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Concept
Polyhydroxyalkanoates
Summary
Polyhydroxyalkanoates or PHAs are polyesters produced in nature by numerous microorganisms, including through bacterial fermentation of sugars or lipids. When produced by bacteria they serve as both a source of energy and as a carbon store. More than 150 different monomers can be combined within this family to give materials with extremely different properties. These plastics are biodegradable and are used in the production of bioplastics.
They can be either thermoplastic or elastomeric materials, with melting points ranging from 40 to 180 °C.
The mechanical properties and biocompatibility of PHA can also be changed by blending, modifying the surface or combining PHA with other polymers, enzymes and inorganic materials, making it possible for a wider range of applications.
To induce PHA production in a laboratory setting, a culture of a micro-organism such as Cupriavidus necator can be placed in a suitable medium and fed appropriate nutrients so that it multiplies rapidly. Once the population has reached a substantial level, the nutrient composition can be changed to force the micro-organism to synthesize PHA. The yield of PHA obtained from the intracellular granule inclusions can be as high as 80% of the organism's dry weight.
The biosynthesis of PHA is usually caused by certain deficiency conditions (e.g. lack of macro elements such as phosphorus, nitrogen, trace elements, or lack of oxygen) and the excess supply of carbon sources. However, the prevalence of PHA production within either a mono-culture or a set of mixed-microbial organisms can also simply be dependent on overall nutrient limitation, not just macro elements. This is especially the case in the 'feast/famine' cycle method for induction of PHA production, wherein carbon is periodically added and depleted to cause famine, which encourages cells to produce PHA during 'feast' as a storage method for periods of famine.
Polyesters are deposited in the form of highly refractive granules in the cells.
Official source
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