Ability of non-aflatoxigenic Aspergillus section Flavi strains to grow in the presence of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and remove it from synthetic wastewater

The mismanagement of wastewater containing 2,4-dichlorophenoxyacetic acid (2,4-D) is responsible for serious environmental pollution. One possible solution to this problem is the implementation of remediation techniques that use living organisms, such as fungi, to reduce herbicide levels in different matrices. This study aimed to characterize and select non-aflatoxigenic Aspergillus section Flavi strains with the ability to tolerate and remove 2,4-D in synthetic agricultural wastewater. Their aflatoxigenicity was assessed through an analytical method, followed by the amplification of the four main genes involved in aflatoxin synthesis. Four non-toxigenic strains (RCA 2, RCA 4, RCA 5, and RCA 10) tolerated up to 25 mM of the herbicide and were subsequently identified as A. oryzae. An ecophysiological assay revealed that the best conditions for their growth were 1 mM of 2,4-D at pH 7 and 25 C, and that only one set of conditions (5 mM of 2,4-D, pH 9, and 25 C) completely inhibited development in one of the strains. Finally, removal assays were performed in synthetic wastewater, in which residual 2,4-D levels were quantified by high-performance liquid chromatography ultraviolet detection (HPLC-UV) and tandem mass spectrometry (MS/MS). Three of the four A. oryzae strains removed over 40% of the herbicide in the medium after 7 d of incubation, and close to or more than 60% after 14 d. Therefore, these strains could potentially be considered for the design of bioaugmentation strategies aimed at reducing 2,4-D contamination in wastewater.