100
G. Grasso et al.
in a 7.5 L bioreactor gave a maximum yield of 58.4 ± 6.4 mg magnetosomes per
liter (Liu et al. 2008).
In another work, the combination of random mutagenesis and DNA sequencing
has been applied to produce and isolate about 30 mutants of the magnetotactic
bacterium Desulfovibrio magneticus RS-1. The role of unexpected genes called mad
genes over the control of the magnetosomes morphology has been highlighted. In the
near future, the combined use of this approach with physical and chemical analytical
techniques could enable a more complete understanding of biomineralization process
in different strains of magnetotactic bacteria (Faivre and Baumgartner 2015). The
magnetic properties of magnetosomes are largely dependent on their shape, size, and
degree of aggregation of magnetite nanoparticles forming the magnetic nanostructure. The key role of protein MamK in the nanoassembly of magnetite nanoparticles
in magnetosomes stable chains has been demonstrated (Bennet et al. 2015).
A strategy for the genomic amplification of single and multiple magnetosome
gene clusters involved in magnetosomes biosynthesis genes have been explored in
M. gryphiswaldense. The results obtained from sequential chromosomal transposition have shown that the tuned expression of the mam and mms gene clusters can be
employed as powerful strategy for the control of magnetosome size and number. More
specifically, the duplication of mamGFDC, mamAB, mms6, and mamXY magnetosome operons has more than doubled the number of magnetosomes and the amplification of the mms6 operon has caused an enlargement of magnetite crystals, compared
to the wild type M. gryphiswaldense strain (Lohße et al. 2016). A successful heterologous expression in the photosynthetic model organism Rhodospirillum rubrum has
been described for a minimal set of genes involved in the magnetosome biosynthesis
in M. gryphiswaldense. This set of genes included mamAB, mamGFDC, mamXY,
and mms6 genes. The findings have shown the production of 24 nm-sized Fe 3 O 4
nanoparticles surrounded by an external organic layer. The magnetic phenotype has
remained stable for at least 40 generations under non-selective conditions (Kolinko
et al. 2014).
The genetic modification of gene(s) encoding magnetosome surface protein(s) for
the production of chimeric anchor gene transcripts has been described for focused
surface functionalization of magnetosome membranes. Different works have reported
the functionalization of magnetosome membranes with enzymes and biomolecules of
interest exploiting the most abundant magnetosome surface proteins MamA, MamF,
and MamG for the production of fusion or chimeric anchors to the magnetosome
membrane. The genetic modification of M. magneticum AMB-1 magnetosomes functionalized with the bacterial enzyme organophosphohydrolase has been reported by
Ginet et al. (2011). The functionalization has been carried out through the fusion of
mamC gene encoding magnetosome membrane protein with opd gene encoding
enzyme organophosphohydrolase from Flavobacterium ATCC 27551. The Opdfunctionalized magnetosomes have been used for the hydrolysis of ethyl-paraoxon
as a model organophosphate pesticide. The Opd-functionalized magnetosomes have
retained a stable catalytic activity over repeated use for pesticide degradation.
Such functionalized magnetic nanoparticles could be used for future applications
in organophosphate pesticides bioremediation (Ginet et al. 2011).
G. Grasso et al.
in a 7.5 L bioreactor gave a maximum yield of 58.4 ± 6.4 mg magnetosomes per
liter (Liu et al. 2008).
In another work, the combination of random mutagenesis and DNA sequencing
has been applied to produce and isolate about 30 mutants of the magnetotactic
bacterium Desulfovibrio magneticus RS-1. The role of unexpected genes called mad
genes over the control of the magnetosomes morphology has been highlighted. In the
near future, the combined use of this approach with physical and chemical analytical
techniques could enable a more complete understanding of biomineralization process
in different strains of magnetotactic bacteria (Faivre and Baumgartner 2015). The
magnetic properties of magnetosomes are largely dependent on their shape, size, and
degree of aggregation of magnetite nanoparticles forming the magnetic nanostructure. The key role of protein MamK in the nanoassembly of magnetite nanoparticles
in magnetosomes stable chains has been demonstrated (Bennet et al. 2015).
A strategy for the genomic amplification of single and multiple magnetosome
gene clusters involved in magnetosomes biosynthesis genes have been explored in
M. gryphiswaldense. The results obtained from sequential chromosomal transposition have shown that the tuned expression of the mam and mms gene clusters can be
employed as powerful strategy for the control of magnetosome size and number. More
specifically, the duplication of mamGFDC, mamAB, mms6, and mamXY magnetosome operons has more than doubled the number of magnetosomes and the amplification of the mms6 operon has caused an enlargement of magnetite crystals, compared
to the wild type M. gryphiswaldense strain (Lohße et al. 2016). A successful heterologous expression in the photosynthetic model organism Rhodospirillum rubrum has
been described for a minimal set of genes involved in the magnetosome biosynthesis
in M. gryphiswaldense. This set of genes included mamAB, mamGFDC, mamXY,
and mms6 genes. The findings have shown the production of 24 nm-sized Fe 3 O 4
nanoparticles surrounded by an external organic layer. The magnetic phenotype has
remained stable for at least 40 generations under non-selective conditions (Kolinko
et al. 2014).
The genetic modification of gene(s) encoding magnetosome surface protein(s) for
the production of chimeric anchor gene transcripts has been described for focused
surface functionalization of magnetosome membranes. Different works have reported
the functionalization of magnetosome membranes with enzymes and biomolecules of
interest exploiting the most abundant magnetosome surface proteins MamA, MamF,
and MamG for the production of fusion or chimeric anchors to the magnetosome
membrane. The genetic modification of M. magneticum AMB-1 magnetosomes functionalized with the bacterial enzyme organophosphohydrolase has been reported by
Ginet et al. (2011). The functionalization has been carried out through the fusion of
mamC gene encoding magnetosome membrane protein with opd gene encoding
enzyme organophosphohydrolase from Flavobacterium ATCC 27551. The Opdfunctionalized magnetosomes have been used for the hydrolysis of ethyl-paraoxon
as a model organophosphate pesticide. The Opd-functionalized magnetosomes have
retained a stable catalytic activity over repeated use for pesticide degradation.
Such functionalized magnetic nanoparticles could be used for future applications
in organophosphate pesticides bioremediation (Ginet et al. 2011).