The yeast Rhodotorula glutinis was examined for its ability to remove Pb 2+ from aqueous solution. Within 10 min of contact, Pb 2+ sorption reached nearly 80% of the total Pb 2+ sorption. The optimum initial pH value for removal of Pb 2+ was 4.5-5.0. The percentage sorption increased steeply with the biomass concentration up to 2 g/l and thereafter remained more or less constant. Temperature in the range 15-45°C did not show any significant difference in Pb 2+ sorption by R. glutinis. The light metal ions such as Na + , K + , Ca 2+ , and Mg 2+ did not significantly interfere with the binding. The Langmuir sorption model provided a good fit throughout the concentration range. The maximum Pb 2+ sorption capacity q max and Langmuir constant b were 73.5 mg/g of biomass and 0.02 l/mg, respectively. The mechanism of Pb 2+ removal by R. glutinis involved biosorption by direct biosorptive interaction with the biomass through ion exchange and precipitation by phosphate released from the biomass. IntroductionBecause of rapid industrialization, an alarming amount of toxic heavy metals has been released into the environment, endangering natural ecosystems and public health. From hundreds to thousands of tons of lead are discharged from electric battery manufacturing, lead smelting, internal combustion engines fueled with leaded petroleum, and mining activities. Lead acts on the central nervous system, on blood pressure and on reproduction [1].Conventional methods for heavy metal removal are precipitation, coagulation, reduction, ion exchange, evaporation and membrane processes. These methods have several disadvantages, such as less-effective removal of metal ions, high reagent requirements, high costs, the generation of toxic sludges, and the problem of the safe disposal of the materials [2]. Biosorption (biological metal removal) processes have distinct advantages over conventional methods; for example, they are highly selective, more efficient, easy to operate, and cost effective.The potential for using microorganisms in the treatment of metal-bearing wastewater has been studied intensively, and many microorganisms including bacteria, fungi, and algae have been found to remove metals from solutions [3,4]. The biosorption of heavy metal ions by microorganisms may be placed into two categories: metabolism-independent entrapment in the cellular structure and subsequent sorption onto the binding sites present in the cellular structure, and metabolism-dependent transport across the cell membrane through the cell metabolic cycle [5]. The metal-sorption mechanisms, including complexation, ion exchange, coordination, adsorption, chelation, and microprecipitation, are complex and are dependent on the chemistry of the metal ions, surface properties of the microorganisms, and cell physiology [6,7]. The biosorption process is affected by the physicochemical influence of the environment, such as pH, temperature, biomass concentration, initial metal concentration, and competing ions [8].Yeasts possess an acknowledged potential for the r...

The aim of this work was to characterize an exopolysaccharide by Rhodotorula glutinis KCTC 7989 and to investigate the effect of the culture conditions on the production of this polymer. The extracellular polysaccharide (EPS) produced from this strain was a novel acidic heteropolysaccharide composed of neutral sugars (85%) and uronic acid (15%). The neutral sugar composition was identified by gas chromatography as mannose, fucose, glucose, and galactose in a 6.7:0.2:0.1:0.1 ratio. The molecular weight of purified EPS was estimated to be 1.0-3.8 x 10(5) Dalton, and the distribution of the molecular weight was very homogeneous (polydispersity index = 1.32). The EPS solution showed a characteristic of pseudoplastic non-Newtonian fluid at a concentration >2.0% in distilled water. The maximum EPS production was obtained when the strain was grown on glucose (30 g/L). Ammonium sulfate was the best suitable nitrogen source for EPS production. The highest yield of EPS was obtained at a carbon to nitrogen ratio of 15. The EPS synthesis was activated at the acidic range of pH 3.0-5.0 and increased when the pH of the culture broth decreased naturally to <2.0 during the fermentation. When the yeast was grown on glucose (30 g/L) and ammonium sulfate (2 g/L) at 22 degrees C at an initial pH of 4.0, EPS production was maximized (4.0 g/L), and the glucose-based production yield coefficient and carbon-based production yield coefficient were 0.30 g of EPS/g of glucose and 0.34 g (carbon of EPS)/g (carbon of glucose), respectively.

Immobilization of a protease, Flavourzyme, by covalent binding on various carriers was investigated. Lewatit R258-K, activated with glutaraldehyde, was selected among the tested carriers, because of the highest immobilized enzyme activity. The optimization of activation and immobilization conditions was performed to obtain high recovery yield. The activity recovery decreased with increasing carrier loading over an optimal value, indicating the inactivation of enzymes by their reaction with uncoupled aldehyde groups of carriers. The buffer concentrations for carrier activation and enzyme immobilization were optimally selected as 500 and 50 mM, respectively. With increasing enzyme loading, the immobilized enzyme activity increased, but activity recovery decreased. Immobilization with a highly concentrated enzyme solution was advantageous for both the immobilized enzyme activity and activity recovery. Consequently, the optimum enzyme and carrier loadings for the immobilization of Flavourzyme were determined as 1.8 mg enzyme/mL and 0.6 g resin/mL, respectively.

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