AIM: This study aimed at unprecedented physical and chemical evaluation of the 'green plastics' polyhydroxyalkanoates (PHAs), in an extremely halotolerant Halomonas elongata strain 2FF under high-salt concentration. METHODS AND RESULTS: The investigated bacterial strain was isolated from the surface water of the hypersaline Fără Fund Lake. The 16S rRNA gene sequence phylogeny and phenotypic analysis indicated that the isolate belonged to H. elongata. PHA inclusions were observed by Sudan Black B, Nile Red staining, and transmission electron microscopy during growth at high salinity (10%, w/v, NaCl) on 1% (w/v) d-glucose. The produced polymer was quantitatively and qualitatively assessed using crotonic acid assay, elemental analysis, Fourier transform infrared and Raman spectroscopies. Additionally, X-ray powder diffraction, 1 H-NMR spectroscopy, and differential scanning calorimetry were applied. The investigations showed that the intracellular polymer was polyhydroxybutyrate (PHB) of which the strain produced up to 40 wt% of total cell dry weight after 48 h. The analysis of phaC gene from the isolated H. elongata strain indicated that the encoded PHA synthase belongs to Class I PHA synthase family. CONCLUSIONS: Overall, our investigations pointed out that the halotolerant H. elongata strain 2FF was capable to produce significant amounts of PHB from d-glucose, and PHAs from various carbon substrates at high-salt concentrations. SIGNIFICANCE AND IMPACT OF THE STUDY: The tested strain showed the ability for significant production of natural, biodegradable polymers under nutrient limitation and hypersaline conditions suggesting its potentiality for further metabolic and molecular investigations towards enhanced biopolymer production. Additionally, this study reports on the unprecedented use of Raman and XPRD techniques to investigate PHAs of an extremely halotolerant bacterium, thus expanding the repertoire of physical methods to study green plastics derived from extremophilic microorganisms.

Department of Aquatic Microbial Ecology Institute of Hydrobiology Biology Center of the Academy of Sciences of the Czech Republic České Budějovice Czech Republic

Department of Biomolecular and Molecular Physics National Institute for Research and Development of Isotopic and Molecular Technologies Cluj Napoca Romania

Department of Biomolecular Physics Faculty of Physics Babeș Bolyai University Cluj Napoca Romania

Department of Experimental Biology and Biochemistry National Institute of Research and Development for Biological Sciences Institute of Biological Research Cluj Napoca Romania

Department of Molecular Biology and Biotechnology Faculty of Biology and Geology Babeş Bolyai University Cluj Napoca Romania

Electron Microscopy Center Babeș Bolyai University Cluj Napoca Romania

INCDO INOE 2000 Research Institute for Analytical Instrumentation Cluj Napoca Romania

Molecular Biology Center Institute for Interdisciplinary Research in Bio Nano Sciences Babeş Bolyai University Cluj Napoca Romania

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