Native european soil bacteria as next-generation bio-inoculants for soybean nitrogen fixation

Overview

Soybean is the most important legume worldwide and is of growing importance in the European Union. Its yield heavily depends on the efficiency of symbiotic nitrogen fixation by rhizobia bacteria, which requires field inoculation. Since 1980, soybean fields have been massively inoculated with the exotic G49 Bradyrhizobium strain, and non-native strains have also been introduced through seeds. This research investigates whether endemic European populations of soil bacteria represent a promising reservoir of bio-inoculants to improve the efficiency of symbiotic nitrogen fixation in soybean. By isolating and characterizing chimeric, locally adapted strains from French soils, the project seeks to generate next-generation inoculants optimized for European conditions, potentially reducing the environmental and economic costs of nitrogen fertilization.

Technical specifications

Research approach and capabilities:

• Laboratory inoculation of soybean cultivars adapted to EU conditions using soil samples from various locations, including areas with and without legumes, and both wild and agricultural settings
• Isolation of bacteria from root nodules following controlled inoculation
• Harvesting of soybean nodules from a local experimental station with over 30 years of soybean cultivation history and from farmer network fields
• Long-term storage of strains and soil samples at -80°C
• Sequencing of housekeeping genes for strain characterization
• Assessment of symbiotic performance using acetylene reduction assays
• Infectivity evaluation through competition assays with fluorescently tagged reference strains (G49 and USDA110)
• Assembly and characterization of a core collection of compatible rhizobia native from French soils

Key scientific insights:

• Genetic material exchange between bacteria commonly occurs in soils, particularly within the Bradyrhizobium genus
• Endemic legumes may serve as intermediate hosts and sources of inoculants for soybean in temperate countries
• Recently evolved chimeric strains exist in soils and may be well-adapted to local European conditions

Technology readiness level

This research is at an early-to-mid stage of development. The team has demonstrated the ability to isolate functional rhizobia species from soybean nodules using French soil samples under controlled conditions and has established methods for evaluating symbiotic efficiency and infectivity. Future validation efforts focus on building a comprehensive core collection of compatible rhizobia strains native to French soils, with detailed characterization of their symbiotic performance and competitiveness against existing reference strains. The work aims to develop optimized inoculant candidates tailored for European soybean cultivation conditions.