Extrusion of PHA-containing bacterial biomass and the fate of endotoxins: A cost-reducing platform for applications in molding, coating and 3D printing

Manufacturing polyhydroxyalkanoate (PHA) polymers is expensive compared to oil-based plastic with as much as 50% of the cost attributed to purification. We have processed PHA-containing bacterial biomass directly by extrusion to avoid purification steps to produce new biocomposites for applications in moulding, coating and 3D printing. Direct incorporation of PHA-containing bacteria into biocomposites provides two significant advantages for cost reduction, firstly by avoiding PHA purification, and secondly by incorporating biomass as a low-cost sustainable filler in the new materials. Three key steps were required: firstly biomass containing > 50% by weight of PHA was prepared for three different PHAs (PHB, PHBV and mcl-PHA) so as to avoid the need to add extra purified PHA as previously reported; extruded biocomposites were prepared to analyse the fate of whole cells and ensure that the properties of the PHA were maintained and the impact of the biomass filler assessed; and thirdly that the bioavailability of bacterial endotoxins (pyrogens) which are present at very high levels in many PHA-producing bacterial strains was assessed and shown to be significantly reduced during extrusion to levels similar to commercially-produced purified PHB. These three steps have opened a route to whole-cell PHA-based biocomposites that will be less expensive to produce compared to purified PHA. The identification of an endotoxin-free Gram-negative production host enhances the suitability of sphingomonads as a new endotoxin-free PHA production platform.