[Diversity of thaumarchaeal nitrite reductase (nirK) -like genes in environments].

Nitrite reductase encoded by nirK is a key enzyme to denitrification, and is found in ammonia-oxidizing archaea (AOA). Based on the diversity of nirK, it was good to study the functions of nitrite reductase to AOA on denitrification.We constructed nirK gene clone libraries based on the nirK gene PCR products of water, sediment and soil, screened the positive clones by restriction fragment length polymorphism ( RFLP), and sequenced the representative fragments from positive clones.RFLP analysis of the clone libraries shows that there were 10 OTUs in fresh water and sediment, 8 in vegetable soil and its nearby water. Phylogenetic analysis indicated that the amino acid sequences of these nirK were most closely related to the Candidatus Nitrosopumilus koreensis AR1 and Nitrosopumilus maritimus SCM1 with similarities ranging from 53% to 68%. Diversity index of clone libraries shows there were many different types of nirK genes in all samples. Diversity and evenness index of nirK gene of water samples was higher than soil samples whreas vegetable field samples were the richest.Thaumarchaeote nirK gene had high diversity in soil and freshwater environments which were very different from ocean sample. The nirK gene encoding nitrite reductase might be important for thaumarchaeote denitrification.