Integrative Chemical and Omics Analyses Provide Insights into Pentlandite Bioleaching by Acidithiobacillus ferriphilus WGS1

Pentlandite bioleaching offers a potentially low-energy route for nickel recovery from low-grade sulfide resources, but increasing pulp density may constrain acidophilic microorganisms through metal accumulation, mineral buffering, mass-transfer limitation, and surface-product deposition. This study evaluated pentlandite bioleaching by the nickel-resistant Acidithiobacillus ferriphilus WGS1 at pulp densities of 1%, 5%, and 10% (w/v). Leaching performance and associated interfacial and cellular responses were examined using solution chemistry, mineral and surface characterization, electrochemical measurements under 40 g/L Ni2+, and genome-guided transcriptomics. After 30 days at 35 °C, Ni leaching efficiencies reached 99.2%, 97.1%, and 95.7% at 1%, 5%, and 10% pulp densities, respectively, compared with 27.2%, 14.2%, and 0.76% in the corresponding sterile controls. The inoculated systems maintained lower pH and higher ORP than the sterile controls, while the residues showed pentlandite alteration, Ni depletion, secondary Fe-bearing phase formation, and changes in surface sulfur speciation. Under 40 g/L Ni2+, the WGS1-containing system showed a lower charge-transfer resistance and a higher corrosion current density than the abiotic system. Transcriptomic comparison between the 10% and 1% pulp-density groups identified 640 differentially expressed genes and highlighted candidate responses associated with Ni homeostasis, Fe/S oxidation, respiratory electron transfer, and energy conservation. Integration of the physicochemical, mineralogical, electrochemical, and transcriptomic results supports a literature-informed working model for WGS1-associated pentlandite bioleaching under high-pulp-density conditions.