sp. G2112 Detoxifies Phenazine-1-carboxylic Acid by 5 Glucosylation.

Microbial symbionts of plants constitute promising sources of biocontrol organisms to fight plant pathogens. sp. G2112 and sp. G124 isolated from cucumber () leaves inhibited the plant pathogens and . When sp. G2112 and sp. G124 were co-cultivated, a red halo appeared around sp. G2112 colonies. Metabolite profiling using liquid chromatography coupled to UV and mass spectrometry revealed that the antibiotic phenazine-1-carboxylic acid (PCA) released by sp. G124 was transformed by sp. G2112 to red pigments. In the presence of PCA (>40 µg/mL), sp. G2112 could not grow. However, already-grown sp. G2112 (OD > 1.0) survived PCA treatment, converting it to red pigments. These pigments were purified by reverse-phase chromatography, and identified by high-resolution mass spectrometry, NMR, and chemical degradation as unprecedented 5-glucosylated phenazine derivatives: 7-imino-5-(1'β-D-glucopyranosyl)-5,7-dihydrophenazine-1-carboxylic acid and 3-imino-5-(1'β-D-glucopyranosyl)-3,5-dihydrophenazine-1-carboxylic acid. 3-imino-5-(1'β-D-glucopyranosyl)-3,5-dihydrophenazine-1-carboxylic acid did not inhibit sp. G2112, proving that the observed modification constitutes a resistance mechanism. The coexistence of microorganisms-especially under natural/field conditions-calls for such adaptations, such as PCA inactivation, but these can weaken the potential of the producing organism against pathogens and should be considered during the development of biocontrol strategies.