Mannans are the major constituents of the hemicellulose fraction in softwoods and show widespread distribution in plant tissues. The major mannan-degrading enzymes are β-mannanases, β-mannosidases and β-glucosidases. In addition to these, other enzymes such as α-galactosidases and acetyl mannan esterases, are required to remove the side chain substituents. The mannanases are known to be produced by a variety of bacteria, fungi, actinomycetes, plants and animals. Microbial mannanases are mainly extracellular and can act in wide range of pH and temperature because of which they have found applications in pulp and paper, pharmaceutical, food, feed, oil and textile industries. This review summarizes the studies on mannanases reported in recent years in terms of important microbial sources, production conditions, enzyme properties, heterologous expression and potential industrial applications.
Laccases (benzenediol: oxygen oxidoreductase, EC 126.96.36.199) are multi-copper enzymes which catalyze the oxidation of a wide range of phenolic and non-phenolic aromatic compounds in the presence or absence of a mediator. Till date, laccases have mostly been isolated from fungi and plants, whereas laccase from bacteria has not been well studied. Bacterial laccases have several unique properties that are not characteristics of fungal laccases such as stability at high temperature and high pH. Bacteria produce these enzymes either extracellularly or intracellularly and their activity is in a wide range of temperature and pH. It has application in pulp biobleaching, bioremediation, textile dye decolorization, pollutant degradation, biosensors, etc. Hence, comprehensive information including sources, production conditions, characterization, cloning and biotechnological applications is needed for the effective understanding and application of these enzymes at the industrial level. The present review provides exhaustive information of bacterial laccases reported till date.
Degradation of residual lignin in kraft pulp by chemical bleaching is implicated in causing environmental pollution. The use of thermo- and alkali-tolerant bacterial laccases is considered to be important biological alternative to chemical processing. Laccases from Bacillus species have shown promise in this respect but their intracellular/spore bound presence make their industrial application economically unfeasible. We report here on a novel extracellular active thermo-alkali-stable laccase (SN4 laccase) which is active at 90 °C and pH 8.0 using 2,6-dimethoxyphenol as substrate from Bacillus tequilensis SN4. SN4 laccase retained 27 % activity for 5 min at 100 °C and more than 80 % activity for 24 h at 70 °C. The enzyme is also stable at a higher pH (9.0–10.0). Enzyme production was optimized by submerged fermentation. Relatively high yields (18,356 nkats ml−1) of SN4 laccase was obtained in a medium containing 650 μM MnSO4, 350 μM FeSO4, and 3.5 % ethanol. A 764-fold increase in laccase activity was observed under optimal conditions. In addition, reduction in kappa number and increase in brightness of softwood pulp by 28 and 7.6 %, respectively, were observed after treatment with SN4 laccase without a mediator. When N-hydroxybenzotriazole was used as a mediator, the kappa number was decreased to 47 % and brightness was increased to 12 %.
Carrageenan, one of the phycocolloids is a sulfated galactan made up of linear chains of galactose and 3,6-anhydrogalactose with alternating α-(1 → 3) and β-(1 → 4) linkages and further classified based on the number and the position of sulfated ester(s); κ-, ι- and λ-carrageenan. Enzymes which degrade carrageenans are called k-, ι-, and λ-carrageenases. They all are endohydrolases that cleave the internal β-(1–4) linkages of carrageenans yielding products of the oligo-carrageenans. These enzymes are produced only by bacteria specifically gram negative bacteria. Majority of the marine bacteria produce these enzymes extracellularly and their activity is in wide range of temperature. They have found potential applications in biomedical field, bioethanol production, textile industry, as a detergent additive and for isolation of protoplast of algae etc. A comprehensive information shall be helpful for the effective understanding and application of these enzymes. In this review exhaustive information of bacterial carrageenases reported till date has been done. All the aspects like sources, production conditions, characterization, cloning and- biotechnological applications are summarized.
Paper manufacturing industries depend mainly on forests for wood, which is the basic raw material. Forest plays an important role in balancing the ecosystem to protect forest deinking and bleaching (recycling) of waste paper had gained a lot of importance. Conventional chemical deinking processes require large amount of chemicals which are toxic and hazardous to the environment, hence other effective deinking methods are needed. Enzymatic deinking (cellulolytic, hemicellulolytic and ligninolytic) has attracted enormous attention because of high efficacy and minimum environmental impact. For bleaching, enzymatic action (individual as well as in combination), along with physical treatment, makes the pulp more accessible to the chemicals and also to the amount of chemicals required to obtain similar levels of brightness. Strength properties and brightness of the pulp are improved by these treatment methods. With minimum impact on the environment, this review gives comprehensive information about the various methods used for the recycling of waste paper.
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