Anika Rütten (Stuttgart / DE), Inge Schwedt (Marburg / DE), Maike Eckert (Stuttgart / DE; Marburg / DE), Franka Kemmler (Stuttgart / DE), Fabian M. Commichau (Stuttgart / DE)
The best known and most widely used herbicide worldwide is glyphosate [1]. The non-selective, systemic broad-spectrum herbicide glyphosate (N-(phosphonomethyl)-glycine) is used against all types of weeds that compete with agricultural crops [1]. Glyphosate acts specifically on the 5-enolpyruvyl shikimate-3-phosphate (EPSP) synthase, which makes the EPSP synthase of bacteria an attractive target for antibiotics and herbicides. The EPSP synthase is involved in the synthesis of chorismate from shikimate-3-phosphate (S3P) and phosphoenolpyruvate (PEP), which is an essential precursor for the de novo synthesis of aromatic amino acids, folates (essential for purine and pyrimidine synthesis) and quinones (essential electron carrier in the respiratory chain) [2]. It has already been shown that the enzyme function of EPSP synthase in Bacillus subtilis is essential for growth in minimal medium and complex medium such as LB [3]. A B. subtilis deletion mutant in which the aroE gene coding for EPSP synthase has been deleted can still grow in complex BHI medium [3]. This is possible because B. subtilis apparently has unknown uptake systems for all chorismate derivatives and aromatic amino. Nevertheless, it has not yet been possible to cultivate an aroE deletion mutant stably in a minimal medium. For this purpose, the exact, minimal nutrient composition is to be determined. This can be achieved by characterizing suppressors of the aroE deletion mutant, which frequently contain mutations in genes encoding the ResED 2-component system, which is responsible for switching from aerobic to anaerobic metabolism [4]. This indicates that there is an imbalance in the menaquinone pool and the NADH+H+/NAD+ ratio during growth of the aroE mutant in minimal medium, which can be restored by suppressor mutations. Comprehensive suppressor analysis to understand the effect of aroE deletion on the physiology of the cell will be done. Also, stably growing aroE mutants will be established to identify additional glyphosate targets in B. subtilis. Subsequently, identification of aromatic amino acid transporters in B. subtilis will be performed.
[1] Duke and Powles (2008) Pest Manag Sci 64: 319-325.
[2] Hermann and Weaver (1999) Annu Rev Plant Physiol Plant Mol Biol 50: 473-503.
[3] Schwedt et al. (2023) Environ Microbiol 25: 3604-3622.
[4] Härtig and Jahn (2012) Adv Microb Physiol 61: 195-216.
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