Microbial Enzymes in Nanotechnology …
191
and Lateef 2016; Lateef et al. 2016e; Elegbede and Lateef 2020). As such, many
microbial enzymes have been produced and deployed for the synthesis of various
metallic nanoparticles (Table 1, Fig. 1).
Studies have shown that the synthesized proteins or enzymes and reducing agents
like organic acids, amino acids and peptides in biological constituents are accountable for nanoparticles bioproduction. These compounds contain functional groups
that get involved in the reduction and consequently the synthesis in addition to the
stabilization of nanoparticles (Safaepour et al. 2009). Also, it has been reported from
FTIR analysis in several studies that biomolecules loaded with amine (N–H) and
hydroxyl (O–H) groups were liable for the reduction, capping as well as stabilization of nanoparticles; thus, these demonstrate the contribution of proteins in the
biosynthetic process (Elegbede et al. 2019; Shankar et al. 2014).
These proteins are believed to create electrostatic attraction of negatively charged
carboxylic groups, thus stabilizing the nanoparticles by capping to avoid their aggregation through the creation of repulsive forces (El-Batal et al. 2015). Durán et al.
(2015) described in a review article that residues of peptides and amino acid such
as arginine, cysteine, lysine and methionine have been engaged in the biosynthesis
AgNPs. Also, Slocik et al. (2005) found out that tyrosine residues on viral capsid
surface keenly activated the reduction AuCl 4
− which resulted in the fabrication of
AuNPs. Proteins responsible for PtNP production from Acinetobacter calcoaceticus
have also been purified according to Gaidhani et al. (2014). Likewise, gold nanoplates
were biosynthesized utilizing 28 KDa purified protein obtained from Chlorella
vulgaris (Xie et al. 2007a). URAK purified from Bacillus cereus NK1 was employed
for the biosynthesis of AgNPs (60 nm) and AuNPs (20 nm) which occurred at 5 min
and 12 h after addition of NaOH, respectively (Deepak et al. 2011).
In recent times, majority of the biofabricated nanoparticles are made by using
fungal and bacterial cells but not purified enzymes and this may lead to several problems especially in scaling up for applications industrially. The foremost difficulty
in this cell-based procedure is binding of the biosynthesized nanoparticles to the
microbial biomass and this necessitates further steps of microbial cells breakdown
and then nanoparticles isolation for purification of nanoparticles. Although culture
supernatants are preferable to microbial biomass in nanoparticles biosynthesis on
account of the lower costs, maintenance and simplicity for application, they also
suffer from drawbacks such as limited numbers of microbes possessing vital secretory
proteins for biosynthesis and the requirement for downstream processes for purification. Also, both microbial biomass and culture supernatant cannot be reused making
the biosynthetic process non-economic particularly for applications in industries.
However, enzymatically synthesized nanoparticles have some advantages over those
synthesized by microbial biomasses and culture supernatants. There is considerable
decrease of the downstream purification steps, and they have superior prospects for
use in industries as they can be immobilized for recycling (Gholami-Shabani et al.
2015).
Enzyme technology has successfully gained access into nanobiotechnology, as
result of biosynthesis via enzymes being proteinous in nature and thus can operate
as bioreducing agents of bulk materials (Elegbede et al. 2020). Enzymes can as well
191
and Lateef 2016; Lateef et al. 2016e; Elegbede and Lateef 2020). As such, many
microbial enzymes have been produced and deployed for the synthesis of various
metallic nanoparticles (Table 1, Fig. 1).
Studies have shown that the synthesized proteins or enzymes and reducing agents
like organic acids, amino acids and peptides in biological constituents are accountable for nanoparticles bioproduction. These compounds contain functional groups
that get involved in the reduction and consequently the synthesis in addition to the
stabilization of nanoparticles (Safaepour et al. 2009). Also, it has been reported from
FTIR analysis in several studies that biomolecules loaded with amine (N–H) and
hydroxyl (O–H) groups were liable for the reduction, capping as well as stabilization of nanoparticles; thus, these demonstrate the contribution of proteins in the
biosynthetic process (Elegbede et al. 2019; Shankar et al. 2014).
These proteins are believed to create electrostatic attraction of negatively charged
carboxylic groups, thus stabilizing the nanoparticles by capping to avoid their aggregation through the creation of repulsive forces (El-Batal et al. 2015). Durán et al.
(2015) described in a review article that residues of peptides and amino acid such
as arginine, cysteine, lysine and methionine have been engaged in the biosynthesis
AgNPs. Also, Slocik et al. (2005) found out that tyrosine residues on viral capsid
surface keenly activated the reduction AuCl 4
− which resulted in the fabrication of
AuNPs. Proteins responsible for PtNP production from Acinetobacter calcoaceticus
have also been purified according to Gaidhani et al. (2014). Likewise, gold nanoplates
were biosynthesized utilizing 28 KDa purified protein obtained from Chlorella
vulgaris (Xie et al. 2007a). URAK purified from Bacillus cereus NK1 was employed
for the biosynthesis of AgNPs (60 nm) and AuNPs (20 nm) which occurred at 5 min
and 12 h after addition of NaOH, respectively (Deepak et al. 2011).
In recent times, majority of the biofabricated nanoparticles are made by using
fungal and bacterial cells but not purified enzymes and this may lead to several problems especially in scaling up for applications industrially. The foremost difficulty
in this cell-based procedure is binding of the biosynthesized nanoparticles to the
microbial biomass and this necessitates further steps of microbial cells breakdown
and then nanoparticles isolation for purification of nanoparticles. Although culture
supernatants are preferable to microbial biomass in nanoparticles biosynthesis on
account of the lower costs, maintenance and simplicity for application, they also
suffer from drawbacks such as limited numbers of microbes possessing vital secretory
proteins for biosynthesis and the requirement for downstream processes for purification. Also, both microbial biomass and culture supernatant cannot be reused making
the biosynthetic process non-economic particularly for applications in industries.
However, enzymatically synthesized nanoparticles have some advantages over those
synthesized by microbial biomasses and culture supernatants. There is considerable
decrease of the downstream purification steps, and they have superior prospects for
use in industries as they can be immobilized for recycling (Gholami-Shabani et al.
2015).
Enzyme technology has successfully gained access into nanobiotechnology, as
result of biosynthesis via enzymes being proteinous in nature and thus can operate
as bioreducing agents of bulk materials (Elegbede et al. 2020). Enzymes can as well