All AOB in the surface sediments belonged to two populations of β- Proteobacteria subclasses, Nitrosomonas (92.7 % identity) and Nitrosospira (97.8 % identity), except those in the surface sediments of the low-density treatment group, which contained only Nitrosomonas. Nitrosopumilus (93.7 % identity) was the main AOA in all groups, whereas no Nitrosotalea sequence was detected in the three treatment groups. The abundance of the bacterial amoA gene was higher than that of the archaeal amoA gene in all groups. The results suggest that bioturbation of Tubificid worms promote the release of nitrogen and phosphorus in surface sediment.

Clone libraries and real-time PCR were applied to analyze the community composition and abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in surface sediments. To better understand the effects of Tubificid worm bioturbation on ammonia-oxidizing microorganisms in surface lake sediment, sediment-water microcosms with different densities of Tubificid worms were constructed.

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