Responsible Consumption and Production

Nitrogen-based fertilizers are necessary for agriculture, as they offset nutrient outputs caused by industrial agricultural practices, and increase crop yields. The human population is expected to increase by 2.25 billion in the next 40 years [1]. This growth projection, coupled with suboptimal growing conditions associated with climate change, will further necessitate the use of fertilizer. However, these fertilizers often run-off into bodies of water, causing eutrophication. Agricultural run-off is largely due to inefficient fertilizer application methods, the principal cause of which is the risk-adverse inclination of farmers. Since farmers have uncertainty about considerations such as weather and soil nitrogen levels in a given year, they have a tendency to apply more fertilizer than necessary to minimize risk and maximize profit [2]. For this reason, Nitrogen Use Efficiency (NUE), the ratio of crop yield to fertilizer application, is often low, with one study estimating the average global NUE to be 47% [3]. Our proposed fertilizer would increase NUE and decrease run-off by removing the possibility of under-application. The ammonia output of our bacteria would be continually adjustable, incentivizing farmers to apply more moderate amounts of fertilizer. Additionally, optimal fertilizer application is a function of factors such as crop type, growth stage, and soil type [4]. The versatility of our fertilizer would enable farmers to more readily match the nutrient needs of their crops, improving the efficacy of agriculture as well as small scale farming practices.

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Climate Action

The Haber-Bosch process is the primary method of producing ammonia for agricultural use, yet this procedure has significant environmental consequences. An estimated 1.4% of global carbon dioxide emissions derive from the Haber-Bosch process, which also consumes 1% of global energy production [5]. Additionally, most nitrogen from synthetic fertilizers is lost before it can be used by plants, and part of this excess ends up in the atmosphere. Reactive nitrogen species in the atmosphere acidify rain, and contribute to air pollution, with an estimated 30% of PM2.5 particles in the U.S and 50% of PM2.5 particles in the EU originating from agricultural ammonia [6]. The implementation of microbes in production has the potential to replace traditional industrial practices. As an example, a 2017 paper published in The Journal of CO2 Utilization used microbes to synthesize methanol, ethanol, and formic acid, and demonstrated that the energy costs of microbial production were lower than that of conventional processes [7]. The energetic and climate production costs associated with the Haber-Bosch process would be replaced with the production costs of our modified bacteria, arabinose, and IPTG. Moreover, microbially produced ammonia would have a greatly attenuated effect on climate in comparison to conventional production methods.

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Life on Land

Fertilizer use is associated with risks to biodiversity due to the disruption of normal environmental cycles [8]. Upon use of synthetic fertilizers, community composition changes and soil acidifies, altering the original environment and providing conditions which may not be suitable for all organisms [9]. Since our fertilizer aims to add just enough nitrogen to support agriculture while minimizing excess, these effects to life on land would be greatly diminished.

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Life Below Water

Eutrophication is characterized by an increased incidence of algal blooms, hypoxic conditions, and ocean acidification, all of which have severe ramifications for marine ecosystems. Algal blooms are harmful for several reasons: overgrowths can block light for other plants, certain blooms produce toxins which induce illness and death in marine life, mammals, and birds, and the decomposition of dead algae depletes the marine ecosystem of oxygen [10]. As these algae decay, large amounts of dissolved carbon dioxide are produced as well, a phenomenon which eventually leads to ocean acidification [11]. The consequences of eutrophication have synergistic effects on marine ecosystems. For example, corals and marine organisms that grow exoskeletons or shells are especially vulnerable to acidification. Coral reef ecosystems provide support to thousands of organisms and help mitigate coastal erosion. Similarly, many organisms that grow exoskeletons occupy lower trophic levels, meaning other organisms are reliant on them for sustenance [12]. For this reason, the effects of ocean acidification and eutrophication are wide reaching and highly detrimental to marine life. Our fertilizer would mitigate the damage to marine ecosystems by preventing nutrient pollution. In our fertilizer, nitrogen fixation is dependent upon the presence of both arabinose and IPTG, without which the promoter for the nitrogenase gene remains inactivated. Therefore, even if fertilizer run-off does occur, the risk of continued fixation is minimal. Additionally, synthetic fertilizers add disproportionately high levels of nitrogen to the soil, since most is before it can be used by the plant. Since our modified E. Coli continually converts nitrogen to a usable form, the nitrogen soil concentration would never have to be as high as the concentration for traditional fertilizers. Therefore, nitrogen run-off would occur at much lower concentrations.

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Clean Water and Sanitation

Synthetic fertilizers have human health consequences as well. The leaching of agricultural nitrogen introduces nitrate into groundwater, and high nitrate concentrations in drinking water can affect blood oxygen levels, resulting in “Blue baby syndrome” [13]. Nitrate prevalence in drinking water has also been associated with increased risks of certain cancers, birth defects, and nervous system damage [14]. As mentioned in the “Life Below Water” section, run-off from our fertilizer would contain greatly attenuated amounts of nitrogen, and drinking water sources would experience less nitrogen pollution.