Precision Microbial Nanobiosynthesis: Knowledge …
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to produce significantly smaller AgNPs and Ag 2 S NPs comparing with the S. oneidensis MR-1, 24.4 ± 0.8 nm versus 40.9 ± 1.0 nm for AgNPs and 27.6 ± 6.4 versus
53.4 ± 12.4 for Ag 2 S NPs, respectively. Furthermore, compared to NPs produced
by S. oneidensis MR-1, the AgNPs and Ag 2 S NPs from the S. oneidensis mutant
(mtrC-omcA) have shown higher antibacterial activity against E. coli and higher
catalytic activity in methylviologen reduction, respectively. These results suggested
that through the controlled expression of the genes encoding outer membrane c-type
cytochromes in S. oneidensis MR-1, a possibility to control NPs size and properties
of the extracellular biogenic NPs may be exerted (Ng et al. 2013).
The genetic modification of one component of extracellular electron transfer chain
in S. oneidensis MR-1 has been also exploited by Tian et al. (2017) for the production
of SeNPs or CdSe nanoparticles with fine-tuned composition, morphology, and size.
In particular, the S. oneidensis mutant with the tetrahaem c-type cytochrome CymAencoding gene deleted (cymA) has exhibited a rapid and a high production of
hexagonal, ultrafine, and uniform-sized CdSe nanoparticles (average diameter = 3.3
± 0.6 nm). In the S. oneidensis mutant that overexpressed cymA gene, PYYDTcymA, production of a larger-sized (average diameter = 104.6 ± 8.4 nm) spherical
SeNPs has been observed (Tian et al. 2017).
4.2 Microbial Synthesis of Magnetosomes, Frustules,
Nanowires, and Nanocellulose
Many studies using genetically engineered microbial strains for the biosynthesis
of magnetosomes, frustules, bacterial nanowires, and bacterial nanocellulose have
been extensively reported in the literature. The genomes of numerous magnetotactic
bacteria strains of have been sequenced, but standardized protocols for genetic manipulation are only available for the bacteria Magnetospirillum gryphiswaldense and M.
magneticum.
4.2.1 Magnetosomes
In particular, M. magneticum strain AMB-1 has been the most studied for the
magnetite biomineralization process, also because Magnetospirillum species are easy
to grow under laboratory conditions compared to other magnetotactic bacteria. The
research on the other magnetotactic bacteria is still in progress. Liu et al. (2008)
have obtained a mutant of M. gryphiswaldense named ‘NPHB’ from a conjugation
experiment with a donor strain of E. coli. The M. gryphiswaldense NPHB mutant has
showed a higher ATP hydrolyzing activity and a higher magnetosomes production
yield 35% and 69% higher, respectively, compared to the wild type strain. Concerning
magnetosomes production yield, M. gryphiswaldense NPHB mutant strain cultured
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to produce significantly smaller AgNPs and Ag 2 S NPs comparing with the S. oneidensis MR-1, 24.4 ± 0.8 nm versus 40.9 ± 1.0 nm for AgNPs and 27.6 ± 6.4 versus
53.4 ± 12.4 for Ag 2 S NPs, respectively. Furthermore, compared to NPs produced
by S. oneidensis MR-1, the AgNPs and Ag 2 S NPs from the S. oneidensis mutant
(mtrC-omcA) have shown higher antibacterial activity against E. coli and higher
catalytic activity in methylviologen reduction, respectively. These results suggested
that through the controlled expression of the genes encoding outer membrane c-type
cytochromes in S. oneidensis MR-1, a possibility to control NPs size and properties
of the extracellular biogenic NPs may be exerted (Ng et al. 2013).
The genetic modification of one component of extracellular electron transfer chain
in S. oneidensis MR-1 has been also exploited by Tian et al. (2017) for the production
of SeNPs or CdSe nanoparticles with fine-tuned composition, morphology, and size.
In particular, the S. oneidensis mutant with the tetrahaem c-type cytochrome CymAencoding gene deleted (cymA) has exhibited a rapid and a high production of
hexagonal, ultrafine, and uniform-sized CdSe nanoparticles (average diameter = 3.3
± 0.6 nm). In the S. oneidensis mutant that overexpressed cymA gene, PYYDTcymA, production of a larger-sized (average diameter = 104.6 ± 8.4 nm) spherical
SeNPs has been observed (Tian et al. 2017).
4.2 Microbial Synthesis of Magnetosomes, Frustules,
Nanowires, and Nanocellulose
Many studies using genetically engineered microbial strains for the biosynthesis
of magnetosomes, frustules, bacterial nanowires, and bacterial nanocellulose have
been extensively reported in the literature. The genomes of numerous magnetotactic
bacteria strains of have been sequenced, but standardized protocols for genetic manipulation are only available for the bacteria Magnetospirillum gryphiswaldense and M.
magneticum.
4.2.1 Magnetosomes
In particular, M. magneticum strain AMB-1 has been the most studied for the
magnetite biomineralization process, also because Magnetospirillum species are easy
to grow under laboratory conditions compared to other magnetotactic bacteria. The
research on the other magnetotactic bacteria is still in progress. Liu et al. (2008)
have obtained a mutant of M. gryphiswaldense named ‘NPHB’ from a conjugation
experiment with a donor strain of E. coli. The M. gryphiswaldense NPHB mutant has
showed a higher ATP hydrolyzing activity and a higher magnetosomes production
yield 35% and 69% higher, respectively, compared to the wild type strain. Concerning
magnetosomes production yield, M. gryphiswaldense NPHB mutant strain cultured