The Inherent Conflicts in Developing Soil Microbial Inoculants

Certain soil microorganisms can perform agriculturally valuable functions such as ethylene reduction, plant pathogen suppression, and soil nutrient solubilization. Interest and investment in developing soil microbial inoculants to enhance these functions has recently surged, but in-field product success remains unpredictable and unreliable. Microbial inoculants tend to be chosen based on their activity in controlled laboratory screenings and for ease of mass cultivation, with minimal regard for ecologically relevant traits that will both allow them to survive in the field during a target functional period and prevent excessive persistence. We highlight the conflicting roles of microbial inoculant traits at each product stage, and how this may complicate selection for microorganisms that function as desired in the field. Potentially beneficial microorganisms have been inoculated into agricultural soils for years. However, concurrent with sequencing advances and successful manipulation of host-associated microbiomes, industry and academia have recently boosted investments into microbial inoculants, convinced they can increase crop yield and reduce fertilizer and pesticide requirements. The efficacy of soil microbial inoculants remains unreliable, and unlike crop breeding, in which target traits (e.g., yield) have long been considered alongside environmental compatibility, microbial inoculant ecology is not sufficiently integrated into microbial selection and production. We propose a holistic temporal model of the shifting constraints on inoculants at five stages of product development and application, and highlight potential conflicts between stages. We question the feasibility of developing ideal soil microbial inoculants with current approaches. Potentially beneficial microorganisms have been inoculated into agricultural soils for years. However, concurrent with sequencing advances and successful manipulation of host-associated microbiomes, industry and academia have recently boosted investments into microbial inoculants, convinced they can increase crop yield and reduce fertilizer and pesticide requirements. The efficacy of soil microbial inoculants remains unreliable, and unlike crop breeding, in which target traits (e.g., yield) have long been considered alongside environmental compatibility, microbial inoculant ecology is not sufficiently integrated into microbial selection and production. We propose a holistic temporal model of the shifting constraints on inoculants at five stages of product development and application, and highlight potential conflicts between stages. We question the feasibility of developing ideal soil microbial inoculants with current approaches. multiple microbial taxa that are co-cultured and/or co-inoculated to an environment. These may be taxa that are expected to perform complementary functions, or that could perform the same function but under different environmental conditions. the successful survival and growth of a microbial strain or consortium after being introduced into a novel environment (e.g., an agricultural soil). the preparation and stabilization of microbial cells in a manner that can be stored prior to application. bacteria, fungi, or other microorganisms, typically isolates, that are intentionally introduced to an environment to enhance a target function. Examples include microorganisms used in biocontrol or to promote plant growth. May be a single strain or a consortium. the complex assemblage of microorganisms living in a defined environment (e.g., soil). Although often used to refer to bacteria and/or fungi, it also includes archaea, viruses, protists, and other organisms. All of these microorganisms may impact inoculant establishment. survival over time of a viable microbial population. Could be viewed positively (e.g., inoculants persist during target functional period in soils) or negatively (e.g., inoculants persist after defined functional periods, with unknown downstream impacts). a trait that is beneficial in one context (e.g., at one stage of inoculant development) may be detrimental in another context. for microorganisms, traits are jointly determined by genes and the environment. They are an observable component of the microbial phenotype, and may contribute to the survival of a microorganism in the environment or an agriculturally relevant function (e.g., nutrient solubilization). Factoring Ecological, Societal, and Economic Considerations into Inoculant DevelopmentBell et al.Trends in BiotechnologyJune, 2019In BriefThere are many paths toward effective microbial inoculants for agriculture. Considering what is practical for the present day technological and farming landscape should not limit our creativity in developing innovative technologies. However, factors including production costs, practicality of implementation, and technology adoption by farmers will drive the success of new management approaches. Full-Text PDF Field-Specific Microbial Consortia Are Feasible: A Response to Kaminsky et al.Ashutosh AwasthiTrends in BiotechnologyJune, 2019In BriefKaminsky et al. (Trends Biotechnol. 2019:37;140–151) discuss the conflicts in developing microbial inoculants for agriculture. The authors affirm that microbial inoculants should perform across a wide range of environments but rule out the feasibility of personalized inoculants for individual fields. Here, I propose customized microbial consortia for specific field environments. Full-Text PDF