1. Definition of PHA and bioplastics

PHAs (polyhydroxyalkanoates) are biopolymers accumulated within bacterial cells in the form of granules. This accumulation occurs when a nutrient (source of nitrogen, phosphate, trace elements, etc.) necessary for their growth becomes limiting, in the presence of an excess of carbonaceous substrate. In the case of the microorganisms concerned, we can also speak of a nutritional imbalance favoring the synthesis of these reserve molecules. The term "reserve" is used because the aim of the bacteria is to build up an energy and nutritional reserve to cope with a prolonged situation unfavorable to growth. Many bacteria (Gram-positive and Gram-negative), some cyanobacteria and rare eukaryotic cells are involved in this synthesis. Nearly 300 microorganisms have been identified as capable of synthesizing these biopolymers. But to date, only a few have the potential for industrial development. PHAs...