Plant Genetic Engineering: Effective Production of Cellulosic Bio-fuel

Abstract

Biofuels provide a potential route to avoiding the global political instability and environmental issues that arise from reliance on petroleum. Currently, most biofuel is in the form of ethanol generated from starch or sugar, but this can meet only a limited fraction of global fuel requirements. Conversion of cellulosic biomass, which is both abundant and renewable, is a promising alternative. However, the cellulases and pretreatment processes involved are very expensive. Genetically engineering plants to produce cellulases and hemicellulases, and to reduce the need for pretreatment processes through lignin modification, are promising paths to solving this problem, together with other strategies, such as increasing plant polysaccharide content and overall biomass.

Table of Contents

Abstractii

Introduction1

The basics of cellulosic ethanol production1

The Cellulosic Ethanol Production Process2

Cell-wall-deconstructing enzymes3

Genetic manipulation of feedstock crops4

Production of hydrolysis enzymes in plants4

Increasing plant cellulosic biomass6

Decreasing the need for pretreatment7

Conclusion7

End Notes9

Plant Genetic Engineering: Effective Production of Cellulosic Bio-fuel

Introduction

Finite petroleum reserves and the increasing demands for energy in industrial countries have created international unease. For example, the dependence of the United States on foreign petroleum both undermines its economic strength and threatens its national security [1]. As highly populated countries such as China and India become more industrialized, they too might face similar problems. It is also clear that no country in the world is untouched by the negative environmental effects of petroleum extraction, refining, transportation and use. For these reasons, governments around the world are increasingly turning their attention to biofuels as an alternative source of energy.

The biofuel that is expected to be most widely used around the globe is ethanol, which can be produced from abundant supplies of biomass from all land plants and plant-derived materials, including animal manure, starch, sugar and oil crops that are already used for food and energy. In addition, ethanol has a low toxicity, is readily biodegradable and its use produces fewer air-borne pollutants than petroleum fuel. The growth of feedstock crops for bioethanol production also reduces greenhouse gas levels, mainly because of the use of atmospheric carbon dioxide in photosynthesis. Although the conversion of biomass to ethanol and the burning of ethanol produce emissions, the net effect can be a large reduction in greenhouse gas emissions compared with petroleum fuel, meaning that the use of bioethanol does not contribute to an increase in net atmospheric carbon dioxide[2].

Starch- and sugar-derived ethanol already makes a relatively small but significant contribution to global energy supplies. In particular, Brazil produces relatively cheap ethanol from the fermentation of sugarcane sugar to supply one quarter of its ground transportation fuel. In addition, the United States produces ethanol from corn grain. However, even if all the corn grain produced in the United States were converted into ethanol, this could only supply about 15% of that country's transportation fuels. Meeting US fuel requirements using starch would mean that corn grain production must be increased or corn grain be diverted from other uses. For example, 50.8% of total US corn grain production is currently used for livestock feed[3], and ...