Microbial keratinases and their prospective applications: an overview

Microbial keratinases have become biotechnologically important since they target the hydrolysis of highly rigid, strongly cross-linked structural polypeptide “keratin” recalcitrant to the commonly known proteolytic enzymes trypsin, pepsin and papain. These enzymes are largely produced in the presence of keratinous substrates in the form of hair, feather, wool, nail, horn etc. during their degradation. The complex mechanism of keratinolysis involves cooperative action of sulfitolytic and proteolytic systems. Keratinases are robust enzymes with a wide temperature and pH activity range and are largely serine or metallo proteases. Sequence homologies of keratinases indicate their relatedness to subtilisin family of serine proteases. They stand out among proteases since they attack the keratin residues and hence find application in developing cost-effective feather by-products for feed and fertilizers. Their application can also be extended to detergent and leather industries where they serve as specialty enzymes. Besides, they also find application in wool and silk cleaning; in the leather industry, better dehairing potential of these enzymes has led to the development of greener hair-saving dehairing technology and personal care products. Further, their prospective application in the challenging field of prion degradation would revolutionize the protease world in the near future.     

Microbial mannanases: an overview of production and applications

Microbial mannanases have become biotechnologically important since they target the hydrolysis of complex polysaccharides of plant tissues into simple molecules like manno-oligosaccharides and mannoses. The role of mannanases in the paper and pulp industry is well established and recently they have found application in the food and feed technology, coffee extraction, oil drilling and detergent industry. Mannanses are enzymes produced mainly from microorganisms but mannanases produced from plants and animals have also been reported. Bacterial mannanases are mostly extracellular and can act in a wide range of pH and temperature, though acidic and neutral mannanases are more common. This review will focus on complex mannan structure and the microbial enzyme complex involved in its complete breakdown, mannanase sources, production conditions and their applications in the commercial sector. The reference to plant and animal mannanases has been made to complete the overview. However, the major emphasis of the review is on the microbial mannanases.     

Microbial keratinases: industrial enzymes with waste management potential

Proteases are ubiquitous enzymes that occur in various biological systems ranging from microorganisms to higher organisms. Microbial proteases are largely utilized in various established industrial processes. Despite their numerous industrial applications, they are not efficient in hydrolysis of recalcitrant, protein-rich keratinous wastes which result in environmental pollution and health hazards. This paved the way for the search of keratinolytic microorganisms having the ability to hydrolyze “hard to degrade” keratinous wastes. This new class of proteases is known as “keratinases”. Due to their specificity, keratinases have an advantage over normal proteases and have replaced them in many industrial applications, such as nematicidal agents, nitrogenous fertilizer production from keratinous waste, animal feed and biofuel production. Keratinases have also replaced the normal proteases in the leather industry and detergent additive application due to their better performance. They have also been proved efficient in prion protein degradation. Above all, one of the major hurdles of enzyme industrial applications (cost effective production) can be achieved by using keratinous waste biomass, such as chicken feathers and hairs as fermentation substrate. Use of these low cost waste materials serves dual purposes: to reduce the fermentation cost for enzyme production as well as reducing the environmental waste load. The advent of keratinases has given new direction for waste management with industrial applications giving rise to green technology for sustainable development.     

Microbial xylanases: Engineering, production and industrial applications

Enzymatic depolymerization of hemicellulose to monomer sugars needs the synergistic action of multiple enzymes, among them endo-xylanases (EC 3.2.1.8) and β-xylosidases (EC 3.2.1.37) (collectively xylanases) play a vital role in depolymerizing xylan, the major component of hemicellulose. Recent developments in recombinant protein engineering have paved the way for engineering and expressing xylanases in both heterologous and homologous hosts. Functional expression of endo-xylanases has been successful in many hosts including bacteria, yeasts, fungi and plants with yeasts being the most promising expression systems. Functional expression of β-xylosidases is more challenging possibly due to their more complicated structures. The structures of endo-xylanases of glycoside hydrolase families 10 and 11 have been well elucidated. Family F/10 endo-xylanases are composed of a cellulose-binding domain and a catalytic domain connected by a linker peptide with a (β/α)(8) fold TIM barrel. Family G/11 endo-xylanases have a β-jelly roll structure and are thought to be able to pass through the pores of hemicellulose network owing to their smaller molecular sizes. The structure of a β-d-xylosidase belonging to family 39 glycoside hydrolase has been elucidated as a tetramer with each monomer being composed of three distinct regions: a catalytic domain of the canonical (β/α)(8) - TIM barrel fold, a β-sandwich domain and a small α-helical domain with the enzyme active site that binds to d-xylooligomers being present on the upper side of the barrel. Glycosylation is generally considered as one of the most important post-translational modifications of xylanases, but a few examples showed functional expression of eukaryotic xylanases in bacteria. The optimal ratio of these synergistic enzymes is very important in improving hydrolysis efficiency and reducing enzyme dosage but has hardly been addressed in literature. Xylanases have been used in traditional fields such as food, feed and paper industries for a longer time but more and more attention has been paid to using them in producing sugars and other chemicals from lignocelluloses in recent years. Mining new genes from nature, rational engineering of known genes and directed evolution of these genes are required to get tailor-made xylanases for various industrial applications.     

