Abstract
Agriculture uses many food production chains, and herbicides participate in this process by eliminating weeds through different biochemical strategies. However, herbicides can affect non-target organisms such as bacteria, which can suffer damage if there is no efficient control of reactive oxygen species. It is not clear, according to the literature, whether the efficiency of this control needs to be selected by the presence of xenobiotics. Thus, the Pseudomonas sp. CMA 6.9 strain, collected from biofilms in an herbicide packaging washing tank, was selected for its tolerance to pesticides and analyzed for activities of different antioxidative enzymes against the herbicides Boral®, absent at the isolation site, and Heat®, present at the site; both herbicides have the same mode of action, the inhibition of the enzyme protoporphyrinogen oxidase. The strain showed tolerance to both herbicides in doses up to 45 times than those applied in agriculture. The toxicity of these herbicides, which is greater for Boral®, was assessed by means of oxidative stress indicators, growth kinetics, viability, and amounts of peroxide and malondialdehyde. However, the studied strain showed two characteristic antioxidant response systems for each herbicide: glutathione-s-transferase acting to control malondialdehyde in treatments with Boral®; and catalase, ascorbate peroxidase, and guaiacol peroxidase in the control of peroxide induced by Heat®. It is possible that this modulation of the activity of different enzymes independent of previous selection characterizes a system of metabolic plasticity that may be more general in the adaptation of microorganisms in soil and water environments subjected to chemical contaminants. This is relevant to the impact of pesticides on the diversity and abundance of microbial species as well as a promising line of metabolic studies in microbial consortia for use in bioremediation.
Highlights
IntroductionThe herbicides used to combat weeds have become indispensable in agriculture, increasing productivity and causing several environmental problems, such as impacts on non-target organisms (Thiour-Mauprivez et al, 2019).Bacterial communities can undergo intense changes in their diversity when in contact with herbicides, which can affect soil and water quality, as in cases of exposure to 2,4-D (Moretto et al, 2017; Meena et al, 2020), atrazine, diuron (Moretto et al, 2017) and mesotrione (Du et al, 2018), by triazines in groundwater (Mauffret et al, 2017), and atrazine, glyphosate, malathion, carbaryl, and permethrin in container aquatic habitats (Muturi et al, 2017)
The herbicide alachlor caused a reduction in biomass and inhibited bacterial growth in river waters collected from the Saskatchewan River, Saskatoon, SK, Canada, when they were inoculated in bioreactors (Paule et al, 2016)
The 22 (32.8%) that were herbicide tolerant were grown on Luria Bertani Broth (LB) + herbicides and based on optical density (OD) data, the most tolerant strain was identified as Pseudomonas sp
Summary
The herbicides used to combat weeds have become indispensable in agriculture, increasing productivity and causing several environmental problems, such as impacts on non-target organisms (Thiour-Mauprivez et al, 2019).Bacterial communities can undergo intense changes in their diversity when in contact with herbicides, which can affect soil and water quality, as in cases of exposure to 2,4-D (Moretto et al, 2017; Meena et al, 2020), atrazine, diuron (Moretto et al, 2017) and mesotrione (Du et al, 2018), by triazines in groundwater (Mauffret et al, 2017), and atrazine, glyphosate, malathion, carbaryl, and permethrin in container aquatic habitats (Muturi et al, 2017). The herbicide alachlor caused a reduction in biomass and inhibited bacterial growth in river waters collected from the Saskatchewan River, Saskatoon, SK, Canada, when they were inoculated in bioreactors (Paule et al, 2016). When subjected to stressful environmental conditions, bacterial strains can naturally produce reactive oxygen species (ROS) in large quantities. Contaminants, such as herbicides, cause oxidative stress through the generation of ROS, which interact with the cell membrane and can cause lipid peroxidation (Dourado et al, 2015). As a way of preventing or reducing these types of imbalances, bacteria have developed response systems to protect membrane integrity, such as modulating the activity of antioxidant enzymes (Martins et al, 2011; Lemire et al, 2017)
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