Abstract
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 Streptomyces species in the rhizosphere typically concurs root impairment associated with ARD. However, possible roles of Streptomyces 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-HRMSn) to evaluate the chemical ecology of an apple root-associated Streptomyces ciscaucasicus 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 Streptomyces pulveraceus strain ES16 and the pathogen Cylindrocarpon olidum. 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 HRMSn 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 S. ciscaucasicus strain GS2 in the rhizosphere.
Highlights
The recultivation of plants in the soil where identical species were previously cultivated may reduce plant growth and lower fruit yield and quality [1]
We evaluated the dynamics of siderophore production under the combined influence of chemical and biological One Strain Many Compounds (OSMAC) triggers, temporally over 3, 7, and 14 days, to discern the strain’s siderophore-mediated chemical ecology
Their uptake is enabled via a group of chemically diverse small organic molecules known as siderophores, with receptors that have a high affinity for the valuable ferric ion
Summary
The recultivation of plants in the soil where identical species were previously cultivated may reduce plant growth and lower fruit yield and quality [1]. S. ciscaucasicus GS2 started producing ferrioxamine B (1) already by the third day in axenic culture and all co-cultivations on GYM agar and PDA. During co-cultivation with C. olidum, the bacterium started producing compound 3 at high amounts (I ≈ E6), which remained the same throughout the 14 days of observation, while in axenic cultures and during co-cultivation with S. pulveraceus ES16, the intensities were 20-fold less (I ≈ 4.47E6 vs I ≈ 5.3E4 and vs I ≈ 2.1E4) on the third day and increased with time (to I ≈ E6). Desferrioxamine D2 (6) was not produced by S. ciscaucasicus GS2 in axenic cultures on any tested media and during co-cultivation with C. olidum, similar to compound 5 It was only produced during co-cultivation with S. pulveraceus ES16 on PDA and GYM agar. From the seventh to the 14th day, there was a very slight increase observed in both cases
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