The application of purple non-sulfur bacteria for microbial mixed culture polyhydroxyalkanoates production

Polyhydroxyalkanoates (PHA) are a group of biopolymers produced naturally by microorganisms with properties similar to various petroleum-based plastics. However, to date their commercial production has remained uncompetitive due to substrate, sterilization, aeration and processing costs. Purple non-sulfur bacteria (PNSB) are a group of anoxygenic photoheterotrophic bacteria that have the ability to accumulate PHA under unbalanced conditions in anaerobic environments and constant feeding with high conversion ratios. Such characteristics could potentially overcome some of the bottlenecks of conventional chemoheterotrophic PHA production. Yet these organisms have received relatively limited attention. This review explores the factors involved in the PHA accumulation process from PNSB, highlighting the differences to conventional PHA production and the areas yet to be optimized. The roles of fermentation systems, carbon substrate, feeding conditions, nutrients, pH and various aspects of light are reviewed to understand their role in PHA accumulation in PNSB.