Author(s) :

Audrey Farrell, Robert Samples, Riccardo Racicot, Lesley-Ann Giddings.

Volume/Issue :

Abstract :

Siderophores, iron-chelating secondary metabolites, are crucial to plant growth and commonly produced by organisms in the rhizosphere. These specialized molecules have found applications across a wide range of industries, such as medicine and bioremediation. Members of the Lamiaceae family are environmentally beneficial for phytoremediation, the removal of heavy metals from soil, as chelated metals do not impact essential oil production. Herein, we used culture-based screening, genome sequencing, and LC-MS/MS metabolomics to recover and characterize a siderophore-producing bacterial isolate from the rhizosphere of Melissa officinalis, a medicinal member of the Lamiaceae family not previously studied in this context, and to evaluate cerium-associated changes in its metabolomic profile as an initial, exploratory step toward assessing its relevance to bioremediation. Using a Chrome Azurol S (CAS) assay, we isolated siderophore-producing bacteria. Genomic sequencing revealed that an isolate was Streptomyces sp. (AF-1A) with a genome size of 7.9 Mbp and 71.96% GC content. antiSMASH analysis revealed three siderophore biosynthetic gene clusters, one of which corresponded to the known cluster for desferrioxamines B and E. Several siderophores, including desferrioxamines B, E, D1, and G1, desoxynocardamine, and desmethylenylnocardamine, were putatively identified using LC-MS/MS. The latter four show a statistically significant increase in relative abundance in the presence of the rare earth element cerium; the remaining two (desferrioxamines B and E) were present at levels too low for quantitative comparison and were identified from MS/MS fragmentation alone. Nearly 40% of Streptomyces sp. AF-1A molecular features were exclusive to the rare earth element cerium conditions, suggesting this strain has a strong response in siderophore biosynthesis to lanthanide elicitation. AF- 1A shows a metabolomic response to environmental levels of cerium, warranting further investigation as a candidate for siderophore-based bioremediation strategies, pending direct tests of metal tolerance, chelation efficiency, and process-scale feasibility.