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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 phaCand phaE, their identities to those from Haloarcula quadratawere 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 Haloarculasp.strain CEJ40-10 was a potential PHB-candidate for industrial scale production using starchy substrates.

Microbial production of bioplastics, derived from poly(3-hydroxybutyrate) (PHB), have provided a promising alternative towards plastic pollution. Compared to other extremophiles, halophilic archaea are considered as cell factories for PHB production by using renewable, inexpensive carbon sources, thus decreasing the fermentation cost. This study is aimed at screening 33 halophilic archaea isolated from three enrichment cultures from Tunisian hypersaline lake, Chott El Jerid, using starch as the sole carbon source by Nile Red/Sudan Black staining and further confirmed by PCR amplification of phaC and phaE polymerase genes. 14 isolates have been recognized as positive candidates for PHA production and detected during both seasons. The identification of these strains through 16S rRNA gene analyses showed their affiliation to Halorubrum, Natrinema, and Haloarcula genera. Among them, three PHB-producing strains, CEJ34-14, CEJ5-14, and CEJ48-10, related to Halorubrum chaoviator, Natrinema pallidum, and Haloarcula tradensis were found to be the best ones reaching values of 9.25, 7.11, and 1.42% of cell dry weight (CDW), respectively. Our findings highlighted that Halorubrum, Natrinema, and Haloarcula genera were promising candidates for PHB production using soluble starch as a carbon source under high salinity (250 g L-1 NaCl).