Page 105 - Biofuels Refining and Performance

88 Chapter Three

S. cerevisiae and Z. mobilis cannot utilize pentoses [14, 57]. Several
genetic modifications have been performed for utilization of arabinose
and xylose by Z. mobilis. However, S. cerevisiae has been more welcomed
for industrial application, probably because of the industrial problems
that may arise in working with bacteria. Separation of S. cerevisiae from
fermentation media is much easier than separation of Z. mobilis, which
is an important characteristic for reuse of the microorganisms in ethanol
production processes.
Using genetically engineered bacteria for ethanol production is also
applied in many studies. Ingram et al. [58] have reviewed metabolic
engineering of bacteria for ethanol production. Recombinant Escherichia
coli is a valuable bacterial resource for ethanol production. Construction
of E. coli strains to selectively produce ethanol was one of the first suc-
cessful applications of metabolic engineering. E. coli has several advan-
tages as a biocatalyst for ethanol production, including the ability to
ferment a wide spectrum of sugars, no requirements for complex growth
factors, and prior industrial use (e.g., for production of recombinant
protein). The major disadvantages associated with using E. coli cultures
are a narrow and neutral pH growth range (6.0–8.0), less hardy cultures
compared to yeast, and public perceptions regarding the danger of E. coli
strains. Lack of data on the use of residual E. coli cell mass as an ingre-
dient in animal feed is also an obstacle to its application [8].
Recently, the Japanese Research Institute of Innovative Technology
for the Earth (RITE) developed a microorganism for ethanol production.
The RITE strain is an engineered strain of Corynebacterium glutamicum
that converts both pentose and hexose sugars into alcohol. The central
metabolic pathway of C. glutamicum was engineered to produce ethanol.
A recombinant strain that expressed the Z. mobilis gene coding for pyru-
vate decarboxylase and alcohol dehydrogenase was constructed [59].
RITE and Honda jointly developed a technology for production of ethanol
production from lignocellulosic materials using the strain. It is claimed
that application of this strain by using engineering technology from
Honda enables a significant increase in alcohol conversion efficiency, in
comparison to conventional cellulosic–bioethanol production processes.

3.11.3 Filamentous fungi
A great number of molds are able to produce ethanol. The filamentous
fungi Fusarium, Mucor, Monilia, Rhizopus, Ryzypose, and Paecilomyces are
among the fungi that can ferment pentoses to ethanol [33]. Zygomycetes
are saprophytic filamentous fungi, which are able to produce several
metabolites including ethanol. Among the three genera Mucor, Rhizopus,
and Rhizomucor, Mucor indicus (formerly M. rouxii) and Rhizopus oryzae
have shown good performances on ethanol productivity from glucose,