Journal of Microbiology

Research Article

Dissimilatory nitrate reductions in soil Neobacillus and Bacillus strains under aerobic condition: Seohyun Ahn, Min Cho, Michael J. Sadowsky, Jeonghwan Jang; J. Microbiol. 2025;63(2):e2411019. Published online February 27, 2025; DOI: https://doi.org/10.71150/jm.2411019

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Abstract PDF Supplementary Material: Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were thought to be carried-out by anaerobic bacteria constrained to anoxic conditions as they use nitrate (NO3-) as a terminal electron acceptor instead of molecular O2. Three soil bacilli, Neobacillus spp. strains PS2-9 and PS3-12 and Bacillus salipaludis PS3-36, were isolated from rice paddy field soil in Korea. The bacterial strains were selected as possible candidates performing aerobic denitrification and DNRA as they observed to reduce NO3- and produce extracellular NH4+ regardless of oxygen presence at the initial screening. Whole genome sequencing revealed that these strains possessed all the denitrification and DNRA functional genes in their genomes, including the nirK, nosZ, nirB, and nrfA genes, which were simultaneously cotranscribed under aerobic condition. The ratio between the assimilatory and dissimilatory NO3- reduction pathways depended on the availability of a nitrogen source for cell growth, other than NO3-. Based on the phenotypic and transcriptional analyses of the NO3- reductions, all three of the facultative anaerobic strains reduced NO3- likely in both assimilatory and dissimilatory pathways under both aerobic and anoxic conditions. To our knowledge, this is the first report that describes coexistence of NO3- assimilation, denitrification, and DNRA in a Bacillus or Neobacillus strain under aerobic condition. These strains may play a pivotal role in the soil nitrogen cycle.

Review

Denitrifying Woodchip Bioreactors: A Microbial Solution for Nitrate in Agricultural Wastewater—A Review: Sua Lee , Min Cho , Michael J. Sadowsky , Jeonghwan Jang; J. Microbiol. 2023;61(9):791-805. Published online August 18, 2023; DOI: https://doi.org/10.1007/s12275-023-00067-z

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Nitrate ( NO3 −) is highly water-soluble and considered to be the main nitrogen pollutants leached from agricultural soils. Its presence in aquatic ecosystems is reported to cause various environmental and public health problems. Bioreactors containing microbes capable of transforming NO3 − have been proposed as a means to remediate contaminated waters. Woodchip bioreactors (WBRs) are continuous flow, reactor systems located below or above ground. Below ground systems are comprised of a trench filled with woodchips, or other support matrices. The nitrate present in agricultural drainage wastewater passing through the bioreactor is converted to harmless dinitrogen gas ( N2) via the action of several bacteria species. The WBR has been suggested as one of the most cost-effective NO3 −-removing strategy among several edge-of-field practices, and has been shown to successfully remove NO3 − in several field studies. NO3 − removal in the WBR primarily occurs via the activity of denitrifying microorganisms via enzymatic reactions sequentially reducing NO3 − to N2. While previous woodchip bioreactor studies have focused extensively on its engineering and hydrological aspects, relatively fewer studies have dealt with the microorganisms playing key roles in the technology. This review discusses NO3 − pollution cases originating from intensive farming practices and N-cycling microbial metabolisms which is one biological solution to remove NO3 − from agricultural wastewater. Moreover, here we review the current knowledge on the physicochemical and operational factors affecting microbial metabolisms resulting in removal of NO3 − in WBR, and perspectives to enhance WBR performance in the future.

Citations

Citations to this article as recorded by

Complete genome sequence of Neobacillus sp. strain OS1-2, a denitrifying bacterium isolated from apple orchard soil
Jinwoo Ahn, Jeonghwan Jang, Elinne Becket
Microbiology Resource Announcements.2024;[Epub] CrossRef

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