Microbial production of 2,3-butanediol for industrial applications

Journal of Industrial Microbiology & Biotechnology - 2,3-Butanediol (2,3-BD) has great potential for diverse industries, including chemical, cosmetics, agriculture, and pharmaceutical areas....     

Biochemical features of microbial keratinases and their production and applications

Keratinases are exciting proteolytic enzymes that display the capability to degrade the insoluble protein keratin. These enzymes are produced by diverse microorganisms belonging to the Eucarya, Bacteria, and Archea domains. Keratinases display a great diversity in their biochemical and biophysical properties. Most keratinases are optimally active at neutral to alkaline pH and 40–60°C, but examples of microbial keratinolysis at alkalophilic and thermophilic conditions have been well documented. Several keratinases have been associated to the subtilisin family of serine-type proteases by analysis of their protein sequences. Studies with specific substrates and inhibitors indicated that keratinases are often serine or metalloproteases with preference for hydrophobic and aromatic residues at the P1 position. Keratinolytic enzymes have several current and potential applications in agroindustrial, pharmaceutical, and biomedical fields. Their use in biomass conversion into biofuels may address the increasing concern on energy conservation and recycling.     

Bacterial alginate production: an overview of its biosynthesis and potential industrial production

Alginate is a linear polysaccharide that can be used for different applications in the food and pharmaceutical industries. These polysaccharides have a chemical structure composed of subunits of (1–4)-β-d-mannuronic acid (M) and its C-5 epimer α-l-guluronic acid (G). The monomer composition and molecular weight of alginates are known to have effects on their properties. Currently, these polysaccharides are commercially extracted from seaweed but can also be produced by Azotobacter vinelandii and Pseudomonas spp. as an extracellular polymer. One strategy to produce alginates with different molecular weights and with reproducible physicochemical characteristics is through the manipulation of the culture conditions during fermentation. This mini-review provides a comparative analysis of the metabolic pathways and molecular mechanisms involved in alginate polymerization from A. vinelandii and Pseudomonas spp. Different fermentation strategies used to produce alginates at a bioreactor laboratory scale are described.     

Microbial production of omega-3 fatty acids: an overview

The essence of appropriate nutritional intake on a regular basis has a great impact in maintaining fundamental physiological functions and the body metabolism. Considering how pivotal maintaining a nourishing fat diet is to human health, Omega-3 fatty acids have gained a lot of attention in recent times. Omega-3 fatty acids (n-3 FAs) such as eicosapentaenoic acid (EPA) and DHA are considered as essential fatty acids (EFAs) offering enormous nutritional benefits: from playing a major role in the prevention and treatment of a number of human diseases, such as cardiovascular disorders and neurological disorders, to having anti-inflammatory properties, to providing joint support, etc. Hence, their incorporation into our daily diet is of great importance. Also, both EPA and DHA have been shown to be therapeutically significant in treating several infectious diseases. EFAs were initially thought to be marine in origin, produced by fishes. Consequentially, this led to the increase in the industrial extraction of fish oils for meeting the commercial need for of n-3-rich dietary supplements. Although fish oil supplementation met almost all of the dietary demand for EFAs, they did come with a fair share of drawbacks such as undesirable odour and flavour, heavy metal contamination, extinction of fish species, etc. Oleaginous micro-organisms are a promising alternative for the production of a more sustainable, consistent and quality production of n-3 FAs. Thus, the entire review focuses on understanding the eco-friendlier production of n-3 FAs by micro-organisms.     

Microbial xylanases and their industrial applications: a review

Despite an increased knowledge of microbial xylanolytic systems in the past few years, further studies are required to achieve a complete understanding of the mechanism of xylan degradation by microorganisms and their enzymes. The enzyme system used by microbes for the metabolism of xylan is the most important tool for investigating the use of the second most abundant polysaccharide (xylan) in nature. Recent studies on microbial xylanolytic systems have generally focussed on induction of enzyme production under different conditions, purification, characterization, molecular cloning and expression, and use of enzyme predominantly for pulp bleaching. Rationale approaches to achieve these goals require a detailed knowledge of the regulatory mechanism governing enzyme production. This review will focus on complex xylan structure and the microbial enzyme complex involved in its complete breakdown, studies on xylanase regulation and production and their potential industrial applications, with special reference to biobleaching.     

