Haloarchaea as Cell Factories to Produce Bioplastics

Abstract

Plastic pollution is a worldwide concern causing the death of animals (mainly aquatic fauna) and environmental deterioration. Plastic recycling is, in most cases, difficult or even impossible. For this reason, new research lines are emerging to identify highly biodegradable bioplastics or plastic formulations that are more environmentally friendly than current ones. In this context, microbes, capable of synthesizing bioplastics, were revealed to be good models to design strategies in which microorganisms can be used as cell factories. Recently, special interest has been paid to haloarchaea due to the capability of some species to produce significant concentrations of polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), and polyhydroxyvalerate (PHV) when growing under a specific nutritional status. The growth of those microorganisms at the pilot or industrial scale offers several advantages compared to that of other microbes that are bioplastic producers. This review summarizes the state of the art of bioplastic production and the most recent findings regarding the production of bioplastics by halophilic microorganisms with special emphasis on haloarchaea. Some protocols to produce/analyze bioplastics are highlighted here to shed light on the potential use of haloarchaea at the industrial scale to produce valuable products, thus minimizing environmental pollution by plastics made from petroleum.

Keywords: bioplastics; haloarchaea; polyhydroxyalkanoates (PHA); polyhydroxybutyrate (PHB); polyhydroxyvalerate (PHV).

Figure 1

Chemical structure of polyhydroxyalkanoates (PHAs).

Figure 2

Main metabolic pathways for PHA synthesis. (A) synthesis from pyruvate; (B) synthesis through beta-oxidation of fatty acids; (C) synthesis through the pathway of fatty acid synthesis.

Figure 3

Electronic microscopy picture of Haloferax mediterranei cells showing PHA granules.

Figure 4

Current and forecast global production capacities of bioplastics [163].

Figure 5

2019 biodegradable plastic production [2].

Figure 6

Global production capacities of biodegradable plastics 2019 (by market segment).