Biodegradation of polyhydroxyalkanoates

One of the principal reasons for the continued research on PHA as an environmentally friendly plastic is because they are biodegradable in landfill, compost and aquatic 

Upon degradation, oligomers and monomers of PHA are produced, which are then assimilated by the microorganisms as nutrients. Electron microscopy analysis of PHA films revealed that degradation occurs at the surface via enzymatic hydrolysis. The degradation is therefore a function of the surface area available for microbial colonisation. 

Besides the environmental factors, the microstructure and properties of the PHA materials themselves can significantly affect the degradation rates [203-205] this includes factors such as monomer composition, crystallinity, plasticisers or additives added to the polymer, and surface area [206]. 

Intracellular PHA depolymerases are unable to hydrolyse extracellular PHA, and vice versa. This is due to differences in the two biophysical conformations of PHA when present in different conditions. Within the cell, PHA exists in an amorphous (native) form and is covered by a monolayer of phospholipid embedded with several proteins. Within the cell, such granules are known as native PHA granules or nPHA . After the release of these native granules from the cell either by cell lysis or solvent extraction processes or after the damage of the surface layer, the polymer denatures and becomes crystalline. This type of PHA granules is known as denatured PHA granules or dPHA .  

---

Jendrossek D, Schirmer A, Schlegel HG (1996) Biodegradation of polyhydroxyalkanoic acids. Appl Microbiol Biotechnol 46 451-463... 

Byrom D. The synthesis and biodegradation of polyhydroxyalkanoates from bacteria, Int Biodeter. Biodegrad. 31 (1993) 199. 

Mergaert, J., Wouters, A., Swings, J. and Kersters, K. (1992) Microbial flora involved in the biodegradation of polyhydroxyalkanoates, in Biodegradable Polymers and Plastics, (eds M. Vert et al. Royal Society of Chemistry, Cambridge, pp. 95-100. 

Jendrossek D, Backhaus M, Andermann M (1995) Characterization of the Comamonas sp. poly(3-hydroxybutyrate) (PHB) depolymerase and of its structural gene. Can J Microbiol 41 160-169 Jendrossek D, Schirmer A, Schlegel HG (1996) Biodegradation of polyhydroxyalkanoic adds. Appl Microbiol Biotechnol 46 451—463 John ME, Keller G (1996) Metabolic pathway engineering in cotton biosynthesis of polyhydroxybutyrate in fiber cells. Proc Natl Acad Sd USA 93 12768-12773... 

J. Mergaert, A. Wouters, J. Swings and K. Kersters, "Microbial flora involved in the biodegradation of polyhydroxyalkanoates", in "Biodegradable Polymers and Plastics", M. Vert, J. Feijen, A. Albertsson, G. Scott and E. Chiellini eds.. Royal Society of Chemistry, London, 95-100, 1992. 

---