Overview
ISO 17601:2025 - Soil quality - Estimation of abundance of selected microbial gene sequences by quantitative polymerase chain reaction (qPCR) from DNA directly extracted from soil - defines a standardized qPCR workflow to quantify selected microbial gene sequences in soil DNA extracts. The document specifies the crucial steps for assay design, calibration, validation and reporting so laboratories can estimate the abundance of targeted microbial groups in the soil microbiome using quantitative PCR (qPCR).
Keywords: ISO 17601:2025, soil quality, qPCR, quantitative PCR, soil DNA, microbial gene sequences, soil microbiome, environmental DNA.
Key topics and requirements
- Principle and scope: qPCR using fluorescent DNA-binding dye to estimate abundance of selected gene sequences; results are an estimation of gene copy number, not direct organism counts.
- Test materials and reagents: guidance on DNA templates, bacterial isolates, plasmid standards, enzymes, buffers and culture media.
- Assay design: amplicon/primer design, preparation of qPCR standards (cloned targets, plasmid or artificial DNA), and use of non-template controls (NTC).
- Calibration and standardization: preparation of qPCR standard curves and calibration for reliable copy-number estimation.
- Soil DNA handling: procedures for DNA extraction (referencing ISO 11063), soil DNA template preparation and inhibition testing to detect PCR inhibitors common in soil extracts.
- qPCR procedure and validation: recommended steps for running qPCR assays, validation criteria, calculation of gene copy number in extracts, and examination of critical steps.
- Quality assurance: international ring test methodology (Annex B) to assess repeatability and reproducibility across laboratories.
- Supporting information: examples of established primer systems and a TaqMan assay description (Annexes C and A).
Applications and users
ISO 17601:2025 is relevant for:
- Environmental and soil testing laboratories implementing soil microbial abundance assays.
- Soil ecologists, agronomists and researchers monitoring the soil microbiome and functional groups (e.g., denitrifiers).
- Agricultural and land management programs tracking soil health, remediation monitoring, and impact assessment.
- Regulatory and standards organizations seeking harmonized methods for soil quality evaluation.
Practical uses include routine monitoring of microbial functional markers, comparing treatments or sites (using relative changes or external controls), and supporting research on soil biodiversity and biogeochemical processes. Users should note that gene copy numbers can vary by species (ribosomal operon copy number) and that soil DNA includes sequences from dead cells.
Related standards
- ISO 11063 - Soil quality: Direct extraction of soil DNA
- ISO 18400-206 - Soil quality: Sampling and handling for microbiological assessments
ISO 17601:2025 provides a standardized, reproducible qPCR framework for robust quantification of microbial gene sequences in soil, supporting consistent soil quality assessment and comparable environmental data.
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