Production of Polyhydroxyalkanoates by Two Halophilic Archaeal Isolates from Chott El Jerid Using Inexpensive Carbon Sources

Abstract

The large use of conventional plastics has resulted in serious environmental problems. Polyhydroxyalkanoates represent a potent replacement to synthetic plastics because of their biodegradable nature. This study aimed to screen bacteria and archaea isolated from an extreme environment, the salt lake Chott El Jerid for the accumulation of these inclusions. Among them, two archaeal strains showed positive results with phenotypic and genotypic methods. Phylogenetic analysis, based on the 16S rRNA gene, indicated that polyhydroxyalkanoate (PHA)-producing archaeal isolates CEJGTEA101 and CEJEA36 were related to Natrinema altunense and Haloterrigena jeotgali, respectively. Gas chromatography and UV-visible spectrophotometric analyses revealed that the PHA were identified as polyhydroxybutyrate and polyhydroxyvalerate, respectively. According to gas chromatography analysis, the strain CEJGTEA101 produced maximum yield of 7 wt % at 37 °C; pH 6.5; 20% NaCl and the strain CEJEA36 produced 3.6 wt % at 37 °C; pH 7; 25% NaCl in a medium supplemented with 2% glucose. Under nutritionally optimal cultivation conditions, polymers were extracted from these strains and were determined by gravimetric analysis yielding PHA production of 35% and 25% of cell dry weight. In conclusion, optimization of PHA production from inexpensive industrial wastes and carbon sources has considerable interest for reducing costs and obtaining high yield.

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

“…The present study is a continuity of our previous work [ 9 ], proposing the possibility to enlarge our knowledge about PHB secretion by a large number of haloarchaeal strains from Chott El Jerid due to their several advantages: firstly, their growth at high salinity minimized microbial contamination. Secondly, the high osmotic pressure in their cells facilitated the PHB recovery.…”

“…Later, Han et al [ 30 ] confirmed the detection of phaEC genes in 18 PHB or poly(3-hydroxybutyrate-co-hydroxyvalerate) PHBV producers, including Haloarcula , Halorubrum , Natrinema , and other genera by utilizing carbohydrates either glucose or fructose [ 30 ]. More recently, it was reported that these two genes were detected in the genome of Natrinema altunense CEJGTEA101, isolated from Chott El Jerid [ 9 ].…”

“…The strain Escherichia coli was used as a negative control. Natrinema altunense strain CEJGTEA101 [KY129977] was identified as a PHA-producing isolate in our previous work [ 9 ] and was used as a positive control in this study. After 15 days of incubation at 37°C, the isolates which revealed orange fluorescence after exposure of plates to UV light were selected as PHA accumulators [ 27 ].…”

“…Poly(3-hydroxybutyrate) (PHB) was the first bioplastic found in species of Dead Sea Halobacterium described in 1972 [ 6 ]. Since then, microorganisms including extremely halophilic archaea belonging to the genera Haloquadratum , Halorubrum , Halobacterium , Haloterrigena , Haloferax , Natronococcus , Natronobacterium , Haloarcula , Natrinema , Halogeometricum , Halopiger , Halobiforma , and Halococcus have also been found to accumulate considerable amounts of PHB [ 7 – 9 ] using colony/cell staining methods, molecular tools targeting PHA synthase genes, and analytical techniques such as Fourier transform infrared spectroscopy, crotonic acid assays, gas chromatography, and liquid chromatography [ 10 ].…”

“…These organisms could utilize various renewable carbon sources and release the PHB easily by cell lysis in distilled water, thus lowering its high production cost [ 11 ]. Several recent investigations have shown that the productivities of PHB by archaeal strains were obtained using glucose as the sole carbon source [ 9 , 12 , 13 ] than with other substrates (wastes and pretreated vinasse) [ 14 , 15 ]. However, few studies based on the exploration of PHB production by archaeal species using starch have been reported, despite its wide availability [ 16 , 17 ].…”