This study analyzed the thermostability and effect of calcium ions on the enzymatic activity of α-amylase produced by Bacillus licheniformis strain LB04 isolated from Espinazo Hot springs in Nuevo Leon, Mexico. The enzyme was immobilized by entrapment on agar-agarose beads, with an entrapment yield of 19.9%. The identification of the bacteria was carried out using 16s rDNA sequencing. The enzyme was purified through ion exchange chromatography (IEX) in a DEAE-Sephadex column, revealing a protein with a molecular weight of ≈130 kDa. The enzyme was stable at pH 3.0 and heat stable up to 80 °C. However, the optimum conditions were reached at 65 °C and pH 3.0, with a specific activity of 1851.7 U mg⁻¹ ± 1.3. The agar-agarose immobilized α-amylase had a hydrolytic activity nearly 25% higher when compared to the free enzyme. This study provides critical information for the understanding of the enzymatic profile of B. licheniformis strain LB04 and the potential application of the microorganisms at an industrial level, specifically in the food industry.

Maize and Indian mustard plants were studied to: 1) investigate the effect of Cl⁻ complexation on Cd uptake from soil historically amended with sewage sludge (Cd 58 mg kg⁻¹) and, 2) model the uptake of Cd by these plants with a Free Ion Activity Model (FIAM). Plants were treated with NaCl (50 to 300 mM in the soil pore water) along with controls using Na₂SO₄. Cadmium enhanced solubility in soil by Cl⁻ generally reflected increases in Cd uptake by both plants. The free ion Cd²⁺ activity in soil solution, as modeled by WHAM-VI, remained almost unchanged despite the wide range of NaCl concentrations. Therefore, Na⁺ exchange for Cd²⁺ could not fully explain the differences in Cd content between the Cl⁻ treatments because of the high buffering Cd²⁺ capacity in soil. Activities of Cd-chloro complexes showed the best correlations with the Cd concentrations in the plants compared to the activity of Cd²⁺. The FIAM showed a reasonable good fit for the plants when assuming competition by Cd²⁺ and CdCl⁺ for root sorption sites. Indirect evidence suggests that CaSO₄ precipitation may have limited the formation of CdSO₄ complexes and reduced Cd soil solubility. The implications of these results for phytoremediation are discussed.