with known function (Richter et al. 2007). Generic transporters and cation diffusion
facilitators control influx and efflux of diverse solutes necessary for metabolism and
in this case, might possibly transport iron for the biomineralization of magnetite
(Sch€ uler 2008; Jogler and Sch€ uler 2009). HtrA-like proteases are normally found in
the periplasm where they degrade misfolded proteins (Pallen and Wren 1997).
Magnetosome-related proteins can be proteolytically cleaved and could be potential
targets of these respective proteases (Arakaki et al. 2003). The development of
genetic systems for some MTB provided the base to selectively determine in vivo
the function of involved proteins (Matsunaga et al. 1992; Schultheiss and Sch€ uler
2003). MamG, F, D, and C have been shown to have an influence on crystal size and
possibly morphology (Scheffel et al. 2008). MamK and MamJ have been made
responsible for chain alignment of magnetosomes along the cell axis, as will be
explained in Sect. 3.2.4 (Komeili et al. 2006; Pradel et al. 2006; Scheffel et al.
2006). Fusions with fluorescent reporters helped determine the localization of some
proteins, including MamA, MamC, MamJ, and MamK (Komeili et al. 2004;
Komeili et al. 2006; Scheffel et al. 2006; Lang and Sch€ uler 2008). Additionally,
recombinant expression of magnetosome-related proteins has shed some light on
their possible functions (Arakaki et al. 2003; Pradel et al. 2006; Scheffel and
Sch€ uler 2007; Taoka et al. 2007). For example, Mms6 has been proposed as a
potential magnetite crystal nucleator or growth modulator by face-selective adhesion (Arakaki et al. 2003). All these approaches give us a first glimpse in
comprehending the molecular basis of magnetite biomineralization, but many
details remain poorly understood.
1.3 Magnetosomes
As only magnetite-forming bacteria have been obtained in axenic culture so far, our
knowledge about the chemistry, molecular biology, and genetics has mainly been
obtained from these strains. Future studies on greigite formers will hopefully
provide insights on their respective differences. In the following sections, we will
present the current knowledge on how magnetite is biomineralized in MTB and
which biological and chemical factors influence the specific properties of the
magnetosome particles.
1.3.1 Magnetite Biomineralization Pathway
The intracellular formation of magnetite nanocrystals requires the accumulation of
substantial amounts of iron from the surrounding environment and a precisely
coordinated biological machinery to transport and deposit it under the right
conditions for the formation of the magnetite phase. This chemistry must be highly
1 Magnetite Biomineralization in Bacteria
9
facilitators control influx and efflux of diverse solutes necessary for metabolism and
in this case, might possibly transport iron for the biomineralization of magnetite
(Sch€ uler 2008; Jogler and Sch€ uler 2009). HtrA-like proteases are normally found in
the periplasm where they degrade misfolded proteins (Pallen and Wren 1997).
Magnetosome-related proteins can be proteolytically cleaved and could be potential
targets of these respective proteases (Arakaki et al. 2003). The development of
genetic systems for some MTB provided the base to selectively determine in vivo
the function of involved proteins (Matsunaga et al. 1992; Schultheiss and Sch€ uler
2003). MamG, F, D, and C have been shown to have an influence on crystal size and
possibly morphology (Scheffel et al. 2008). MamK and MamJ have been made
responsible for chain alignment of magnetosomes along the cell axis, as will be
explained in Sect. 3.2.4 (Komeili et al. 2006; Pradel et al. 2006; Scheffel et al.
2006). Fusions with fluorescent reporters helped determine the localization of some
proteins, including MamA, MamC, MamJ, and MamK (Komeili et al. 2004;
Komeili et al. 2006; Scheffel et al. 2006; Lang and Sch€ uler 2008). Additionally,
recombinant expression of magnetosome-related proteins has shed some light on
their possible functions (Arakaki et al. 2003; Pradel et al. 2006; Scheffel and
Sch€ uler 2007; Taoka et al. 2007). For example, Mms6 has been proposed as a
potential magnetite crystal nucleator or growth modulator by face-selective adhesion (Arakaki et al. 2003). All these approaches give us a first glimpse in
comprehending the molecular basis of magnetite biomineralization, but many
details remain poorly understood.
1.3 Magnetosomes
As only magnetite-forming bacteria have been obtained in axenic culture so far, our
knowledge about the chemistry, molecular biology, and genetics has mainly been
obtained from these strains. Future studies on greigite formers will hopefully
provide insights on their respective differences. In the following sections, we will
present the current knowledge on how magnetite is biomineralized in MTB and
which biological and chemical factors influence the specific properties of the
magnetosome particles.
1.3.1 Magnetite Biomineralization Pathway
The intracellular formation of magnetite nanocrystals requires the accumulation of
substantial amounts of iron from the surrounding environment and a precisely
coordinated biological machinery to transport and deposit it under the right
conditions for the formation of the magnetite phase. This chemistry must be highly
1 Magnetite Biomineralization in Bacteria
9