Nitrogen oxides (NOx), produced during combustion, represent key fine particulate matter (particles with a diameter ≤2.5 microns) and ozone precursors in the troposphere. They are widely associated with adverse health and environmental effects and hence their accumulation increases economic and societal burdens. In particular, nitrous oxide (N2O) is a potent greenhouse gas with a 300-fold higher global warming potential than carbon dioxide over a 100-year time period, and thus represent the major ozone-depleting substance in the stratosphere. Denitrification, performed by specific microorganisms under anaerobic conditions, is the reduction of nitrates back into nitrogen (N2) to complete the nitrogen cycle. Nitrous oxide reductase (NosZ) is the enzyme that generates N2 in the final denitrification process. It has high biotechnological potential, and its structure and reaction mechanism were revealed recently; however, an industrially relevant model organism that can generate N2 has not been established to date. Here, we show that an engineered Escherichia coli strain harboring nos operon genes (nosRZLDFY, tat, and apbE) can produce N2 in vivo with a rate reaching up to 0.196 mmol/[g dry cell weight (DCW) h]. In addition to essential components for in vivo N2 generation in E. coli (nosRDFY, apbE, and the core nosZ), Cu2+ and Mg2+ were required for the maturation of NosZ and the ApbE reaction, respectively. Furthermore, E. coli has the ability to utilize the ferrous ethylenediaminetetraacetic acid [Fe(II)EDTA]-nitric oxide (NO) complex, as catalyzed by cytosolic anaerobic nitric oxide reductase (NorV), and regenerate Fe(II)EDTA, which is used as a rapid absorbent of NOx in a chemical absorption-biological reduction process. This overall design for creating N2-producing E. coli will be useful in engineering strains for NOx removal systems to reduce harmful greenhouse gases in the environment.

Air-purifying Escherichia coli for the conversion of NOx to N2

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ACS Fall 2022

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