Isolation of native cadmium-tolerant bacteria and fungi from cacao (Theobroma cacao L.) - Cultivated soils in central Colombia

Abstract

Cadmium (Cd) is one of the most toxic heavy metals for human health. It can be present in multiple food products, including cocoa cultivated in regions with high soil Cd concentrations. A strategy to minimize Cd uptake by cacao trees is using cadmium-tolerant bacteria (CdtB) and filamentous fungi (CdtF) to reduce Cd availability in soils. We isolated culturable CdtB and CdtF from different locations in a cocoa-producing region in central Colombia. A total of 42 CdtB and 30 CdtF morphotypes were isolated from locations with varying natural Cd concentrations. In vitro characterizations showed that in addition to their resistance to Cd, bacteria and fungi are involved in the nutrient cycling of N, P, and C in the soil. Bacterial morphotypes from genera Pseudomonas and Burkholderia grew in concentrations up to 140 mg kg−1 Cd. Among the isolated fungi, P. igniaria, Metarhizium sp., and Annulohypoxylon sp. were the most resistant, with the highest average Cd bioaccumulation, Cd remotion, and tolerance. We present new information about the native culturable bacterial morphotypes associated with cacao plants and, to the best of our knowledge, this is the first report of Cd-TF associated with cacao crops. Our results expand the knowledge about culturable CdtB and CdtF in cacao-cultivated soils and their interaction with key soil elements, with the potential to develop integrated soil management strategies.