Glyphosate (GS) inhibits the 5-enolpyruvyl-shikimate-3-phosphate (EPSP) synthase that is required for aromatic amino acid, folate and quinone biosynthesis in Bacillus subtilis and Escherichia coli. The inhibition of the EPSP synthase by GS depletes the cell of these metabolites, resulting in cell death. Here, we show that like the laboratory B. subtilis strains also environmental and undomesticated isolates adapt to GS by reducing herbicide uptake. Although B. subtilis possesses a GS-insensitive EPSP synthase, the enzyme is strongly inhibited by GS in the native environment. Moreover, the B. subtilis EPSP synthase mutant was only viable in rich medium containing menaquinone, indicating that the bacteria require a catalytically efficient EPSP synthase under nutrient-poor conditions. The dependency of B. subtilis on the EPSP synthase probably limits its evolvability. In contrast, E. coli rapidly acquires GS resistance by target modification. However, the evolution of a GS-resistant EPSP synthase under non-selective growth conditions indicates that GS resistance causes fitness costs. Therefore, in both model organisms, the proper function of the EPSP synthase is critical for the cellular viability. This study also revealed that the uptake systems for folate precursors, phenylalanine and tyrosine need to be identified and characterized in B. subtilis.
Bibliographical noteFunding Information:
This work was supported by the University of Göttingen, the BTU Cottbus‐Senftenberg and the University of Hohenheim. We are grateful to the members of the Commichau laboratory for helpful comments. We acknowledge Jörg Stülke for financial and staff support and for providing laboratory space. The acknowledge funding from Deutsche Forschungsgemeinschaft (CO 1139/2‐2). We thank the participants of the microbiological practical course at the BTU Cottbus‐Senftenberg for isolating the environmental isolates. We are grateful to Georg Aschenbrand, Rica Bremenkamp, Yann Kurzaj, Sabine Lentes, Gisela Nagler and Carolina Santos for the help with some experiments. Open Access funding enabled and organized by Projekt DEAL. Bacillus
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