Ciprofloxacin triggers L-glutamate production by Corynebacterium glutamicum

Ciprofloxacin, an inhibitor of bacterial gyrase and topoisomerase IV, was shown to inhibit growth of C. glutamicum with concomitant excretion of L-glutamate. C. glutamicum strains overproducing L-lysine, L-arginine, L-ornithine, and putrescine, respectively, produced L-glutamate instead of the desired amino acid when exposed to ciprofloxacin. Even in the absence of the putative L-glutamate exporter gene yggB, ciprofloxacin effectively triggered L-glutamate production. When C. glutamicum wild type was cultivated under nitrogen-limiting conditions, 2-oxoglutarate rather than L-glutamate was produced as consequence of exposure to ciprofloxacin. Transcriptome analysis revealed that ciprofloxacin increased RNA levels of genes involved in DNA synthesis, repair and modification. Enzyme assays showed that 2-oxoglutarate dehydrogenase activity was decreased due to ciprofloxacin addition. Here, it was shown for the first time that production of L-glutamate by C. glutamicum may be triggered by an inhibitor of DNA synthesis and L-glutamate titers of up to 37 ± 1 mM and a substrate specific L-glutamate yield of 0.13 g/g were reached. The gene expression was analyzed in the C. glutamicum WT strain. Direct comparison and analysis of expression response to 4 µg/ml ciprofloxacin addition in CGXII minimal medium with 10 g/L glucose.