Why must high-pressure sterilization at 121°C be used for fungal media? Ensure Sterile Experimental Baselines

High-pressure sterilization at 121°C is mandatory because it is the specific thermal threshold required to destroy resilient microbial spores, not just active bacteria. Treating fungal media and biomass samples at this temperature for 20 minutes creates a truly sterile microenvironment, eliminating the natural microbial load found on raw materials like rice straw.

Sterilization is not merely a cleaning step; it is a prerequisite for data validity. By completely eliminating environmental competitors, you ensure that any observed biological activity is the direct result of your specific target fungi, rather than random contamination.

The Biological Necessity of 121°C

Overcoming Natural Resistance

Standard boiling at 100°C is insufficient for scientific applications. While it kills active bacteria, it often fails to destroy dormant bacterial spores.

High-pressure equipment allows steam to reach 121°C. This temperature is critical because it is high enough to penetrate and destroy the protective outer shells of these spores, preventing them from germinating later.

The "Dirty" Nature of Biomass

Raw biomass materials, such as rice straw, are naturally populated with a vast array of environmental microorganisms. These native microbes are well-adapted to the substrate and can rapidly outgrow introduced species if not removed.

Without high-pressure sterilization, the biomass remains a "noisy" environment biologically. This makes it impossible to establish a controlled baseline for your experiment.

Ensuring Experimental Validity

Eliminating Resource Competition

When you inoculate target fungi—such as Phanerochaete chrysosporium or Thermomyces lanuginosus—they need exclusive access to nutrients to function efficiently.

Sterilization removes competition. This allows your target fungi to perform directional biodegradation without fighting native microbes for the carbon and nitrogen sources within the media.

Attributing Cause and Effect

The primary goal of this preparation is to prove causality. You need to know that the biodegradation effects you observe are caused solely by the fungi you introduced.

If the media is not sterilized at 121°C, any data you collect is compromised. You cannot confirm if the biomass breakdown was caused by your fungus or by a surviving environmental contaminant.

Common Pitfalls and Considerations

The Risk of Incomplete Sterilization

Reducing the temperature or time (e.g., to preserve sensitive compounds) is a common error. If the core of the biomass does not reach 121°C for the full 20 minutes, pockets of contamination will survive.

Chemical Alteration of Substrates

It is important to acknowledge that high heat can slightly alter the chemical structure of biomass. However, in biodegradation studies, the priority is absolute sterility to ensure the validity of the biological agent's performance.

Applying This to Your Research

To ensure your data stands up to peer review, align your sterilization protocol with your specific experimental goals:

• If your primary focus is attribution of effect: You must use high-pressure sterilization at 121°C to guarantee that all degradation is attributable only to your inoculated strain.
• If your primary focus is process efficiency: You must ensure a competitor-free environment so your target fungi can achieve maximum biodegradation rates without inhibition.

Reliable science begins with a clean baseline; high-pressure sterilization provides the blank canvas your fungi need to perform.

Summary Table:

Parameter	Standard Boiling (100°C)	High-Pressure Sterilization (121°C)
Microbial Target	Active bacteria only	Active bacteria + Resilient spores
Effect on Biomass	Incomplete decontamination	Complete elimination of native microbes
Data Validity	High risk of contamination/noise	Controlled, reproducible results
Biological Goal	General cleaning	Total sterility & directional biodegradation

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References

1. Meng Li, Zhenzhong Gao. Synergistic effect of mixed fungal pretreatment on thermogravimetric characteristics of rice straw. DOI: 10.15376/biores.16.2.3978-3990

This article is also based on technical information from Kintek Solution Knowledge Base .