Bacterial polyhydroxyalkanoates

Abstract

Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyalkanoates (HAs) synthesized by numerous bacteria as intracellular carbon and energy storage compounds and accumulated as granules in the cytoplasm of cells. More than 80 HAs have been detected as constituents of PHAs, which allows these thermoplastic materials to have various mechanical properties resembling hard crystalline polymer or elastic rubber depending on the incorporated monomer units. Even though PHAs have been recognized as good candidates for biodegradable plastics, their high price compared with conventional plastics has limited their use in a wide range of applications. A number of bacteria including Alcaligenes eutrophus, Alcaligenes latus, Azotobacter vinelandii, methylotrophs, pseudomonads, and recombinant Escherichia coli have been employed for the production of PHAs, and the productivity of greater than 2 g PHA/L/h has been achieved. Recent advances in understanding metabolism, molecular biology, and genetics of the PHA‐synthesizing bacteria and cloning of more than 20 different PHA biosynthesis genes allowed construction of various recombinant strains that were able to synthesize polyesters having different monomer units and/or to accumulate much more polymers. Also, genetically engineered plants harboring the bacterial PHA biosynthesis genes are being developed for the economical production of PHAs. Improvements in fermentation/separation technology and the development of bacterial strains or plants that more efficiently synthesize PHAs will bring the costs down to make PHAs competitive with the conventional plastics. © 1996 John Wiley & Sons, Inc.

An Operational Framework for the Advancement of a Molecule-to-Biosphere Stoichiometry Theory

“…Relatively neglected in stoichiometry are storage organelles and associated storage molecules ( Table 1). In many organisms-like in most autotrophs and prokaryotes (Lee, 1996;Raven, 1997), storage is a major process that may disrupt the functional link described above between cell stoichiometry and other organelles (Lukas et al, 2011), as well as play many other unforeseen roles (e.g., the many roles of polyphosphates, in Bjorkman, 2014). The role of other cellular components, such as mitochondria and intracellular membranes has been given very little consideration too.…”

Crystallization Kinetics of Poly(3-hydroxybutyrate) Granules in Different Environmental Conditions

“…PHB granules heated (80 -140˚C) in acidic solution (pH 2) crystallized into partial spherulitic structures from heterogeneous nuclei (n = 0.2140) at moderate growth rates (k = 0.0725 -0.1215). PHB granules suspended in solutions of increasing pH (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) at room temperature crystallized instantaneously from heterogeneous nuclei at granule surfaces (n = 0) and high growth rates (k = 0.0428-0.7553).…”

“…From observation it is apparent that Avrami's exponent remains constant with temperature, so that n = 0.2140. Further analysis shows that the crystallization growth rate parameter increases with temperature and may follow the Arrhenius equation previously mentioned (4). Rewriting the Arrhenius equation in linear form (6) [29,30]:…”

“…In nature, PHB biopolyesters are accumulated in microbial cells as tiny intracellular amorphous granules (0.2 -0.5 μm in diameter) (see Figure 1(a)) [1][2][3][4][5]. PHB granules can be extracted from microbial cells and purified by a number of different recovery processes [6][7][8][9].…”

“…Interestingly, in different environmental conditions the rate and extent of PHB crystallization varies, which may affect the degree of particle aggregation, resulting in different size and morphology of the biopolyester granules. Purified PHB particles may be useful in a variety of applications because PHB is completely biodegradable and biocompatible [2,4,5].…”