BIODEGRADATION OF LIGNIN AND XYLON K R.pptx

BIODEGRADATION OF LIGNIN AND XYLON K R.pptx

1. BIODEGRADATION OF LIGNIN AND XYLAN K R MICRO NOTES 1

2. LIGNIN K R MICRO NOTES 2

3. Lignin is an important component of the plant cell wall .where it provides structural support, helps in water and nutrients transport, and protects from chemical and biological attacks. The complex aromatic polymers known as lignin are produced by the oxidative reaction of 4-hydroxyphenylpropanoids. Lignin is an amorphous, highly branching, three-dimensional phenolic polymer. Lignin makes up between 15 and 30 percent of the weight of lignocellulosic biomass, which is an essential component. It is the most prevalent aromatic biopolymer and contains around 30% of the planet's organic carbon. The major constituents of lignin are thought to be chemical species such as hydroxycinnamyl alcohols (or monolignols), coniferyl alcohol, sinapyl alcohol, and often small amounts of p- coumaryl alcohol . INTRUDUCTION: K R MICRO NOTES 3

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5. The biological degradation of lignin is one of the most important steps in the biospheric carbon and oxygen cycle. Much of the lignin biosynthesized by plants is mineralized and returned to the atmosphere as CO2, yet the microbiology of lignin degradation is not well understood. The range of microorganisms now known to degrade lignin includes a wide variety of both fungi and bacteria. Besides, microorganisms like cyanobacteria and actinomycetes are also known for the degradation of lignin; however, the level of degradation varies with microorganisms. The degradation and transformation of lignocellulosic wastes are attributed to the metabolism of indigenous microorganisms. Different microbial population dominates at various stages and has distinct roles in the degradation of organic matter. MICROORGANISMS INVOLVED IN LIGNIN DEGRADATION K R MICRO NOTES 5

6. Bacterial degradation of wood generally occurs slowly, and on wood surfaces with high moisture content. bacteria usually invade wood cells simultaneously with fungi. The occurrence of lignin-degrading enzymes has been observed in Mycobacterium tuberculosum, M. avium, Pseudomonas syringae, P. aeruginosa, P. putida, Bordetella pertussis, Xanthomonas campestris, Escherichia coli. Traditionally, it has been suggested that actinomycetes play a role in lignocellulose breakdown, but details of the scale and methods used for such breakdown are less known. Lignin-degrading enzymes have been observed in five different species of  Streptomyces; Streptomyces antibioticus, S. griseus, S. coelicolor, S. cyaneus,  and  S. lavendulae . Among different wood-decaying fungi, only the white rots have the potential to degrade all three major components of wood entirely. These fungi mainly belong to the Ascomycetes, Deuteromycetes, or Basidiomycetes group continuation: K R MICRO NOTES 6

7. Lignin does not contain hydrolyzable linkages, stereo-irregular compound, Primarily, three different enzymes are involved in lignin degradation; manganese peroxidase (MnP), lignin peroxidase (LiP), and laccases. However, many other enzymes are participating in lignin degradation. Lignin peroxidases (LiP): Lignin peroxidase is an extracellular heme-containing peroxidase that is dependent on H2O2 and degrades a variety of lignin-related compounds. These peroxidases preferably oxidize methoxylated aromatic ring without a free phenolic group. Methoxylated benzenes and benzyl alcohols are the simplest aromatic substrates for lignin peroxidase. LiP is used commercially to mineralize a variety of recalcitrant aromatic compounds, like three- and four-ring polyaromatic hydrocarbons, polychlorinated biphenyls, and natural dyes. ENZYMES INVOLVED IN THE DEGRADATION OF LIGNIN K R MICRO NOTES 7

8. Manganese peroxidase is an extracellular heme-containing peroxidase with lignin-reducing capabilities that needs Mn2+ as its reducing substrate. These enzymes are iron protoporphyrin IX (heme) prosthetic groups attached to glycosylated proteins. The enzyme converts phenolic compounds into phenoxyl radicals by oxidizing Mn2+ to Mn3+. The resulting Mn3+ is very reactive and forms complexes with organic acids that chelate, like oxalate or malate. Because the MnP- Mn complex has a lower redox potential than lignin peroxidase, it preferentially oxidises phenolic substrate. The phenoxyl radicals produced could undergo further reactions, ultimately releasing CO2.After that, phenoxyl radicals developed. MANGANESE PEROXIDASES (MnP): K R MICRO NOTES 8

