ISOLATION AND POTENTIAL APPLICATIONS OF AN EXOPOLYSACCHARIDE PRODUCED BY THE EXTREME HALOPHILIC ARCHAEON HALOTERRIGENA TURKMENICA

Haloterrigena turkmenica, an extreme halophilic archaeon isolated from sulfate saline soil in Turkmenistan, was originally described as Halococcus turkmenicus, and successively transferred to the new genus Haloterrigena. It is a Gram-negative chemoorganotrophic, carotenoid-containing microbe, with shape variable from coccoid or oval to rod. Its optimal growth parameters are: temperature comprised between 37 and 50°C, pH ranging from 7.0 to 7.2 and 2M NaCl. H. turkmenica belongs to the euryarchaeal family of Halobacteriaceae and, as many others halophilic microorganisms, is able to synthesize molecules of important biotechnological interest such as carotenoids and biopolymers. Among biopolymers, exopolysaccharides (EPS) are macromolecules excreted into the culture medium as defense against predation and physical and chemical agents (e.g. high temperature and salinity). They are of significant importance from an industrial viewpoint, because they can have several applications in the pharmaceutical, cosmetic, food and other industrial fields as gelling, emulsifier and stabilizing agents. H. turkmenica was able to synthesize an exopolysaccharide when grown at 37°C in its usual medium (Halobacteria medium M372 from DSMZ) added with different sugars at 1% (w/v) concentration. The EPS for characterization studies was isolated from the culture supernatant of the microorganism after growth in Halobacteria medium supplemented with glucose. Firstly, the glucose culture was analyzed at different times in order to establish the phase of growth corresponding to the highest EPS amount, and maximum yield of 211 mg/L was achieved in the stationary phase. After purification, EPS properties of relevant interest such as emulsifying and antioxidant capacities were investigated. In fact, EPS exhibiting emulsifying capacity could be used in the food industry as emulsifier, while those provided with antioxidant power could find application as prophylactic agents in several areas, e.g. pharmaceutics and cosmetics. The emulsifying activity was tested in a mixture hydrophobic phase:water 1:1 (v/v) where hydrophobic solvents were olive or mineral oil, toluene and xylene, and compared with that of Triton X-100 chosen as control. The EPS produced by H. turkmenica showed an emulsifying capacity comparable to that showed by Triton X-100 when measured against olive oil. The ferric reducing power (FRAP) and the total antioxidant capacity (TAC) assays demonstrated that the biopolymer was endowed with antioxidant power and this property was dose-dependent as a linear increase of the activity was measured when the EPS concentration increased.