Production of Poly(3-Hydroxybutyrate) by Haloarcula, Halorubrum, and Natrinema Haloarchaeal Genera Using Starch as a Carbon Source

Abstract

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).

Characterization of Polyhydroxybutyrate, PHB, Synthesized by Newly Isolated Haloarchaea Halolamina spp.

“…Extremophilic microorganisms, particularly haloarchaea, show all the optimum features to be a good candidate to produce PHA on a large scale: Microbial growth can be achieved by using waste carbon sources and there is no need for medium sterilization, minimal risk of contamination by other microorganisms, use of brines or seawater for medium preparation, recovery of the salts used in the medium, and a simple cell lysis process with water to harvest the polymer granules [ 7 , 8 ]. Consequently, as bioplastic producers, haloarchaea have advantages over other bacterial strains, hence minimizing the production cost of PHA [ 9 , 10 ]. Consequently, finding new PHA producers within haloarchaea is crucial for cost-effective polymer manufacturing.…”

A polyhydroxyalkanoate synthesised by halophilic archaeon Natrialba swarupiae

“…7 Using renewable, low-cost carbon sources, the halophilic archaea, as cell factories, are believed to synthesize PHA, lowering the cost of fermentation in comparison to other extremophiles. 8…”

“…7 Using renewable, low-cost carbon sources, the halophilic archaea, as cell factories, are believed to synthesize PHA, lowering the cost of fermentation in comparison to other extremophiles. 8 Several studies have shown that haloarcheon Haloferax mediterranei can utilize a variety of industrial and domestic wastes as carbon sources for making PHA in a very efficient way, e.g., olive oil waste water, crude glycerol phase, starch waste, surplus whey. [9][10][11][12] Also, a lot of research has shown that the PHA produced by Haloferax mediterranei is a mixture of 3-hydroxybutyrate and 3hydroxyvalerate, when different carbon sources were used in the growth medium.…”

Metagenomic assembled genomes indicated the potential application of hypersaline microbiome for plant growth promotion and stress alleviation in salinized soils

“…The adequate amount of nitrogen and sulfur has been linked to increased plant growth. Furthermore, the genus Halorubrum is known to produce carotenoids and poly(3-Hydroxybutyrate) with diverse biotechnological applications ( 41 , 42 ). The species Halovenus aranensis and Halovenus carboxidivorans have exhibited the production of carotenoids and carbon monoxide oxidizing capacity ( 43 , 44 ).…”