Page 19 - Advances in bioenergy (2016)

Chapter 1

Figure 1.1 Strategies of metabolic engineering revolve around the understanding,
design, and engineering of metabolic networks and pathways to produce desired
molecular products from biological platforms. These strategies employ techniques and
technologies from a range of disciplines, from omics technology to synthetic biology.

Figure 1.2 Metabolic network of biofuel production pathways and intermediates for the
conversion of feedstocks to fuels (bold text): current biofuels ( ), higher chain
alcohols ( ), lignocellulosic fermentation ( ), and fatty acid derivatives ( ).
Engineering the desired biofuel pathway requires maximizing flux through the relevant
nodes while minimizing metabolite flux to competing branches. This can involve tuning
expression of intermediate reaction steps, deletion of competing pathways, or

manipulation of distal enzymatic or regulatory targets.
Chapter 2

Figure 2.1 Cellulose structure is formed by β-(1,4)-linked D-glucose units, where

adjacent D-glucoses are flipped making cellobiose the fundamental repeating unit. The
inter- and intramolecular hydrogen bonds (shown as dots) and van der Waals
interactions form recalcitrance microfiber structures.

Figure 2.2 An overview of cellulose hydrolysis by the synergistic action of cellulolytic
enzymes; the β-1,4-endoglucanases (EG5) catalyze the hydrolysis of the main chain of
cellulose located in the amorphous region, resulting in nonoxidized chain ends,
whereas polysaccharide monooxygenases of GH family 61 (CEL61) catalyze
oxidatively possibly the crystalline region, resulting in oxidized chain ends.
Cellobiohydrolases hydrolyze cellulose chain ends from the reducing (CBH7) or
nonreducing (CBH6) end in a processive manner to produce cellobiose or oxidized
cellobiose, depending on the preceded family of enzymes that made the nick on
cellulose surface. The processive action of cellobiohydrolases generates a majority of
cellobiose that could be further hydrolyzed to D-glucose by β-D-glucosidases (BGL3).

Figure 2.3 Microbial conversion of glucose to ethanol under anaerobic conditions. The
enzymes catalysing the main biochemical steps are indicated. Most microorganisms
catabolize glucose through the glycolytic pathway (EMP). Although there are many
aerobic bacterial species that use the ED pathway, Zymomonas is the only known
microbial genus that uses this pathway under anaerobic conditions. LFP, pyruvate
formate lyase; LDH, lactate dehydrogenase; PEP: phosphoenolpyruvate; PPP, pentose

phosphate pathway; DHAP, dihydroxyacetone phosphate; KDPG, 2-keto-3-deoxy-6-
phosphogluconate.

Chapter 4

Figure 4.1 Schematic flow diagram of a biomass catalytic pyrolysis unit: regenerator
(D-101), biomass feed hopper (D-61), mixing zone (D-201), reactor/riser (D-202),
stripper (D-301), lift line (D-305), bio-oil recovery vessels (D-402, D-407), and heat
exchangers (HE-101, HE-401, and HE-403).