Siderophore Production by a Rhizosphere-Associated Streptomyces from Cyperus virens

Rhizosphere microbiomes produce iron chelators or siderophores to capture ferric iron, an essential nutrient for growth that is not always bioavailable. Plants with siderophore activity aid in phytoremediation by removing heavy metals and other pollutants. The Cyperus genus of plants has a high affinity for iron uptake in the phytoremediation of wastewater. Herein, we isolated a siderophore-producing microbe from the rhizosphere of Cyperus virens, an understudied member of this genus, using the Chrome Azurol S (CAS) assay. While this isolate has siderophore activity, it did not exhibit antimicrobial activity when plated on Aspergillus niger, A. flavus, or Bacillus subtilis. The isolate was identified as Streptomyces sp. PD-S100-1 through genomic sequencing and de novo assembly with a draft genome size of 8.2 Mbp and 73% GC content. antiSMASH analysis of the genome identified several siderophore biosynthetic gene clusters, including those involved in the production of mirubactin A and bacillibactin. Liquid chromatography-mass spectrometry (LC-MS) detected several siderophores, including mirubactin A–D, enterobactin, and other catecholates from these siderophore families. The positive CAS assay, siderophore gene cluster identification, and LC-MS/MS analyses show that the rhizosphere of C. virens contains siderophore-producing bacteria. Most detected metabolites, including enterobactin, increased in the presence of cerium, a lanthanide involved in the expression of secondary metabolites, whereas mirubactin production was reduced. The presence of rhizosphere siderophore-producing bacteria suggests that C. virens may have potential applications in environmental phytoremediation, targeting pollutants from wastewater, mining, agriculture, and energy production. KEYWORDS: Siderophore; Mirubactin A; Enterobactin; Bacillibactin; Rhizosphere; Cyperus virens; Streptomyces; CAS Assay