9. A class of lignin-degrading enzymes known as laccases consists of N-glycosylated extracellular blue oxidases and an active site with four copper atoms dispersed among various binding sites. Laccases catalyze the reduction of oxygen to water after oxidizing a number of aromatic hydrogen donors. Additionally, laccases not only decarboxylate and attack the methoxy side chains or groups of phenolic and methoxyphenolic acids, but also oxidize them. For the oxidation of substances like 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy) propan-1,3-diol (I) and phenolic lignin model compounds like phenol red in the presence of redox mediators, a number of fungal laccases have been taken into consideration. Many resistant chemicals, including chlorophenols, polycyclic aromatic hydrocarbons (PAHs), lignin-related compounds, and organophosphorus compounds, have been reported to be oxidized by laccases. LACCASES: K R MICRO NOTES 9

10. Moisture content: Degradation of lignin occurs most rapidly when the source is completely saturated, and free water is present. Nitrogen: the rate of lignin degradation increases with the increase in nitrogen concentration but only to a certain degree. Glucose: lignin degradation slows down with the addition of glucose as an excess of readily available energy source like glucose causes decreased consumption of lignin. Aeration: The rate of lignin and carbohydrate metabolism increases with the increase in oxygen content in the environment. Factors affecting lignin degradation: K R MICRO NOTES 10

11. Depolymerization : The depolymerization of aryl and biaryl compounds, such as -aryl ethers, is the initial stage of lignin degradation. Depolymerization of lignin happens as a result of the cleavage of the -O-4 ether bond, which accounts for at least 50% of all lignin connections. In this stage, the lignin polymer's length is reduced to create dimeric or oligomeric units, which can then be further broken down into smaller molecules. Different lignin-degrading enzymes, such as peroxidases and phenol oxidases, which are present in many bacteria, catalyse depolymerization in microorganisms. These enzymes target the lignin at random, then break down the phenolic group into free radicals, which cause the depolymerization of the lignin. Process of lignin degradation: K R MICRO NOTES 11

12. The smaller molecules of lignin formed after depolymerization are now taken by different microorganisms that catalyze a series of conversion by various in vivo enzymes. The mineralization and solubilization of oligomers and monomers result in the formation of CO2 and other essential molecules that can be utilized by the organisms. Solubilization and Mineralization: K R MICRO NOTES 12

13. Figure: Lignin biodegradation reactions. Reactions include propyl side-chain oxidation/cleavage (reaction 1), ring hydroxylation (reaction 2), and demethylation (reaction 3). Reaction 1 is characteristic of the white-rot fungus, whereas reactions 2 and 3 are characteristic of brown-rot fungus. K R MICRO NOTES 13

14. XYLAN K R MICRO NOTES 14

15. Xylans are a kind of polysaccharides that aid in the cross-linking of cellulose. Xylans play an important role in the integrity of the plant cell wall and increase cell wall recalcitrance to enzymatic digestion; thus, they help plants to defend against herbivores and pathogens (biotic stress). They are made up of -(14)-linked xylose sugar residues with side branches of -arabinofructose and -glucuronic acids. The three classes of xylans are glucoronoxylans, arabinoxylans, and glucoronoarabinoxylans.The repeating structure of xylans is absent, and many of its variations are unknown. The O-2 linked xylose residues that are frequently seen as substitutes for feruloylarabinofuranosyl side chains are a characteristic of xylans.Most xylans are to some extent acetylated, particularly in dicot secondary walls. On the O-3 and to a lesser extent on the O-2 of xylose residues, acetyl groups are connected. Introduction: K R MICRO NOTES 15

16. Structure of xylan in hardwood K R MICRO NOTES 16

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18. Bacterial xylanases are produced by bacteria like Bacillus and Streptomyces. The xylanase preparation from the alkalophile Bacillus degrades arabinoxylan to xylobiose and xylotriose as major end products with smaller amounts of higher xylooligosaccharides . Example : K R MICRO NOTES 18

19. Extracellular activity of xylan K R MICRO NOTES 19

20. Soil Microbiology(Fourth Edition of Soil Microorganisms and plant growth) - N.S.Subba Rao Soil microbiology - R.R Mishra https://microbenotes.com/microbial-degradation-of-hemicellulose/ https://microbenotes.com/microbial-degradation-of-lignin/ REFFERENCES: K R MICRO NOTES 20

21. THANK YOU K R MICRO NOTES 21