Microbial alkaline pectinases and their industrial applications: a review

The biotechnological potential of pectinolytic enzymes from microorganisms has drawn a great deal of attention from various researchers worldwide as likely biological catalysts in a variety of industrial processes. Alkaline pectinases are among the most important industrial enzymes and are of great significance in the current biotechnological arena with wide-ranging applications in textile processing, degumming of plant bast fibers, treatment of pectic wastewaters, paper making, and coffee and tea fermentations. The present review features the potential applications and uses of microbial alkaline pectinases, the nature of pectin, and the vast range of pectinolytic enzymes that function to mineralize pectic substances present in the environment. It also emphasizes the environmentally friendly applications of microbial alkaline pectinases thereby revealing their underestimated potential. The review intends to explore the potential of these enzymes and to encourage new alkaline pectinase-based industrial technology. Electronic Publication     

Bacteriophages and its applications: an overview

Bacteriophages (or phages), the most abundant viral entity of the planet, are omni-present in all the ecosystems. On the basis of their unique characteristics and anti-bacterial property, phages are being freshly evaluated taxonomically. Phages replicate inside the host either by lytic or lysogenic mode after infecting and using the cellular machinery of a bacterium. Since their discovery by Twort and d’Herelle in the early 1900s, phage became an important agent for combating pathogenic bacteria in clinical treatments and its related research gained momentum. However, due to recent emergence of bacterial resistance on antibiotics, applications of phage (phage therapy) become an inevitable option of research. Phage particles become popular as a biotechnological tool and treatment of pathogenic bacteria in a range of applied areas. However, there are few concerns over the application of phage-based solutions. This review deals with the updated phage taxonomy (ICTV 2015 Release and subsequent revision) and phage biology and the recent development of its application in the areas of biotechnology, biosensor, therapeutic medicine, food preservation, aquaculture diseases, pollution remediation, and wastewater treatment and issues related with limitations of phage-based remedy.     

Biotechnological applications and prospective market of microbial keratinases

Keratinases are well-recognized enzymes with the unique ability to attack highly cross-linked, recalcitrant structural proteins such as keratin. Their potential in environmental clean-up of huge amount of feather waste has been well established since long. Today, they have gained importance in various other biotechnological and pharmaceutical applications. However, commercial availability of keratinases is still limited. Hence, to attract entrepreneurs, investors and enzyme industries it is utmost important to explicitly present the market potential of keratinases through detailed account of its application sectors. Here, the application areas have been divided into three parts: the first one is dealing with the area of exclusive applications, the second emphasizes protease dominated sectors where keratinases would prove better substitutes, and the third deals with upcoming newer areas which still await practical documentation. An account of benefits of keratinase usage, existing market size, and available commercial sources and products has also been presented.     

Microbial polysaccharides with actual potential industrial applications

The microbial polysaccharides reviewed include xanthan gum, scleroglucan, PS-10, PS-21 and PS-53 gums, polysaccharides from Alcaligenes sp., PS-7 gum, gellan gum, curdlan, bacterial alginate, dextran, pullulan, Baker's Yeast Glycan, 6-deoxy-hexose-containing polysaccharides and bacterial cellulose. Factors limiting the commercial potential of certain microbial polysaccharides such as availability, rheological properties, and polyvalency are outlined. The polysaccharides are classified according to their uses as viscosity-increasing agents and as gelling agents. A third category includes polysaccharides with specific applications such as tailor-made dextran and pullulan and polysaccharides used as substrates for the preparation of rare sugars. The difficulties encountered in development of a polysaccharide at the industrial level are pointed out.     

Microbial transglutaminase: An overview of recent applications in food and packaging

Abstract

The glue of proteins, microbial transglutaminase (MTG) has been adopted in the food processing industries for its broad enzymatic action. Microorganisms such as Streptoverticillium and Streptomyces are the major sources, to decrease the cost of manufacturing animal origin transglutaminase. The net % increase of its demands in the food processing is estimated at 21.9% per year. In fact, MTG is consumed by most food industries, spanning the meat, dairy, seafood and fish, plant proteins, edible film preparation and more. It used to improve gelation and change foaming, emulsification, viscosity, consistency and water-holding capacity properties. This paper presents an overview of the literature that described and explored the recent microbial origins, production media and applications of microbial transglutaminase.     

