Isolation of a lipase-producing strain from yuncheng salt lake and enhancement of lipase activity via UV mutagenesis.

Enhancing lipase activity and tolerance can help address energy and environmental challenges. Expanding lipase sources, increasing their activity, and improving their tolerance under various conditions are urgently needed. A water sample collected from Yuncheng Salt Lake was plated using the "double-layer plate" method to isolate "hard-to-culture" microbes, and a selective medium was used to screen the isolated strain L5, which showed lipase activity. Gram staining and morphological observation, combined with 16 S rRNA gene sequencing and phylogenetic analysis, were used to preliminarily identify this isolate. Culture conditions and enzymatic reaction parameters before and after UV mutagenesis were optimized, and the lipase activities of the parent and mutant strains were compared. The results showed that strain L5, isolated from Yuncheng Salt Lake, possessed lipase activity, was Gram-positive, and was preliminarily identified as a Bacillus seohaeanensis-like strain. The optimum NaCl concentration for the growth of L5 was 15.0%, the optimum pH was 8.0, and the highest cell density was reached at 48 h. For the crude lipase of L5, the optimum NaCl concentration was 25.0%, the optimum reaction temperature was 35.0 °C, and the highest activity was observed at pH 8.0. Trichloromethane had only a minor effect on enzyme activity. After UV mutagenesis and screening, mutant strain L5M exhibited significantly enhanced lipase activity, with maximum activity achieved at 25.0% NaCl, 35.0 °C, and pH 8.0. The mutated enzyme not only tolerated trichloromethane but also retained appreciable activity after tris-aminomethane treatment. Under the optimized conditions, the lipase activity of the mutated strain L5M reached 161.4 ± 5.4 U/mL, 2.96-fold higher than that before UV mutagenesis (54.6 ± 4.7 U/mL). UV mutagenesis improved L5 lipase activity and tolerance, showing better application prospects in environments with drastically fluctuating conditions.