How fungi "eat" oil: can nature clean contaminated soil on its own?

Oil pollution is usually associated with heavy machinery, spill collection, chemical reagents, and lengthy restoration work. However, there is another approach — putting nature itself to work. Certain fungi are capable of breaking down complex hydrocarbons found in petroleum, converting hazardous pollutants into simpler compounds. This method is known as mycoremediation.

This does not mean that fungi literally consume oil as food. Their mycelium — an interconnected network of thin filaments — secretes enzymes outward that can break down molecules that are extremely resistant to most organisms. It is precisely this ability that turns fungi into a potential tool for restoring contaminated soil and water bodies.

Why fungi can break down petroleum products

The so-called white-rot fungi are of particular interest to scientists. In nature, they perform a crucial job: decomposing wood. To do this, they must break down lignin, one of the most resistant components of plant tissue.

The issue is that the chemical structure of lignin largely resembles that of certain persistent petroleum pollutants. Therefore, the enzymatic system developed by fungi to decompose wood proved capable of acting on a wide range of hydrocarbons as well. Fungi secrete enzymes such as laccases, lignin peroxidases, and manganese peroxidases into the external environment. These trigger a chain of oxidative reactions through which complex organic molecules gradually break down into simpler ones.

Polycyclic aromatic hydrocarbons, or PAHs, are especially important in this regard. They form as part of oil and petroleum products and are exceptionally persistent in the environment. Some of them are toxic, while specific compounds possess carcinogenic properties.

What happens to oil after fungi appear

First, the mycelium begins to spread throughout the contaminated substrate. The vast network of hyphae allows fungi to penetrate soil significantly deeper than could be achieved by simply applying a biological agent. Simultaneously, the fungus secretes various compounds that help make hydrophobic petroleum hydrocarbons more accessible for subsequent breakdown. This is important because oil does not mix well with water and is therefore not always accessible to microorganisms.

Then, the enzymatic attack begins. Peroxidases and laccases oxidize complex molecules, disrupting their structure. For example, PAHs may first transform into intermediate, more reactive compounds, after which the decomposition process continues. Similar transformations occur with alkanes and cycloalkanes: long hydrocarbon chains are sequentially oxidized, forming alcohols, aldehydes, and carboxylic acids. However, there is an important caveat: the fungus does not necessarily reduce the oil to carbon dioxide and water entirely on its own. In practice, it is far more often a collaborative effort of an entire microbial community.

Fungi and bacteria work as a team

Once the fungus breaks down large and persistent molecules, the resulting compounds become much more convenient food for bacteria. Bacteria of the genera Pseudomonas, Rhodococcus, Alcanivorax, and others can work in contaminated soil. They continue splitting the intermediate products formed after the action of fungal enzymes.

This creates a kind of biological chain: the fungus makes the complex pollutant accessible, and bacteria continue processing it. Therefore, in real-world systems, using a single specific organism may be less promising than creating a microbial community in which different species complement each other. Ultimately, part of the organic compounds can be mineralized to carbon dioxide and water, while part of the carbon is used by the microorganisms themselves for growth.

Which fungi are used for this

One of the most thoroughly studied candidates remains the oyster mushroom (Pleurotus ostreatus). It grows well on straw, sawdust, and other plant materials, possessing a developed enzyme system typical of white-rot fungi. Researchers are also studying representatives of the genera Trametes, Ganoderma, Coriolopsis, and Polyporus. Additionally, various species of Aspergillus, Penicillium, Trichoderma, and other mold fungi capable of participating in hydrocarbon decomposition are found in oil-contaminated soils.

Strains discovered directly in oil-polluted areas are of particular interest. Such organisms are already adapted to a toxic environment and can potentially prove more effective than species grown under completely different conditions.

How the technology is used in practice

One of the simplest options is to use spent mushroom substrate left over from industrial cultivation of edible mushrooms. It already contains mycelium and its metabolic byproducts. Such material can be mixed with contaminated soil while maintaining the necessary moisture and oxygen supply. Essentially, an environment is created where the fungal mycelium gets the opportunity to spread through the contaminated substrate and gradually act on the hydrocarbons.

Another option is bioaugmentation, where selected fungal strains are specifically introduced into contaminated soil. At the same time, specialists can adjust environmental conditions: adding sources of nitrogen and phosphorus, organic materials, or biochar to stimulate the microbial community. For oil pollution in water and coastal zones, mycelium-based structures are also being considered. For instance, biodegradable materials capable of simultaneously retaining part of the pollution and creating conditions for its subsequent biological degradation are being researched.

How well it works

In laboratory experiments, the results can look impressive: depending on the fungus species, pollution composition, and experimental conditions, the reduction in total petroleum hydrocarbon concentration sometimes reaches 60–90%. For individual strains and specific compounds, the figures can be even higher. Some studies reported the breakdown of a significant portion of individual PAHs — up to 85–99% under certain conditions.

However, these numbers cannot be directly extrapolated to real-world oil spills. A laboratory experiment and a contaminated territory are completely different systems. In a test tube or controlled microcosm, one can maintain the required temperature, humidity, acidity, and nutrient concentration. In nature, all these parameters change constantly.

Why fungi haven't yet become a universal cleanup tool

The main challenge of mycoremediation is not proving that a fungus can break down hydrocarbons, but achieving effective performance in a real natural environment.

In heavily contaminated soil, the concentration of toxic substances can be too high even for a resistant fungal strain. In other cases, the introduced organism competes with local microbiota and simply fails to spread properly.

Temperature, humidity, oxygen content, soil acidity, and the carbon-to-nitrogen-to-phosphorus ratio all matter. Changing even one of these factors can significantly affect the speed of the process.

There is another issue: the disappearance of the petroleum pollutant itself does not yet mean the territory is completely safe. As complex hydrocarbons decompose, intermediate compounds may form, making it necessary to monitor not only the amount of remaining petroleum products but also the composition of the resulting substances.

An additional tool, not a replacement

Therefore, it is currently more reasonable to view mycoremediation not as a replacement for all existing cleanup methods, but as part of an integrated technology.

Mechanical methods allow for the quick removal of the bulk of spilled oil. After that, biological methods can be used for further cleanup of the soil or area from remaining pollutants that are physically difficult to collect.

This approach can be particularly promising where using heavy machinery is expensive or technically difficult. Furthermore, agricultural waste, straw, sawdust, and spent mushroom substrates can be repurposed to grow the fungi.

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