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.

Assessment of the Synergic Effect between Lysinibacillus sphaericus S-Layer Protein and Glyphosate in the Lethality of the Invasive Arboviral Vector Aedes albopictus

“…Mortality observed in glycine assays cannot be attributed to synergistic effects, as glycine showed to be non-toxic by itself. These results are of importance since L. sphaericus has been shown to degrade glyphosate into environmentally inert (and even beneficial) products [ 26 , 27 ]. The L. sphaericus -mediated release of orthophosphates and glycine from glyphosate into the environment may be a way to take advantage of a widely detrimental chemical and turn it into crop and plant growth promotion.…”

“…As mentioned before, this glyphosate concentration was chosen as it is the most widely used formulation in Colombia for pests and illicit crops control [ 8 ]. Equal concentrations were used for both glycine and phosphate, as the stoichiometry of glyphosate break up yields a 1:1 product/reactant ratio [ 26 ]. Previous studies into the mosquitocidal action of the S-Layer protein against Culex quinquefasciatus have shown significant results at concentrations as low as 500 ppm [ 26 , 31 ].…”

“…Equal concentrations were used for both glycine and phosphate, as the stoichiometry of glyphosate break up yields a 1:1 product/reactant ratio [ 26 ]. Previous studies into the mosquitocidal action of the S-Layer protein against Culex quinquefasciatus have shown significant results at concentrations as low as 500 ppm [ 26 , 31 ]. Given how comparative studies have pointed at C. quinquefasciatus being considerably more susceptible to L. sphaericus biocontrollers than Aedes aegypti [ 32 ], an experimental concentration of 1500 ppm of the S-Layer protein was chosen.…”

“…Though studies have been conducted on several of the mosquitocidal pathways present in L. sphaericus strains [ 23 , 24 ], the roles that proteins such as the surface layer (S-Layer) protein and other derivates from the vegetative [ 25 ] L. sphaericus cell play in mosquitocidal action are open to further study, as their mechanisms and roles have not been explained in full. Though the most widely produced by-product of glyphosate mineralization is the highly toxic Aminomethylphosphonic Acid (AMPA) [ 26 ], previous studies have shown that L. sphaericus is able to degrade glyphosate into less dangerous compounds (orthophosphate ion and glycine, which are non-toxic) through the sarcosine oxidase metabolic pathway [ 26 , 27 ]. This raises the need to not only evaluate the role of glyphosate itself, but also the role its by-products may have in possible synergistic effects when in contact with this bacterium and its proteins.…”

Role of soil bacterial consortia on glyphosate degradation and growth of maize seedlings

“…The first pathway produces AMPA which is more toxic than glyphosate (Landry et al, 2005). In the Sarcosine pathway, the enzymatic reaction produced free phosphate ions and sarcosine which is further broken down into formaldehyde and glycine (Duke and Powles, 2008;Rodríguez et al, 2019).…”