Page 71 - Biodegradable Polyesters

3.3 The Diversity of Biopolyesters 49

Pseudomonas aeruginosa

Polyester granulum

Figure 3.2 Electron microscopy image of Pseudomonas aeruginosa-accumulating polyester
granules. (Ref. [17], reprinted with permission of Horizon Scientific Press.)
necessitates that the soluble PHA synthases are transformed into amphipathic
enzymes upon elongation of water-insoluble polyester chains, which remain
covalently attached to the enzyme. As such, a self-assembly process might be
instigated, leading to the formation of insoluble cytoplasmic inclusions with a
proposed phospholipid monolayer and covalently attached PHA synthases at the
surface.
PHA research has spent many years in order to properly comprehend the pro-
duction of these biopolymers and to examine the isolated crystallized biopoly-
mers, its material properties, and possible application [10, 12, 18, 19]. There is
greater understanding of the applied potential of biological and biopolymer-based
self-assembly systems as well as bio-nanostructures, the granules formed inside
the bacterial cells which can be functionalized by bioengineering; with this, the
interest from the greater scientific community is also increasing.
In 2002, one of the original world-wide granted patents was filed, related to
ex vivo applications of engineered biopolyester nanoparticles. The size, core
composition, and surface functionality can be highly controlled and provides a
platform technology for the production of functionalized, biocompatible, and
biodegradable nanoparticles, which can be applied for drug delivery, diagnostics,
bioseparation, protein immobilization, and so on [20–22]. These bioparticles
could be used to display proteins or for protein production [20, 22, 23]. The
molecular tools for the production of tailor-made beads will be compiled with.

3.3
The Diversity of Biopolyesters

The biologically produced biopolyesters comprise a complex class of polyox-
oesters [1–4] The majority of prokaryotes synthesize PHB and/or other PHAs
composed of medium-chain length (R)-3-hydroxyfatty acids (6–14 carbon atoms)
as reserve material. These polyesters are deposited as spherical water-insoluble
inclusions in the cytoplasm (Figure 3.2). The biopolyester comprises the core of
the granule. More than 150 different hydroxyalkanoic acids are known to occur
as parts of PHAs implying that the respective CoA thioester are accepted as
substrates by the PHA synthases (Figure 3.1). Some representative constituents
are displayed in Figure 3.3.