Dilemma in Carotenoids Versus Polyhydroxyalkanoates (PHAs) Synthesis Using Haloarchaea as Cell Factories

Microorganisms of the Haloferacaceae and Halobacteriaceae families (Archaea Domain) have been revealed as key players for the bioproduction of polyhydroxyalkanoates (PHAs), a family of natural, biodegradable polyesters produced by different types of microorganisms as intracellular carbon and energy storage reserves and stress-resistance tools. Recent works have optimized the production of high-quality PHAs using cost-efficient processes that involve even the valorization of residues from other industrial processes, which are used as raw material for haloarchaeal growth and PHA production. Considering the physicochemical properties of those biopolymers, poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) is currently a target in many biotech-based processes aiming at the production of bioplastics. In this context, the haloarchaeon Haloferax mediterranei is probably the most well-examined archaeal cell factory for PHBV production, with some successful processes already described to produce significant concentrations of PHBV. However, the go-to-market haloarchaeal PHBV strategy continues to be limited by the capacity to produce quantities of PHBV sufficient to meet market demands due to several biological and technological limitations. In this perspective, risks and limitations to produce haloarcheal PHBV, as well as hot topics that may contribute to accelerating the efficient upscaling production of PHBV (in terms of cost and time), are also discussed.