Enzymes in certain bacteria help to produce a host of natural, biodegradable polyesters from basic nutrients.

Bacterial bioplastics are polyesters produced naturally by certain bacteria. These polyesters serve as carbon stores when carbon is plentiful but limited supplies of other nutrients make continued growth and reproduction impossible. The variety of polymers that these bacteria produce is quite broad. In addition, the enzymes responsible for polyester polymerization are so flexible that they can theoretically catalyze the polymerization of any simple organic molecule that contains the appropriate hydroxyl (OH) and carboxyl (COOH) groups needed to form an “ester” bond.

References

“Polyhydroxyalkanoates (PHAs; also known as bacterial bioplastics) accumulate as carbon reserve material in response to the availability of excess carbon source when growth is limited owing to starvation of other nutrients such as nitrogen and phosphorus…PHAs can vary substantially in composition, as there are over 150 known constituents, resulting in an enormous diversity of material properties. PHAs exhibit a crystallinity ranging from 30% to 70% and a melting temperature of 50 °C to 180 °C; these thermoplastic material properties make PHAs commercially relevant as renewable and biodegradable alternatives to oil-based plastics.” (Rehm 2010:9)

“Bacterial bioplastics can be processed into materials that are suitable to replace oil-based materials in many applications, including film, fibres, moulded products, extruded goods, coatings and adhesives.” (Rehm 2010:10)

“Owing to the broad substrate specificity of [the enzyme] PHA synthase (PhaC), any organic molecules containing a carboxyl and a hydroxyl group that can be converted to the respective CoA thioester can, in principle, be incorporated into a high-molecular-mass PHA72. The biosynthesis pathways of the activated PHA precursor, (R)-3-hydroxyacyl-CoA, have been extensively studied and exploited through metabolic engineering, leading to the production of modified PHAs…” (Rehm 2010:10)

E. coli harbouring the polyhydroxybutyrate (PHB) biosynthesis genes from Ralstonia eutropha [now known as Cupriavidus necator] (and, if relevant, genes from other bacterial species) has been commonly used for the production of PHA composed of (R)-3-hydroxybutyrate and (R)-3-hydroxyvalerate and/or (R)-3-hydroxyhexanoate, and these polymers show material properties (such as increased elasticity and decreased brittleness) that are preferred for various industrial applications” (Rehm 2010:11)

“[T]he cell, as a biosynthesis machine, can use cheap carbon sources as precursor substrates, such as waste products (glycerol, whey and so on)” (Rehm 2010:12)

Journal article
Bacterial polymers: biosynthesis, modifications and applicationsNature Reviews MicrobiologyJune 28, 2010
Rehm BHA

Journal article
Perspectives for Biotechnological Production and Utilization of Biopolymers: Metabolic Engineering of Polyhydroxyalkanoate Biosynthesis Pathways as a Successful ExampleMacromol. BiosciFebruary 12, 2001
Steinbüchel A

Living System/s

Organism
Soil bacteriumRalstonia eutrophaSpecies