Isolation and characterization of denitrifiers from woodchip bioreactors for bioaugmentation application

Aims: This study was done to obtain denitrifiers that could be used for bioaugmentation in woodchip bioreactors to remove nitrate from agricultural subsurface drainage water. Methods and Results: We isolated denitrifiers from four different bioreactors in Minnesota, and characterized the strains by measuring their denitrification rates and analysing their whole genomes. A total of 206 bacteria were isolated from woodchips and thick biofilms (bioslimes) that formed in the bioreactors, 76 of which were able to reduce nitrate at 15°C. Among those, nine potential denitrifying strains were identified, all of which were isolated from the woodchip samples. Although many nitrate-reducing strains were isolated from the bioslime samples, none were categorized as denitrifiers but instead as carrying out dissimilatory nitrate reduction to ammonium. Conclusions: Among the denitrifiers confirmed by ¹⁵N stable isotope analysis and genome analysis, Cellulomonas cellasea strain WB94 and Microvirgula aerodenitrificans strain BE2.4 appear to be promising for bioreactor bioaugmentation due to their potential for both aerobic and anaerobic denitrification, and the ability of strain WB94 to degrade cellulose. Significance and Impact of the Study: Denitrifiers isolated in this study could be useful for bioaugmentation application to enhance nitrate removal in woodchip bioreactors.