Abstract
Callisto®, containing the active ingredient mesotrione (2-[4-methylsulfonyl-2-nitrobenzoyl]1,3-cyclohenanedione), is a selective herbicide that controls weeds in corn crops and is a potential environmental contaminant. The objective of this work was to evaluate enzymatic and structural changes in Pantoea ananatis, a strain isolated from water, in response to exposure to this herbicide. Despite degradation of mesotrione, probably due a glutathione-S-transferase (GST) pathway in Pantoea ananatis, this herbicide induced oxidative stress by increasing hydrogen peroxide production. Thiol fragments, eventually produced after mesotrione degradation, could be involved in increased GST activity. Nevertheless, there was no peroxidation damage related to this production, as malondialdehyde (MDA) synthesis, which is due to lipid peroxidation, was highest in the controls, followed by the mesotrione- and Callisto®-treated cultures at log growth phase. Therefore, P. ananatis can tolerate and grow in the presence of the herbicide, probably due an efficient control of oxidative stress by a polymorphic catalase system. MDA rates depend on lipid saturation due to a pattern change to a higher level of saturation. These changes are likely related to the formation of GST-mesotrione conjugates and mesotrione degradation-specific metabolites and to the presence of cytotoxic adjuvants. These features may shift lipid membrane saturation, possibly providing a protective effect to bacteria through an increase in membrane impermeability. This response system in P. ananatis provides a novel model for bacterial herbicide tolerance and adaptation in the environment.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-016-0240-x) contains supplementary material, which is available to authorized users.
Highlights
Pesticides have been widely used to increase crop production, yet there are concerns about the adverse effects that these chemicals have on wildlife because many agrochemicals are not readily degraded by microorganisms (Copley 2009)
Lipid membrane changes in response to herbicide cytotoxicity The concentration of MDA was examined in the controls, mesotrione- and Callisto®-treated cultures to determine the amount of lipid peroxidation and herbicide cytotoxicity (Fig. 8)
reactive oxygen species (ROS)-induced damage can be assessed by quantification of hydrogen peroxide (H2O2) in cells, which is one of the main causes of oxidative stress (Gratão et al 2012), and MDA levels can be used as a marker of oxidative stress (Cabiscol et al 2000)
Summary
Pesticides have been widely used to increase crop production, yet there are concerns about the adverse effects that these chemicals have on wildlife because many agrochemicals are not readily degraded by microorganisms (Copley 2009). Mesotrione (2-[4-methylsulfonyl-2-nitrobenzoyl]1,3cyclohenanedione), the active ingredient of the herbicide Callisto®, is used for selective pre- and post-emergent control of broadleaf weeds in corn crops (Batisson et al 2009). This chemical, which is naturally produced by the plant Callistemon citrinus, functions by inhibiting the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD) and interferes with carotenoids synthesis (Mitchell et al 2001). Mesotrione has been shown to be an environmental contaminant (Stoob et al 2005) Both 4-methylsulfonyl-2-nitrobenzoic acid (MNBA) and 2-amino-4-methylsulfonyl benzoic acid (AMBA) have been described as products of mesotrione degradation by Bacillus sp., (Durand et al 2006) with AMBA being more cytotoxic than the active ingredient mesotrione (Mitchell et al 2001; Bonnet et al 2008). A recent study reported that other products, in addition to AMBA, are produced through mesotrione degradation by Pantoea ananatis (Pileggi et al 2012)
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