Effective mycoremediation coupled with bioaugmentation studies: An advanced study on newly isolated Aspergillus sp. in Type-II pyrethroid-contaminated soil

Highlights

• Worldwide consumption of pyrethroids contributes to soil and water pollution.

• Assessment of removal efficiency of Aspergillus sp. (PYR-P2) in liquid systems and soil.

• Optimization of significant factors to improve the mycoremediation potential of the strain PYR-P2.

• Fungal-augmented removal studies in real field soil (natural and sterile) systems under optimized conditions.

• Ultra-high-performance liquid chromatography and Gas chromatographic-mass spectrometric studies for residual analyses.

Abstract

The intensive application of type-II pyrethroid worldwide in agricultural and residential practices potentially contributes to soil and water pollution, raising various concerns about environmental and public health. In the present study, robust fungus (strain PYR-P2) with high pyrethroids degradation potential was isolated from pesticide-contaminated soil. The strain was identified based on morphology and molecular characteristics, as Aspergillus sp. The screening of the transforming ability of strain PYR-P2 was evaluated in minimal salt media (MSM), where the fungus utilized up to 500 mg L⁻¹ of pyrethroid mixture (cypermethrin (CYP), cyfluthrin (CYF), cyhalothrin (CYH)). With this in view, central composite design (CCD) with three independent variables (pH, temperature, and initial concentration) was employed to identify the optimal conditions for achieving maximum pyrethroid removal. Under optimal conditions, strain PYR-P2 was implemented for the bioaugmentation studies in natural and sterile soil (NS/SS) systems spiked with pyrethroid (single and mixture) at a concentration of 100 mg kg⁻¹. The highest pyrethroid removal percentages were observed in fungally augmented NS, accompanied by a decrease in pyrethroid half-life (t_1/2). Herein, the observed half-life (t_1/2) of pyrethroids in the fungally augmented NS varied between 1.48 and 2.69 d, with equally good values recorded in SS as 1.65–3.10 d. Taken together, the mycoremediation study employing fungal (strain PYR-P2) augmentation under optimized conditions represents an efficient strategy to restore pyrethroid-contaminated soil.

Introduction

Pyrethroids (PYR) are a synthetic neurotoxin based on the natural pyrethrin-based insecticides (Li et al., 2016; Van Thriel et al., 2012); globally used in agricultural as well as domestic practices, to kill pests by disrupting their nervous system (Brander et al., 2016). Pyrethroids have been the leading insecticides since the 1980s (Aksakal et al., 2010; Shen et al., 2012); most of them are chiral molecules and exist as a mixture of isomers (Murcia-Morales et al., 2019; Saillenfait et al., 2015). It quickly enters soil ecosystems through direct spraying on the soil surface during application and dripping from stems; and later spreads throughout ecosystems and water (Yang and Ji, 2015; Song et al., 2015). Their excessive consumption strongly affects non-target organisms and pollutes the terrestrial and aquatic environment (Cycon and Piotrowska-Seget, 2016). Soil contamination with pesticides induces adverse effects on organisms, as well as on the structure and function of the soil ecosystem (Gestel et al., 2009). Unfortunately, the neurotoxic effects are not selective enough to prevent damage in non-target species, including humans (Garí et al., 2018). In humans, by-products of pyrethroid have been found, confirming widespread exposure to pesticides (Gangola et al., 2018).

In this respect, there is a growing public concern about the negative impacts imposed by pesticides on wildlife and the environment, besides the adverse health effects on humans. Initially, pyrethroids were perceived to have low mammalian to plant toxicity; recently, their carcinogenic, neurotoxic, and immunity-suppressive potential, as well as reproductive toxicity, have been found (Markou et al., 2018). Pesticides exposure has been associated with several health effects, including respiratory, gastrointestinal, reproductive and neurological problems (Garí et al., 2018). Also, some of the pyrethroids have been detected as possible human carcinogens by the Environmental Protection Agency (EPA) of the USA (Zhang et al., 2010). Moreover, enormous studies have shown that pyrethroids are particularly toxic to non-target species especially aquatic, thus rendering pyrethroid contamination a serious environmental issue.

