Isolation and identification of nitrogen-fixing bacteria from Miscanthus giganteus roots and rhizosphere for biofertilizer development

Overview

This research opportunity focuses on identifying and characterizing nitrogen-fixing bacteria living in the roots and rhizosphere soil of Miscanthus x giganteus, a perennial grass recognized as a promising bioproduct and bioenergy crop. Miscanthus is unusually nitrogen-efficient and often does not respond to nitrogen fertilizers, suggesting that plant-associated microbial communities may supply a portion of the crop's nitrogen needs. The goal of this work is to isolate these understudied microbial strains, confirm their nitrogen-fixing capability, and taxonomically identify them, laying the groundwork for potential biofertilizer products that could reduce synthetic fertilizer inputs in Miscanthus and other cropping systems.

Technical specifications

Research approach and methods:

• Stable isotope tracing: Incorporation of ¹⁵N₂ gas into soil and root tissues is used to directly measure nitrogen fixation activity in the rhizosphere and within surface-sterilized roots.
• Culture-based isolation: Enrichment cultures with tailored media will be used to isolate free-living nitrogen fixers from rhizosphere soil and endophytic nitrogen fixers from root tissue.
• Taxonomic identification: DNA sequencing approaches, including 16S rRNA gene region sequencing and metagenomic sequencing, will be used to identify isolated strains and characterize the microbial community.
• Quantification of nitrogen fixation: ¹⁵N₂ gas incorporation assays applied to cultured isolates will measure how much nitrogen each strain can fix under laboratory conditions.

Preliminary findings:

• ¹⁵N₂ incorporation experiments confirm active nitrogen fixation in both Miscanthus rhizosphere soil and surface-sterilized root tissue.
• Culture-based work coupled with DNA sequencing has identified candidate free-living nitrogen fixers, including Bacillus, Sporolactobacillus, and Dysgonomonas, in rhizosphere soil.
• Endophytic nitrogen-fixing activity has been detected in surface-sterilized roots, though the responsible organisms have not yet been identified or isolated.

Technology readiness level

This opportunity is at an early-stage, discovery-phase research level. Preliminary data already demonstrate that nitrogen fixation is occurring in Miscanthus rhizosphere soil and root tissue and that candidate free-living nitrogen fixers can be recovered through culture-based methods. The next steps involve isolating endophytic strains, quantifying their nitrogen-fixing capacity in culture, and completing taxonomic identification. Biofertilizer product development, field validation, and commercial formulation would follow the successful completion of this foundational research.