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Scanning electron microscopy of hyphal ectobiont bacteria within mycelial extracellular matrices

Summary

Researchers studied how bacteria (Bacillus subtilis) attach to mushroom fungi (Lion’s Mane/Hericium erinaceus) in liquid cultures. Using a special drying technique and electron microscopy, they were able to see tiny structures where bacteria stick to the fungal threads. These structures are made of slimy substances produced by the fungus and could potentially allow bacteria to influence the fungus’s electrical and physical properties.

Background

Fungi and bacteria form important ecological interactions in various environments. Understanding the physical attachment of bacterial ectobionts to fungal hyphae is crucial for comprehending their roles in soil health, biotechnological applications, and disease processes. However, distinguishing true ectobiont attachment from trivial stochastic mixing has remained challenging.

Objective

To investigate the attachment of Bacillus subtilis bacteria to Hericium erinaceus fungal hyphae within mycelial biofilms using scanning electron microscopy. The study aimed to develop a method to assess physical attachment and reveal nanoscale surface-interfacing structures that could mediate contact-dependent modulation of fungal physiology.

Results

The mean biofilm area was 3.90 μm² ± 0.72 μm² with 18.33% ± 5.52% coverage. Mean bacterial length was 1.4 μm ± 0.4 μm and width was 0.5 μm ± 0.1 μm. Mean attachment structure length to hyphae was 0.3 μm ± 0.1 μm. Nanoscale surface-interfacing exopolymeric substances were preserved and visible in all triplicate samples, confirming true ectobiont attachment rather than stochastic mixing.

Conclusion

The graded dehydration protocol successfully identified bacterial ectobionts attached to fungal hyphae through exopolymeric substance-mediated structures. This method provides a biophysical basis for understanding contact-dependent modulation of fungal physiology and electrophysiology. The preservation of nanoscale attachment features enables future investigation of potential functional roles beyond mechanical anchoring.
  • Published in:Biophysics Reports (New York),
  • Study Type:Experimental Research,
  • Source: PMID: 40945792, DOI: 10.1016/j.bpr.2025.100233
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