Production of Siderophores by an Apple Root-Associated Strain GS2 Using Chemical and Biological OSMAC Approaches.

Apple Replant Disease (ARD) is a significant problem in apple orchards that causes root tissue damage, stunted plant growth, and decline in fruit quality, size, and overall yield. Dysbiosis of apple root-associated microbiome and selective richness of species in the rhizosphere typically concurs root impairment associated with ARD. However, possible roles of secondary metabolites within these observations remain unstudied. Therefore, we employed the One Strain Many Compounds (OSMAC) approach coupled to high-performance liquid chromatography-high-resolution tandem mass spectrometry (HPLC-HRMS) to evaluate the chemical ecology of an apple root-associated strain GS2, temporally over 14 days. The chemical OSMAC approach comprised cultivation media alterations using six different media compositions, which led to the biosynthesis of the iron-chelated siderophores, ferrioxamines. The biological OSMAC approach was concomitantly applied by dual-culture cultivation for microorganismal interactions with an endophytic strain ES16 and the pathogen . This led to the modulation of ferrioxamines produced and further triggered biosynthesis of the unchelated siderophores, desferrioxamines. The structures of the compounds were elucidated using HRMS and by comparison with the literature. We evaluated the dynamics of siderophore production under the combined influence of chemical and biological OSMAC triggers, temporally over 3, 7, and 14 days, to discern the strain's siderophore-mediated chemical ecology. We discuss our results based on the plausible chemical implications of strain GS2 in the rhizosphere.