Norma Urtiz-Estrada

The increasing global demand for energy has intensified the need for lithium, a critical component in rechargeable batteries and electric vehicles. However, conventional lithium extraction methods are associated with significant environmental impacts. In this study, a one-step bioleaching approach for lithium recovery from mineral concentrates was evaluated using native microbial consortia and isolated bacterial strains. A suitable culture medium was selected, individual strains were isolated, and bioleaching experiments were conducted using a Box–Behnken experimental design. Lithium solubilization and cell density were assessed under different agitation conditions, pulp concentrations, and initial pH values. The highest lithium solubilization (99%) was achieved under non-agitated conditions, with a pulp concentration of 30% and an initial pH of 6. Three bacterial strains (ITDB101, ITDR102, and ITDN103) were identified. The native microbial consortium and the biotic control exhibited the highest lithium solubilization efficiencies (94.5% and 96.3%, respectively), outperforming the individual strains, which achieved solubilization values ranging from 91.73% to 93.27%. X-ray diffraction analysis identified five mineral phases in the concentrate, and comparisons among treatments revealed changes in these phases following bioleaching, supporting the potential of this process as an environmentally friendly alternative for lithium extraction.

Yeast surface display is a powerful strategy for enzyme immobilization and whole-cell biocatalysis; however, the intracellular processing of heterologous enzymes during secretion and anchoring remains poorly understood. In this study, a GH5 endoglucanase gene (eglS, 1.4 kb) from Bacillus subtilis, originally isolated from a paper mill effluent, was cloned into the pYD1 vector and expressed in Saccharomyces cerevisiae EBY100 using the Aga1–Aga2 surface display system. The recombinant strain produced clear degradation halos on carboxymethyl cellulose (CMC) plates, confirming cellulolytic activity at the whole-cell level. Zymographic analysis revealed multiple active enzyme forms depending on the cellular fraction analyzed. Intracellular extracts displayed active bands ranging from 70 to 57 kDa, consistent with immature or partially processed Aga2 fusion proteins, whereas cell wall-associated fractions showed active bands between 55 and 35 kDa, suggesting proteolytic processing during secretion and surface anchoring. The apparent specific activity of the cytoplasmic fraction was 5.33 ± 0.31 U mg⁻¹, while the cell wall-associated fraction exhibited a higher apparent specific activity (58.4 ± 10.1 U mg⁻¹). Although these values were obtained from non-purified fractions and therefore do not represent intrinsic enzymatic constants, they indicate a relative enrichment of catalytically active enzyme in the cell wall-associated fraction, consistent with functional surface display. The presence of multiple active enzyme forms and the enhanced catalytic efficiency observed in the cell wall-associated fraction suggest that the engineered yeast strain may serve as a promising whole-cell biocatalyst, with potential applications in consolidated bioprocessing (CBP) strategies for lignocellulosic biomass conversion.