Microplastics mitigate the effects of glyphosate on the shikimic acid pathway enzymes in cyanobacteria

Abstract

Microplastics, an environmental contaminant, can directly harm aquatic organisms and alter the toxicity and availability of other pollutants. The herbicide glyphosate (N-(phosphonomethyl) glycine) exerts its toxicity by inhibiting 5-enol-pyruvyl-shikimate-3-phosphate synthase (EPSPS), a key enzyme belonging to shikimic acid pathway that leads to the biosynthesis of aromatic amino acids; tolerance, instead, is dependent on a glyphosate -resistant EPSPS. We tested the effects of 0,2mM glyphosate alone and in combination with 170 mg/mL polyethylene microplastics (MPs) on the expression of EPSPS and chorismate synthase (ChS) on a culture of the cyanobacterium Limnospira maxima. Glyphosate caused the highest mortality after one week, with the resistant population surviving thereafter.However, when the culture was exposed to the combined treatment the mortality decreased. Proteomic profiles of treated cultures demonstrated that both enzymes were accumulated during the 21 days glyphosate treatment, suggesting that the surviving population of L. maxima might express glyphosate-resistant target enzymes. Treatment with combined solution caused a decrease of EPSPS and ChS levels compared to those of glyphosate alone. Our results strongly suggest that microplastics mitigate the toxicity of glyphosate towards target enzymes of the shikimic acid pathway, thereby increasing the resistance capacity of the L. maxima strain.

Keywords:

• Limnospira maxima
• glyphosate resistance
• microplastics
• EPSP synthase
• chorismate synthase

Acknowledgment

The authors express their gratitude to Mauro Francesco La Russa for providing the microplastic samples, to Elvira Brunelli for facilitating access to the microscope and image capture, and to Liliana Bernardo for taxonomic assistance. The authors thank the PON, Grant number a3_00341A S.I.L.A. - Integrated System of Environmental Laboratories-University of Calabria for mass spectrometry equipment.

Author Contributions

Conceptualization, S.M.; methodology, A.P. D.N. D.O.; formal analysis, A.P. D.N. D.O.; investigation, D.N.; resources, S.M. and A.P.; writing—original draft preparation, A.P. and S.M.; writing—review and editing, S.M. and A.P.; supervision, S.M. All authors have read and agreed to the published version of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Regione Calabria Grant/Award number CUP: J22C17000120001 Progetto SILA_4.0_CAPITALE_UMANO; PON “Sistema Integrato di Laboratori per l’Ambiente (S.I.L.A.) – PON a3_00341.