UV-Mutated Salt Lake Bacterium Triples Lipase Output for Greener Industry

Deep in the briny waters of Yuncheng Salt Lake in China’s Shanxi Province, scientists have unearthed a microscopic workhorse with the potential to reshape how industry handles fats, oils, and biodiesel. A research team led by Kai Chen and Chuanxu Wang of Yuncheng University has isolated a halophilic bacterium capable of producing a robust, salt-loving lipase enzyme, then supercharged its output nearly threefold using nothing more than ultraviolet light. The findings, published in the journal International Microbiology, offer a striking example of how extreme environments can yield enzymes that conventional laboratory strains simply cannot match.

The story begins with a problem that has long frustrated microbiologists: most microorganisms in nature refuse to grow on standard laboratory media. In a salt lake where salinity reaches nearly 29 percent, the microbial residents are especially finicky, often depending on chemical signals and metabolites from neighboring species to survive. To overcome this, the team employed a clever technique known as the double-layer plate method. Rather than isolating bacteria alone, they first cultivated a fast-growing helper strain from the same lake water, then poured a fresh layer of nutrient agar over it, sandwiching the helper below while spreading diluted lake samples on top. The helper strain, safely separated by the agar barrier, released diffusible growth factors that seeped upward and coaxed reluctant organisms into growth without physical contact.

This approach proved remarkably effective. From the double-layer plates, the researchers recovered sixteen isolates whose growth was dramatically stimulated by the helper strain, including three that barely grew at all without it. When these isolates were screened on medium containing Tween-20, a detergent substrate that lipase-producing microbes visibly break down, six strains developed telltale precipitation zones. One of them, designated strain L5, produced the largest and clearest zone, signaling the strongest lipolytic activity. Gram staining revealed a rod-shaped, Gram-positive bacterium, and sequencing of its 16S rRNA gene placed it firmly within the Bacillus seohaeanensis lineage, with sequence similarity exceeding 97.1 percent.

Characterizing strain L5 revealed a set of growth preferences that immediately marked it as something unusual. The bacterium reached peak density in medium containing 15 percent sodium chloride, thriving across a range of 12 to 18 percent and maintaining measurable growth even at a staggering 30 percent salinity. Its optimal pH was a mildly alkaline 8.0, and cell density peaked after 48 hours of incubation at 37 degrees Celsius. These traits classify L5 as a borderline extreme halophile, an organism that has evolved its entire cellular machinery to function in conditions that would rapidly desiccate and kill ordinary bacteria. The researchers noted that this classification places the strain squarely within a group of microbes whose intracellular enzymes require salt to maintain their folded, active conformations.

When the team turned to the crude lipase secreted by L5, the enzyme’s profile proved even more interesting than the organism itself. Maximum catalytic activity emerged at 25 percent sodium chloride, a concentration at which most industrial enzymes would be irreversibly inactivated. The optimal reaction temperature was a moderate 35 degrees Celsius, yet the enzyme retained substantial activity even at 50 degrees, reaching 32.3 units per milliliter at that elevated temperature. Activity peaked at pH 8.0 and remained strong from pH 7.0 through 10.0, dropping only under acidic conditions. Perhaps most notably, the enzyme shrugged off trichloromethane exposure, retaining approximately 77.9 percent of its original activity after treatment, while formaldehyde, glacial acetic acid, and isopropanol proved far more damaging. This combination of halotolerance, alkaline preference, and solvent resistance is rare in mesophilic lipases and positions the L5 enzyme as a candidate for processes involving high-salt organic wastewater, textile processing, and tanning operations where conditions fluctuate wildly.

Yet even the most promising wild isolate rarely produces enough enzyme for commercial viability. Wild-type strains typically secrete low titres, and the gap between laboratory discovery and industrial production is often bridged by mutagenesis breeding. The team chose ultraviolet irradiation, a classical and widely used physical mutagen prized for its simplicity, speed, and track record in industrial microbiology. Exposing L5 cultures to a 30-watt UV lamp at a fixed distance of 20 centimeters, they tested exposure times ranging from 30 seconds to 240 seconds. Lethality climbed steeply with duration, reaching 77.5 percent at 60 seconds and 99.2 percent at 240 seconds. From the survivors of the 120-second treatment, they selected a colony designated L5M that displayed the highest lipase activity among all mutants screened.

