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Isolation, Production, Partial Purification, and Biochemical Characterization of a Thermophilic Alkaline Protease from Tuwa Hot Spring with Industrial Applications

Researchers isolated and characterized a highly thermostable and alkaline protease from *Bacillus licheniformis* MT_1, a bacterium found in Tuwa Hot Spring, Gujarat, which demonstrates optimal activity at pH 9.0 and 80°C, stability in harsh industrial conditions, and significant potential for detergent applications.

Original authors: Trivedi Mansi, Arya Prashant, Patel Jigisha, Patadia Hemantkumar

Published 2026-08-04

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Trivedi Mansi, Arya Prashant, Patel Jigisha, Patadia Hemantkumar

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine the microscopic world as a bustling city where tiny organisms are constantly building, breaking, and recycling. Among their most useful tools are enzymes, which act like specialized molecular scissors or glue. These biological tools are incredibly efficient, working faster and cleaner than many man-made chemicals. One specific type of enzyme, called a protease, is famous for its job of cutting up proteins. You might have seen these in action if you've ever used a stain remover on a shirt with a spaghetti sauce spill; the enzyme hunts down the protein in the stain and snips it into tiny, washable pieces.

Scientists are always on the hunt for "super-enzymes" that can work in tough conditions, like boiling hot water or very soapy environments, because these are the conditions found in industrial factories and laundry machines. Usually, enzymes are fragile and fall apart under such stress, but some microbes living in extreme places, like volcanic hot springs, have evolved to build enzymes that are tough as nails. These "thermophilic" (heat-loving) and "alkaline" (soap-loving) enzymes are the holy grail for industries looking to save energy and reduce pollution. The big question is: can we find a new, super-tough enzyme in a specific hot spring in India that is ready for real-world use?

This paper tells the story of a team of researchers who went on a treasure hunt in the Tuwa hot spring in Gujarat, India, to find exactly that. They collected water samples from the steaming, alkaline waters and started looking for bacteria that could survive the heat. Out of 25 different bacterial strains they found, they picked the five strongest protein-cutters and focused on one champion: a bacterium named Bacillus licheniformis MT_1. This little microbe turned out to be a factory for a very special enzyme.

The researchers grew this bacterium in large tanks and then tried to clean up the enzyme it produced, separating it from the other junk in the mixture. They used a method called "ammonium sulfate precipitation," which is a bit like adding salt to a soup to make the good ingredients clump together so they can be scooped out. This process made the enzyme about 1.08 times purer and kept 90.82% of the original enzyme's power, which is a pretty good recovery rate. When they looked at the enzyme under a microscope using a technique called SDS-PAGE, they saw a single, strong band, confirming they had a fairly clean sample. They calculated that this enzyme weighs about 29 kDa, which is like a medium-sized molecular brick.

The real magic happened when they tested how this enzyme behaved. They found that it loves heat and soap. Its "sweet spot" for working is at a temperature of 80°C and a pH of 9.0. To put that in perspective, 80°C is almost as hot as a boiling kettle, and a pH of 9.0 is quite alkaline, similar to baking soda or mild soap. Even after sitting in that hot environment for a long time, the enzyme didn't give up; it kept over 92% of its strength. It also showed it could handle being around certain metals like magnesium and manganese, which actually helped it work even better, though it got a little grumpy around iron. Interestingly, it could survive in some organic liquids (like ethanol) but got confused by others (like acetone).

The team also checked how fast the enzyme worked and how much "food" (protein) it needed to get going. They found it had a very strong appetite for its food, with a low number called a Km of 0.25 g%, meaning it grabs onto protein molecules very tightly. It could also work at a maximum speed (Vmax) of 5000 U/mL, which is a very high rate of cutting.

To see if this enzyme was actually useful, the researchers put it to work in two real-world scenarios. First, they tested it in a laundry setting. They took stained cotton cloth and washed it with just water, just detergent, just the enzyme, or a mix of detergent and enzyme. The mix of detergent and enzyme was the clear winner, cleaning the stains much better than anything else. This suggests the enzyme plays well with commercial laundry detergents. Second, they tried to clean old X-ray films. These films have a gelatin layer that holds silver, which is valuable but hard to recover. The enzyme successfully ate away the gelatin in 60 minutes at 65°C, leaving the silver behind without using harsh chemicals. Finally, they tried to remove hair from goat skin, a process called dehairing used in making leather. The enzyme did a great job, removing the hair completely in 18 hours without damaging the skin, which is a big improvement over the harsh chemicals usually used.

In short, the researchers found a tough, heat-loving enzyme in an Indian hot spring that is ready to help clean clothes, recycle silver from old films, and make leather more sustainably. While the enzyme is currently only "partially purified" (meaning it's not 100% pure yet), the results suggest it is a strong candidate for industrial use. The team notes that more testing is needed to fully understand its structure and to confirm these results with even more experiments, but the initial findings are very promising for green, eco-friendly industrial processes.

