Abstract A mitigation strategy involving the application of cadmium-tolerant bacteria (CdtB) was assessed in cacao soils in farms in Arauca, Colombia. The bacterial strain used, Pseudomonas chlororaphis CdtBSO has exhibited an ability to immobilise cadmium, reducing its bioavailability to cacao. The aim of this study was to increase the immobilization activity of CdtB in cacao soils in Arauca. Five treatments combining different concentrations of CdtB with a synthetic fertiliser (Agrocacao) and zeolite were established. The cadA gene as marker for Cd immobilization was detected using droplet digital PCR (ddPCR). Moreover, the metabolic activity of CdtB was assessed using isothermal microcalorimetry (IMC). Maximum thermal performance was observed in the treatments where the most CdtB was applied. However, the results were highly dependent on the site. An increase in soil Cd content six months after application of the treatments was observed suggesting increased immobilization rates of the metal in the soil. The explanation of possible immobilisation mechanisms varied between treatments. However, the treatment showing the most positive trends included 50% CdtB and 50% Agrocacao. The detection of the cadA gene, revealed variations in the relative abundance of the copies of the gene in the assessed soils. This work contributes to the knowledge on soil Cd bioremediation using CdtB, through the application of innovative approaches to monitoring, such as ddPCR and IMC. It enriches the information available on the application of physicochemical and biological amendments for the remediation of Cd in real cacao crop conditions.
Alvarez-Rubiano et al. (Thu,) studied this question.