Bacterial isolates from Argentine Pampas and their ability to degrade glyphosate

Abstract

Glyphosate is a synthetic phosphonate compound characterized by a carbon‑phosphorus bond. Glyphosate based herbicides (GBH) are widely distributed in most of the economically productive lands in which crop production is mainly based on glyphosate-resistant genetically modified plants. Naturally, glyphosate is remediated by soil microorganisms, which accelerate its degradation. Technology based on microorganisms is considered highly efficient, low-cost and eco-friendly to remediate contaminated environments, denoting the importance of characterizing new bacterial strains able to degrade glyphosate to perform its bioremediation. In this work, 13 different bacterial strains able to grow in GBH as only phosphorous source were isolated from different environmental samples from the Argentine vastly productive glyphosate-resistant soybean crop area. These strains were identified and they belong to the genera Acinetobacter, Achromobacter, Agrobacterium, Ochrobactrum, Pantoea and Pseudomonas. Their ability to grow and consume GBH, glyphosate or the aminomethylphosphonic acid (AMPA), another phosphonate derived from glyphosate degradation, was evaluated. The best degradation performance was observed for bacteria from the genera Achromobacter, Agrobacterium and Ochrobactrum. The genome of the highly efficient GBH degrader Agrobacterium tumefaciens CHLDO was sequenced revealing the presence of a phn cluster, responsible for phosphonate metabolization. Expression analysis of A. tumefaciens CHLDO phn genes in the presence of 1.5 mM GBH compared to inorganic phosphorous showed that most of them are highly expressed during growth in the presence of the herbicide, suggesting a strong participation of phn cluster in GBH degradation. The importance of discovering new bacterial strains and the value of deciphering molecular determinants of GBH degradation give promising tools for bioremediation techniques to be used in glyphosate-contaminated environments is discussed.