Polyhydroxyalkanoates (PHAs) are leading "green" alternatives for the production of biodegradable plastics. They accumulate inside archaea and bacteria as the sources of carbon and energy under stress conditions. This study evaluates the biosynthesis of poly(3-hydroxybutyrate) (PHB), one of the major PHAs, in the extremely halophilic archaeon Haloarcula sp. TG1 by microscopic, spectroscopic, and thermal analyses. The PHB production by TG1 strain was optimized in terms of growth conditions and media. The optimum PHB content (34.6% of the biomass) was obtained in Mineral Salt Medium (MSM) cultures containing 5 M NaCl and 4% glucose, at pH 7.35, incubated for 72 h at 37 degrees C. Replacement of glucose with starch or glycerol lowered the PHB content in biomass. Alternatively, agricultural wastes (sugar beet pulp, corn cob, and hazelnut husk) were used as cheap carbon sources. The highest PHB content (45.6% of the biomass) was obtained using sugar beet pulp treated with recombinant endoglucanase (rCKT3eng), while PHB amount was 17.8% of the biomass with chemically hydrolyzed sugar beet pulp. In conclusion, PHB production by Haloarcula sp. TG1 was shown to be promising biotechnologically, using a low-cost fermentation medium at optimal culture conditions.