Overproduction of poly(3-hydroxybutyrate) by the extremely halophilic archaeon Haloarcula sp. CEJ40-10 using starchy substrate

Abstract

Polyhydroxyalkanoates (PHAs), green alternatives to petroleum-derived plastics, possess desired features that make them preferred for various applications. Poly(3-hydroxybutyrate) (PHB), one of the most known representative of PHAs, could be synthesized by haloarchaeal species but their production amounts are relatively low compared to those of poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) obtained by haloarchaea. This is the first report describing an overproduction of PHB by a wild-type halophilic archaeon isolated from southern Tunisia, Chott El Jerid. According to the 16S rRNA gene sequence analysis, the isolate CEJ40-10 was affiliated with the species of the genus Haloarcula (97.5% similarity). Regarding the phylogeny based on the amino acid sequences of the PHA synthase subunits encoded by phaC and phaE, their identities to those from Haloarcula quadrata were 99% and 100%, respectively. This strain could accumulate maximum PHA using 1% (w/v) starch at pH 6, after incubation for 72 h at 37 °C with high salt content (30% NaCl). The replacement of starch with glucose or sugar wastewater lowered the polymer yield. Four extraction methods were performed in order to achieve the maximum efficiency of polymer recovery. Hypochlorite digestion of biomass gave a high recovery yield, reaching 72.8% of its total dry mass. Furthermore, analytical methods such as the Fourier transform infrared (FTIR) spectroscopy, gas chromatography (GC), and UV–visible spectrophotometry indicated that the composition of the polymer was a homopolymer PHB. Our findings showed that Haloarcula sp. strain CEJ40-10 was a potential PHB-candidate for industrial scale production using starchy substrates.