Cold-active microbial enzymes and their biotechnological applications

Microorganisms known as psychrophiles/psychrotrophs, which survive in cold climates, constitute majority of the biosphere on Earth. Their capability to produce cold-active enzymes along with other distinguishing characteristics allows them to survive in the cold environments. Due to the relative ease of large-scale production compared to enzymes from plants and animals, commercial uses of microbial enzyme are alluring. The ocean depths, polar, and alpine regions, which make up over 85% of the planet, are inhabited to cold ecosystems. Microbes living in these regions are important for their metabolic contribution to the ecosphere as well as for their enzymes, which may have potential industrial applications. Cold-adapted microorganisms are a possible source of cold-active enzymes that have high catalytic efficacy at low and moderate temperatures at which homologous mesophilic enzymes are not active. Cold-active enzymes can be used in a variety of biotechnological processes, including food processing, additives in the detergent and food industries, textile industry, waste-water treatment, biopulping, environmental bioremediation in cold climates, biotransformation, and molecular biology applications with great potential for energy savings. Genetically manipulated strains that are suitable for producing a particular cold-active enzyme would be crucial in a variety of industrial and biotechnological applications. The potential advantage of cold-adapted enzymes will probably lead to a greater annual market than for thermo-stable enzymes in the near future. This review includes latest updates on various microbial source of cold-active enzymes and their biotechnological applications.

Agricultural Residues as Raw Materials for Pulp and Paper Production: Overview and Applications on Membrane Fabrication

The need for pulp and paper has risen significantly due to exponential population growth, industrialization, and urbanization. Most paper manufacturing industries use wood fibers to meet pulp and paper requirements. The shortage of fibrous wood resources and increased deforestation are linked to the excessive dependence on wood for pulp and paper production. Therefore, non-wood substitutes, including corn stalks, sugarcane bagasse, wheat, and rice straw, cotton stalks, and others, may greatly alleviate the shortage of raw materials used to make pulp and paper. Non-woody raw materials can be pulped easily using soda/soda-AQ (anthraquinone), organosolv, and bio-pulping. The use of agricultural residues can also play a pivotal role in the development of polymeric membranes separating different molecular weight cut-off molecules from a variety of feedstocks in industries. These membranes range in applications from water purification to medicinal uses. Considering that some farmers still burn agricultural residues on the fields, resulting in significant air pollution and health issues, the use of agricultural residues in paper manufacturing can eventually help these producers to get better financial outcomes from the grown crop. This paper reviews the current trends in the technological pitch of pulp and paper production from agricultural residues using different pulping methods, with an insight into the application of membranes developed from lignocellulosic materials.

Production of eco-friendly and better-quality sugarcane bagasse paper using crude xylanase and pectinase biopulping strategy

This research aimed to investigate the efficiency of crude xylanase-pectinase in pulping of sugarcane bagasse. Optimum biopulping was obtained, using xylanase-pectinase dose 200-60 IU/g, bagasse/liquid ratio 1:10 and 1.0% Tween 80 concentration at 55 °C temperature, pH 8.5 and period of treatment 180 min. Treatment of sugarcane bagasse samples with these enzymes generated pulp with lower rejections (58.76%), total solids (12.64%), kappa number (47.77%), higher screened pulp yield (10.66%), along with enhanced optical and physical properties, in comparison with a chemical pulp. Bagasse biopulping resulted in a 13% decrease in alkali dose to obtain the optical and physical properties similar to those achieved under the 100% alkali dose. The breaking length, burst factor, tear index, double fold, gurley porosity and viscosity were improved by 15.19, 37.64, 2.47, 37.77, 35 and 23.17%, respectively, after bleaching treatment of biopulped samples. Thus, enzymatic pulping is an eco-friendly environmentally sustainable approach, since it reduces the use of pulping chemicals and simultaneously improves the paper quality. This is the first report, showing pulping of sugarcane bagasse, with crude xylanase-pectinase, produced by an isolate.

Influence of mechanical operation on the biodelignification of Leucaena leucocephala by xylanase treatment

This study aimed at energy reduction during pulping of L. leucocephala by passing the wood chips through an impressafiner followed by xylanase pretreatment. An impressafiner compressed the chips and converted them into spongy materials. Wood chips of L. leucocephala with or without de-structuring and de-structured wood chips followed by enzymatic treatment were subjected to Kraft pulping at different temperatures varying from 135 to 170 °C and active alkali varying from 12 to 20% (as Na₂O) to observe effect on screened pulp yield and kappa number. The de-structured wood chips followed by enzymatic treatment produced a pulp yield of 48.2% and kappa number 18.6. L. leucocephala without de-structuring produced a pulp yield of 50.1% and kappa number 23.7. When the pulp was subjected to oxygen delignification to reduce kappa number in the vicinity of 18.6, pulp showed shrinkage by 6.64% compared to Kraft pulp of de-structured wood chips followed by enzymatic treatment. Kraft pulp produced from de-structured wood chips of L. leucocephala followed by enzymatic treatment showed net saving of US$ 163.15 per digester over Kraft pulp produced without de-structuring of wood chips of L. leucocephala. Moreover, the pulp obtained by de-structuring followed by enzymatic treatment showed improvement in pulp brightness and physical strength properties including tensile, tear, and burst index significantly compared to pulp obtained without de-structuring.

