nirK-harboring denitrifiers are more responsive to denitrification- inducing conditions in rice paddy soil than nirS-harboring bacteria.

We analyzed the quantity and diversity of nitrite reductase genes (nirS and nirK) in rice paddy soil before and after inducing denitrification. A quantitative PCR analysis showed that the copy number of nirK, but not nirS, increased significantly in response to the denitrification-inducing conditions. Diverse nirS and nirK clones were identified by clone library analyses. Clones related to the NirS of Burkholderiales and Rhodocyclales, and NirK distantly related to known denitrifiers increased their proportion in response to the denitrification-inducing conditions, and therefore, might be involved in denitrification in rice paddy soil.