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Aims:  To isolate and characterize a methyl parathion (MP)‐mineralizing bacterium, and to elucidate the degradative pathway of MP and localize the responsible degrading genes. Methods and Results:  A bacterial strain, designated B2, capable of mineralizing MP was isolated from the MP‐polluted soil. Analysis of the 16S rRNA gene sequence and phenotypic analysis suggested that strain B2 had a close relationship with Ochrobactrum anthropi. B2 could totally degrade MP and four metabolites [p‐nitrophenol (PNP), 4‐nitrocatechol (4‐NC), 1,2,4‐benzenetriol (BT) and hydroquinone (HQ)] were identified by HPLC and gas chromatography‐mass spectrometry analyses. Plasmid curing of strain B2 resulted in the loss of ability of B2 to degrade PNP, but not the ability to hydrolyse MP. Conclusions:  Ochrobactrum sp. B2 can mineralize MP rapidly via PNP, 4‐NC, BT and HQ pathway. B2 harbours a plasmid encoding the ability to degrade PNP, while MP‐hydrolysing activity is encoded on the bacterial chromosome. Significance and Impact of the Study:  This new bacterial strain (B2) capable of mineralizing MP will be useful in a pure‐culture remediation process of organophosphate pesticides and their metabolites such as nitroaromatics.

Traditional culture-based technique and 16S rDNA sequencing method were used to investigate the mucosa-associated autochthonous microbiota of grass carp (Ctenopharyngodon idellus). Twenty-one phylotypes were detected from culturable microbiota, with Aeromonas, Shewanella, Lactococcus, Serratia, Brevibacillus, Delftia, Pseudomonas, Pantoea, Enterobacter, Buttiauxella and Yersinia as their closest relatives. Genomic DNA was directly extracted from the gut mucosa of C. idellus originating from six different geographical regions, and used to generate 609 random bacterial clones from six clone libraries and 99 archaeal clones from one library, which were grouped into 67 bacterial and four archaeal phylotypes. Sequence analysis revealed that the intestinal mucosa harboured a diversified bacterial microbiota, where Proteobacteria, Firmicutes and Bacteroidetes were dominant, followed by Actinobacteria, Verrucomicrobia and DeinococcusThermus. The autochthonous bacterial communities in the gut mucosa of fish from different aquatic environments were not similar (C s < 0.80), but c-Proteobacteria was a common bacterial class. In comparison to bacterial communities, the archaeal community obtained from one library consisted of Crenarchaeota and Euryarchaeota. These results demonstrate that molecular methods facilitate culture-independent studies, and that fish gut mucosa harbours a larger bacterial diversity than previously recognized. The grass carp intestinal habitat selects for specific bacterial taxa despite pronounced differences in host environments.