A Comprehensive Insight into Fungal Enzymes: Structure, Classification, and Their Role in Mankind's Challenges

Enzymes have played a crucial role in mankind's challenges to use different types of biological systems for a diversity of applications. They are proteins that break down and convert complicated compounds to produce simple products. Fungal enzymes are compatible, efficient, and proper products for many uses in medicinal requests, industrial processing, bioremediation purposes, and agricultural applications. Fungal enzymes have appropriate stability to give manufactured products suitable shelf life, affordable cost, and approved demands. Fungal enzymes have been used from ancient times to today in many industries, including baking, brewing, cheese making, antibiotics production, and commodities manufacturing, such as linen and leather. Furthermore, they also are used in other fields such as paper production, detergent, the textile industry, and in drinks and food technology in products manufacturing ranging from tea and coffee to fruit juice and wine. Recently, fungi have been used for the production of more than 50% of the needed enzymes. Fungi can produce different types of enzymes extracellularly, which gives a great chance for producing in large amounts with low cost and easy viability in purified forms using simple purification methods. In the present review, a comprehensive trial has been advanced to elaborate on the different types and structures of fungal enzymes as well as the current status of the uses of fungal enzymes in various applications.

Characterizing Fungal Decay of Beech Wood: Potential for Biotechnological Applications

The biotechnological potential of nine decay fungi collected from stored beech logs at a pulp and paper factory yard in Northern Iran was investigated. Beech blocks exposed to the fungi in a laboratory decay test were used to study changes in cell wall chemistry using both wet chemistry and spectroscopic methods. Pleurotus ostreatus, P. pulmonarius, and Lentinus sajor-caju caused greater lignin breakdown compared to other white-rot fungi, which led to a 28% reduction in refining energy. Trametesversicolor caused the greatest glucan loss, while P. ostreatus and L. sajor-caju were associated with the lowest losses of this sugar. Fourier transform infrared spectroscopy (FTIR) analyses indicated that white-rot fungi caused greater lignin degradation in the cell walls via the oxidation aromatic rings, confirming the chemical analysis. The rate of cellulose and lignin degradation by the T.versicolor and Pleurotus species was high compared to the other decay fungi analyzed in this study. Based on the above information, we propose that, among the fungi tested, P. ostreatus (27.42% lignin loss and 1.58% cellulose loss) and L. sajor-caju (29.92% lignin loss and 5.95% cellulose loss) have the greatest potential for biopulping.

Inhibition of Phenolics Uptake by Ligninolytic Fungal Cells and Its Potential as a Tool for the Production of Lignin-Derived Aromatic Building Blocks

Lignin is the principal natural source of phenolics but its structural complexity and variability make it difficult to valorize through chemical depolymerization approaches. White rots are one of the rare groups of organisms that are able to degrade lignin in ecosystems. This biodegradation starts through extracellular enzymes producing oxidizing agents to depolymerize lignin and continue with the uptake of the generated oligomers by fungal cells for further degradation. Phanerochaete chrysosporium is one of the most studied species for the elucidation of these biodegradation mechanisms. Although the extracellular depolymerization step appears interesting for phenolics production from lignin, the uptake and intracellular degradation of oligomers occurring in the course of the depolymerization limits its potential. In this study, we aimed at inhibiting the phenolics uptake mechanism through metabolic inhibitors to favor extracellular oligomers accumulation without preventing the ligninases production that is necessary for extracellular depolymerization. The use of sodium azide confirmed that an active transportation phenomenon is involved in the phenolics uptake in P. chrysosporium. A protocol based on carbonyl cyanide m-chlorophenyl hydrazone enabled reaching 85% inhibition for vanillin uptake. This protocol was shown not to inhibit, but on the contrary, to stimulate the depolymerization of both dehydrogenation polymers (DHPs) and industrial purified lignins.

Biobleaching: An eco-friendly approach to reduce chemical consumption and pollutants generation

The pulp and paper industry is known to be a large contributor to environmental pollution due to the huge consumption of chemicals and energy. Several chemicals including H2SO4, Cl2, ClO2, NaOH, and H2O2 are used during the bleaching process. These chemicals react with lignin and carbohydrates to generate a substantial amount of pollutants in bleach effluents. Environmental pressure has compelled the pulp and paper industry to reduce pollutant generation from the bleaching section. Enzymes have emerged as simple, economical, and eco-friendly alternatives for bleaching of pulp. The pretreatment of pulp with enzymes is termed as biobleaching or pre-bleaching. Different microbial enzymes such as xylanases, pectinases, laccases, manganese peroxidases (MnP), and lignin peroxidases are used for biobleaching. Xylanases depolymerize the hemicelluloses precipitated on pulp fiber surfaces and improves the efficiency of bleaching chemicals. Xylanase treatment also increases the pulp fibrillation and reduces the beating time of the pulp. Pectinases hydrolyze pectin available in the pulp fibers and improve the papermaking process. Laccase treatment is found more effective along with mediator molecules (as a laccase-mediator system). Biobleaching of pulp results in the superior quality of pulp along with lower consumption of chlorine-based chemicals and lower generation of adsorbable organic halidesadsorbable organic halides (AOX. An enzyme pretreatment reduces the kappa number of pulp and improves ISO brightness significantly. Better physical strength properties and pulp viscosity have also been observed during biobleaching of pulp.