Enrichment of lithium by lithium-accumulating bacteria and its enhancement by electrical stimulation

Bioaccumulation of lithium by lithium-accumulating bacteria is a promising alternative approach for unconventional lithium resources extraction. Current researches on the bioaccumulation of lithium remain insufficient. To isolate lithium-accumulating bacteria, 10 lithium-tolerant bacteria strains with various lithium tolerance (30-100 g/L LiCl) were isolated from sediment of the Zongmahai Salt Lake in Qinghai Province. Brevibacterium profundi NCSL-YWD1 and Staphylococcus saprophyticus NCSL-YWH2 exhibited the highest lithium tolerance by secreting more extracellular polymeric substances (EPS) with fulvic-acid and aromatic protein substances and altering the morphologies with irregular shapes. Also, they demonstrated promising lithium removal potential in 3 simulated systems including seawater (0.17  mg/L Li), oilfield brine (40  mg/L Li), and salt lake brine (180  mg/L Li). Typically, NCSL-YWH2 performed excellent lithium-accumulating capacity (2.59 mg Li/g dry cell) with the removal ratio of 23.7% from the solution of 40 mg/L Li, which was the highest microbial lithium-enrichment among the publicly available studies. Furthermore, electrical stimulation (electric field of 0.8 V/cm) was applied for the first time to enhance lithium-accumulation to 4.08 mg Li/g dry cell, with the increased removal ratio of 35.6% and reduced time of 1 h from the solution of 40 mg/L Li, attributed to mechanisms of the electroporation, electrophoresis, and possible depolarization. This study isolated a lithium-accumulating bacteria strain with the highest Li accumulation and first revealed the enhancement potential of electrical stimulation on lithium accumulation.