Biopolymer-mediated Ca and Mn accumulation and biomineralization

Abstract

Various metals are known to be accumulated by both intra- and extracellular biopolymers. Such accumulations may lead to the formation of biominerals, whereby the biopolymers may assume a regulatory role in crystallization processes. Two examples are discussed that are studied in our laboratory, calcium and manganese. Emiliania huxleyi is a unicellular marine alga that produces calcite discs - coccoliths - within an intracellular vacuole. Much attention has been given to the probable involvement of a complex acidic polysaccharide that is associated with the crystalline phase. E. huxleyi is the most productive lime-secreting species on earth and is likely to play an important role in the oceanic carbon cycle. Manganese-oxidizing bacteria occur associated with recent sedimentary Mn-deposits. Manganese oxidation in two species is briefly discussed. There are strong indications suggesting that extracellular biopolymers regulate the binding of reduced manganese and its subsequent oxidation. Biopolymer-mediated metal accumulation and biomineralization occur at a huge scale in the biosphere, and hence may have important geological implications. The processes may be utilized for the reclamation of heavy metals from natural and polluted environments, for the prevention of 'scaling' in industrial practice, and for the treatment of pathological (de)mineralizations in humans.