Screening and Isolation of Protease Producing Bacteria from Kitchen Exhaust

About Author: Debashish Satpathy
Roland Institute of Pharmaceutical Sciences

Protease is any enzyme that conducts proteolysis by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain. They are also called proteolytic enzymes or proteinases.

Classification Proteases are currently classified into six groups:
Serine proteases
Threonine proteases
Cysteine proteases
Aspartic acid proteases
Glutamic acid proteases

The threonine and glutamic acid proteases were not described until 1995 and 2004, respectively. The mechanism used to cleave a peptide bond involves making an amino acid residue that has the cysteine and threonine (peptidases) or a water molecule (aspartic acid, metallo- and glutamic acid peptidases) nucleophilic so that it can attack the peptide carbonyl group. One way to make a nucleophile is by a catalytic triad, where a histidine residue is used to activate serine, cysteine, or threonine as a nucleophile.

Reference ID: PHARMATUTOR-ART-1110

Proteases occur naturally in all organisms. These enzymes are involved in a multitude of physiological reactions from simple digestion of food proteins to highly-regulated cascades (e.g., the blood-clotting cascade, the complement system, apoptosis pathways, and the invertebrate prophenoloxidase-activating cascade). Peptidases can either break specific peptide bonds (limited proteolysis), depending on the amino acid sequence of a protein, or break down a complete peptide to amino acids (unlimited proteolysis). The activity can be a destructive change, abolishing a protein's function or digesting it to its principal components; it can be an activation of a function, or it can be a signal in a signaling pathway. Bacterium also secretes proteases to hydrolyse the peptide bonds in proteins and therefore break the proteins down into their constituent monomers.Proteases are also a type of exotoxin, which is virulence factor in bacteria pathogenesis. Bacteria exotoxic proteases destroy extracellular structures. Protease enzymes are also found used extensively in the bread industry in Bread improver.

Proteases are involved in digesting long protein chains into short fragments, splitting the peptide bonds that link amino acid residues. Some of them can detach the terminal amino acids from the protein chain (exopeptidases, such as aminopeptidases, carboxypeptidase A); the others attack internal peptide bonds of a protein (endopeptidases, such as trypsin, chymotrypsin, pepsin, papain, elastase).

Proteases are used throughout an organism for various metabolic processes. Acid proteases secreted into the stomach (such as pepsin) and serine proteases present in duodeum (trypsin and chymotrypsin) enable us to digest the protein in food; proteases present in blood serum (thrombin, plasmin, Hageman factor, etc.) play important role in blood-clotting, as well as lysis of the clots, and the correct action of the immune system. Other proteases are present in leukocytes (elastase, cathepsin G) and play several different roles in metabolic control. Proteases determine the lifetime of other proteins playing important physiological role like hormones, antibodies, or other enzymes -- this is one of the fastest "switching on" and "switching off" regulatory mechanisms in the physiology of an organism. By complex cooperative action the proteases may proceed as cascade reactions, which result in rapid and efficient amplification of an organism's response to a physiological signal.

Proteolytic enzymes are ubiquitous in occurrence, being found in all living organisms, and are essential for cell growth and differentiation. The extracellular proteases are of commercial value and find multiple applications in various industrial sectors. Although there are many microbial sources available for producing proteases, only a few are recognized as commercial producers. A good number of bacterial alkaline proteases are commercially available, such as subtilis in Carlsberg, subtilis in BPN' and Savinase, with their major application as detergent enzymes. However, mutations have led to newer protease preparations with improved catalytic efficiency and better stability towards temperature, oxidizing agents and changing wash conditions.

Sources of bacterial proteases
Protease production is an inherent capacity of all microorganisms and a large number of microbes belonging to bacteria, fungi, yeast and actinomycete are known to produce proteases. Bacteria are the predominant group of alkaline protease producers, the genus Bacillus being the most common source (Gupta et al., 2002 b). Some of the potential alkaline protease producing bacilli are strains of B. lichiniformis, B. subtilis and B. amyloliquifaciens. Pseudomonas, Flavobacterium, Halobacterium, Vibrio, Serratia, Staphylococcus, Brevibacterium, Alcaligenes have also been explored for protease production (Gupta et al., 2005). Among actinomycetes, strains of Streptomyces, Nocardia and Nocardiopsis are potential ones. In fungi, aspergili is the most exploited group and the strains of Neurospora, Penicillium, Ophiostoma, Myxococcus, Rhizopus etc. are common producers of proteases (Gupta et al., 2005). Only those microbes that produce substantial amounts of extracellular enzyme are of industrial importance. Several products based on bacterial proteases have been launched successfully in the market in past few years

Proteases have considerable application in the detergent, leather tanning and food industries (Kelly and Fogarty, 1976; Godfrey and Reichelt, 1985). At present a large proportion of commercial proteases are derived from neutrophilic Bacillus species. Different alkaline protease producing alkaliphilic microbial strains were isolated in many laboratories (Horikoshi and Akiba, 1982; Durham et al., 1987; Takami et al., 1989; Yum et al., 1994). Alkaline proteases produced by alkaliphilic strains showed better resistance to alkali and some other denaturing chemicals in the reaction mixture and have higher affinity towards proteinaceous substrates, properties which are very important for application in the detergent and leather tanning industries (Kalisz, 1988). This has given the impetus for the continuous search of alkaliphiles producing novel alkaline proteases. Naturally occurring alkaline habitats are found in different parts of the world. Isolation and screening of alkaliphiles from such habitats is expected to give alkaline protease producing microorganisms potentially useful for many applications.



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