The results of the mutagenesis were striking. Under optimized conditions of 25 percent sodium chloride, 35 degrees Celsius, and pH 8.0, the mutant strain L5M produced a crude lipase with a maximum activity of 161.4 plus or minus 5.4 units per milliliter, compared with 54.6 plus or minus 4.7 units per milliliter from the parent strain. That represents a 2.96-fold enhancement achieved through a single round of UV exposure and screening. At the enzyme’s optimal salt concentration, activity jumped from 37.6 to 133.9 units per milliliter, an approximately 3.6-fold increase at that specific point. Across the temperature range from 20 to 50 degrees Celsius, the mutant enzyme consistently surpassed the parent’s peak activity, and at 50 degrees it still delivered 120.4 units per milliliter. Every pH value tested also exceeded the pre-mutation maximum, with the mutant reaching 152.3 units per milliliter at pH 8.0.

Tolerance improvements extended beyond raw activity figures. The mutant lipase not only maintained robust resistance to trichloromethane, retaining 126.6 units per milliliter after solvent treatment, but also acquired a new tolerance to tris-aminomethane, a buffering compound that had nearly destroyed the parent enzyme’s activity, reducing it to just 3.4 units per milliliter. The mutant retained 85.4 units per milliliter under the same treatment. The organism itself also showed expanded resilience, growing vigorously across a broader salinity range and tolerating pH values up to 10.0 with less decline than the parental strain. These gains suggest that UV-induced mutations affected not only the lipase structural gene or its regulatory elements but potentially the broader cellular stress-response networks that govern enzyme stability in harsh environments.

The implications reach well beyond a single enzyme. Lipases of the EC 3.1.1.3 class are among the most versatile industrial biocatalysts, driving reactions in biodiesel synthesis, food processing, pharmaceutical production, and flavor chemistry, where they catalyze the formation of short-chain esters such as ethyl hexanoate, the compound responsible for pineapple and apple aromas. The current benchmark enzyme, Candida antarctica lipase B, suffers from poor thermal stability above 60 degrees Celsius and restrictive patent protection on commercial formulations. Enzymes from halophilic sources like L5M offer a complementary solution, maintaining catalytic efficiency under the high-salt, alkaline, and solvent-laden conditions that define many real-world industrial processes without requiring costly buffer exchanges or pretreatment steps.

The study also demonstrates that the double-layer plate method, adapted here for the first time to a hypersaline inland lake, provides a practical pipeline for recovering hard-to-culture extremophiles in a form compatible with enzyme-directed screening. By embedding a helper strain between two agar layers, the technique preserves the metabolic interdependencies that sustain microbial life in situ while allowing conventional purification downstream. Combined with UV mutagenesis, it offers a low-cost, equipment-light strategy for converting environmental biodiversity into industrial biocatalysts. As demand grows for enzymes that can operate in seawater-based biorefineries, high-salinity waste streams, and fluctuating thermal environments, the halophilic Bacillus strains of salt lakes like Yuncheng are likely to attract increasing attention as natural repositories of robust, commercially valuable biological catalysts.

Subject of Research: Isolation and UV-mutagenesis enhancement of a halophilic lipase-producing Bacillus strain from Yuncheng Salt Lake

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

Article References: Isolation of a lipase-producing strain from yuncheng salt lake and enhancement of lipase activity via UV mutagenesis. (n.d.). https://doi.org/10.1007/s10123-026-00900-6

Image Credits: AI Generated

DOI: 10.1007/s10123-026-00900-6

Keywords: lipase, halophilic bacteria, Yuncheng Salt Lake, UV mutagenesis, Bacillus, extremozymes, biodiesel, salt tolerance, industrial enzymes, biocatalysis, microbiology, enzyme engineering