Glyphosate Bioremediation through the Sarcosine Oxidase Pathway Mediated by Lysinibacillus sphaericus in Soils Cultivated with Potatoes

Abstract

Glyphosate-based herbicides (GBH) use has increased drastically over the last decade. This is true especially for potato crops due to their fast harvest cycle and high market demand. In 2015, the World Health Organization (WHO) classified glyphosate and its breakdown product amidomethylphosphonic acid (AMPA) as probably carcinogenic to humans, and it has been reported that these compounds disrupt the ecological and nutritional equilibrium of soils. However, microorganisms with the sarcosine oxidase gene, such as Lysinibacillus sphaericus, can degrade glyphosate through the Carbon-Phosphorus (C-P) pathway without leading to AMPA production. The aim of this study was to evaluate the addition of the plant growth-promoting bacteria (PGPB) L. sphaericus as a bioremediation agent in a potato crop sprayed with a GBH, in conjunction with the nitrogen fixation activity mediated by the bacteria. To that end, a GBH solution was used to treat a potato field, and different treatments (glyphosate (G), bacteria (B), bacteria+glyphosate (BG), and negative control (C)) were evaluated by measuring the glyphosate, AMPA, nitrates, and ammonium concentrations. BG treatment showed a 79% reduction of glyphosate concentration in soil, leading to minimal AMPA production, compared to the 23% reduction observed after G treatment. Furthermore, the ammonium concentrations were significantly higher in samples treated with BG and in C samples (p < 0.005). Therefore, we propose the addition of L. sphaericus as a good bioremediation strategy for soils sprayed with GBH.