Ammonia oxidizing bacteria in a nitrite-accumulating membrane bioreactor

The ammonia oxidizing to nitrite is a key step in biological nitrogen removal process. This study has identified the ammonia oxidizing gene diversity of a nitrite accumulated intermittent aerated sequencing batch membrane bioreactor (SBMBR) by using the traditional culturing method and gene cloning techniques. The culturing experiments showed that 15 and six amoA PCR products were obtained from 389 heterotrophic- and 202 autotrophic-isolates, respectively. However, only two amoA PCR products of the autotrophic-isolates were sequenced successfully due to the low copy numbers of the amoA gene. In addition, only one 16S rRNA gene of these two amoA-contained isolates was amplified successfully. The 16S rRNA gene analysis revealed that this amoA-contained isolate was similar to Bacillus krulwichiae, a kind of nitrite reducing bacteria. The nitrite reductase gene nirS was further detected successfully from this amoA-contained isolate to confirm the nitrite reducing ability. Finally, this study also only obtained two successfully amoA sequences from 121 cloned colonies. The similarities of nucleic acid and amino acid from both culturing and gene cloning methods showed that the homology of amoA gene was between 73.2 and 95.4%, while the deduced amino acid was from 76.4 to 100.0%.