Recombinant DNA technology as a tool for improving production of polyhydroxyalkanoates by the natural producers

Polyhydroxyalkanoates (PHAs) are a group of the biodegradable polyesters, and represent an alternative to conventionally used petroleum-based plastics resistant to biodegradation. The production is not cost-competitive compared to conventional plastics, although, there are several bacterial producers capable of PHA accumulating up to 80 % of their cells dry weight using low-cost substrates. PHA production can be improved by transferring specific enzymes or entire metabolic pathways from the most efficient producers to other natural producers. Therefore, the review is focused on genetic modification of bacterial producers, namely the genera Cupriavidus, Pseudomonas, Halomonas, Aeromonas and Bacillus, for efficient industrial production of PHAs. Recombinant PHA producer can use non-traditional substrates like agro-industrial wastes, namely whey, lignocellulose or glycerol. It is possible to influence the shape and size of the producer's cell by over-expression or knockout of selected genes or to affect its preference for a specific component of a culture medium by modulation of a producer's basal metabolism. The costs of PHA production still be reduced by simplifying the downstream process by enzymatic hydrolysis of selected parts of the cell or blocking the protective mechanisms of the cell against its autolysis caused by the ionic strength of the solution.