Abstract

Heavy metal contamination poses a global threat due to its high toxicity and widespread occurrence. Among various methods, phytoremediation has emerged as a preferred approach for the bioremediation of heavy metal-contaminated soils. The search for microorganisms that facilitate phytoremediation has become critically important to advance ecosystem remediation efforts. In recent decades, plant growth promoting bacterias (PGPB) have garnered significant attention. In this context, the strain MOD5IV was isolated from the rhizosphere of a Caesalpinia spinosa plant thriving on mining waste in Andacollo, Chile. This strain was initially selected for its plant growth-promoting properties. This study presents a comprehensive analysis of the strain's functional and genomic characteristics. MOD5IV exhibited notable PGPB features, including phosphate and potassium solubilization, nitrogen fixation, phytohormone production (IAA), and growth promotion of Arabidopsis thaliana. Genomic analysis, conducted using both Illumina® and Nanopore® platforms, revealed a chromosome size of 5,254,635 bp and nine distinct plasmids housing over six thousand genes. Phylogenetic analysis classified the strain within the species Priestia megaterium (formerly Bacillus). Functional gene annotation identified 16 genes associated with tolerance to metals and metalloids, including arsenic (arsB/arsC) and copper (copC/copD), as well as genes conferring resistance to cadmium, lead, mercury, zinc, and cobalt. The strain exhibited high tolerance to multiple metals, notably copper, arsenic, chromium, and lead. Regarding its PGPB capabilities, MOD5IV possesses 21 genes related to siderophore production, 12 for nutrient solubilization, 10 for IAA synthesis, and 11 for nitrogen fixation. Furthermore, MOD5IV showed the ability to promote the growth of C. spinosa grown on tailing material in laboratory experiments, increasing its capacity to accumulate copper. Overall, Priestia megaterium MOD5IV exhibits promising traits for use in microbe-assisted phytoremediation of metal-contaminated soils.