Cypermethrin, cyhalothrin, and cyfluthrin belong to the pyrethroid group, invariably used in a variety of crops to improve product quality. The combination of intensive agriculture and modern stream networks may increase the diffusion of these pesticides in the environment (Birolli et al., 2019; Gangola et al., 2018). Persistent use has resulted in their frequent out-reaching occurrences in soil and water as well, especially wreaking havoc on to aquatic bodies. Microbial bioremediation provides an economically and ecologically favorable opportunity to eliminate toxic pollutants from the environment (Gangola et al., 2018).

The use of bioremediation extends physical and chemical technologies since they are inefficient or expensive, also generate a lot of toxic waste (Gangola et al., 2018). Microbial biodegradation is one of the pivotal solutions for the bioremediation of soils contaminated by pesticides. However, the pesticide degrading ability of autochthonous microbes is very restrained in the natural ecosystem (McCoy et al., 2012; Liu et al., 2014; Liu et al., 2017). Given this, the addition of exogenous microbes/ameliorates has been considered as a practical approach to increasing the effectiveness of bioremediation (Cai et al., 2010; Liu et al., 2017). Several studies have been documented on the biodegradation of pyrethroids by bacteria such as Acinetobacter baumannii ZH-14 (Zhan et al., 2018); Bacillus licheniformis B-1 and Sphingomonas sp. SC-1 (Liu et al., 2014); Bacillus cereus (Liu et al., 2015; Zhang et al., 2016); Ochrobactrum lupini DG-S-01; Serratia spp. Strain JC1 and JCN 13 (Zhang et al., 2010); and Pseudomonas aeruginosa GF31 (Tang et al., 2017); however, relatively few studies have been reported with fungi, such as Cladosporium sp. (Chen et al., 2011); Acremonium sp. CBMAI 1676; Microsphaeropsis sp. CBMAI 1675; and Westerdykella sp. CBMAI 1679 (Birolli et al., 2016; Seleghim et al., 2018).

We focused our work on the mycoremediation of mixture of three commonly applied type-II pyrethroids: Cyfluthrin [α-cyano (4-fluoro-3-phenoxyphenyl)methyl-3- (2,2-dichloroethenyl)-2,2-dimethyl cyclopropane carboxylate], Cyhalothrin [α-cyano-3-phenoxybenzyl-3-[(Z)-2-chloro-3,3,3-trifluoropropenyl]-2,2-dimethylcyclopropanecarboxylate], and Cypermethrin [α-cyano-3-phenoxybenzyl-3-(2,2-dichlorovinyl) −2,2-dimethyl cyclopropane carboxylate]; extensively used in residential and agricultural practices (Chen et al., 2013). Two major metabolites (3-phenoxybenzoic acid and 3-phenoxybenzaldehyde) of most of the type-II pyrethroids, with cyfluthrin metabolized into 4-fluoro-3-phenoxybenzoic acid (4-F-3-PBA) (Garí et al., 2018) are often detected in the environment; being more mobile and persistent into the environment pose greater risk than parent compound (Yang and Ji, 2015; Chen et al., 2011). Several isolated bacterial strains capable of bio transforming pyrethroids have already been reported, as discussed above. Nevertheless, the combination of these pesticides has not been studied comprehensively in real field soil. Additionally, there are no data from fungi mediated bioaugmentation studies in the pyrethroid contaminated soil.

In this study, pyrethroid degrading fungi were isolated from pesticide-contaminated agricultural soil using enrichment culture technique, identified and characterized using morphological and molecular (18S rDNA sequencing) techniques. Preliminary examination of fungi for their ability to transform a mixture of given pyrethroids revealed that strain PYR-P2 was able to mineralize the pesticides competently. The objectives of taken study were, therefore, to: (i) investigate the efficacy of fungal isolate at varied concentrations of pyrethroid (single/mixture), (ii) Bioaugmentation studies in real field soil (natural and sterile soils), (iii) Qualitative and quantitative studies for residue analysis, (iv) Identification of metabolites using Gas chromatographic-mass spectroscopic studies. Thereupon, the study will provide pertinent information on the mixture of pyrethroid biotransformation (e.g., dissipation kinetics and metabolite analysis utilizing robust strain PYR-P2.