Chlorinated herbicides are one of the main types of pesticide used in agriculture. In Argentina, 2,4-dichlorophenoxyacetic acid (2,4-D) is the most applied herbicide for the control of broadleaf weeds, but the risks it poses for the environment and human health are cause for great concern. A promising technology to remove this kind of pollutants, or neutralize them in such a way that they become less or non-toxic, is the use of degrading or detoxifying microorganisms from contaminated sites. Filamentous fungi can bioremediate xenobiotics thanks to their efficient enzymatic machinery. However, most studies on the degradation of 2,4-D have been carried out with bacteria, and little is known about whether it can be efficiently biodegraded by fungi. In the environment, fungal strains and native microbiota may detoxify contaminants through mechanisms like biosorption, bioabsortion, biotransformation, and/or degradation. Whether these processes occur separately or simultaneously depends on the metabolic ability of the strains that conform the microbial community. Another important concern when attempting to introduce detoxifying microorganisms into a contaminated environment is the GRAS (“Generally Recognized As Safe”) assessment or status. These are studies that help predict a biodegrading microorganism’s pathogenicity, toxicity,and infectivity before in situ application. This application, moreover, is regulated by different legal frameworks. The present review aims to outline the main aspects of 2,4-D degradation by fungi, and to summarize the current state of research on the topic in Argentina.

Agriculture is one of the bases of the Argentine economy. Glyphosate is undoubtedly one of the most important herbicides used. The increasing consumption and the efficiency of glyphosate-based herbicides have encouraged several studies on their persistence in soils, their effects on soil microbiota and their degradation processes. Fungi have been reported as being the main herbicide-degrading microorganisms as well as the most tolerant to environmental stress conditions. This study evaluated the growth performance of Aspergillus section Flavi and Aspergillus niger aggregate strains on Czapek Dox media supplied with a commercial glyphosate formulation as sole source of carbon (CZC), phosphorus (CZP) or nitrogen (CZN). Six Aspergillus spp. strains were evaluated. Each medium was stab-inoculated with fungal spores from 7-day old cultures. Two measures of colony radii were taken daily. All of the Aspergillus section Flavi strains showed a significant increase (from 24 to 44%) in growth rate on the CZN medium, as compared to controls. The A. niger aggregate strains exhibited the same behavioral pattern under all the conditions tested, except on the CZN medium. Velutinous or slightly floccose colonies with abundant sporulation were observed on CZP. Moreover, the colonies produced sparse sporulation on CZC or CZN media, being their appearances completely different from those on the CZP medium. This study establishes that A. section Flavi and A. niger aggregate strains can grow in vitro in the presence of glyphosate, especially when it is used as a sole source of phosphorus or nitrogen.

The effect of mixtures of antioxidants butylated hydroxyanisol (BHA) and propyl paraben (PP) on lag phase, growth rate and ochratoxin A (OTA) production by four Aspergillus section Nigri strains was evaluated on peanut meal extract agar (PMEA) under different water activities (a_w). The antioxidant mixtures used were: BHA + PP (mM), M1 (0.5 + 0.5), M2 (1.0 + 0.5), M3 (2.5 + 0.5), M4 (0.5 + 1.0), M5 (1.0 + 1.0), M6 (2.5 + 1.0), M7 (5.0 + 2.5) and M8 (10 + 2.5). The mixture M8 completely suppressed mycelial growth for all strains. A significant stimulation in OTA production was observed with mixtures M1 to M5 mainly at the highest a_w; whereas M6, M7 and M8 completely inhibited OTA production in all strains assayed; except M6 in A. carbonarius strain (RCP G). These results could enable a future intervention strategy to minimize OTA contamination.

The current agricultural system has led to the development of glyphosate (GP)-resistant weeds, causing an increase in GP doses and applications. Native mycota of pesticide-contaminated sites are the major source of pesticide-degrading microorganisms. The aims of the present study were to isolate the GP-tolerant culturable mycota in two soils with different pesticide exposure from Córdoba, Argentina, and to evaluate the growth parameters in native fungal isolates in the presence of GP and the effective dose that caused 50% growth reduction. The results showed that the genera Fusarium, Aspergillus, Mucor, Penicillium and Sterilia were the prevalent fungi isolated from soils both exposed and not-exposed to pesticides. The highest value (>100mM) of effective concentration of herbicide that caused 50% growth inhibition (EC50), was found for Trichoderma isolates. Sterilia spp. had EC50 values of 100mM, while Aspergillus spp. and Mucor had EC50 values between 50 and 100mM. The growth rate evaluation varied according to the isolates and GP concentrations. The data showed that all Aspergillus spp., Trichoderma spp., Mucor and three Sterilia spp. had the best growth performance in media supplied with GP after a variable acclimation period. This study provides valuable data for further studies that would allow to know the metabolic capacity of these fungal species that can be potential candidates for GP removal from contaminated environments.