Production and functional characterization of an opine-type metallophore from the endophytic Priestia sp. GS2 with potential for heavy metal chelation and plant growth promotion

Iron and other metal deficiencies in soil are significant challenges in agriculture, as almost 30% of the world’s farmland consists of calcareous soils, limiting the availability of these essential cations for plants. Although plants have developed a few strategies to mitigate such deficiencies and their negative effects on their health and development, they are insufficient, and plants heavily rely on microorganisms in their vicinity. Among the many plant-associated microorganisms, endophytic bacteria constitute the most interesting and least known group, as they live inside plant tissues without causing any apparent harm to their host. Under metal-deprived conditions, many endophytes synthesize metallophores, low-mass compounds that bind a broad range of heavy metal ions, thereby enhancing their availability. This study characterizes the metallophore-producing endophytic strain Priestia sp. GS2 (originally isolated from Galium aparine L.) and investigates the influence of culture conditions on metallophore production using single-factor experiments and the Taguchi experimental design. Functional characterization indicates that the produced metallophore is predominantly carboxylate in nature, consistent with opine metallophore biosynthetic gene cluster identified in strain’s genome. In addition to its Fe-chelating capacity, the metallophore exhibited affinity for Cu 2+ , Ni 2+ , and Co 2+ . The most consistent and beneficial priming effects of this metallophore on beetroot seeds are observed under Zn, Cd, Hg, and Co stress, through improvement of germination rates, root elongation and increased plant biomass. These findings demonstrate the broad metal-chelating capacity of metallophore produced by Priestia sp. GS2 and its potential beneficial effects on seed germination and plant growth under metal stress conditions. The cell-free metallophore-enriched preparation obtained from this bacterium represents a promising candidate for further investigation as a biostimulant to support crop production in metal-contaminated soils.