Full text loading...
Chapter 5 : Consolidated Bioprocessing of Cellulosic Biomass to Ethanol Using Thermophilic Bacteria
Category: Applied and Industrial Microbiology
Ebook: Choose a downloadable PDF or ePub file. Chapter is a downloadable PDF file. File must be downloaded within 48 hours of purchase
This chapter considers use of thermophilic bacteria to produce ethanol in a consolidated bioprocessing (CBP) configuration. It mainly focuses on cellulose conversion, as it represents the largest technical challenge for development of CBP-enabling microorganisms, with an emphasis on recent developments pertaining to processing of cellulose by cellulolytic microorganisms. Thermophilic bacteria was first considered for CBP with respect to diversity and ecology, utilization of nonglucose sugars, and ethanol tolerance. Since some pretreatment processes solubilize essentially all of the hemicellulose, it may or may not be necessary that insoluble hemicellulose be enzymatically hydrolyzed in the context of industrial processing of cellulosic biomass. The major component of angiosperm hemicellulose is xylan that can be esterified or acylated by phenolic residues such as ferulic acid and p-coumaric acid. Therefore, it is not surprising that hemicellulolytic bacteria must express a large set of cooperating enzymes in order to efficiently and completely hydrolyze hemicellulose and assimilate products of this hydrolysis. The authors concluded that a system similar to catabolite repression may be responsible for the apparent inhibition of cellulase synthesis and proposed that over time as cellobiose was metabolized, its concentration would drop below the point necessary to inhibit cellulase transcription. This work contradicted earlier studies which had concluded that the endoglucanase activity in C. thermocellum was constitutive.
Physiological characteristics and phenotypes of discussed species
Comparative rates of cellulose hydrolysis under dilute conditions