LIGNOCELLULOSE DEGRADATION

1. Legnicellolusic Biomass and
its microbial degradation
AN INTRODUCTION

2. Introduction
Need of renewable sources of energy
1. Decrease harmful effect of Climate Change
2. Fulfill future energy demands
Biomass is one of the source for renewable energy as production of biofuels.
The International Energy Agency (IEA) defines biomass as
“any plant matter that could be used directly as fuel or converted
into fuels, electricity or heat”

3. Lignocellulose
Plant cell wall polysaccharides are the most abundant organic
compounds found in nature.
Cellulose,
 Hemicelluloses
 Pectin
Lignin

4. Cellulose
The major constituent of plant cell wall
 Consists of ß-1,4 linked D-glucose units
 Linear polymeric chains of about 8000-12 000 glucose units.
Microbfibrils: crystalline form, chains together by H-bonds to form highly insoluble structures
Also having amorphous region with in microfibrils

6. Hemicelluloses
2nd most Polysaccharides in plant cell wall
Types based on sugars present in the backbone of the structural polymer.
A. Xylan.
B. Xyloglucan.
C. Galactomannan and Galactoglucomannan.

7. Schematicrepresentationofthethreemajorhemicellulosestructures.
A.Xylan.B.Xyloglucan.C.Galactomannan
(upperleft)andGalactoglucomannan(lowerright).

8. Pectin
Heteropolysaccharides, containing a backbone of α-1,4-linked D-galacturonic acid.
Two Region
1.Smooth α-1,4-linked D-galacturonic acid
2.Hairy Region (α-1,2-linked L-rhamnose)

9. Pectin Structure

10. Lignin
Phenolic polymers
Ether and Carbon-Carbon linkage provide complexity and rigidity to plant cell wall

11. Cell Wall Degrading Mechanism
Saphrophitism
Production and secretion of enzymes
Cell Wall Degrading Enzymes (CWDEs)
Releasing monomers that can be used by the microorganism as chemical energy.

12. Genus of CWDEs Producing Bacteria
Clostridium
Ruminococcus
Caldicellulosiruptor
Butyrivibrio
Acetivibrio
Cellulomonas
 Erwinia
Thermobifida,
Fibrobacter
Cytophaga, and Sporocytophaga.

13. Genus of CWDEs Producing Fungi
Distributed within the entire kingdom,
 Chytridomycetes to the advanced Basidiomycetes.

14. Cellusome Complex
Enzymes with a variety of activities
Polysaccharide lyases,
Carbohydrate esterases and
Glycoside hydrolases
Scafolding activity of dockerins part of cellusome make protein-protein cohesion allows
hydrolytic enzyeme to enter cell wall
Both Bacteria and fungal strain produce cellusome complex

15. Ethanol production from lignocellulosic biomass
Utilization of lower value substrate having promising future for ethanol production such as
baggase and wheat, maize straws and plant residues
Steps involved during lignocellulosic biomass conversion to ethanol
(i) Delignification in order to release free cellulose and hemicellulose from the lignocellulosic
material
(ii) Depolymerization of the carbohydrates polymers from the cellulose and hemicellulose to
generate free sugars
(iii) Fermentation of mixed hexose and pentose sugars to finally produce
ethanol

16. C6 and C5 carbohydrates
C6 polysaccharides are fermented by different bacterial and fungal strains
Presence of C5 sugars such as xylanose and aribanose present challenge for lignocellulosic
biomass
Naturally occurring organism having capabilities to delignify the biomass.

17. Microbial Degradation
Cellulose Degradation
Three classes of enzymes for its degradation:
1. β-1,4-endoglucanases (EGL)
2. Exoglucanases/Cellobiohydrolases (CBH)
3.β-glucosidase (BGL).

18. Hemicellulose Microbial Degradation

20. Pectin Degradation
Endo- and exo-polygalacturonases for smooth region
Endo- and exo-rhamnogalacturonases, xylogalacturonases, α-rhamnosidases, glucuronyl
hydrolases, and unsaturated rhamnogalacturonan hydrolases for hairy region

21. Lignin Degradation
Extracellular
Oxidative not hydrolytic
Lignin peroxidase (lip) (non-phenolic)
Laccase (lac)
 Manganese peroxidase (Mn+3 )
(Mnp), versatile peroxidase
H2O2-generating enzymes such as glyoxal oxidase (glox) and aryl alcohol oxidase (AOO)

22. Conclusion

23. Future research Gateways:
1. To identify naturaly occurring micro ogranisms having degrading capabilities of biomass to
produce ethanol.
2. To produce Genetically improve strains of bacteria and fungi that can
able to efficiently degrade the plant biomass.
and Strains that could be great producers of CWDEs, producing enzymatic cocktails or
cellusome for conversion of lignocellolusic biomass to ethanol.

24. Further study
Aerobic and An aerobic micro organism
Group of Enzyme
Induction of different enzymes
Gene expression