86
G. Grasso et al.
Liu et al. 2010; Zhang et al. 2011). In the genus Magnetospirillum, the most widely
exploited and studied magnetotactic bacteria genus, microaerobic (O 2 tension < 10%)
or anaerobic conditions have enhanced magnetosomes production yield. The composition of culture medium has also shown to be an important factor. The use of
nitrate and Fe(III) citrate as nitrogen and iron sources, respectively, has improved
magnetosomes formation in Magnetospirillum strains (Heyen and Schüler 2003). As
reported by Alphandéry et al. (2012), the presence of iron-chelating agents in culture
medium with a concentration range between 0.4 and 40 μM (i) stimulated the cellular
growth (ii) it enhanced the production of magnetosomes and (iii) it modified the
size and chain length of magnetosomes in Magnetospirillum magneticum AMB-1.
In addition, remarkable changes in these magnetosome properties have resulted in
improved heating properties of magnetosomes. The heating properties of magnetosomes are important for possible application in cancer focal therapies like magnetic
hyperthermia.
3 The Biochemistry Behind Microbial Nanobiosynthesis
The understanding of the involved biochemical mechanisms of nanomaterials
synthesis by microorganisms is a key aspect of nanobiotechnology research in order
to define more reliable and reproducible nanobiosynthetic methods and to spur future
developments through the wide opportunities offered by genetic engineering tools
(see Sect. 4). The main results of research concerning the identification of biochemical mediators involved in microbial nanobiosynthesis are summarized in Table 2.
During the last years, the knowledge about the biosynthetic mechanisms of nanostructured materials of microbial origin like diatom frustules, magnetosomes, bacterial
nanowires, and bacterial nanocellulose has evolved, providing significant insights
into fundamental aspects of biochemical mechanisms and the molecular and enzymatic components involved. Concerning diatom cell wall silicification and frustules
biogenesis, the complete understanding of cellular processes involved is still a challenge. A greater knowledge has been achieved about the role of proteins silaffins and
long-chain polyamines in biosilicification process (Kröger and Poulsen 2008) and the
possible involvement of cellular translocators (Yee et al. 2020). The magnetosome
biogenesis in Magnetospirillum species is a very complex and still not completely
elucidated process. To date, six different incomplete models have been proposed to
elucidate magnetosome formation (Yan et al. 2017). Concerning bacterial nanowires,
most of the studies have focused on Geobacter sulfurreducens (Lovley and Walker
2019), on other Gram-negative bacteria (Hospenthal et al. 2017) and some studies
have been conducted on cyanobacteria Microcystis (Sure et al. 2015) and Synechocystis (Chen et al. 2020). The molecular mechanisms of bacterial nanocellulose
biosynthesis by Komagataeibacter genus are very well characterized (Jacek et al.
2019a).
In addition to these aforementioned unique nanostructured materials of microbial origin, microorganisms have showed the ability to synthesize nanoparticles
G. Grasso et al.
Liu et al. 2010; Zhang et al. 2011). In the genus Magnetospirillum, the most widely
exploited and studied magnetotactic bacteria genus, microaerobic (O 2 tension < 10%)
or anaerobic conditions have enhanced magnetosomes production yield. The composition of culture medium has also shown to be an important factor. The use of
nitrate and Fe(III) citrate as nitrogen and iron sources, respectively, has improved
magnetosomes formation in Magnetospirillum strains (Heyen and Schüler 2003). As
reported by Alphandéry et al. (2012), the presence of iron-chelating agents in culture
medium with a concentration range between 0.4 and 40 μM (i) stimulated the cellular
growth (ii) it enhanced the production of magnetosomes and (iii) it modified the
size and chain length of magnetosomes in Magnetospirillum magneticum AMB-1.
In addition, remarkable changes in these magnetosome properties have resulted in
improved heating properties of magnetosomes. The heating properties of magnetosomes are important for possible application in cancer focal therapies like magnetic
hyperthermia.
3 The Biochemistry Behind Microbial Nanobiosynthesis
The understanding of the involved biochemical mechanisms of nanomaterials
synthesis by microorganisms is a key aspect of nanobiotechnology research in order
to define more reliable and reproducible nanobiosynthetic methods and to spur future
developments through the wide opportunities offered by genetic engineering tools
(see Sect. 4). The main results of research concerning the identification of biochemical mediators involved in microbial nanobiosynthesis are summarized in Table 2.
During the last years, the knowledge about the biosynthetic mechanisms of nanostructured materials of microbial origin like diatom frustules, magnetosomes, bacterial
nanowires, and bacterial nanocellulose has evolved, providing significant insights
into fundamental aspects of biochemical mechanisms and the molecular and enzymatic components involved. Concerning diatom cell wall silicification and frustules
biogenesis, the complete understanding of cellular processes involved is still a challenge. A greater knowledge has been achieved about the role of proteins silaffins and
long-chain polyamines in biosilicification process (Kröger and Poulsen 2008) and the
possible involvement of cellular translocators (Yee et al. 2020). The magnetosome
biogenesis in Magnetospirillum species is a very complex and still not completely
elucidated process. To date, six different incomplete models have been proposed to
elucidate magnetosome formation (Yan et al. 2017). Concerning bacterial nanowires,
most of the studies have focused on Geobacter sulfurreducens (Lovley and Walker
2019), on other Gram-negative bacteria (Hospenthal et al. 2017) and some studies
have been conducted on cyanobacteria Microcystis (Sure et al. 2015) and Synechocystis (Chen et al. 2020). The molecular mechanisms of bacterial nanocellulose
biosynthesis by Komagataeibacter genus are very well characterized (Jacek et al.
2019a).
In addition to these aforementioned unique nanostructured materials of microbial origin, microorganisms have showed the ability to synthesize nanoparticles