Microbial-Mediated Nanoparticles for Sustainable Environment …
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antimicrobial activity against Escherichia coli, methicillin-resistant Staphylococcus
aureus-LY, Pseudomonas aeruginosa, and Candida albicans.
Commendable potential of AgNPs can be ascribed to its ability of disrupting
the bacterial membrane’ integrity through development of adsorptive interactions,
bacterial cellular division shutting down accomplished via complete prevention of
DNA replication since AgNPs interact with the enzymatic thiol groups and bases
having phosphorus. AgNPs are also effective antimicrobial agents because they can
form free radicals leading to induction of oxidative stress (Soenen et al. 2011). In
addition to the AgNPs’ inherent potential in prevention of different microbes, the
morphological aspects can also play an influential role, and thus, variable extents of
antimicrobial activities are being reported for differently shaped AgNPs (Pal et al.
2007; Paredes et al. 2014). Furthermore, this activity also results from electrostatic
attraction developed between the bacterial cells having negative charge and NPs
being positively charged. Albeit, there is a great deal of dissimilarity between grampositive and gram-negative bacteria in terms of their cell membrane, but majority of
them express a negative charge by the dint of carboxyl, phosphatic and amino groups.
Gram-negative bacteria’s cell wall is composed of a layer of lipopolysaccharide that
has lipids and polysaccharides having been bonded to one another through covalent
linkage with a negative charge. Even then, the positively charged AgNPs are provided
with weaker penetrability barricade. However, in case of the gram-positive bacteria,
the cell wall is made up of thick layer having peptidoglycans in which there is a
considerable cross-linking of the polysaccharide chains arranged in a linear manner
through shorter peptides leading to the formation of a rigid structure having three
dimensions. Such rigidity in the cell wall layer hinders AgNPs attachment to the cell
wall, and penetration is affected (Tamboli and Lee 2013).
7 Conclusions and Future Prospects
The tremendous work done in the last decades in the field of environmental nanobiotechnology for fabrication of metallic NPs using microbial nano-factories as biotemplates for stabilizing and reducing purposes has been commendable. A great
deal of metallic, metal oxide, metal chalcogenide, and semiconductor materials has
been fabricated using number of microbial species, i.e., bacteria, fungi, yeast, actinomycetes, and viruses. Reduction of NPs done via microbial route signifies not
only a facile and eco-friendly mode but is also economically valid in comparison
to costly and complicated physicochemical reactions marked by inducing profound
toxicity toward environment. Through microbes mediated biomimetic NPs synthesis,
NPs of various shapes, sizes, and polydispersity extent can be efficiently developed
and used for different applications, especially for detoxification of the ecospheric
zones. Though great deal of work has been done and different microbes have been
proven to be adopted as effective nano-biotechnological tools for NPs synthesis, yet
keeping in mind the huge diversity of microbial world, many species needs to be
explored in future researches for hunting the best of agents for NPs make up to be
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antimicrobial activity against Escherichia coli, methicillin-resistant Staphylococcus
aureus-LY, Pseudomonas aeruginosa, and Candida albicans.
Commendable potential of AgNPs can be ascribed to its ability of disrupting
the bacterial membrane’ integrity through development of adsorptive interactions,
bacterial cellular division shutting down accomplished via complete prevention of
DNA replication since AgNPs interact with the enzymatic thiol groups and bases
having phosphorus. AgNPs are also effective antimicrobial agents because they can
form free radicals leading to induction of oxidative stress (Soenen et al. 2011). In
addition to the AgNPs’ inherent potential in prevention of different microbes, the
morphological aspects can also play an influential role, and thus, variable extents of
antimicrobial activities are being reported for differently shaped AgNPs (Pal et al.
2007; Paredes et al. 2014). Furthermore, this activity also results from electrostatic
attraction developed between the bacterial cells having negative charge and NPs
being positively charged. Albeit, there is a great deal of dissimilarity between grampositive and gram-negative bacteria in terms of their cell membrane, but majority of
them express a negative charge by the dint of carboxyl, phosphatic and amino groups.
Gram-negative bacteria’s cell wall is composed of a layer of lipopolysaccharide that
has lipids and polysaccharides having been bonded to one another through covalent
linkage with a negative charge. Even then, the positively charged AgNPs are provided
with weaker penetrability barricade. However, in case of the gram-positive bacteria,
the cell wall is made up of thick layer having peptidoglycans in which there is a
considerable cross-linking of the polysaccharide chains arranged in a linear manner
through shorter peptides leading to the formation of a rigid structure having three
dimensions. Such rigidity in the cell wall layer hinders AgNPs attachment to the cell
wall, and penetration is affected (Tamboli and Lee 2013).
7 Conclusions and Future Prospects
The tremendous work done in the last decades in the field of environmental nanobiotechnology for fabrication of metallic NPs using microbial nano-factories as biotemplates for stabilizing and reducing purposes has been commendable. A great
deal of metallic, metal oxide, metal chalcogenide, and semiconductor materials has
been fabricated using number of microbial species, i.e., bacteria, fungi, yeast, actinomycetes, and viruses. Reduction of NPs done via microbial route signifies not
only a facile and eco-friendly mode but is also economically valid in comparison
to costly and complicated physicochemical reactions marked by inducing profound
toxicity toward environment. Through microbes mediated biomimetic NPs synthesis,
NPs of various shapes, sizes, and polydispersity extent can be efficiently developed
and used for different applications, especially for detoxification of the ecospheric
zones. Though great deal of work has been done and different microbes have been
proven to be adopted as effective nano-biotechnological tools for NPs synthesis, yet
keeping in mind the huge diversity of microbial world, many species needs to be
explored in future researches for hunting the best of agents for NPs make up to be