Table 1.

Main characteristics of the model bacterial polymers BC, PHA, and PGA.

	BC	PHA	PGA
Chemical structure	Polysaccharide (Figure 1A) Glucose (glc) homopolymer. Properties of the polymer depend on culture conditions Hydrophilic	Polyester (Figure 1B) High diversity. Polymer properties rely on its monomer combination Hydrophobic	Polyamide (Figure 1C) Anionic. D- or L-glutamic acid (glu) homopolymers, or D-/L-glu copolymers Hydrophilic
Industrial production prototype bacteria	Species belonging to Komagataeibacter genus, K. xylinus	High diversity Scl-PHA Cupriavidus necator, Halomonas spp. Mcl-PHA Pseudomonas spp.	Bacillus spp., B. subtilis
Precursors at industrial production level	Direct: sugars, preference depends on the species	Direct: fatty acids	Direct: glutamic acid
	Indirect: ethanol, converted into acetate, and, finally, glc through tricarbolxylic acid cycle (TCA) and gluconeogenesis (GNG) (Figure 2)	Indirect: sugars through TCA and de novo synthesis of fatty acids (Figure 3)	Indirect: sugars, through TCA and alpha-ketoglutarate (α–KG) conversion into glutamic acid (Figure 4)
Culture conditions for pure cultures industrial production	Submerged fermentation Mainly in static conditions for biomedical applications	Submerged fermentation Batch and Fed-Batch strategies	Submerged and solid-state fermentation
Downstream processing	Extracellular polymer. Easy, cheap purification, isolation, and alkali treatment	Intracellular polymers. Costly purification, cell lysis, release, and polymer isolation	Extracellular polymer. Precipitation by chelation, solubility reduction or filtration