272

17 Utilization of Microbial Potential for Bioethanol Production from Lignocellulosic Waste

Table 17.3

Biological pretreatment techniques for lignocellulosic biomass and

corresponding benefits.

Sl. No.

Biomass

Microorganisms

Effects

References

1.

Corn stalks

Irpex lacteus

Hydrolysis yield is 82%

[22]

2.

Corn stover

Fungal consortium

Removal of lignin by 43.8%

[23]

3.

Corn stover

Ceriporiopsis

subvermispora

Two to three-times

increase was observed in

reducing sugar yield

[24]

4.

Bamboo culms

Punctualaria sp.

TUFC20056

Removal of lignin by 50%

[25]

5.

Plant biomass

Fungal consortium

Total termination of use of

hazardous reagents

[26]

6.

Straw

Fungal consortium

Seven times increment in

hydrolysis

[27]

7.

Wheat straw

Ceriporiopsis

subvermispora

Minimum cellulose loss

[28, 29]

8.

Eucalyptus

grandis saw

dust

Pleurotusostreatus/

Pleurotus

pulmonarius

Twenty times increment

in hydrolysis

[30]

steps during production process. To overcome this hurdle, breakdown of the lignin is

essential to alter the LCB backbone and allow further bioprocessing of the feedstock

[31]. The process of biological pretreatment of LCB prior to its enzymatic sacchari-

fication holds promise as an eco-friendly and cost-effective method. This avoidance

of the formation of inhibitory substances and subsequent removal of antimicrobial

agents present in the substrate without significant energy consumption renders the

technique immensely beneficial, as compared to the various pretreatment processes

conventionally applied in industries [20, 32, 33].

17.3.1

Potential Microorganisms Involved in Lignin Degradation

17.3.1.1

Lignin Degrading Fungi

Various studies on filamentous fungi have revealed that white- and brown-rot fungi

can degrade LCB effectively and are widely employed in the pretreatment process.

White-rot fungi are known to actively participate in the breakdown of cellulose,

hemicellulose, and lignin. Brown-rot fungi on the other hand are restricted to the

cellulose and hemicellulose fractions with minimal effect on lignin. These fungi are

known to be the potential degraders of bermuda grass, beech wood, bamboo culms,

oak wood, and red pine [34–36] as highlighted in Table 17.4. White-rot fungi are fre-

quently used for lignolytic pretreatment as whole cell microorganisms. These fungi

possess an intricate lignolytic system that secretes extracellular enzymes that effec-

tively metabolize lignin.