Cold-adapted denitrifying bacteria in woodchip bioreactor

Authors: JANG, JEONGHWAN - University Of Minnesota; ANDERSON, EMILY - University Of Minnesota; Venterea, Rodney - Rod; SADOWSKY, MICHAEL - University Of Minnesota; ROSEN, CARL - University Of Minnesota; Feyereisen, Gary; ISHII, SATOSHI - University Of Minnesota

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2019
Publication Date: 4/2/2019
Citation: Jang, J., Anderson, E., Venterea, R.T., Sadowsky, M., Rosen, C., Feyereisen, G.W., Ishii, S. 2019. Cold-adapted denitrifying bacteria in woodchip bioreactor. Frontiers in Microbiology. 10(635):1-12. https://doi.org/10.3389/fmicb.2019.00635.
DOI: https://doi.org/10.3389/fmicb.2019.00635

Interpretive Summary: Nitrate contamination of groundwater and surface water is a concern in many part of the USA, and agriculture is considered an important source of this contamination. Woodchip bioreactor technology removes nitrate from agricultural subsurface drainage waters using denitrifying microorganisms. Although woodchip bioreactors have demonstrated success in many field locations, low water temperature can significantly limit bioreactor efficiency and performance. To improve bioreactor performance, it is important to identify the microbes responsible for nitrate removal under cold conditions. Therefore, in this study, we identified and characterized cold-adapted denitrifiers using culture-independent and -dependent approaches. By comparative 16S rRNA analysis as well as culture isolation technique, Pseudomonas spp., Polaromonas spp., and Cellulomonas spp. were identified as being important bacteria responsible for denitrification in woodchip bioreactor microcosms under relatively low-temperature conditions (15°C). Genome analysis of Cellulomonas sp. strain WB94 confirmed the presence of nitrite reductase gene nirK. Transcription levels of this nirK were significantly higher in the denitrifying microcosms than in the non-denitrifying microcosms. Strain WB94 was also capable of degrading cellulose and other complex polysaccharides. Taken together, our results suggest that Cellulomonas sp. denitrifiers could degrade woodchips to provide carbon source and electron donors to themselves and other denitrifiers in woodchip bioreactors. By inoculating these cold-adapted denitrifiers (i.e., bioaugmentation), it might be possible to increase the nitrate removal rate of woodchip bioreactors under cold temperature conditions. Results of this study will be useful to scientists, engineers and regulatory personnel interested in devising effective strategies for reducing nitrate contamination of groundwater and surface water.

Technical Abstract: Woodchip bioreactor technology removes nitrate from agricultural subsurface drainage waters using denitrifying microorganisms. Although woodchip bioreactors have demonstrated success in many field locations, low water temperature can significantly limit bioreactor efficiency and performance. To improve bioreactor performance, it is important to identify the microbes responsible for nitrate removal under cold conditions. Therefore, in this study, we identified and characterized cold-adapted denitrifiers using culture-independent and -dependent approaches. By comparative 16S rRNA analysis as well as culture isolation technique, Pseudomonas spp., Polaromonas spp., and Cellulomonas spp. were identified as being important bacteria responsible for denitrification in woodchip bioreactor microcosms under relatively low-temperature conditions (15°C). Genome analysis of Cellulomonas sp. strain WB94 confirmed the presence of nitrite reductase gene nirK. Transcription levels of this nirK were significantly higher in the denitrifying microcosms than in the non-denitrifying microcosms. Strain WB94 was also capable of degrading cellulose and other complex polysaccharides. Taken together, our results suggest that Cellulomonas sp. denitrifiers could degrade woodchips to provide carbon source and electron donors to themselves and other denitrifiers in woodchip bioreactors. By inoculating these cold-adapted denitrifiers (i.e., bioaugmentation), it might be possible to increase the nitrate removal rate of woodchip bioreactors under cold temperature conditions.