PHAs are biodegradable, organic, non-toxic polyesters that are produced by certain bacteria and plants. PHA granules accumulated in the microbial cell are called carbonosomes.
They serve as storage reservoirs and hence the fermentation needs feast and famine regimes in a sequential system or in a single system. Simple fed-batch systems due to their dilution effect on the media make
it complicated to achieve targeted PHA yields, resulting in the subsequent downstream processing being less economically viable.
An alternative is to use repeated fed-batch and fed-batch with cell recycling to allow accumulation of biomass and PHAs in the biomass. There is growing interest in using mixed cultures on
mixed waste streams to reduce the costs associated with aseptic mono-culture fermentation.