Abstract Polymetallic nodules and crusts, hydrothermal vents from the Deep Sea
are economically interesting, since they contain alloying components, e.g., manganese or cobalt, that are used in the production of special steels; in addition, they
contain rare metals applied for plasma screens, for magnets in hard disks, or in
hybrid car motors. While hydrothermal vents can regenerate in weeks, polymetallic
nodules and seamount crusts grow slowly. Even though the geochemical basis for
the growth of the nodules and crusts has been well studied, the contribution of
microorganisms to the formation of these minerals remained obscure. Recent HRSEM (high-resolution scanning electron microscopy) analyses of nodules and
crusts support their biogenic origin. Within the nodules, bacteria with surface Slayers are arranged on biofilm-like structures, around which Mn deposition starts. In
crusts, coccoliths represent the dominant biologically formed structures that act as
bio-seeds for an initial Mn deposition. In contrast, hydrothermal vents have apparently an abiogenic origin; however, their minerals are biogenically transformed by
bacteria. In turn, strategies can now be developed for biotechnological enrichment
as well as selective dissolution of metals from such concretions. We are convinced
that the recent discoveries will considerably contribute to our understanding of the
participation of organic matrices in the enrichment of those metals and will provide
the basis for feasibility studies for biotechnological applications.
4.1 Introduction
It is amazing that the composition of elements in the seawater is so different from
the (secondary) minerals in the polymetallic nodules, the Co-rich crusts as well as in
the hydrothermal vents that accrue in this environment. While in the seawater, the
elements Na, Cl, K, and Ca (e.g., in form of ions or salts) are dominant, the marine
(secondary) minerals are composed in the first place of Si [silicon] (clay), Fe [iron]
(e.g., magnetite/goethide), Mn [manganese] (pyrolusite, braunite), and S (pyrite).
Impressive examples are Mn and Fe, that occur in the seawater in only extremely
low concentrations (~0.0004 ppm), while they are dominant in the polymetallic
nodules or Co-rich crusts (Mero 1962), in which they represent over 30% of the
material. Because of the pressing demands for such raw materials, the commercial
exploitation of the gigantic occurrences of nodules and crusts on the ocean floors is
to be expected (Schrope 2007). Attempts for a sustainable exploitation of Mn and
its associated elements/minerals from the marine environment have to rely on the
same abiogenic (mineralization) and biogenic (biomineralization) processes/
strategies like those implemented in the synthesis of those deposits. Therefore, in
this review, the focus is put on the underlying biological/biochemical processes,
since the molecules involved are accessible at an “unlimited” scale by molecular
biological and cell biological approaches. This concept of molecular biomineralization (nature as a model) will contribute to an understanding of biomineral
formation in a causal analytic manner and might allow a sustainable exploitation
of those natural resources in an environment-friendly way.
78
X. Wang et al.
are economically interesting, since they contain alloying components, e.g., manganese or cobalt, that are used in the production of special steels; in addition, they
contain rare metals applied for plasma screens, for magnets in hard disks, or in
hybrid car motors. While hydrothermal vents can regenerate in weeks, polymetallic
nodules and seamount crusts grow slowly. Even though the geochemical basis for
the growth of the nodules and crusts has been well studied, the contribution of
microorganisms to the formation of these minerals remained obscure. Recent HRSEM (high-resolution scanning electron microscopy) analyses of nodules and
crusts support their biogenic origin. Within the nodules, bacteria with surface Slayers are arranged on biofilm-like structures, around which Mn deposition starts. In
crusts, coccoliths represent the dominant biologically formed structures that act as
bio-seeds for an initial Mn deposition. In contrast, hydrothermal vents have apparently an abiogenic origin; however, their minerals are biogenically transformed by
bacteria. In turn, strategies can now be developed for biotechnological enrichment
as well as selective dissolution of metals from such concretions. We are convinced
that the recent discoveries will considerably contribute to our understanding of the
participation of organic matrices in the enrichment of those metals and will provide
the basis for feasibility studies for biotechnological applications.
4.1 Introduction
It is amazing that the composition of elements in the seawater is so different from
the (secondary) minerals in the polymetallic nodules, the Co-rich crusts as well as in
the hydrothermal vents that accrue in this environment. While in the seawater, the
elements Na, Cl, K, and Ca (e.g., in form of ions or salts) are dominant, the marine
(secondary) minerals are composed in the first place of Si [silicon] (clay), Fe [iron]
(e.g., magnetite/goethide), Mn [manganese] (pyrolusite, braunite), and S (pyrite).
Impressive examples are Mn and Fe, that occur in the seawater in only extremely
low concentrations (~0.0004 ppm), while they are dominant in the polymetallic
nodules or Co-rich crusts (Mero 1962), in which they represent over 30% of the
material. Because of the pressing demands for such raw materials, the commercial
exploitation of the gigantic occurrences of nodules and crusts on the ocean floors is
to be expected (Schrope 2007). Attempts for a sustainable exploitation of Mn and
its associated elements/minerals from the marine environment have to rely on the
same abiogenic (mineralization) and biogenic (biomineralization) processes/
strategies like those implemented in the synthesis of those deposits. Therefore, in
this review, the focus is put on the underlying biological/biochemical processes,
since the molecules involved are accessible at an “unlimited” scale by molecular
biological and cell biological approaches. This concept of molecular biomineralization (nature as a model) will contribute to an understanding of biomineral
formation in a causal analytic manner and might allow a sustainable exploitation
of those natural resources in an environment-friendly way.
78
X. Wang et al.