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Role of microorganisms in degradation of cellulose, hemicellulose, and lignin

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In this presentation, degradation of three major biopolymers of plant-biomass has been explained. The focus is on identifying predominate microorganisms involved in degradation and enzymes they secrete.

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Role of microorganisms in degradation of cellulose, hemicellulose, and lignin

  1. 1. Role of Microorganisms in Degradation of Cellulose, Hemicellulose, and Lignin Submitted by: Prakhar Deroliya, 183180009 M. Tech-1st year Swastik Sahoo, 18I180004 M. Sc-1st year Submitted to: Prof. Suparna Mukherji Head of Department CESE, IITB Center for Environment Science and Engineering Indian Institute of Technology Bombay 1
  2. 2. Outline • Introduction • Cellulose and role of microbes in its biodegradation • Hemicellulose and role of microbes in its biodegradation • Lignin and role of microbes in its biodegradation • Summary 2
  3. 3. Introduction • Cellulose, hemicellulose, & lignin are predominate biopolymers of plant cell wall • Together, they are termed as Lignocellulose Cellulose • Cellulose >> important structural component of primary cell wall of green plants, algae & oomycetes • A major component (up to 45 %) of plant biomass • Also present in secondary cell wall which increases wall rigidity 3
  4. 4. Introduction… Hemicellulose • Hemicellulose makes up 25-30 % of total wood dry weight • Present along with cellulose in almost all plant cell walls Lignin • Lignin is also an important component in plant cell wall • A group of complex organic polymers of plant cell wall • Held with cellulose, hemicellulose, and pectin • Imparts mechanical strength to plant cell wall 4
  5. 5. Cellulose and Role of Microorganisms in its Degradation • Cellulose > the most abundant biopolymer on this earth. • Hydrophilic, insoluble and chiral • The monomeric unit is D-glucose linked together with β-1,4 glycosidic bond > forms linear chain • Subunits of this chain > cellobiose • Linear chains > elemental fibrils > microfibrils > macrofibrils 5
  6. 6. Key enzymes involved in cellulose degradation KeyEnzymesInvolved Endoglucanases Cellobiohydrolases β-glucosidase • EGs are capable of breaking β-1-4 glycosidic bonds between D-glucose units. • Release new terminal ends in the process • Effective in degrading amorphous cellulose • Cannot degrade crystalline cellulose efficiently • CBHs also cleave β-1-4 glycosidic bond. • Can degrade both amorphous and crystalline cellulose, also degrade EG- generated chain ends • Key enzyme for converting cellobiose units to glucose > β-glucosidase 6
  7. 7. Degradation ways and important microorganisms • Aerobic degradation  90 to 90 % of cellulose degradation is by aerobic degradation  Synergistic relationship between celluolytic and non-cellulolytic organisms is essential. 15 fold increase in activity if in synergy  End products are carbon dioxide and water  Well studied organisms are Cellulomonas, Pseudomonas, and Streptomyces.  Trichoderma reesei is commercially successful and prevalent aerobic microorganism • Anaerobic degradation • 5 to 10 % of cellulose degradation is by this mechanism • Use cellulosome >> a large complex of enzymes • End products are carbon dioxide, methane and water • Cellulosome has a protein which binds the enzyme complex to the substrate. • Example: Clostridium thermocellum 7
  8. 8. Hemicellulose and Role of Microorganisms in its Degradation • Monomeric units of hemicellulose are D- xylose, D-mannose, D-galactose, D- glucose, L-arabinose, 4-O-methyl- glucuronic, D-galacturonic and D- glucuronic acid • Predominate linkage > β-1,4 glycosidic bond. Also, β-1,3 glycosidic bonds are found at some places • Polysaccharides > glucose, xylose, mannose, galactose, rhamnose, and arabinose • Present in all plant cell walls with cellulose • Less resistant against biodegradation • Easily hydrolyzed by dilute acid or base as well as a large group of hemicellulase enzymes 8
