Microbial bioindicators associated with cadmium uptake in sixteen genotypes of .

Recent regulatory limits on concentrations of cadmium (Cd), an element of concern for human health, have made Cd reduction a key issue in the global chocolate industry. Research into Cd minimization has investigated soil management, cacao genetic variation, and postharvest processing, but has overlooked the cacao-associated microbiome despite promising evidence in other crops that root-associated microorganisms could help reduce Cd uptake. A novel approach combining both amplicon and metagenomic sequencing identified microbial bioindicators associated with leaf and stem Cd accumulation in sixteen field-grown genotypes of . Sequencing highlighted over 200 amplicon sequence variants (ASVs) whose relative abundance was related to cacao leaf and stem Cd content or concentration. The two highest-accumulating genotypes, PA 32 and TRD 94, showed enrichment of four ASVs belonging to the genus , the family , and the order . ASVs whose relative abundance was most negatively associated with plant Cd were identified as sp. (β = -2.21), (β = -2.17), and (β = -2.03) for prokaryotes, and (β = -4.58) and two unidentified ASVs (β = -4.32, β = -3.43) for fungi. Only two ASVs were associated with both leaf and stem Cd, both belonging to the . Of 5543 C d-associated gene families, 478 could be assigned to GO terms, including 68 genes related to binding and transport of divalent heavy metals. Screening for Cd-related bioindicators prior to planting or developing microbial bioamendments could complement existing strategies to minimize the presence of Cd in the global cacao supply.