Enabling Biological Nitrogen Fixation for Cereal Crops in Fertilized Fields

Abstract

Agricultural productivity relies on synthetic nitrogen fertilizers, yet half of that reactive nitrogen is lost to the environment. There is an urgent need for alternative nitrogen solutions to reduce the water pollution, ozone depletion, atmospheric particulate formation, and global greenhouse gas emissions associated with synthetic nitrogen fertilizer use. One such solution is biological nitrogen fixation (BNF), a component of the complex natural nitrogen cycle. BNF application to commercial agriculture is currently limited by fertilizer use and plant type. This paper describes the identification, development, and deployment of the first microbial product optimized using synthetic biology tools to enable BNF for corn (Zea mays) in fertilized fields, demonstrating the successful, safe commercialization of root-associated diazotrophs and realizing the potential of BNF to replace and reduce synthetic nitrogen fertilizer use in production agriculture. Derived from a wild nitrogen-fixing microbe isolated from agricultural soils, Klebsiella variicola 137-1036 (“Kv137-1036”) retains the capacity of the parent strain to colonize corn roots while increasing nitrogen fixation activity 122-fold in nitrogen-rich environments. This technical milestone was then commercialized in less than half of the time of a traditional biological product, with robust biosafety evaluations and product formulations contributing to consumer confidence and ease of use. Tested in multi-year, multi-site field trial experiments throughout the U.S. Corn Belt, fields grown with Kv137-1036 exhibited both higher yields (0.35 ± 0.092 t/ha ± SE or 5.2 ± 1.4 bushels/acre ± SE) and reduced within-field yield variance by 25% in 2018 and 8% in 2019 compared to fields fertilized with synthetic nitrogen fertilizers alone. These results demonstrate the capacity of a broad-acre BNF product to fix nitrogen for corn in field conditions with reliable agronomic benefits.

Genetically engineered crops for sustainably enhanced food production systems

“…In another study, CRISPR/Cas9 triple knockout of pyl1 , pyl4 , and pyl6 , OsPYL abscisic acid receptor gene family displayed high-temperature tolerance, increased grain yield, and lower preharvest sprouting in comparison to wild type ( Miao et al., 2018 ). Genome-edited crops contribute towards improved water and nitrogen use efficiency as demonstrated through field trial and experimental data ( Wen et al., 2021 ). Research on enhanced drought tolerance of cotton developed through genome editing tools demonstrated environmental footprint of cotton production ( Peng et al., 2021 ).…”

Environmental Galenics: large-scale fortification of extant microbiomes with engineered bioremediation agents

“…[ 52 ]. Current advances in engineering root-associated diazotrophs [ 53 ] and the prospects of implementing N2-fixation in plants [ 54 , 55 ] can deliver new species (or their combination thereof) improved in their ability to capture atmospheric carbon into their biomass and expanding the green cover of our planet. Alas, this is not the end of the challenge: much of the vegetal matter can subsequently decay and be degraded by microorganisms which may release CO 2 back to the atmosphere.…”

Harnessing belowground processes for sustainable intensification of agricultural systems

“…A potentially promising avenue represents the editing of the genome of bacterial strains via synthetic biology to increase their N fixation capacity under field condition and to render a commercial application as bio-fertilizers a successful endeavour. Such an approach was reported for a free-living strain of Klebsiella variicola , where the authors replaced the nifL gene, which usually represses N fixation under conditions of sufficient N availability, with a constitutive promoter to obtain a strain that could still fix N under field conditions (Wen et al 2021 ). In a number of trials where the strain was applied in addition to inorganic fertilizers in corn fields, increased yields of around 3% and lower within-field yield variance were observed as compared to fields that were only subjected to inorganic fertilization.…”