BIOPOL - PHB Accumulation in Micro-organisms

PHB material was first described in 1926 by Lemoigne. PHB is a very common and widespread storage material in many micro-organisms. PHB has been found to be a very basic polymer of variety of chemically similar polymers, the polyhydroxyalkonates. Poly - beta hydroxy butyrate (PHB) accumulates as energy reserve material in many micro-organisms like Alcaligenes, Azotobacter, Bacillus, Nocardia, Pseudomonas, Rhizobium etc. PHB has physical properties comparable with polypropylene (PP). Poly - beta hydroxy butyrate (PHB) consists repeat units of CH(CH₃)-CH₂ -CO-O. The difference is that PP shows insignificant degradation while PHB shows complete degradation. PHB sinks while PP floats. Therefore, degradation is easy at sediment. Alcaligenes eutrophusand Azotobacter beijerinckii can accumulate upto 70% of their dry weight of PHB. These micro-o rganisms can produce the polymer in environment of N and P limitation. Minimum 40-50% of the dry weight of this polymer is required for making the process commercially viable. Extraction of PHB is done by using solvents like halogenated hydrocarbons and purification is done. Moulding and extrusion of dried cells directly is possible when PHB contents are high. A lot of work is done on engineering polymeric properties of PHB. However PHB is suitable for specialized areas like biomedical use and speciality coatings. 

PHB Accumulation in Micro-organisms

Organisms with PHB accumulation	% of dry weight of the cell
Alcaligenes eutrophus	96
Azospirillum	75
Azotobacter	73
Baggiatoa	57
Leptothrix	67
Methylocystis	70
Pseudomonas	67
Rhizobium	57
Rhodobacter	80