Environmental Rhizosheath Microbiome Sampling Protocol

M. Asaduzzaman Prodhan^*

🌱 What is the Rhizosheath?

The rhizosheath is the soil that remains tightly adhered to plant roots after gently shaking off loose soil. It is distinct from:

• Bulk soil: ≥5–10 cm away from roots
  
• Rhizosphere: loosely attached soil removed by gentle shaking
  
• Rhizoplane: microbes on the root surface after sheath removal
  
• Endosphere: microbes inside root tissue (after surface sterilization)
  

CONTENT

This repository provides a field and lab workflow for collecting and processing rhizosheath soil samples for microbiome analysis (16S/ITS/shotgun metagenomics).

It includes:

1. A detailed Standard Operating Procedure (SOP)
2. Metadata recording guidelines
3. Lab Processing
4. Common Pitfalls & Fixes
5. A 1-page printable field sheet (PDF) for use during sampling
6. Notes

1. Standard Operating Procedure (SOP)

🧰 1.1 Materials Checklist

• Sterile nitrile gloves, masks
  
• 70% ethanol spray + wipes
  
• Sterile forceps, scissors/secateurs, spatulas, brushes
  
• Sterile tubes (2 mL, 15/50 mL), Whirl-Pak bags
  
• Preservation:
  
  • DNA only: dry ice + cooler; later −20/−80 °C
    
  • DNA/RNA: LifeGuard Soil, DNA/RNA Shield, RNAlater-Soil
    
• Cooler with ice/dry ice, zip bags
  
• Permanent marker, waterproof labels
  
• Metadata sheets (paper or digital)
  
• Sterile field blanks (air, tool, transport)
  

📋 1.2 Sampling Steps

1. Pre-label tubes with: project, site, date, plant ID, replicate, and fraction (“rhizosheath”).
   
2. Excavate roots carefully (10–20 cm depth) keeping sheath intact.
   
3. Shake gently to remove loose bulk soil. Collect bulk/rhizosphere separately if needed.
   
4. Scrape tightly adhering soil (the rhizosheath) into sterile tubes.
   
5. Prevent contamination: change gloves between plants, sterilize tools with 70% ethanol, and use blanks.
   
6. Preserve immediately: keep cold on dry ice or add preservative. Record metadata.
   
7. Storage: −80 °C (DNA) or per preservative instructions as soon as possible.
   

🗒️ 2. Metadata to Record

• Site / GPS / Date / Time
  
• Plant species (take photo if possible)
  
• Root depth, soil type/texture, visible moisture
  
• Temperature, sun/shade, recent rain/irrigation
  
• Preservation method and time to cold storage
  
• Operator / notes
  

🧪 3. Lab Processing

3.1. Receipt & storage
- Log samples and cross-check metadata.
- Store at −80 °C or as preservative guidelines recommend.

3.2. Rhizosheath cleanup
- If root+sheath were collected, brush soil from roots in a sterile hood.
- Process roots separately for rhizoplane/endosphere if required.

3.3. Subsampling & extraction
- Use ~0.25–0.5 g soil per extraction.
- Pool only within the same replicate (never across plants unless intended).
- Use bead-beating and inhibitor removal steps (rhizosheath often contains sticky polymers).

3.4. QC and downstream
- Quantify DNA (Qubit), check purity (A260/280).
- For amplicons: use 16S primers (e.g., 515F/806R for bacteria/archaea).
- For shotgun: ensure ≥1–5 ng/µL high-quality DNA.

⚠️ 4. Common Pitfalls & Fixes

• Not enough soil: target fibrous fine roots; pool segments if necessary.
  
• Cross-contamination: enforce glove/tool changes; use field blanks.
  
• DNA inhibition: bead-beat strongly; use inhibitor removal columns.
  
• Sandy soils: treat remaining soil after minimal shaking as rhizosheath; document soil texture.
  
• Clayey soils: pre-sieve gently in the lab to remove root debris.
  

📄 5. 1-Page Field Sheet

A 1-page printable PDF was generated for quick use in the field.
It includes: - Materials checklist with tick boxes
- Step-by-step field protocol
- Metadata table for sample recording

👉 Download Rhizosheath Field Sheet (PDF)

📌 6. Notes

• Always follow local land access and biosecurity regulations.
  
• Clean boots and tools between sites to avoid cross-contamination of soil biota.
  
• Include controls: bulk soil, rhizosphere, blanks, and mock communities.