6.1 Introduction
New drugs, especially antibiotics, are needed to counter the spread of antibioticresistant pathogens and to combat several diseases (Payne et al. 2007; Olano et al.
2009). It is widely known that the most promising source of new drugs remain
natural products such as biomolecules especially those of microbial origin (Bull and
Stach 2007). Members of the Actinobacteria group produce about 45% of all
microbial bioactive molecules such as secondary metabolites or, more precisely,
specialized metabolites (Bérdy 2005; Hoskisson et al. 2015). In particular, Streptomyces and Amycolatopsis genera produce as part of their normal life cycle specialized metabolites that represent about 65% of the antimicrobial drugs used in clinical
(McLean et al. 2016). However, from the study of their genomes, it is known that
they have the genetic ability to produce many more of these molecules. Both
microbial genera may have between 20 and 50 biosynthetic pathways, but only
very few of them are expressed under common laboratory conditions (McLean et al.
2016). It is believed that the biochemical diversity encoded by these “silent” or
“unproductive” biosynthetic pathways is an untapped promising source of new
antibacterial molecules and other therapeutic agents (Goodfellow and Fiedler
2010). Hence, identification and cloning of clusters of biosynthetic genes encoding
potential chemically novel antimicrobial drugs are an emerging technology.
In search of novel biomolecules, nanoscience and nanotechnology are emerging
fields which involve the synthesis and application of nanoscale materials such as
nanoparticles (NPs) (Golinska et al. 2017). Due to miniaturization (1–100 nm), the
change in the physicochemical properties produces novel attributes of nanomaterials.
Thus, NP applications are growing on several areas like biomedical, pharmaceutical,
catalysis, and drug delivery, among others. The metallic NPs are considered as most
promising since they contain remarkable antibacterial properties due to their large
surface area related to volume ratio. Metallic NPs which have gained immense
attention in recent years are silver, gold, platinum, palladium, titanium, iron, aluminum, and copper. Among the abovementioned metals, silver (Ag) is the most important in NP synthesis since AgNPs have many uses in the medical field. Silver is antiinflammatory, antitumor (Beeler and Singh 2016), and fundamentally antimicrobial,
which arouses great expectations in the search for new sources of AgNPs due to the
drastic increase in microbial resistance to antibiotics (WHO 2015).
Researchers are immensely interested in NP synthesis by physical or chemical
methods, and these NPs are designated as engineered NPs (ENPs). However, the
conventional chemical methods for the synthesis of ENPs use high energy levels,
making their production very expensive. Besides, the use of toxic chemicals and
nonpolar solvents in the ENPs synthesis limits their applications in clinical areas.
Nano-biosynthesis, on the other hand, is a “green technology” by which NPs are
obtained through biological processes such as the reduction of a metal salt by the
action of biomolecules. In this context, biomolecules (mostly proteins) from plants,
algae, bacteria, and fungi can act as reducing and/or stabilizing agents for the
formation of monodispersed NPs (Siddiqi and Husen 2016). Nanoparticles
6 Nanoparticles for New Pharmaceuticals: Metabolites from Actinobacteria
197
New drugs, especially antibiotics, are needed to counter the spread of antibioticresistant pathogens and to combat several diseases (Payne et al. 2007; Olano et al.
2009). It is widely known that the most promising source of new drugs remain
natural products such as biomolecules especially those of microbial origin (Bull and
Stach 2007). Members of the Actinobacteria group produce about 45% of all
microbial bioactive molecules such as secondary metabolites or, more precisely,
specialized metabolites (Bérdy 2005; Hoskisson et al. 2015). In particular, Streptomyces and Amycolatopsis genera produce as part of their normal life cycle specialized metabolites that represent about 65% of the antimicrobial drugs used in clinical
(McLean et al. 2016). However, from the study of their genomes, it is known that
they have the genetic ability to produce many more of these molecules. Both
microbial genera may have between 20 and 50 biosynthetic pathways, but only
very few of them are expressed under common laboratory conditions (McLean et al.
2016). It is believed that the biochemical diversity encoded by these “silent” or
“unproductive” biosynthetic pathways is an untapped promising source of new
antibacterial molecules and other therapeutic agents (Goodfellow and Fiedler
2010). Hence, identification and cloning of clusters of biosynthetic genes encoding
potential chemically novel antimicrobial drugs are an emerging technology.
In search of novel biomolecules, nanoscience and nanotechnology are emerging
fields which involve the synthesis and application of nanoscale materials such as
nanoparticles (NPs) (Golinska et al. 2017). Due to miniaturization (1–100 nm), the
change in the physicochemical properties produces novel attributes of nanomaterials.
Thus, NP applications are growing on several areas like biomedical, pharmaceutical,
catalysis, and drug delivery, among others. The metallic NPs are considered as most
promising since they contain remarkable antibacterial properties due to their large
surface area related to volume ratio. Metallic NPs which have gained immense
attention in recent years are silver, gold, platinum, palladium, titanium, iron, aluminum, and copper. Among the abovementioned metals, silver (Ag) is the most important in NP synthesis since AgNPs have many uses in the medical field. Silver is antiinflammatory, antitumor (Beeler and Singh 2016), and fundamentally antimicrobial,
which arouses great expectations in the search for new sources of AgNPs due to the
drastic increase in microbial resistance to antibiotics (WHO 2015).
Researchers are immensely interested in NP synthesis by physical or chemical
methods, and these NPs are designated as engineered NPs (ENPs). However, the
conventional chemical methods for the synthesis of ENPs use high energy levels,
making their production very expensive. Besides, the use of toxic chemicals and
nonpolar solvents in the ENPs synthesis limits their applications in clinical areas.
Nano-biosynthesis, on the other hand, is a “green technology” by which NPs are
obtained through biological processes such as the reduction of a metal salt by the
action of biomolecules. In this context, biomolecules (mostly proteins) from plants,
algae, bacteria, and fungi can act as reducing and/or stabilizing agents for the
formation of monodispersed NPs (Siddiqi and Husen 2016). Nanoparticles
6 Nanoparticles for New Pharmaceuticals: Metabolites from Actinobacteria
197