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Alkylphenol polyethoxylates (APEOn) were an extensively-used non-ionic surfactants. When these componds are discharged into natural environment, alkylphenol such as nonylphenol and octylphenol are often found to be as accumulates metabolites. However, alkylphenol is more recalcitrant than APEOn and has been demonstrated as an environmental hormone with estrogenic-like activity. However, only a few studies were reported on the biodegradation of alkylphenol. This study isolated two octylphenol-degrading bacteria from topsoil of farm, which was frequently sprayed by pesticides and surfactant. They were respectively identified as Pseudomonas nitroreducens OP1 and Pseudomonas sp. OP2 by BioLog breathprint, 16S rDNA sequence analysis, fatty acid fingerprint and negative for gelatin hydrolysis activity. Both of them were able to grow on octylphenol (0.001~0.01%) as sole carbon source. The strains OP1 and OP2 showed a specific growth rate of 0.17d-1 and 0.31 d-1 as 0.005% octylphenol as sole carbon source, respectively. After 16 days of cultivation, the strains OP1 and OP2 were able to remove 82% and 46% of octylphenol, respectively. Both strains OP1 and OP2 further revealed an oxygen uptake activity of 5.3 and 4.4 nmole/min respectively using octylphenol as the transformation substrate with 1.5 ml cell suspension of OD=0.3. They also showed 6.1 and 3.0 nmole/min of oxygen uptake rate when octylcatechol as used as a substrate. In addition, Western blotting and C23O dioxygenase activity assay also showed that no catechol 2,3-dioxygenase-like enzyme for the cleavage of aromatic ring was detected in both strains OP1 and OP2 grown on octylphenol as the sole carbon source.
The study further investigated the bioremediation of octylphenol polyethoxylates (OPEOn) and its primary metabolite, OP in soil microcosms with bacteria exogenously added. Two surfactant-degrading bacteria, P. nitroreducens TX1 and P. putida TX2 were respectively added with Pseudomonas sp. OP2 in different OPEOn-contained microcosms to understand the removal of octylphenol polyethoxylates and octylphenol. The strain TX1 was able to degrade OPEOn and formed octylphenol, while the strain TX2 revealed activities to degrade both of OPEOn and OP. The strain Pseudomonas sp. OP2 was further added into an octylphenol-contained microcosm and the variation of octylphenol was then analyzed. The bacterial communities were analyzed by 16S based denaturing gradient gel electrophoresis (DGGE) of rRNA genes by 24 bacterial strains, which were totally cloned from soils in all microcosms. Among these endogenous bacteria, Alcaligenes faecalis (AF155147)、Stenotrophomonas maltophilia (AJ293470)、Aeromonas sp (AB076858) have been found as alkylphenol-degrading bacteria, in precious study. The analysis of bacteria communities indicated that no obvious effect was observed in the endogenous bacteria community when strains OP2, TX1 and TX2 were exogenously added in these microcosms. When P. nitroreducens TX1 and P. putida TX2 were exogenously added in the OPEOn-contained microcosms, both of them were able to enhance the OPEOn removal by 1.5 fold and also found as the dominant bacterial as well as endogenous bacteria such as Herbaspirillum sp. Chnp3-5、Phyllobacterium myrsinace、Brucellaceae bacterium、Stenotrophomonas maltophilia and Aeromonas hydropila. Moreover, the exogenous strain Pseudomonas sp. OP2 was demonstrated to be able to extra remove 15-20% of OP in soil microcosms, and was also the dominant bacteria as well as endogenous strains Aeromonas hydropila、 Pseudomonas sp YG-1 and Alcaligenes faecalis within four months of operation periods. The study showed that endogenous bacteria was able to remove partial OPEOn in microcosms. However, the removal of OPEOn and its metabolite OP were obviously enhanced when strain P. putida TX2 and Pseudomonas sp. OP2 was exogenously added in soil microcosms. Almost all of OPEOn and 25% of OP was able to be removed respectively. These indicated that these two strains, showed the most potential in the application of OP bioremediation.
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