27-08-2012, 11:41 AM
THE ROLE OF MICROBES IN METAL TRANSFORMATION
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CHARACTERS OF LOWER VALENCY METAL ION
Soluble and stable
Accumulated under reductive condition
Readily oxidized into its higher valence metal ion
PROBLEMS REGARDING IONIC METAL
Unavailability of metal ion under oxidative condition at neutral to alkaline pH (higher valence of metal ion insoluble at neutral to alkaline pH)
Toxicity of metal ion under oxidative condition at acidic pH (higher valence of metal ion soluble at acidic pH)
CHELATION OF HIGHER VALENCE METAL BY PRODUCING CHELATING AGENT
Chelating agents entrapped the insoluble higher valence metals
Enterobacteria produce Enterobactin and Enterochelin (derivatives of Phenol-Catechol)
Streptomyces and other bacteria produce Ferrioxamine (derivatives of Hydroxamic acids)
Chelating agents have multiple hydroxyl or carbonyl groups
METAL ABSORBING MICROBES
Pseudomonas aeruginosa, Saccharomyces cerevisiae, Rhizopus arrhizus, and Aspergillus niger
ALGAE: Chlorella pyrenoidosa, C. vulgaris, Chaetoceros calcitrans, Stichococcus bacillaris, Chlamydomonas reinharti, Scenedesmus quadricauda, Ascopenyellum sp., and Sargassum sp.