17.6 Conclusion and Future Prospects

279

Table 17.5

List of microorganisms, biomass, and ethanol yielded.

Sl. No.

Microorganism

Bioethanol yield (%)

Biomass

References

1.

Pichia stipitis NRRL

Y-7124

Pichia stipitis

0.35 g/g yield

0.41 g/g yield

Wheat

straw

[20, 33]

2.

Genetically modified

organism, E. coli KO11

91.50% yield, 3.15% (w/v)

ethanol titer

Bagasse

[20]

3.

Candida shehatae

NCL-3501

Saccharomyces

cerevisiae ATCC 26603

Pichia stipites NRRL

Y-7124

0.45 and 0.5 g/g of sugar taken

up, production from auto

hydrolysate by free and

immobilized cells in 48 h. 0.37

and 0.47 g/g of sugar taken

up, production from acid

hydrolysate by free and

immobilized cells in 48 h.

Ethanol production was 4 g/l

Ethanol production was 6 g/l

Rice

straw

[25]

enzyme, and other components are sent for wastewater treatment. Different

organisms tend to yield different quantities of ethanol with respect to fermentation

of specific substrates. The ethanol yields by microorganisms from diverse substrates

are listed in Table 17.5.

17.6

Conclusion and Future Prospects

Many researchers have independently reported the potential role of different

fungi and bacteria in the bioprocessing of LCB to bioethanol. However, their

large-scale implementation in industries is limited because of high cultivation

time and selective performance of microbes to substrates. Recent advancement in

biotechnology has opened doors for application of genetically engineered microbial

strain to manipulate their biosynthetic pathways for rapid production of enzymes in

short span of time. These enzymes can also be tailored to produce effective results

increasing the yield. Microbes can also be engineered to overcome the toxic and

inhibitory substances produced during the fermentation process by activating their

survival mechanisms through altered stress response genes, membrane proteins,

and heat shock proteins. Efforts can be made to study the interactions between

potential microbes and their use as a consortium in depolymerization and sacchar-

ification process. The recalcitrant nature of LCB for hydrolysis, release of inhibitory

substances, and long resident time has negatively impacted the bioethanol pro-

duction. However, with proper selection of microbes and optimized techniques,

application of microbes in bioethanol production can be commercialized.