Effects of earthworms on nitrogen transformation and the correspond genes (amoA and nirS) in vermicomposting of sewage sludge and rice straw.

The effects of earthworms on nitrogen transformation and the responsible functional genes during disposal of sewage sludge and rice straw were investigated in this study. Vermicomposting resulted in the lower pH and total organic carbon (TOC) compared to the control treatment without earthworms. Moreover, the presence of earthworms could promote the nitrogen mineralization and nitrification process in vermicomposting. Earthworms increased the activity of ammonia monooxygenase and abundance of amoA-nitrifier and reduced its diversity, whereas they reduced the density of nirS-denitrifying bacteria but enhanced its diversity. Nitrosospira was the dominant amoA-nitrifier and earthworms stimulated its growth in the vermicomposting. The presence of earthworms could also affect the community composition of nirS-denitrifying bacteria despite most of the nirS-denitrifier was not be classified at the genus level. In conclusion, the presence of earthworms had significant influence on the diversity and abundances of amoA and nirS genes and affect the nitrogen bio-transformation in vermicomposting.