Microbial enzymes: new industrial applications from traditional screening methods

Enzymes have applications in many fields, including organic synthesis, clinical analysis, pharmaceuticals, detergents, food production and fermentation. The application of enzymes to organic synthesis is currently attracting more and more attention. The discovery of new microbial enzymes through extensive and persistent screening will open new, simple routes for synthetic processes and, consequently, new ways to solve environmental problems.     

Microbial production and applications of chiral hydroxyalkanoates

Polyhydroxyalkanoates (PHA) are a family of polyesters consisting of over 150 chiral hydroxyalkanoic acids (HA). This paper reviews the physiological functions of (R)-3-hydroxybutyric acid (3HB) and (R)-4-hydroxybutyric acid and summarizes the technologies developed to produce various HA [3HB, (R)-3-hydroxyoctanoic acid, (R)-3-hydroxydecanoic acid, etc.] and the applications of chiral HA. Their outlooks and perspectives are discussed.     

Microbial production of bacteriocins: Latest research development and applications

Bacteriocins are low molecular weight peptides secreted by the predator bacterial cells to kill sensitive cells present in the same ecosystem competing for food and other nutrients. Exceptionally few bacteriocins along with their native antibacterial property also exhibit additional anti-viral and anti-fungal properties. Bacteriocins are generally produced by Gm+, Gm– and archaea bacteria. Bacteriocins from Gm?+?bacteria especially from lactic acid bacteria (LAB) have been thoroughly investigated considering their great biosafety and broad industrial applications. LAB expressing bacteriocins were isolated from fermented milk and milk products, rumen of animals and soil using deferred antagonism assay. Nisin is the only bacteriocin that has got FDA approval for application as a food preservative, which is produced by Lactococcus lactis subsp. Lactis. Its crystal structure explains that its antimicrobial properties are due to the binding of NH₂ terminal to lipid II molecule inhibiting the peptidoglycan synthesis and carboxy terminal forming pores in bacterial cell membrane leading to cell lysis. The hinge region connecting NH₂ and carboxy terminus has been mutated to generate mutant variants with higher antimicrobial activity. In a 50 ton fermentation of the mutant strain 3807 derived from L. lactis subsp. lactis ATCC 11454, 9,960?IU/mL of nisin was produced. Currently, high purity of nisin (>99%) is very expensive and hardly commercially available. Development of more advanced tools for cost-effective separation and purification of nisin would be commercially attractive. Chemical synthesis and heterologous expression of bacteriocins ended in low yields of pure proteins. At present, bacteriocins are almost solely applied in food industries, but they have a great potential to be used in other fields such as feeds, organic fertilizers, environmental protection and personal care products. The future of bacteriocins is largely dependent on getting FDA approval for use of other bacteriocins in addition to nisin to promote the research and applications.     

Microbial cell immobilization in biohydrogen production: a short overview

The high dependence on fossil fuels has escalated the challenges of greenhouse gas emissions and energy security. Biohydrogen is projected as a future alternative energy as a result of its non-polluting characteristics, high energy content (122?kJ/g), and economic feasibility. However, its industrial production has been hampered by several constraints such as low process yields and the formation of biohydrogen-competing reactions. This necessitates the search for other novel strategies to overcome this problem. Cell immobilization technology has been in existence for many decades and is widely used in various processes such as wastewater treatment, food technology, and pharmaceutical industry. In recent years, this technology has caught the attention of many researchers within the biohydrogen production field owing to its merits such as enhanced process yields, reduced microbial contamination, and improved homogeneity. In addition, the use of immobilization in biohydrogen production prevents washout of microbes, stabilizes the pH of the medium, and extends microbial activity during continuous processes. In this short review, an insight into the potential of cell immobilization is presented. A few immobilization techniques such as entrapment, adsorption, encapsulation, and synthetic polymers are discussed. In addition, the effects of process conditions on the performance of immobilized microbial cells during biohydrogen production are discussed. Finally, the review concludes with suggestions on improvement of cell immobilization technologies in biohydrogen production.     

Bromelain: an overview of industrial application and purification strategies

This review highlights the use of bromelain in various applications with up-to-date literature on the purification of bromelain from pineapple fruit and waste such as peel, core, crown, and leaves. Bromelain, a cysteine protease, has been exploited commercially in many applications in the food, beverage, tenderization, cosmetic, pharmaceutical, and textile industries. Researchers worldwide have been directing their interest to purification strategies by applying conventional and modern approaches, such as manipulating the pH, affinity, hydrophobicity, and temperature conditions in accord with the unique properties of bromelain. The amount of downstream processing will depend on its intended application in industries. The breakthrough of recombinant DNA technology has facilitated the large-scale production and purification of recombinant bromelain for novel applications in the future.