title: Extracellular mercury sequestration by exopolymeric substances produced by Yarrowia spp.: Thermodynamics, equilibria, and kinetics studies.
abstract: Exopolymeric substances (EPS) produced by highly mercury-resistant strains of the yeast Yarrowia spp. (Idd1 and Idd2) were isolated and studied for their mercury binding potential. Excellent yield (approximately 0.3 g EPS per gram biomass) of soluble EPS in medium with 3% glucose was observed in the Yarrowia cultures 7 day post-inoculation. A gram dry weight of the EPS consists mainly of carbohydrates (0.4 g), protein (0.3-0.4 g), uronic acid (0.02 g), and nucleic acids (0.002 g). Mercury interactions with the biopolymer were measured as uptake kinetics from a simulated aquatic system and modelled with thermodynamics and calculated mass action equilibria. The EPS forms a complex with Hg2+in water with small activation energy (≤2 kJ mol-1), achieving about 30 mg Hg2+adsorption per gram dry weight of EPS. The adsorption models confirmed complexation of Hg2+by the EPS via heterogeneous multilayer adsorption that obey second-order kinetics at constant rate of 4.0 and 8.1 mg g-1min-1. The EPS used chemisorption as rate-limiting step that controls the uptake of Hg2+from aquatic systems during micro-precipitation as bio-removal strategy. The EPS are promising biotechnological tools to design bioreactors for treatment of mercury-rich industrial wastewater.
authors.affiliation: Department of Civil and Environmental Engineering, Faculty of Engineering, Tohoku-Gakuin University, 1-13-1 Chuo, Tagajo, Miyagi 985-8537, Japan; Department of Microbiology, Faculty of Science, University of Lagos, Akoka, Yaba, Lagos, Nigeria. Electronic address: goyetibo@unilag.edu.ng.
authors.forename: Ganiyu Oladunjoye
authors.initials: GO
authors.lastname: Oyetibo
authors.affiliation: Department of Civil and Environmental Engineering, Faculty of Engineering, Tohoku-Gakuin University, 1-13-1 Chuo, Tagajo, Miyagi 985-8537, Japan. Electronic address: kmiya@mail.tohoku-gakuin.ac.jp.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Miyauchi
authors.affiliation: Department Electronic Engineering, Faculty of Engineering, Tohoku-Gakuin University, 1-13-1 Chuo, Tagajo, Miyagi 985-8537, Japan. Electronic address: hsuzuki@mail.tohoku-gakuin.ac.jp.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Suzuki
authors.affiliation: Graduate School of Environmental Studies, Tohoku University, Sendai, Miyagi 980-8579, Japan. Electronic address: ishikawa@geo.kankyo.tohoku.ac.jp.
authors.forename: Satoru
authors.initials: S
authors.lastname: Ishikawa
authors.affiliation: Department of Civil and Environmental Engineering, Faculty of Engineering, Tohoku-Gakuin University, 1-13-1 Chuo, Tagajo, Miyagi 985-8537, Japan. Electronic address: gendo@mail.tohoku-gakuin.ac.jp.
authors.forename: Ginro
authors.initials: G
authors.lastname: Endo
mesh_terms: D000327:Adsorption; D001704:Biopolymers / Q000378:metabolism; D019149:Bioreactors; D007700:Kinetics; D008628:Mercury / Q000378:metabolism*; D013816:Thermodynamics; D014874:Water Pollutants, Chemical / Q000378:metabolism*; D018508:Water Purification / Q000379:methods*; D025062:Yarrowia / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001704:Biopolymers; D014874:Water Pollutants, Chemical; D008628:Mercury
keywords: Extracellular polymeric substances; Mercury; Mercury bio-removal; Mercury biosorption; Micro-precipitation; Yarrowia