Föreläsning 10: Biological wood degradation (Module 4: Pulping and processing)

Why is it hard for microorganisms to degenerate tree?

Because lignin is a sterical hindrance and is poor in trace elements.

How do microorganisms degrade big tree polymers?

They degrade big tree polymers by secreting enzymes that break down polymers to smaller molecules that are adsorbed.

What three types are “true” tree destroying funguses?

• White rot fungi

• Brown rot fungi

• Soft rot fungi

How do you recognize white rot in tree and what do it degrade? 

• The tree is bleached, soft and easy to break 

• Everything including lignin is degraded 

How do you recognize brown rot in tree and what do it degrade?

• The tree is brown, light and hard but easily pulverized.

• It degrades cellulose and hemicellulose while modifies lignin. A lignin skeleton is left.

What fungi do decrease the trees strength the most? 

Brown rot- because of big depolymerization of cellulose. 

How do you recognize soft rot fungi in tree and what do it degrade?

• Darker wood, breaks more easily

• Degrades cellulose and hemicellulose but not the middle lamella 

Why is sap stain fungi an appearance problem more than a physical problem?

It does not degrade cell walls, only dyes the tree in strong pigments. it looks often like dirt that can be removed

The fastest invader

Why is moulds an appearance problem more than a physical problem?

It do not degrade the cell walls, only grow on surface wood and creating strong colour spores.

In the living tree, wood degrading fungi lives mainly in the heartwood. Why?

Heartwood is a non-living tissue ——> no defenses

In dead wood, wood degrading fungi lives mainly in sap wood. Why?

It is rich in nutrients

What type of rot do cause the biggest strength loss in the pulping industry?

Brown rot

what are the 3 main types of wood degrading enzymes? 

• Cellulases (breaks down cellulose), All cellulases breaks down the β-1,4-bonds hydrolytic.

• Ligninases (breaks down lignin) 

• Hemicellulases (breaks down hemicellulose)

Why is it needed to have different types of cellulases at the same time?

Because different types attack different parts of the cellulose - they cooperate.

The 4 different types:

• Cellobiohydrolase A

• Cellobiohydrolase B

They attack from the ends (non reducing end and reducing end)

• Endoglucanase C (need a carbohydrate binding molecule)

• Endoglucanase D

They attack within the chain.

What is culture filtrates and monocomponents?

Culture filtrates: Containing all types of cellulases and also hemicellulases (comercially product)

Monocomponents: Individual enzymes used separately

What are the two problems of enzymatic attack on lignin? 

• The compact structure of wood does not allow direct contact with lignin on the surface

• The non-phenolic aromates in lignin require very high oxidation potential for bering oxidized and break down. 

How can Ligninase penetrate into the lignified cell wall?

1. Ligninase use oxygen or hydrogen peroxide to oxidize a redox mediatior (I) into its active form (A), that is a radical

2. The activated redox mediator (A) is small enough to penetrate into the lignified cell wall.

3. The activated redox mediator (A) oxidize the lignin that introduce a radical on the lignin. 

4. The activated redox mediator (A) is transferred into its inactive form (I). 

5. The lignin breaks down after the oxidation and the redox mediator (I) goes back to the Ligninase for a new reaction circle. 

Name 4 lignin degraded enzymes

Lignin peroxidase: Able to oxidize non-fenolic lignin

Mangan peroxidase: Oxidize fenolic lignin by Mn2+—→ Mn3+ (Mn3+ oxidize the lignin)

Laccas: Oxidize fenoles with O2

Cellobiosedehydrogenase: Connects cellulose and lignin degradation. CBS creates Fe and H2O2 ——> creates OH radicals that degrade cellulose and lignin! (Fenton reaktionen)

Can wood rot be used for something good?

• Microorganisms is used for waste treatment 

• Wood degrading enzymes are one of the most important producers for technical enzymes.