A systematic reconsideration on proteases

Microbial community in the rhizosphere produces a variety of hydrolytic enzymes that are responsible for the degradation of various components of fungal pathogens. The extracellular hydrolytic enzymes excreted by soil rhizobia degrade cell wall components of plant pathogenic microbes. The enzymes of these types are able to breakdown glycosidic linkages present in the polysaccharide of the cell wall of phytopathogens. In this regard, plant growth-promoting rhizobacteria (PGPR) are known to colonize rhizosphere and enhance plant growth through different mechanisms that include (i) plant growth promotion and (ii) biological control of plant disease. Plant growth promotion mechanisms include mineralization of insoluble substances, production of plant growth hormones, biological nitrogen fixation, and promotion of root growth. Biocontrol mechanism involves competition, antibiosis, parasitism, induction of systemic acquired resistance (SAR), induction of systemic resistance (ISR), soil suppressiveness, and production of various antifungal metabolites; hydrolytic enzymes such as chitinase, glucanase, protease, and cellulase; and antibiotics such as 2,4-diacetyl phloroglucinol (DAPG), amphisin, oomycin A, hydrogen cyanide, phenazine, pyoluteorin, pyrrolnitrin, cyclic lipopeptides, oligomycin A, zwittermicin A, kanosamine, and xanthobaccin. Production of hydrolytic enzymes by PGPR is an important mechanism directed against phytopathogens for sustainable plant disease management. These enzymes break down the cell wall of fungal pathogens causing cell death. This review focuses on the different aspects of various hydrolytic enzymes produced by rhizoflora and their role in sustainable biocontrol of phytopathogens.

Role of Hydrolytic Enzymes of Rhizoflora in Biocontrol of Fungal Phytopathogens: An Overview

The demand of enzymes in industrial sectors is increasing rapidly due to their economical and ecological advantages. Micro-organisms produce different types of extracellular enzymes for maintaining their own metabolism, defense, and normal physiological condition. Among several enzymes, proteases have gained special attention in industrial sectors. Several sources of extracellular enzymes are reported by various researchers, but enzymes obtain from microbial sources have high demand in industries due to lower cost, high production rate, availability, stability, and diversity. Among micro-organism, bacteria and fungi are reported to be good sources of different types of proteases such as alkaline protease, cysteine protease, aspartate protease, and metallo protease. In this review, we have summarized the available information about the sources of bacterial and fungal proteases, their purification strategies and their temperature and pH optima. Due to huge competition, companies are trying to reduce their manufacturing cost and that's why microbial sources of enzymes are important. However, genetically engineered strains or engineered proteases have much more importance over natural isolates/protease in industries due to higher production rate and other advantages. Here we have also summarized the important applications of protease in different industries such as, paper mill, starch degrading sector, food processing factories, and detergent making companies.

Impact of microbial proteases on biotechnological industries.

Extraction and purification of a highly thermostable alkaline caseinolytic protease from wastes Penaeus vannamei suitable for food and detergent industries

A thermostable extracellular alkaline protease producing Bacillus amyloliquefaciens SP1 was isolated from apple rhizosphere having multifarious plant growth promoting activities. Strain SP1 was purified to 6.48-fold using four-step purification protocol and characterized in detail for its robustness and ecofriendly application in leather and detergent industries. Structural analysis revealed that the protease was monomeric and had a molecular weight of 43 kDa. It exhibited optimum activity at 60°C in alkaline environment (pH 8.0) and stable in the presence of surfactants and oxidizing agents. Enzyme was thermostable at 50°C and retained more than 70% activity after 30 min incubation. It has shown stain removal property and dehairing of goat skin without chemical assistance and hydrolyzing fibrous proteins. This protease showed Km of 0.125 mg ml(-1) and V(max) of 12820 μg ml(-1) indicating its excellent affinity and catalytic role. Thermal inactivation of the pure enzyme followed first-order kinetics. The half life of the pure enzyme at 50, 60, and 65°C was 77, 19.80, and 13.33 min, respectively. The activation energy was 37.19 KJ mol(-1). The results suggest that the B. amyloliquefaciens SP1 has a potential application in different industries.

Mohamed S. Abd el Aziz

Papers

Purification and characterization of two thermostable protease fractions from Bacillus megaterium