Since filamentous fungi of Penicillium and Aspergillus genera can colonize very diverse niches, and Ascomycota seems to be the dominant phylum within the microbial group in various contaminated substrates, they possess great potential in the remediation of pesticide-contaminated sites. Different species can remove the pesticides at different rates, and to various extents; however, the fungal ability to resist high concentrations of pesticides is almost unparalleled compared to other microbial groups. Their performance may be further improved by applying indigenous strains isolated from pesticide-contaminated soils and sediments.
1. Introduction
The current agricultural practice is contingent on the use of various pesticides since there is an urgent need to enhance the crop production to supply the rapidly increasing food-demand
[1]. Throughout the globe, approximately 2 million tons of pesticides are produced and utilized annually, and it was estimated that in 2020, the global pesticide usage was approximated to be 3.5 million tons
[2]. The application of pesticides is apparently advantageous since it diminishes the crop infestations, and thus, limits the harvest losses and positively affects the crops quality
[3]. However, due to their potent biological activity as toxins and owing to their extensive or injudicious application, the heavy soil treatment with pesticides can endanger the wildlife. The pesticides and their toxic degradation products can enter the plant tissues and build up in the food chain or remain in the soil and water environments and negatively affect the soil fertility and water quality
[4]. Thus, the pesticides pose a significant risk to the environment and to human health. The alarming increase in the production and usage of pesticides triggered the notion to reduce the impact of pesticides and find sustainable alternative solutions to protect the crops
[5].
Although the role of many pesticides in the environmental deterioration has not been adequately resolved, it is indisputable that they have adverse effects on various non-target organisms
[6]. Thus, the research on advanced practices protecting wildlife, which highlights a more cautious use of synthetic agrochemicals, careful risk assessment, and licensing, is very much needed
[7]. Therefore, the development of ecofriendly technologies focused on reducing the utilization of synthetic pesticides, especially those with high persistence in the environment, has been addressed
[8][9]. More importantly, there is still an issue of developing a proper treatment technology for the remediation of pesticide-contaminated soils. This is a complex problem, since the areas with point-source contamination are usually agricultural soils whose properties should be maintained; thus, aggressive technologies should be omitted
[10]. Among more recent and ecologically acceptable emerging technologies is bioremediation, which involves the utilization of indigenous microflora, adapted or genetically engineered microorganisms or their enzymes for the degradation and conversion of pesticides to another form via co-metabolism or mineralization
[11][12].
2. Degradation of Organochlorine Pesticides by Aspergillus and Penicillium Species
The fungal performance in the biodegradation of the most common organochlorine pesticides (endosulfan and lindane) in culture media, as well as the transformants or end products (Figure 1) formed by the fungi belonging to Aspergillus and Penicillium genera are listed in Table 1.
Figure 1. Proposed metabolic pathway for the degradation of endosulfan by Aspergillus and Penicillium fungal strains.
Table 1. Cultivation conditions and reported performances of filamentous fungi belonging to the genera Aspergillus and Penicillium in the biodegradation of organochlorine pesticides.
3. Degradation of Organophosphorus Pesticides by Aspergillus and Penicillium Species
The performances of strains belonging to Aspergillus and Penicillium genera in the biodegradation of organophosphorus pesticides in culture media are listed in Table 2. The summarized biodegradation pathways for methyl parathion and chlorpyrifos, the most studied organophosphorus pesticides, are depicted in Figure 2 and Figure 3, respectively.
Figure 2. Proposed metabolic pathway for the degradation of methyl parathion by Aspergillus and Penicillium fungal strains.
Figure 3. Proposed metabolic pathway for the degradation of chlorpyrifos by Aspergillus and Penicillium fungal strains.
Table 2. Cultivation conditions and reported performances of filamentous fungi belonging to the genera Aspergillus and Penicillium in the biodegradation of organophosphorus pesticides.
The biodegradation of three pesticides of the different chemical classes, difenoconazole, pendimethalin, and terbuthylazine, by
Penicillium brevicompactum and
A. oryzae was studied by Pinto et al.
[45]. After an 8-day incubation, 99% of pendimethalin was degraded by both fungal strains. Fungi
A. oryzae and
P. brevicompactum were capable of degrading 88% and 92.7% of difenoconazole, while lower removal percentages were exhibited with terbuthylazine approximating 78% and 71%, respectively. More importantly, the authors have highlighted adsorption as a potential mechanism of pesticide removal, characterized by the fast initial removal rates, which may be an efficient mechanism utilized by the fungus to block the xenobiotic uptake.
Derbalah et al.
[46] reported that approximately 93% of the initial famoxadone concentration was degraded within four weeks by strains of
A. niger EB2 and
Penicillium sp. EB3 and the negligible spontaneous degradation was observed in control experiments. The bioassay conducted with
Alternaria solani using the spent medium with degradation products collected at the end of famoxadone treatment showed only slight antifungal activity, indicated by 5% growth inhibition of
A. solani.