Changes of catabolic genes and microbial community structures during biodegradation of nonylphenol ethoxylates and nonylphenol in natural water microcosms

Changes of possible key catabolic genes and microbial community structures during the degradation of NPEOs and NP in natural water microcosms were investigated using the most-probable-number-polymerase chain reaction (MPN-PCR) and terminal restriction fragment length polymorphism (T-RFLP). The copy number of catechol 2,3-dioxygenase (C23O) DNA increased significantly during NPEO and NP degradation, suggesting that meta-cleavage of the aromatic rings of NPEOs and NP might have happened. Catechol 1,2-dioxygenase (C12O) DNA, alkane-catabolic genes (alk), and 16S rDNA, on the other hand, did not change notably, suggesting that the two genes might not be the relevant genes for NPEOs and NP degradation. The 16S rRNA gene-based T-RFLP analysis results indicated that specific and different dominant (or degrading) bacteria should be selected, depending on the substances. A strain with a DNA length of 78 bp, which might be affiliated with the beta subclass of Proteobacteria, became the dominant species for NPEO degradation, while strains at 88 and 198 bp were dominant in the NP microcosm. Diversity of microbial community structure tended to be simplified after NPEO degradation, while that in the NP microcosm remained relatively stable. Five clusters were obtained according to the similarity in community structures of different microcosms by cluster analysis, which were consistent with the biodegradation behaviors of different microcosms. This is the first report on genetic evidence of a possible aromatic ring meta-cleaving pathway of NPEOs and NP in an aquatic environment.