Adverse Metabolic Outcomes in Soil Pseudomonas Species Exposed to Polyethoxylated Tallow Amine and Glyphosate

Polyethoxylated tallow amine (POEA) is a common surfactant used in glyphosate-based herbicide formulations to enhance the bioavailability of the active herbicide ingredient. Toxic effects of POEA exposure are well documented for aquatic organisms, but despite the widespread occurrence of POEA in soils, the potential effects on soil bacteria have not been investigated. Here we examined the growth and metabolic effects of POEA in three strains of plant-beneficial soil Pseudomonas species (Pseudomonas putida KT2440, P. putida S12, and P. protegens Pf-5) grown on succinate, a common root exudate. Compared to the rate of growth on only succinate, the addition of POEA resulted in up to 60% reduction in the biomass growth rate. In the presence of both POEA and glyphosate, the biomass growth rate either remained the same as during exposure to only POEA or decreased by only an additional 5-15%, thus indicating that growth inhibition was primarily caused by POEA. Metabolomics analysis of POEA-exposed cells identified, relative to control cells, disruption of metabolite levels in key biosynthetic pathways: accumulation of ribonucleotides and depletion of amino acids. Kinetic C-13 flux experiments further revealed delayed de novo biosynthesis of pyrimidine ribonucleotides. Our findings thus highlight disconnects between carbon metabolism and biomass biosynthesis as potential adverse metabolic outcomes in POEA-exposed soil-beneficial bacteria.