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Introduction
Enzymes have very old history and they have their existence from the start of ancient civilizations where people were using microbial enzymes in baking, alcohol production, brewing, cheese making etc. However, since then the number of applications of enzymes has increased tremendously with better knowledge about production and purification of enzymes from diverse sources.1 Microorganisms have been known to produce both intracellular and extracellular enzymes commercially.2
Enzymes are becoming alternative to chemical catalysts for better efficiency ensuring economic and ecological sustainability of the industrial processes.3 Proteases are the most dominant group of enzymes from the industry point of view, constituting about sixty percent of the total enzyme market.4 Proteases from microorganisms have been the most widely explored enzymes since the advent of enzymology.5 They account for approximately two-third share of the total commercial protease sale around the globe.6 These enzymes have gained attention not only due to their critical role in metabolic activities in the organisms but also due to their wide applications in industries7 such as food, detergent, bakery, leather, pharma, infant formulas, etc. due to their features like production ease, thermal stability and wide pH range applications.8
Alkaline proteases are the most frequently used industrial enzyme among different types (alkaline, neutral, and acidic) of proteases due to their comparatively high activity and greater stability at high pH.9 Wide range of microbes were found to produce alkaline proteases, including bacteria, yeasts, moulds and mammalian tissues5 and these were isolated from diverse sources as well. However, bacteria were preferred as they grow rapidly under various nutritional and physiochemical conditions, need less space, could be easily maintained and were accessible for genetic operations.2 A large number of bacteria have been reported to produce alkaline proteases e.g. Bacillus, Pseudomonas, Streptomyces, Micrococcus etc. However, Bacillus sp. has been the major source for alkaline protease production, accounting for about 35% of the total microbial enzyme sales.10,11 Since the first alkaline protease ‘Carlsberg’ from Bacillus licheniformis was utilized as a detergent additive in the 1960s, a number of other bacillus species have also been reported to produce alkaline proteases.12
Significant advancements in agriculture, industry, bioinformatics and biotechnology have fueled the search of extremophile microorganisms for alkaline...