strains of the same species produce more NPs, while others destabilize their formation
(Durán et al. 2007). Therefore, it is necessary to make comparisons among microorganisms to identify promising candidates for the synthesis of NPs.
Due to the constant need to improve and optimize human quality of life, scientific
world is constantly looking to develop new drugs. In this context, heavy metalresistant actinobacteria constitute potential biofactories of NPs and source of new
specialized metabolites that could be used as novel and effective antimicrobials. This
premise is based on the hypothesis that (i) microorganisms isolated from contaminated areas possess in their genomes clusters of genes related to the biosynthesis of
specialized biomolecules that allowed them to survive in these extreme environments and (ii) biogenic NPs are synthesized by simple processes of metal reductions
which can naturally occur as part of cellular detoxification mechanisms.
The present book chapter compiles and updates the available information about the
synthesis of NPs by actinobacteria and discusses about the potential of metal-resistant
strains to produce new NPs and specialized metabolites that could be used as novel
and effective antimicrobials. In addition, we explore by means of a purely molecular
approach the search of new antimicrobials from the genomic analysis. An overview
about techniques used for the study and characterization of NPs is also given.
6.2 Mechanisms of Nanoparticle Biosynthesis
Mechanisms of NP biosynthesis are deeply related to the microorganism since each
one may reduce and oxidize the metallic precursor of NPs by different ways. In
general, methods of biosynthesis show relationship with the specific survival strategies of the microorganism (Bansal et al. 2012). As was previously mentioned, it has
been shown that microorganisms utilize defense mechanisms to reduce the environmental toxicity through different ways of NP production. Microbial detoxification
can be made either by biomineralization, biosorption, complexation, precipitation, or
bioaccumulation. Extracellular production of metal NPs has more commercial
applications in several areas. However, since the NP polydispersity is the major
concern, it is important to optimize the conditions for monodispersity in a biological
process (Jain et al. 2015). In case of intracellular production, the accumulated NPs
are of particular dimension and with less polydispersity. Regardless of the biosynthesis mechanism, control over particle size and polydispersity needs to be
established for biotechnological purposes.
6.2.1 Intracellular Synthesis
During intracellular NPs synthesis, metallic ions are attracted to the negatively
charged functional groups along cell wall and nucleated there, initiating the reduction and synthesis of NPs. Kalabegishvili et al. (2015) demonstrated the biosorption
6 Nanoparticles for New Pharmaceuticals: Metabolites from Actinobacteria
199
(Durán et al. 2007). Therefore, it is necessary to make comparisons among microorganisms to identify promising candidates for the synthesis of NPs.
Due to the constant need to improve and optimize human quality of life, scientific
world is constantly looking to develop new drugs. In this context, heavy metalresistant actinobacteria constitute potential biofactories of NPs and source of new
specialized metabolites that could be used as novel and effective antimicrobials. This
premise is based on the hypothesis that (i) microorganisms isolated from contaminated areas possess in their genomes clusters of genes related to the biosynthesis of
specialized biomolecules that allowed them to survive in these extreme environments and (ii) biogenic NPs are synthesized by simple processes of metal reductions
which can naturally occur as part of cellular detoxification mechanisms.
The present book chapter compiles and updates the available information about the
synthesis of NPs by actinobacteria and discusses about the potential of metal-resistant
strains to produce new NPs and specialized metabolites that could be used as novel
and effective antimicrobials. In addition, we explore by means of a purely molecular
approach the search of new antimicrobials from the genomic analysis. An overview
about techniques used for the study and characterization of NPs is also given.
6.2 Mechanisms of Nanoparticle Biosynthesis
Mechanisms of NP biosynthesis are deeply related to the microorganism since each
one may reduce and oxidize the metallic precursor of NPs by different ways. In
general, methods of biosynthesis show relationship with the specific survival strategies of the microorganism (Bansal et al. 2012). As was previously mentioned, it has
been shown that microorganisms utilize defense mechanisms to reduce the environmental toxicity through different ways of NP production. Microbial detoxification
can be made either by biomineralization, biosorption, complexation, precipitation, or
bioaccumulation. Extracellular production of metal NPs has more commercial
applications in several areas. However, since the NP polydispersity is the major
concern, it is important to optimize the conditions for monodispersity in a biological
process (Jain et al. 2015). In case of intracellular production, the accumulated NPs
are of particular dimension and with less polydispersity. Regardless of the biosynthesis mechanism, control over particle size and polydispersity needs to be
established for biotechnological purposes.
6.2.1 Intracellular Synthesis
During intracellular NPs synthesis, metallic ions are attracted to the negatively
charged functional groups along cell wall and nucleated there, initiating the reduction and synthesis of NPs. Kalabegishvili et al. (2015) demonstrated the biosorption
6 Nanoparticles for New Pharmaceuticals: Metabolites from Actinobacteria
199