquinone and 1,2,4-trihydroxybenzene as sole carbon sources.
In conclusion, octylphenol degradation by Alcaligenes sp. SH542 begins with the transformation of octylphenol to its ipsohydroxylated intermediate by type II ipso substitution. After central cleavage, hydroquinone was formed and further transferred to 1,2,4-trihydroxybenzene. No degradation products from 1,2,4-trihydroxybenzene were detected.
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