Microbial dysbiosis and macrofungal outbreaks induced by long-term plant essential oil biocide application in a humid archaeological earthen site.
Zhu C, Jiang L, Wu R, Luo Z, Zheng L
Soil Health
Oregano and cinnamon sprays marketed as natural pest controls for your greenhouse or indoor plants can quietly reshape the whole microbial community living on and around your plants — and the survivors may be exactly the resistant fungi you were trying to stop.
Researchers kept spraying a historic earthen site with a plant-oil-based 'natural' disinfectant made from oregano and cinnamon to kill unwanted microbes. Instead of solving the problem, the repeated treatments killed off the diverse community of bacteria and fungi that normally kept things balanced — and the toughest, most resistant fungi took over and started sprouting mushrooms everywhere. The lesson: even natural treatments can cause big ecological problems when used repeatedly in a closed, humid environment.
Key Findings
Relative humidity above 95% combined with continuous essential oil application between 2022 and 2024 reduced microbial diversity and shifted communities toward resistant bacteria (Pseudomonadota, Actinomycetota) and fungi (Ascomycota, Basidiomycota).
The ecological imbalance culminated in a visible outbreak of Leucocoprinus mushrooms once temperatures exceeded 28°C, demonstrating how biocide-driven dysbiosis can trigger macrofungal proliferation.
Microbial communities adapted metabolically to degrade the essential oil compounds (limonene and pinene degradation pathways enriched), meaning the biocide became less effective over time while the resistant survivors thrived.
chevron_right Technical Summary
Using oregano and cinnamon essential oils as a 'natural' fungicide in an ancient earthen monument backfired: the treatment wiped out diverse microbes, leaving behind resistant fungi that then erupted in a visible mushroom outbreak. The study warns that even green biocides can destabilize microbial ecosystems when used repeatedly in enclosed, humid spaces.
Abstract Preview
The long-term application of plant essential oil (EO)-based biocides is a popular "green" strategy for microbial control in heritage science. However, its ecological consequences in enclosed, humid...
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Oregano is a species of flowering plant in the mint family, Lamiaceae. It was native to the Mediterranean region, but widely naturalised elsewhere in the temperate Northern Hemisphere.