Single-Cell Force Spectroscopy Uncovers Root Zone- and Bacteria-Specific Interactions

Area of Science:

• Microbiology
• Plant Science
• Biophysics

Background:

• Plant growth-promoting rhizobacteria (PGPR) are vital for sustainable agriculture and improving crop yields.
• Understanding the initial attachment mechanisms of PGPR to plant roots is essential for optimizing biofertilizer efficacy.

Purpose of the Study:

• To investigate the nanoscale forces and mechanisms governing the primary attachment of specific PGPR strains (Bacillus velezensis and Pseudomonas defensor) to Arabidopsis thaliana roots.
• To elucidate the roles of bacterial polymers, flagella, and surface physicochemical properties in root colonization.

Main Methods:

• Single-cell force spectroscopy using Atomic Force Microscopy (AFM) to measure forces between individual bacterial cells and root surfaces.
• Utilized silica beads to mimic bacterial surface charges and assess electrostatic forces.
• Examined interactions with abiotic surfaces of varying surface energies to understand hydrophilic and hydrophobic contributions.
• Corroborated AFM findings with parallel fluorescence measurements.

Main Results:

• Distinct attachment strategies were observed between B. velezensis and P. defensor to different root regions.
• Micrometer-long polymers on both bacteria and root surfaces mediate binding.
• Flagella play a differential role in the binding interactions of each PGPR strain.
• Electrostatic, hydrophilic, and hydrophobic forces significantly influence initial bacterial root attachment.

Conclusions:

• Physicochemical differences between PGPR strains and root regions dictate variations in primary attachment.
• This nanoscale understanding of bacterial root colonization is critical for enhancing the effectiveness of PGPR-based biofertilizers in agriculture.