mRNA recovery and denitrification gene expression in clay-soil bacterial communities under different agricultural managements.

Denitrifying bacterial expression was evaluated in a clay-rich soil on wheat cultivation in Agugliano (AN) Italy under different managements (no-tillage and conventional tillage; N-fertilization and without N-fertilization). The expression of genes coding for two nitrate reductases (narG and napA), two nitrite reductases (nirS and nirK), two nitric oxide reductases (cnorB and qnorB) and nitrous oxide reductase (nosZ) was analysed by reverse transcription (RT)-nested PCR. nirK gene expression was more widely distributed in soil environment than nirS gene. The DGGE analyses was performed for nirK, nirS and nosZ and gave prominence to the significant difference between structure community and its actual activity: The DNA analysis showed a wide presence of these genes in soil, while RNA analysis evidenced that denitrifying activity was expressed in few species or groups of species. The soil denitrifying bacterial structure resulted influenced by soil management, conventional tillage or no-tillage, but not by nitrogen fertilization.