The enhanced effect and mechanism of sigma factor RpoF on Li bioleaching by Pseudomonas aeruginosa

As the main component of spent lithium-ion batteries, LiCoO₂ is toxic to ecosystem and human health, moreover Li recovery is of great significance for resources sustainability. Although strain modification is effective, metal liberation is still low since molecular manipulations on functional genes are hard to cause the overall optimization. Based on the bioleaching complexity, global transcription factors show greater advantage in the complex phenotype improvement because they locate at the top of the intracellular pyramid-shaped transcriptional regulatory network and thus tend to yield global disturbance. Herein, Pseudomonas aeruginosa PAO1 with the best performance was selected as a starting strain, which was proved to possess acidolysis and contact mechanisms. Subsequently, various global transcriptional factors were separately introduced and RpoF overexpression strain achieved the maximum Li concentration of 597.9 mg/L, which was 65.38 % higher than the wild-type strain. The comprehensive analysis at the levels of cell, metabolite and gene transcription confirmed RpoF global regulation. At the bioleaching system, the largest viable cell count was increased by 36.65 % to maintain cell populations, the highest 2-keto-D-gluconic acid and D-gluconic acid contents were respectively boosted by 8.51 % and 9.15 % to drive acid hydrolysis, and the most biofilm formation was strengthened by 78.68 % to facilitate cell-to-cell adhesion on the metal powder. Furthermore, biofilm reinforcement was attributed to more c-di-GMP and quorum sensing (QS) signal molecules contents, lower cell motility and higher cell specific surface area. Our results verified that RpoF was an efficient element for engineering bioleaching strains, also deepened the understanding of its regulatory mechanism.