  9. 9. Key enzymes involved in hemicellulose degradation Hemicellulolytic Enzymes Xylan Endo-1,4- beta-xylanase Forms xylose 1,4-beta xylosidase Forms xylose Xylan and Mannan Xylan esterases Form xylose and mannose P-coumaric esterases Forms xylose and Mannose Ferulic esterases Forms xylose and Mannose α-1- arbionfuranos idase Forms xylose and mannose α-1-O- methylglucur onidasse Forms xylose and mannose 9
  10. 10. Key enzymes involved in hemicellulose degradation Hemicellulolytic Enzymes O-acetyl-4-O-methyl glucuronoxylan Endoxylanse Acetyl esterase α-glucuronidase β-xylosidase O- acetylgalactoglu comanann Endomananases 10
  11. 11. Important microorganisms in hemicellulose degradation • White-rot fungus like Phanerochaete chrysosporium which produces xylanases, a major component of hemicellulolytic enzymes • Several aerobic species and ruminal genera bacteria also produce xylanases • Thermophilic xylanases are also found to be secreted by actinobacteria like Thermomonospora and Actinomadura • Hyperthermophilic thermotoga secrets thermostable xylanase • At alkaline pH, Streptomyces viridosporus secrets xylanases • Thermophilic and mesophilic fungi have also been researched for xylanases • β-xylosidase are less common than endo-xylanases. However, they are larger than xylanases. Found in T. reesei, P. chrysosporium, B. stearothermophilus and Butyrivibrio fibrisolvens • Endomananases >> white-rot fungi and ascomycetes • α-galactosidases and acetylglucomananesterases > Aspergillus • β-mannonidases are from the fungi Polyporus sulphureus and A. niger 11
  12. 12. Lignin and Role of Microorganisms in its biodegradation • Lignin cross-links different plant polysaccharides • It is a tasteless, insoluble, fibrous, and hydrophobic • Amorphous heteropolymer • Three methoxylated monolignols precursors • P-coumaryl alcohol (1) • Coniferyl alcohol (2) • Sinapyl alcohol (3) • 4-hydroxyphenylpropanoids are formed with syringyl, p-hydroxyphenyl, and guaiacyl • It provides structural strength, impermeability, microbial-attack-resistant, and oxidative stress 12
  13. 13. Key Enzymes Involved in Degradation of Lignin Ligninolysis Peroxidases Lignin Peroxidase Manganese- dependent peroxidase Versatile Peroxidase Dye- decolorizing peroxidase Laccases 13
  14. 14. Important microorganisms in lignin biodegradation • White-rot fungi, particularly Phanerochaete chrysosporium are capable of degrading wood-lignin with appreciable efficiency • Aspergillus, Myceliophora thermophila, and Chaemotium thermophilum have been used to isolate many ligninolytic enzymes • Actinobacteria and Streptomyces genus has also been reported to carry out degradation of lignin using ligninolytic enzymes 14
  15. 15. Summary 15
  16. 16. List of References Be´ guin, P, Aubert, JP. (1994) The biological degradation of cellulose. FEMS Microbiol Rev, 13:25–58 Brown, Chang. (2014) Exploring bacterial lignin degradation. Current Opinion in Chemical Biology, 19: 1-7. David B Wilson. 2011 Microbial diversity of cellulose hydrolysis. Current Opinion in Microbiology 2011, 14: 259-263 Davin LB, Lewis NG. Lignin primary structures and dirigent sites. Current Opinion in Biotechnology. 16 (4): 407-415 Dimarogona M, Topakas E, Christakopoulos P. (2012) Cellulose degradation by oxidative enzymes. Computational and Structural Biotechnology Journal, 2 (3): e201209015. Gonzalo, Colpa, Habib, Fraaije. 2016 Bacterial enzymes involved in lignin degradation. Journal of Biotechnology, 236 : 110-119. Klemm, Dieter; Heublein, Brigitte; Fink, Hans-Peter; Bohn, Andreas. 2005. Cellulose: Fascinating Biopolymer and Sustainable Raw Material. Angew. Chem. Int. Ed., 44 (22): 3358–93. 16
  17. 17. List of References Pe´rez J, Munoz-Dorado, Rubia T, Martinez J. 2002 Biodegradation and biological treatments of cellulose, hemicellulose and lignin: an overview. Int Microbiol, 5: 53-63. Scheller HV, Ulvskov P. 2010 Hemicelluloses. Annu Rev Plant Biol. ;61:263-89. DOI: 10.1146/annurev-arplant- 042809-11=2315 17
  18. 18. Image sources for-lignocellulose 18
  19. 19. THANK YOU 19