Production of poly-hydroxyalkanoates (PHAs) and exopolysaccharides (EPSs) from the extreme halophilic archaeon Haloterrigena turkmenica.

Microorganisms belonging to the Archaea domain are of significant biotechnological interest as they are able to produce biopolymers provided with interesting properties. The two main polymers produced are poly-hydroxyalkanoates (PHAs) and exopolysaccharides (EPSs). PHAs are accumulated inside the cells providing an internal reserve of carbon and energy. They are very attractive from a biotechnological viewpoint as they possess thermoplastic and elastomeric properties; in addition, they are biodegradable (1). EPSs are secreted into the culture medium as defense against predation and physical and chemical agents (e.g. high temperature and salinity), thus being essential for the survival of microorganisms. They possess multiple applications in the pharmaceutical, food and other industries as gelling, emulsifier and stabilizing agents (2). Among the extremophilic Archaea, halophiles are good producers of PHAs and EPSs. Haloterrigena turkmenica, isolated from sulfate saline soil in Turkmenistan, is a Gram-negative microbe with shape variable from coccoid or oval to rod and relatively fast growth (3). It is a chemoorganotrophic, carotenoid-containing, extreme halophile optimally growing at temperatures from 37 to 50°C, pH 7.0-7.2 and 2M NaCl. For this work, the microorganism was grown in its usual culture medium (Halobacteria medium-HTR), and in the same medium added with 1% (w/v) glucose (HTRG1) or lacking some components (nutrient deficient growth medium-NDMHTRG1). All cultures were analyzed at different times of growth in order to explore the production of PHAs in the cells and EPSs in the culture medium. The presence of the two biopolymers was confirmed by chromatographic analyses and by microscopy after specific cell staining. EPSs were isolated from the culture medium and tested for their emulsifier capacity in a mixture oil:water 1:1 (v/v). PHAs were extracted from cells of H. turkmenica and partially purified.