Improving polyhydroxyalkanoate production from inexpensive carbon sources by genetic approaches: a review

Polyhydroxyalkanoates (PHAs) are a family of biodegradable intracellular polyesters that a number of Eubacteria and Archaea can accumulate for energy and carbon storage. Most of the genetic modifications to the producing bacterial species have been accomplished to clarify basic biochemical, genetic, and metabolic aspects of PHA metabolism. However, due to its plastic-like properties and complete biodegradability, this bio-based polymer has attracted the attention of a variety of manufacturers. A number of genetic approaches have therefore been reported, aimed at improving the performance of the microorganisms with a potential for use in a production process. Indeed, genetic tools may find useful applications in all the phases of the PHA production chain, from the isolation and characterization of new microbial strains through all the production steps until they reach the downstream processes. The substrates generally used for PHA production are expensive, so the search for low-cost feedstock is necessary. These materials, possibly deriving from agri-food processes, are unfortunately not easily degraded or converted directly into PHAs. Thus, the development of engineered microbes is in progress to process waste streams and covert them to valuable polymers. This review will summarize the most relevant results obtained through genetic engineering tools for the production of PHAs from cheap carbon sources in view of possible industrial applications.