Agro-industrial lignocellulosic waste: An alternative to unravel the future bioenergy

Abstract

Dwindling reserves of fossil fuel and petroleum derivatives, rising oil prices, concern about environmental impact, and supply insecurity demand environmentally sustainable energy sources. Production of fuels and chemicals through microbial fermentation of plant material that uses renewable feedstock is a desirable alternative to petrochemicals. Lignocellulose represents the most widespread and abundant source of carbon in nature and is the only source that could provide a sufficient amount of feedstock to satisfy the world's energy and chemical needs in a renewable manner. Typically, most of the agricultural lignocellulosic biomass is comprised of about 10-25% lignin, 20-30% hemicellulose, and 40-50% cellulose. The processing and utilization of this substrate are complex, differing in many aspects from crop-based ethanol production. Sustainable and economically viable manufacturing of bioethanol from lignocellulose raw material is dependent on the availability of a robust ethanol-producing microorganism, able to ferment all sugars present in the feedstock. Thus, an obvious target in the field of metabolic engineering has been the tailoring of such a microorganism, combining advantageous traits from different microorganisms with classical procedures such as random mutagenesis. Nowadays research is being directed to develop metabolically and genetically engineered Saccharomyces strains and other ethanol-fermenting microbes that has the potential to utilize wide range of substrates including pentose and hexose sugars, ability for direct and efficient ethanol production from cellulosic materials, and ability to tolerate ethanol stress. Although it is still in its infancy, metabolic engineering and synthetic biology offer great potential to overcome the challenges associated with lignocellulose bioconversion.