their transverse dimension (Fig. 4.7d and e). It is assumed that those S-layer
structures reduce, due to the enlargement of the bacterial surface and also a
particular chemical/physicochemical composition, e.g., on surface wettability, the
activation energy for the oxidation processes (Kim et al. 2006); Fig. 4.7h.
4.4.6 Biofilm Structures in Polymetallic Nodules
A further input toward an establishment that bio-seeds are causatively involved
in nodule formation came from Crerar and Barnes (1974), who proposed that Mn
(IV) and Fe(III) deposition also involves autocatalytic processes proceeding on
the surfaces of microorganisms which form Mn(IV) oxide from Mn(II). Recently,
an in situ detection of distinct bacterial biofilm in nodules has been reported
(Wang et al. 2009c); Fig. 4.7f and g. From laboratory studies, it is known that
microcolonies in biofilms are surrounded by large amounts of extracellular polymeric
substances (Lawrence et al. 1991). Those polymers are composed of exopolysaccharides, carrying functional polyionic groups [anions like carboxylate (R-COO
À ),
or cations like amino unit (R-NH 3
+
)] that allow a spatial organization of the bacteria to
cope for optimal supply with nutrients (Wolfaardt et al. 1995); Fig. 4.8a. Metal ions
have been found trapped within the biofilm meshwork, and hence are suspected to
have been involved in the microbial lithification also during biogeochemical cycles
(Dupraz and Visscher 2005). The biofilm structures that were identified in nodules
have an intriguingly regular organization. While the rod-like bacteria are arranged in a
spatial organization of palisades, the cocci produce a massy extracellular biofilm
matrix (Wang et al. 2009c, d); Fig. 4.8d, e.
4.4.7 Mineral Deposition
Based on existing data (Zhu et al. 1993) and by application of nuclear microprobe
analyses, Marcus et al. (2004) could confirm and substantiate that nodules grow by
alternating Fe-rich and Mn-rich layers; Fig. 4.9b–d. Since nodules are formed in the
deep-sea within an oxygen-rich bottom zone (Koschinsky and Halbach 1995;
Koschinsky et al. 1997), both Mn and Fe occur primarily in their oxidized forms
as Mn oxyhydroxides that secondarily associate to colloids (Bau et al. 1996). Those
colloidal dispersions carry surface charges, Mn (negative) and Fe (positives), that
have the tendency to form first mixed colloids and then coarse agglomerates,
a process during which also trace metals are scavenged (Koschinsky and Halbach
1995; Koschinsky and Hein 2003). EDX analysis, coupled with HR-SEM, revealed
that the Mn-rich layers in the nodules contain microorganisms, while the Fe-rich
layers are almost free of them (Wang et al. 2009a, c).
90
X. Wang et al.
structures reduce, due to the enlargement of the bacterial surface and also a
particular chemical/physicochemical composition, e.g., on surface wettability, the
activation energy for the oxidation processes (Kim et al. 2006); Fig. 4.7h.
4.4.6 Biofilm Structures in Polymetallic Nodules
A further input toward an establishment that bio-seeds are causatively involved
in nodule formation came from Crerar and Barnes (1974), who proposed that Mn
(IV) and Fe(III) deposition also involves autocatalytic processes proceeding on
the surfaces of microorganisms which form Mn(IV) oxide from Mn(II). Recently,
an in situ detection of distinct bacterial biofilm in nodules has been reported
(Wang et al. 2009c); Fig. 4.7f and g. From laboratory studies, it is known that
microcolonies in biofilms are surrounded by large amounts of extracellular polymeric
substances (Lawrence et al. 1991). Those polymers are composed of exopolysaccharides, carrying functional polyionic groups [anions like carboxylate (R-COO
À ),
or cations like amino unit (R-NH 3
+
)] that allow a spatial organization of the bacteria to
cope for optimal supply with nutrients (Wolfaardt et al. 1995); Fig. 4.8a. Metal ions
have been found trapped within the biofilm meshwork, and hence are suspected to
have been involved in the microbial lithification also during biogeochemical cycles
(Dupraz and Visscher 2005). The biofilm structures that were identified in nodules
have an intriguingly regular organization. While the rod-like bacteria are arranged in a
spatial organization of palisades, the cocci produce a massy extracellular biofilm
matrix (Wang et al. 2009c, d); Fig. 4.8d, e.
4.4.7 Mineral Deposition
Based on existing data (Zhu et al. 1993) and by application of nuclear microprobe
analyses, Marcus et al. (2004) could confirm and substantiate that nodules grow by
alternating Fe-rich and Mn-rich layers; Fig. 4.9b–d. Since nodules are formed in the
deep-sea within an oxygen-rich bottom zone (Koschinsky and Halbach 1995;
Koschinsky et al. 1997), both Mn and Fe occur primarily in their oxidized forms
as Mn oxyhydroxides that secondarily associate to colloids (Bau et al. 1996). Those
colloidal dispersions carry surface charges, Mn (negative) and Fe (positives), that
have the tendency to form first mixed colloids and then coarse agglomerates,
a process during which also trace metals are scavenged (Koschinsky and Halbach
1995; Koschinsky and Hein 2003). EDX analysis, coupled with HR-SEM, revealed
that the Mn-rich layers in the nodules contain microorganisms, while the Fe-rich
layers are almost free of them (Wang et al. 2009a, c).
90
X. Wang et al.