Fatty Acids as Glyphosate Toxicity Indicators in Pseudomonas Fluorescens

Abstract

Herbicides have harmful effects on bacteria, despite not being their primary targets. Herbicide active molecules cause unspecific oxidative stress, affecting soil microbiome function. Microorganisms possess enzymatic and non-enzymatic oxidative stress control systems that enable them to survive in contaminated environments. It is uncertain whether these systems require specific selective pressures to remain effective against contaminants and how the toxicity is signaled. The objective of this work was to analyze the antioxidant enzymes and lipid profiles of a Pseudomonas fluorescens strain, isolated from water used in washing of pesticide containers, as response systems to the herbicide glyphosate, not present at the isolation site. The bacteria showed low growth rates, cell viability and high hydrogen peroxide quantities at 40x and 50x glyphosate concentrations used in agriculture. These findings demonstrate the toxicity of this herbicide to Pseudomonas strain. However, growth rates in the presence of up to 10x were equivalent to the control group, probably because of superoxide dismutase and the catalase isoenzyme activities that managed to maintain peroxide levels under control in the early- and mid-log phases. Identification and quantification of lipids, by gas chromatography and mass spectrometry, showed that specific fatty acids were correlated with high concentrations of glyphosate and specific growth phases in P. fluorescens , through Principal Component Analysis, suggesting a role in modulating responses to glyphosate toxicity. Nevertheless, glyphosate was not present in the isolation site and, therefore, was not previously selective for P. fluorescens . This suggest that the response system is generalist, based on physiological plasticity, indicating substantial adaptative values in environments subjected to intense pesticide contamination. A matter that emerges is what would be the consequences of a system that is able to respond to toxic substances to which soil microbiomes have not had contact on for bacterial diversity and functionality in agricultural soils.