One strategy to reduce investment and operational costs in LC biomass processing is to internalize enzyme
production and combine enzymatic hydrolysis with fermentation.This is known as consolidated bioprocessing
(CBP) and can be achieved using a microorganism that possesses the dual ability to produce biomass-hydrolyzingenzymes and ferment sugars to products of commercial interest, thus allowing a one-pot type bioconversion
process in which process integration is maximized [5].While CBP is considered to be an ultimate aim for
biorefining, the ways to achieve this goal are not simple.Although the number of naturally occurring, biomassdegrading
microorganisms is no doubt large, those that possess the ability to hydrolyze LC biomass and ferment
free sugars into target products, such as ethanol, butanol,hydrogen, fatty acid ethyl esters (FAEE) or isopropanol,
at industrially compatible rates and titers, are probably very rare and so far undiscovered [6]. Additionally, many
of the best known biomass-degrading microorganisms display low β-glucosidase (cellobiase) activity, meaning
that the hydrolysis of cellobiose constitutes a rate-limiting step during the enzymatic processing of cellulose
[7–9]. Therefore, engineering cellobiose-degrading ability into microorganisms is a vital step towards the development
of cellulolytic biocatalysts suitable for CBP. In this respect, examples of recent work performed on Saccharomyces
cerevisiae, the current workhorse of biotechnological processes, are noteworthy [10–12]. In these
studies, even though the engineered S. cerevisiae strains exhibited poor cellulose-degrading ability, the fact that
they both produce significant cellobiase activity means that their incorporation into a simultaneous saccharification
and fermentation (SSF) process is likely to reduce the loading of external cellulases and thus overall process
cost [10].