98
G. Grasso et al.
intrinsic ability to form CdS nanocrystals in the vacuole as cadmium defense mechanism. Such multicompartment steps in S. pombe CdS biosynthesis make difficult the
control and fine-tuning of the CdS nanocrystals properties. Through the described
heterologous expression in E. coli, it has been by-passed the multicompartment steps
that occur in S. pombe (Kang et al. 2008).
The in vivo synthesis of diverse metal NPs has been obtained using recombinant
E. coli DH5α co-expressing genes encoding phytochelatin synthase from the plant
Arabidopsis thaliana and metallothionein from the bacterium Pseudomonas putida.
The products of biosynthesis mediated by the recombinant E. coli DH5α biosynthesis
have included CdSeZn, PrGd, CdCs, and FeCoNPs, all never synthesized before
using chemical methods (Park et al. 2010). Similarly, Choi et al. (2018) have demonstrated the in vivo synthesis of various metal NPs (e.g., CdSeZn, PrGd, CdCs, and
FeCo) never synthesized before by chemical methods in recombinant E. coli DH5α
cells co-expressing system for phytochelatin synthase and/or metallothionein. Yuan
et al. (2019) have recently described AgNPs synthesis by E. coli DH5α transformed
with a gene encoding copper binding protein metallothionein from the yeast Candida
albicans. The expression of metallothionein from C. albicans enhanced both the E.
coli cell growth and AgNPs production yield compared to the control. The biosyntheses of CdS QDs in genetically engineered E. coli have been also reported in
literature. The biosynthesis of CdS QDs in genetically engineered E. coli BL21 has
been obtained through the introduction of genes encoding CDS 7, a histidine-rich
CdS binding peptide (Mi et al. 2011). Monrás et al. (2012) have exploited a wild type
E. coli AG1 overexpressing the gshA gene encoding L-glutamate cysteine ligase, one
of the principal enzymes involved in glutathione biosynthesis.
The genetic screening and the use of appropriate mutants for nanobiosynthesis
are other fundamental biotechnological tools to investigate microbial nanobiosynthetic processes. As for other genetic tools described in this section, genetic studies
on mutants can reveal the essential genetic requirements for the nanobiosynthetic
process and related regulatory mechanisms and highlight the different roles of gene
encoding products in nanomaterial assembly. In particular, gene overexpression can
be employed in mutant genetic studies both for the identification of biochemical
pathway components and to select the most suitable mutant phenotype for a given
nanobiosynthetic process. Finally, comparative analyses of mutant strains can help
to select the most suitable microbial strain for a given nanobiosynthetic product,
according to specific requirements such as production yield, size, morphological and
compositional features of the nanomaterial of interest.
The use of mutants for genes encoding outer membrane c-type cytochromes of
the bacterium S. oneidensis have been investigated to take full advantage in nanoparticles synthesis mediated by these bacterial outer membrane proteins, casting light
upon the possibilities of tuning morphology, size and composition of nanoparticles. The influences of outer membrane c-type cytochromes MtrC and OmcA on
the size and activity of the extracellular silver AgNPs and Ag 2 S NPs produced by
the dissimilatory metal-reducing bacterium S. oneidensis MR-1 have been investigated by Ng et al. (2013). The S. oneidensis mutant (mtrC-omcA) has been able
G. Grasso et al.
intrinsic ability to form CdS nanocrystals in the vacuole as cadmium defense mechanism. Such multicompartment steps in S. pombe CdS biosynthesis make difficult the
control and fine-tuning of the CdS nanocrystals properties. Through the described
heterologous expression in E. coli, it has been by-passed the multicompartment steps
that occur in S. pombe (Kang et al. 2008).
The in vivo synthesis of diverse metal NPs has been obtained using recombinant
E. coli DH5α co-expressing genes encoding phytochelatin synthase from the plant
Arabidopsis thaliana and metallothionein from the bacterium Pseudomonas putida.
The products of biosynthesis mediated by the recombinant E. coli DH5α biosynthesis
have included CdSeZn, PrGd, CdCs, and FeCoNPs, all never synthesized before
using chemical methods (Park et al. 2010). Similarly, Choi et al. (2018) have demonstrated the in vivo synthesis of various metal NPs (e.g., CdSeZn, PrGd, CdCs, and
FeCo) never synthesized before by chemical methods in recombinant E. coli DH5α
cells co-expressing system for phytochelatin synthase and/or metallothionein. Yuan
et al. (2019) have recently described AgNPs synthesis by E. coli DH5α transformed
with a gene encoding copper binding protein metallothionein from the yeast Candida
albicans. The expression of metallothionein from C. albicans enhanced both the E.
coli cell growth and AgNPs production yield compared to the control. The biosyntheses of CdS QDs in genetically engineered E. coli have been also reported in
literature. The biosynthesis of CdS QDs in genetically engineered E. coli BL21 has
been obtained through the introduction of genes encoding CDS 7, a histidine-rich
CdS binding peptide (Mi et al. 2011). Monrás et al. (2012) have exploited a wild type
E. coli AG1 overexpressing the gshA gene encoding L-glutamate cysteine ligase, one
of the principal enzymes involved in glutathione biosynthesis.
The genetic screening and the use of appropriate mutants for nanobiosynthesis
are other fundamental biotechnological tools to investigate microbial nanobiosynthetic processes. As for other genetic tools described in this section, genetic studies
on mutants can reveal the essential genetic requirements for the nanobiosynthetic
process and related regulatory mechanisms and highlight the different roles of gene
encoding products in nanomaterial assembly. In particular, gene overexpression can
be employed in mutant genetic studies both for the identification of biochemical
pathway components and to select the most suitable mutant phenotype for a given
nanobiosynthetic process. Finally, comparative analyses of mutant strains can help
to select the most suitable microbial strain for a given nanobiosynthetic product,
according to specific requirements such as production yield, size, morphological and
compositional features of the nanomaterial of interest.
The use of mutants for genes encoding outer membrane c-type cytochromes of
the bacterium S. oneidensis have been investigated to take full advantage in nanoparticles synthesis mediated by these bacterial outer membrane proteins, casting light
upon the possibilities of tuning morphology, size and composition of nanoparticles. The influences of outer membrane c-type cytochromes MtrC and OmcA on
the size and activity of the extracellular silver AgNPs and Ag 2 S NPs produced by
the dissimilatory metal-reducing bacterium S. oneidensis MR-1 have been investigated by Ng et al. (2013). The S. oneidensis mutant (mtrC-omcA) has been able