Haloarchaea as emerging big players in future polyhydroxyalkanoate bioproduction: Review of trends and perspectives

Haloarchaea comprise the extremely halophilic branch of the phylum Euryarchaeota and they are members of the prokaryotic domain Archaea. They thrive best in extremely saline habitats with salt concentrations of 2–5 mol L–1 NaCl, and thus under conditions of near salt saturation in water. These ancient organisms are among the oldest species on Earth, and are characterized by ether-linked lipids in the cytoplasmic membrane and murein-free cell walls. Haloarchaea are increasingly receiving attention as microbial cell factories for the bioproduction of diverse marketable products, such as bacterioruberin, bacteriorhodopsin, isoprenoids, and polyhydroxyalkanoates (PHAs). These biopolyesters serve as intracellular storage compounds from the secondary metabolism of haloarchaea and many other prokaryotes. Engineered or wild type PHA-producing haloarchaea that utilize inexpensive raw materials for bioproduction, and which only require clean-in-place procedures to run PHA production bioprocesses, are currently undergoing scale-up within the research and development field of Archaea Biotechnology. In addition, PHAs exhibit high potential as both bio-based and biodegradable plastic-like bulk products on the industrial biotechnology market (“White Biotechnology”) for biopolymers. However, PHA production by haloarchaea has not yet reached industrial maturity. The present review discusses the background, previous research, and biological role of PHA biosynthesis in haloarchaea, as well as current trends, and a critical discussion of its potential for broad industrialization.