Process optimization and extraction of alkaline protease from halotolerant Streptomyces sp. VITGS3 and its use as a...

Marine halotolerant actinobacteria are robust microbes poorly explored and barely cultivable in nature. They are a trove of various secondary metabolites and enzymes, especially the alkaline proteases withstanding higher temperatures, pH, and salinity, making them an ideal source with versatile commercial and therapeutic values. This study focuses on extracting and optimizing alkaline protease production from Streptomyces sp. VITGS3 isolated from Puthuvypeen, Kerala. The protease production was optimized by Response Surface Methodology (RSM) using the Box-Behnken model, which used rice bran, wheat bran, skim milk, and casein as substrates. The maximum protease was produced (357 U/mL) using wheat bran (5.5 % w/v) as substrate at pH 9 and incubated at 45 °C for 9 days. The Michaelis-Menten model's enzyme kinetics exhibited a K_m value of 1.42 µM, a V_max of 201.64 µM·min^-1, V₀ of 5.59 µM·min^-1, and K_cat 70013.89 min^-1 suggesting a higher affinity of the enzyme for the substrate (1 % w/v casein). In addition, the protease was inhibited by the phenylmethylsulphonyl fluoride (PMSF), suggesting it belongs to the serine protease family. Finally, the application studies as contact lens cleaners showcased that the isolated protease effectively degraded the protein deposits present in the artificial tear solution without affecting the light transmittance. This is a milestone in the implication of protease on therapeutic applications and further studies on protein specificity, sustained releases, and combination strategies, resulting in crucial challenges in long-term studies, cross-reactivity, storage, and cost-effectiveness.