Cadmium and cadmium-tolerant soil bacteria in cacao crops from northeastern Colombia.

AIMS: This research aims to assess total-cadmium soil content and microbiological aspects to understand the dynamics of culturable cadmium-tolerant bacteria (CdtB) in cacao soils from northeastern Colombia.

METHODS AND RESULTS: An integration of inverted dish plating, Cd determination and a microcalorimetry assay (IMC) was carried out. A farm in Boyacá showed the highest level of total soil Cd (3·74 mg kg-1 ) followed by farms in Santander and Arauca (2·76 and 1·16 mg kg-1 , respectively). Coefficient of determination between total soil Cd and CFU of CdtB was high (R2  = 0·83) for the farm in Boyacá. Moreover, a pool of 129 CdtB was isolated, and phylogeny of 21 CdtB was discussed. Among CdtB strains isolated, Enterobacter sp. CdDB41 showed major Cd immobilization capacity (Qmax of 2·21 and 2·32 J at 6 and 24 mg l-1 of CdCl2 ), with an immobilization rate of 0·220 mg kg-1  h-1 .

CONCLUSIONS: Among CdtB strains isolated, Enterobacter sp. CdDB41 showed major Cd immobilization capacity (Qmax of 2·21 and 2·32 J at 6 and 24 mg l-1 of CdCl2 ), with an immobilization rate of 0·220 mg kg-1  h-1 .

SIGNIFICANCE AND IMPACT OF THE STUDY: Nothing is known about soil CdtB in cacao. Our data showed that CdtB such as Enterobacter sp. has high immobilization capacity. Furthermore, the otavite found in situ might be mineralized due to the bacterial metabolic activity of CdtB.