Trade, Diplomacy, and Warfare: The Quest for Elite Rhizobia Inoculant Strains

Abstract

Rhizobia form symbiotic nitrogen-fixing nodules on leguminous plants, which provides an important source of fixed nitrogen input into the soil ecosystem. The improvement of symbiotic nitrogen fixation is one of the main challenges facing agriculture research. Doing so will reduce the usage of chemical nitrogen fertilizer, contributing to the development of sustainable agriculture practices to deal with the increasing global human population. Sociomicrobiological studies of rhizobia have become a model for the study of the evolution of mutualistic interactions. The exploitation of the wide range of social interactions rhizobia establish among themselves, with the soil and root microbiota, and with the host plant, could constitute a great advantage in the development of a new generation of highly effective rhizobia inoculants. Here, we provide a brief overview of the current knowledge on three main aspects of rhizobia interaction: trade of fixed nitrogen with the plant; diplomacy in terms of communication and possible synergistic effects; and warfare, as antagonism and plant control over symbiosis. Then, we propose new areas of investigation and the selection of strains based on the combination of the genetic determinants for the relevant rhizobia symbiotic behavioral phenotypes.

A Virtual Nodule Environment (ViNE) for modelling the inter-kingdom metabolic integration during symbiotic nitrogen fixation

“…On the other hand, in a highly diverse environment, evolution of strains capable of entering into a highly efficient symbiosis may be favoured, as this would lead to fewer nodules and thus less plant resources being allocated to competing rhizobium strains, thereby limiting the spread of less mutualist (viz. cheater) strains (20, 120).…”

Multidisciplinary approaches for studying rhizobium–legume symbioses

“…The rhizobial life cycle does not occur in isolation. It is also necessary to account for social interactions between rhizobia and host plants, and between rhizobia and competing microbes (Checcucci et al 2017). The rhizobiahost interaction involves a high degree of cooperation between the partners, involving multiple signal exchange events as well as a massive exchange of metabolic resources (Oldroyd and Downie 2008;Oldroyd et al 2011;Udvardi and Poole 2013).…”

“…The influence of soil properties, plant host, and other biotic factors, including microbial communities, bacteriophages, plasmids, and other invasive DNA elements, all surely play a role in the generation of rhizobial diversity (Bromfield et al 1987;Harrison et al 1989;Carelli et al 2000;Silva et al 2007;Talebi et al 2008;Toro et al 2018). Understanding these relationships could potentially allow for the exploitation of the large genetic diversity of rhizobial species for develop-ing elite rhizobial bioinoculants in precision agriculture (Checcucci et al 2017).…”

Biotic and abiotic plant–soil feedback depends on nitrogen‐acquisition strategy and shifts during long‐term ecosystem development

“…The absence of negative biotic PSF in N-fixing plant species in old, severely P-impoverished soils might be related to their similar positive responses to soil biota ( Figure S1). These legume species likely possess the ability to form effective symbiotic relationships with a range of N-fixing rhizobia that are ubiquitous in unsterilised soils (Birnbaum, Bissett, Teste, & Laliberté, 2018;Birnbaum, Bissett, Thrall, & Leishman, 2016;Checcucci, DiCenzo, Bazzicalupo, & Mengoni, 2017). Thus, symbiotic associations between N-fixing rhizobia and legumes might compensate for the potential negative effects of soil-borne pathogens if they enable greater investment of N in plant growth or pathogen defence (Menge & Chazdon, 2016;Menge, Levin, & Hedin, 2008;Vitousek & Field, 1999).…”