Page 89 - Refining Biomass Residues for Sustainable Energy and Bioproducts

64 Refining Biomass Residues for Sustainable Energy and Bioproducts

Table 3.3 Composition and properties of extracellular polymeric substances.
Components Content in Function References
of EPS the EPS
matrix (%)
Polysaccharides 40 95 Adhesion, adsorption of organic Flemming and
and inorganic compounds, Wingender
aggregation of bacterial cells, (2010)
binding of enzymes, nutrient
source retention of water, and
protective barrier to cells
Proteins 1 60 Adhesion, sorption of organic and Flemming and
inorganic compounds, Wingender
aggregation of bacterial cells, (2010)
binding of enzymes, electron
donor or acceptor, retention of
water, and protective barrier to
cells
Nucleic acids 1 10 Adhesion, nutrient source, Flemming and
exchange of genetic Wingender
information, aggregation of (2010)
bacterial cells, export of cell
components, and exchange of
genetic information
Lipids 1 10 Export of cell components Flemming and
Wingender
(2010)
Humic Electron donor or acceptor, Flemming and
substances adhesion Wingender
(2010)

3.4 Molecular aspects of biopolymers

3.4.1 Molecular synthesis of polyhydroxyalkanoate
PHAs are biopolymers used by several microbes as a means of carbon and energy
storage. PHAs have drawn a lot of industrial attention because of its technological
uses as biodegradable plastics. The best studied and usually amassed PHA is poly-
hydroxybutyrate (PHB). Three well-recognized biosynthesis pathways for PHA
have been reported (Tsuge, 2002)(Fig. 3.2). The pathway I is utilized by the large
number of microbes for the formation of poly(3-hydroxybutyryl) (P3HB) monomers
from acetyl-CoA resulting from sugars where a group of enzymes are associated,
such as PhaA (3-ketothiolase), which converts acetyl-CoA to acetoacetyl-CoA,
PhaB (NADPH-dependent acetoacetyl CoA reductase, resulting in 3HB-CoA), and
PhaC (PHA synthase, polymerizing 3HB-CoA to the final monomers). The path-
ways II and III are generally found among Pseudomonas genus. These pathways