Summary: The oxalate–carbonate pathway involves the oxidation of calcium oxalate to low‐magnesium calcite and represents a potential long‐term terrestrial sink for atmospheric CO ₂ . In this pathway, bacterial oxalate degradation is associated with a strong local alkalinization and subsequent carbonate precipitation. In order to test whether this process occurs in soil, the role of bacteria, fungi and calcium oxalate amendments was studied using microcosms. In a model system with sterile soil amended with laboratory cultures of oxalotrophic bacteria and fungi, the addition of calcium oxalate induced a distinct pH shift and led to the final precipitation of calcite. However, the simultaneous presence of bacteria and fungi was essential to drive this pH shift. Growth of both oxalotrophic bacteria and fungi was confirmed by qPCR on the frc (oxalotrophic bacteria) and 16 S rRNA genes, and the quantification of ergosterol (active fungal biomass) respectively. The experiment was replicated in microcosms with non‐sterilized soil. In this case, the bacterial and fungal contribution to oxalate degradation was evaluated by treatments with specific biocides (cycloheximide and bronopol). Results showed that the autochthonous microflora oxidized calcium oxalate and induced a significant soil alkalinization. Moreover, data confirmed the results from the model soil showing that bacteria are essentially responsible for the pH shift, but require the presence of fungi for their oxalotrophic activity. The combined results highlight that the interaction between bacteria and fungi is essential to drive metabolic processes in complex environments such as soil.

Cadmium (Cd) is considered a toxic heavy metal, nevertheless, its toxicity fluctuates for different organisms. Cadmium-tolerant bacteria (CdtB) are a diverse and non-phylogenetically related. Because of their ecological importance these bacteria become particularly relevant when pollution occurs and where human health is impacted. The aim of this minireview is to show the significance, culturable diversity, metabolic detoxification mechanisms of CdtB and their current uses in several bioremediation processes applied to agricultural soils. Further discussion addressed the technological devices and the possible advantages of genetically modified CdtB for diagnostic purposes in the future. Significance and Impact of Study Crop production is adversely affected by the presence of heavy metals in soils dedicated to domesticated plants. These metals ultimately accumulated in seeds or edible parts and enter the human food chain. The exploitation of CdtB capacities for immobilization and cadmium sequestration, in combination with soil management and visitation of agronomic practices, may reduce the Cd levels in farmlands.

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 (Q_max 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 (Q_max 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.

This study represents the first nationwide survey regarding the distribution of Cd content in cacao-growing soils in Colombia. The soil Cd distribution was analyzed using a cold/hotspots model. Moreover, both descriptive and predictive analytical tools were used to assess the key factors regulating the Cd concentration, considering Cd content and eight soil variables in the cacao systems. A critical discussion was performed in four main cacao-growing districts. Our results suggest that the performance of a model using all the variables will always be superior to the one using Zn alone. The analyzed variables featured an appropriate predictive performance, nonetheless, that performance has to be improved to develop a prediction method that might be used nationwide. Results from the fitted graphical models showed that the largest associations (as measured by the partial correlation coefficients) were those between Cd and Zn. Ca had the second-largest partial correlation with Cd and its predictive performance ranked second. Interestingly, it was found that there was a high variability in the factors correlated with Cd in cacao growing soils at a national level. Therefore, this study constitutes a baseline for the forthcoming studies in the country and should be reinforced with an analysis of cadmium content in cacao beans.