John Mcbride

Recent progress in consolidated bioprocessing.

Consolidated bioprocessing, or CBP, the conversion of lignocellulose into desired products in one step without added enzymes, has been a subject of increased research effort in recent years. In this review, the economic motivation for CBP is addressed, advances and remaining obstacles for CBP organism development are reviewed, and we comment briefly on fundamental aspects. For CBP organism development beginning with microbes that have native ability to utilize insoluble components of cellulosic biomass, key recent advances include the development of genetic systems for several cellulolytic bacteria, engineering a thermophilic bacterium to produce ethanol at commercially attractive yields and titers, and engineering a cellulolytic microbe to produce butanol. For CBP organism development, beginning with microbes that do not have this ability and thus requiring heterologous expression of a saccharolytic enzyme system, high-yield conversion of model cellulosic substrates and heterologous expression of CBH1 and CBH2 in yeast at levels believed to be sufficient for an industrial process have recently been demonstrated. For both strategies, increased emphasis on realizing high performance under industrial conditions is needed. Continued exploration of the underlying fundamentals of microbial cellulose utilization is likely to be useful in order to guide the choice and development of CBP systems.

Consolidated bioprocessing for bioethanol production using Saccharomyces cerevisiae.

Consolidated bioprocessing (CBP) of lignocellulose to bioethanol refers to the combining of the four biological events required for this conversion process (production of saccharolytic enzymes, hydrolysis of the polysaccharides present in pretreated biomass, fermentation of hexose sugars, and fermentation of pentose sugars) in one reactor. CBP is gaining increasing recognition as a potential breakthrough for low-cost biomass processing. Although no natural microorganism exhibits all the features desired for CBP, a number of microorganisms, both bacteria and fungi, possess some of the desirable properties. This review focuses on progress made toward the development of bakers yeast (Saccharomyces cerevisiae) for CBP. The current status of saccharolytic enzyme (cellulases and hemicellulases) expression in S. cerevisiae to complement its natural fermentative ability is highlighted. Attention is also devoted to the challenges ahead to integrate all required enzymatic activities in an industrial S. cerevisiae strain(s) and the need for molecular and selection strategies pursuant to developing a yeast capable of CBP.

Energy Myth Three – High Land Requirements and an Unfavorable Energy Balance Preclude Biomass Ethanol from Playing a Large Role in Providing Energy Services

In debates over whether the United States could transition to a transportation sector run on bio-fuels, it is often said that the country does not possess enough land to simultaneously feed and fuel the nation. This chapter explores the potential sufficiency of biomass resources in the context of large-scale provision of energy services. Only cellulosic biomass is considered here, as this class of biomass feedstocks is generally seen as having the greatest potential for large-scale energy production. Analysis is focused on production of ethanol, a promising liquid fuel, and on studies of the biomass resource sufficiency of the United States. Some reference is also made to the more limited literature aimed at the important question of evaluating the potential of biomass energy on a global scale. Ultimately, we believe that biomass merits consideration as a large-scale provider of energy services as the world looks for paths by which to realize a sustainable and secure future. Rather than only adding one more point estimate to the already large pool of evaluations in the literature, we also intend that this chapter contribute to understanding the factors that determine biomass resource sufficiency and why different analyses of this question reach such disparate conclusions.