MYCOREMEDIATION: CAN FUNGI HELP TO SAVE THE WORLD?
This was a question propounded by mycologist Paul Stamets fourteen years ago. Many studies have been published and new companies have arisen since the idea of using fungal mycelium for the restoration of degraded environments and ecosystems- was first stated (Gadd, G 2001, Stamets, P 2005).
Within life cycle, bacteria and fungi are the decomposing agents able to return essential components into the loop for re-construction of living beings.
Mycoremediation is the technology based on the natural biotransformation mechanisms of fungi to convert residues, that might be considered as toxic for humans, into harmless molecules that may then be released to nature. From this perspective, it seems logical to assume that directed screening programs would find microorganisms with the ability to decompose a large variety of chemical structures.
Biomar microbial library contains over 70.000 microorganisms: actinomycetes, cyanobacteria, microalgae and fungi. Some of those fungi have been isolated from contaminated areas and many other from marine or soil samples using media containing the residue we wished to decompose as unique carbon source.
There is also abundant bibliography that describes how microbes can degrade, in laboratory conditions, many different pollutants (Abatenh 2017), for instance mono and polycyclic aromatic hydrocarbons.
Fungi are able to produce a wide variety of enzymes and secondary metabolites as a result of changing environmental conditions. Both the nature of the substrate and fungal plasticity can then be combined to transform contaminated soils and restore devastated areas.
Table 1 shows some articles about the role of well-known mushrooms in the degradation of pollutants as plastics, polyaromatic hydrocarbons, dichlorophenol, radioactive material, oil and heavy metals.
| Fungal strain | Waste/pollutant | Remarks | Reference |
| Pleurotus ostreatus | Oxo biodegradable plastics | Mushroom degraded plastic and grew on it | (da Luz et al 2013) |
| Lentinula edodes | 2,4 dichlorophenol | Mushroom degraded 2,4 dichlorophenol, by using vanillin as activator | (Tsujiyama et al 2013) |
| Pleurotus pulmonarius | Radioactive cellulosic base waste | Waste containing mushroom mycelia was solidified with Portland cement and used as first barrier against the release of radiocontaminants | (Eskander et al 2012) |
| Jelly sp. Schizophyllum commune, Polyporus sp. | Malachite green | 99.7% Jelly sp. 97,5% Schizophyllum commune, 68,5% Polyporus sp of original dye was degraded within ten days | (Rajput et al 2011) |
| Pleurotus pulmonarius | Crude oil | Crude oil was degraded | (Olusola et al 2010) |
| Coriolus versicolor | PAH | ||
| Melanized fungi | Heavy metals
Radionuclides |
Adsorbers of heavy metals and radionuclide contaminants from industrial effluents | (Dadachova et al 2007) |
| Pleurotus platypus, Agaricus bisporus, Calocybe indica | Copper, Zinc, Iron, Cadminum, Lead, Nickle | Mushrooms are efficient biosorbent for the removal of some ions from water solution | (Lamrood et al 2013) |
The amount of waste generated by human activity, toxic and non-toxic, is overwhelming and continuously growing, making its management very difficult and creating high demand for new technologies coming from different knowledge areas. In addition to the waste generated as byproducts of industrial processes, accidental spills are common events. In the particular case of toxic materials spills (hydrocarbons, oils, pesticides, heavy metals, radiation, etc.) are a difficult and expensive threat to clean up.
Although in the lab is not difficult to find microorganisms capable of growing out of different residues and toxic materials, it is not trivial to translate laboratory conditions to the field.
The recovery of contaminated areas is a vast problem that must be addressed from the combination of different disciplines, mainly microbiology, biotechnology, edaphology, marine biology, ecology and engineering.
Microbiology and biotechnology will select the best microbial candidates to degrade the specific residues or toxic materials, as well as define the environmental conditions required for this degradation. Edaphology, marine biology and ecology will study how the introduction of a new microorganism, a large amount of an endemic microorganism or even a consortium of them will impact the surrounding environment. Finally, engineering is a key role of the solution because in many situations the contaminated area will be large or even difficult to access (Sturman et al 1995). There are two options for treatments, in situ or ex situ, and the best one needs to be determined case by case. In some cases the best approach will be to potentiate the growth and metabolism of an autochthonous fungus. In some others will be to inoculate a foreign microorganism capable of degrading the specific pollutant, and sometimes the only option will be to remove the contaminated soil to be treated under controlled conditions by selected fungi. All these cases need to incorporate biotechnological and engineering approaches to define the optimal solution.
While decontamination can be a solution for some of the environmental problems created by toxic residues, it is clear that in order to avoid an even worse scenario than the current one, a profound change in how industries and population manage and perform their activities must happen, and this change must meet emerging sustainability criteria (Pavlovskaia 2014).
Non-toxic residues that are generated as by-products from different industries become a problem as well, because they are produced daily in large quantities and need appropriate and inexpensive waste management. Many of these non-toxic wastes from food, animal feed and agricultural industries could be used as fungal substrate to produce fungal proteins or other interesting metabolites, thus converting industrial by-products into valuable material.
Degradation of many substrates, even toxic materials is an inherent characteristic of fungal metabolism, so incorporating fungi-based transformation processes to deal with the ever increasing amount of byproducts generated by our society needs, could very well be a way of saving the world through fungi.
To learn more:
Gadd, G. 2001. Fungi in Bioremediation. Cambridge University Press.
Singh, H. 2006. Mycoremediation: Fungal Bioremediation. Wiley Interscience.
Marian Vinuesa Navarro
Responsable del Departamento de Micología