Technical Summary: Isolation and Characterization of a Thermophilic Alkaline Protease from Tuwa Hot Spring

Problem Statement
The global enzyme market relies heavily on microbial proteases, particularly for the detergent, leather, and food processing industries. There is a continuous demand for robust enzymes capable of functioning in harsh industrial environments, such as high temperatures and alkaline pH. While thermophilic proteases are recognized for their economic potential, their effective industrial application requires rigorous purification and biochemical characterization. Despite the known microbial diversity of the Tuwa hot spring ecosystem in Gujarat, India, there is a scarcity of comprehensive studies isolating individual thermophilic bacteria from this specific habitat and characterizing their extracellular enzymes for industrial utility, specifically regarding combined thermostability, alkaline tolerance, and compatibility with industrial additives.

Methodology
The study employed a systematic approach to isolate, produce, partially purify, and characterize a novel protease:

Isolation and Screening: Twenty-five thermophilic bacterial isolates were obtained from the Tuwa hot spring (Panchmahal, Gujarat) using nutrient and skim milk agar plates incubated at 55°C. Five potent protease-producing strains were selected for submerged fermentation.
Identification: The most productive isolate, designated MT_1, was identified via 16S rRNA gene sequencing and phylogenetic analysis, confirming it as Bacillus licheniformis. The sequence was deposited in NCBI GenBank (Accession No. PZ221934.1).
Production and Purification: Enzyme production was optimized under submerged fermentation. Partial purification was achieved through ammonium sulfate precipitation (20–70% saturation) followed by dialysis against glycine-NaOH buffer (pH 9.0).
Characterization: The enzyme was subjected to extensive biochemical characterization, including:
- Molecular Weight: Determined via SDS-PAGE.
- Kinetics: Substrate specificity (BSA, gelatin, casein) and kinetic parameters ( $K_m$ , $V_{max}$ ) were analyzed using the Lineweaver–Burk plot.
- Stability Profiles: Effects of pH (6.5–11.0), temperature (20–80°C), metal ions, organic solvents, surfactants, NaCl, and urea were evaluated.
- Industrial Application Tests: Compatibility with commercial detergents (Tide, Rin, Ariel, Wheel), washing performance on dal fry-stained cotton, enzymatic hydrolysis of gelatin from X-ray films, and dehairing of goat skin were assessed.

Key Results

Enzyme Properties: The partially purified B. licheniformis MT_1 protease exhibited an optimal activity at pH 9.0 and 80°C, confirming its alkaline and thermophilic nature. It retained over 92% activity after prolonged exposure to elevated temperatures.
Purification Metrics: Ammonium sulfate precipitation resulted in a 1.08-fold purification with a 90.82% yield and a specific activity of 65.00 U/mg. SDS-PAGE revealed a predominant protein band with an estimated molecular weight of approximately 29 kDa.
Kinetics and Specificity: The enzyme showed the highest activity toward bovine serum albumin (BSA), followed by gelatin and casein. Kinetic analysis yielded a $K_m$ of 0.25 g% and a $V_{max}$ of 5000 U/mL, indicating high substrate affinity and catalytic efficiency.
Stability and Tolerance:
- Metal Ions: Activity was significantly enhanced by $Mg^{2+}$ and $Mn^{2+}$ ions.
- Solvents: The enzyme retained partial activity in the presence of organic solvents (e.g., ethanol, isopropanol, xylene) but was inhibited by acetone.
- Surfactants: The protease showed better compatibility with non-ionic surfactants (Tween 20, Tween 80) than with the anionic surfactant SDS, which caused significant activity loss.
- Salinity and Urea: The enzyme showed sensitivity to NaCl (activity dropped below 60% even at 0.5% concentration) but retained measurable activity at higher concentrations. It demonstrated moderate resistance to urea-induced denaturation.
Industrial Applications:
- Detergents: The enzyme was compatible with commercial detergents and, when combined with them, demonstrated superior stain removal efficacy on protein-based stains compared to detergent or enzyme alone.
- Silver Recovery: The protease effectively hydrolyzed the gelatin layer of X-ray films at 65°C, facilitating the separation of silver particles.
- Leather Processing: The enzyme achieved complete dehairing of goat skin within 18 hours, producing leather with good texture and quality, offering a potential alternative to chemical dehairing methods.

Significance and Claims
The paper claims that the Bacillus licheniformis MT_1 protease represents a promising candidate for industrial applications due to its unique combination of thermostability, alkaliphilicity, and compatibility with industrial additives. The authors highlight its potential as a detergent additive, a biocatalyst for eco-friendly silver recovery from X-ray films, and a sustainable agent for leather dehairing. The study emphasizes that while the enzyme is partially purified, its biochemical profile supports its utility in harsh processing conditions.

Limitations and Future Perspectives
The authors modestly note that the study is limited to partial purification; further chromatographic techniques (ion-exchange, gel-filtration) are required for highly purified enzyme preparation for detailed structural and mechanistic studies. Additionally, the study did not perform quantitative statistical analysis based on independent biological replicates, and future work should include these to validate the findings. The molecular weight was determined via SDS-PAGE, but no activity-based electrophoretic characterization or advanced proteomic analysis was conducted.

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