Microbial-Mediated Nanoparticles for Sustainable Environment …
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enzymes. Such approach has been recently adopted by using various bacterial strains,
e.g., Bacillus sp. and Pseudomonas sp., for conversion of metal ions to their elemental
forms in nanoscale as elucidated in Table 1.
Microbial green NPs synthesized with bacterial strains, especially lactic acid
bacteria (LAB), are highly cherished by the dint of their safe use in handling and
processing of the food grade materials referred to as “generally recognized as safe”
when it comes to the production and preservation of food. Additionally, some strains
of LAB are also associated with the exhibition of the probiotic characteristics for
humans and other animal species in case of ingestion and contribute to the general
promotion of health (George Kerry et al. 2018). LAB has been used for the fabrication
of selenium (Moreno-Martin et al. 2017), gold (Nair and Pradeep 2002), and Ag NPs
(Garmasheva et al. 2016). In a generalized manner, LAB acts as an efficient nanobiofactory for NPs synthesis. LAB is a gram-positive bacterial strain, and thus, it has
a thicker cellular wall comprising of chemical constituents such as peptidoglycan,
proteinaceous substances, polysaccharides, and lipo-teichoic acid. In terms of NPs,
the different layers in LAB cell are the functional attachment sites for metallic ions
to be biosorbed and bioreduced as a result of comparatively negative electro-kinetic
characteristics leading to the attraction of metallic cations for initiation of the NPs
greener synthesis. Furthermore, there is also considerable evidence suggesting the
green synthesis of metallic or metallic oxide NPs to be highly impacted by reducing
microbial species’ potential in tolerating the metallic ions. Augmented metallic stress
will ultimately contribute to the microbial activity by initiating an interaction between
metallic ions and bacterial cells giving rise to particles have nano-range size.
Biosorption and bioaccumulation have been identified as eminent bacterial strategies being adopted for combating metal toxicity. Biosorption activates passive mechanisms and are primarily non-metabolically aided procedures associated with the
attachment, ionic exchange, chelation, and precipitative mechanisms completely
dependent upon the composition of bacterial cellular wall in terms of different functional groups presence (Sintubin et al. 2009). In the consequent manner, there is
bioaccumulation based on the entrance of the metallic ions inside cell body and
interaction between metal ion and bacterial cell’s intracellular structures is initiated.
An exclusive example of this phenomenon are some of the microbes showing coping
mechanisms in response to heavy metal triggered damage by means of direct deliverance of metals, e.g., Hg, Pb, and As from periplasmic to cytoplasm regions for
the metal binding proteinaceous substances to start working. Thus, the heavy metals
detoxification potential of microbes is explained by this phenomenon. This process
is highly facilitated by the existence of reductase enzymes reducing metallic salts
to nanoscale materials and leading to green NPs having narrower size distribution
and lesser extent of polydispersity (Hulkoti and Taranath 2014). The involvement of
various membrane transporters has been known for the transportation of the transition
metallic cations, however, the exact underlying mechanism needs to be explored yet.
Synechocystis and Synechococcus sp. of cyanobacteria have an ability to assemble
the proteins and cations in form of metallic clusters, e.g., Fe, Mn, and Cu, inside
their cellular regions and later consuming them for different metabolic processes,
e.g., photosynthetic and respiratory processes.
297
enzymes. Such approach has been recently adopted by using various bacterial strains,
e.g., Bacillus sp. and Pseudomonas sp., for conversion of metal ions to their elemental
forms in nanoscale as elucidated in Table 1.
Microbial green NPs synthesized with bacterial strains, especially lactic acid
bacteria (LAB), are highly cherished by the dint of their safe use in handling and
processing of the food grade materials referred to as “generally recognized as safe”
when it comes to the production and preservation of food. Additionally, some strains
of LAB are also associated with the exhibition of the probiotic characteristics for
humans and other animal species in case of ingestion and contribute to the general
promotion of health (George Kerry et al. 2018). LAB has been used for the fabrication
of selenium (Moreno-Martin et al. 2017), gold (Nair and Pradeep 2002), and Ag NPs
(Garmasheva et al. 2016). In a generalized manner, LAB acts as an efficient nanobiofactory for NPs synthesis. LAB is a gram-positive bacterial strain, and thus, it has
a thicker cellular wall comprising of chemical constituents such as peptidoglycan,
proteinaceous substances, polysaccharides, and lipo-teichoic acid. In terms of NPs,
the different layers in LAB cell are the functional attachment sites for metallic ions
to be biosorbed and bioreduced as a result of comparatively negative electro-kinetic
characteristics leading to the attraction of metallic cations for initiation of the NPs
greener synthesis. Furthermore, there is also considerable evidence suggesting the
green synthesis of metallic or metallic oxide NPs to be highly impacted by reducing
microbial species’ potential in tolerating the metallic ions. Augmented metallic stress
will ultimately contribute to the microbial activity by initiating an interaction between
metallic ions and bacterial cells giving rise to particles have nano-range size.
Biosorption and bioaccumulation have been identified as eminent bacterial strategies being adopted for combating metal toxicity. Biosorption activates passive mechanisms and are primarily non-metabolically aided procedures associated with the
attachment, ionic exchange, chelation, and precipitative mechanisms completely
dependent upon the composition of bacterial cellular wall in terms of different functional groups presence (Sintubin et al. 2009). In the consequent manner, there is
bioaccumulation based on the entrance of the metallic ions inside cell body and
interaction between metal ion and bacterial cell’s intracellular structures is initiated.
An exclusive example of this phenomenon are some of the microbes showing coping
mechanisms in response to heavy metal triggered damage by means of direct deliverance of metals, e.g., Hg, Pb, and As from periplasmic to cytoplasm regions for
the metal binding proteinaceous substances to start working. Thus, the heavy metals
detoxification potential of microbes is explained by this phenomenon. This process
is highly facilitated by the existence of reductase enzymes reducing metallic salts
to nanoscale materials and leading to green NPs having narrower size distribution
and lesser extent of polydispersity (Hulkoti and Taranath 2014). The involvement of
various membrane transporters has been known for the transportation of the transition
metallic cations, however, the exact underlying mechanism needs to be explored yet.
Synechocystis and Synechococcus sp. of cyanobacteria have an ability to assemble
the proteins and cations in form of metallic clusters, e.g., Fe, Mn, and Cu, inside
their cellular regions and later consuming them for different metabolic processes,
e.g., photosynthetic and respiratory processes.