A Brief Review on Biosynthesis of Nanoparticles by Using Bacteria

Richard Feynman introduced the main idea of nanotechnology in 1959. Professor Norio Taniguchi of Tokyo Science University first used the term nanotechnology. The Greek word "nano" means "extremely small," and it is synonymous with dwarf. Typically, nanoparticles range in size from 0.1 to 1000 nm in every spatial dimension and are created through two main methods: top-down and bottom-up. In the first, materials are molded and etched into smaller components, and in the second, structures are put together to create functional devices. Due to the numerous uses of nanomaterials in the biomedical, agricultural, catalysis, optical, and electronic domains, nanotechnology is currently a frontier of research. Because of their unique biological, chemical, and physical characteristics relative to the corresponding bulk materials, inorganic nanoparticles (NP) have garnered a lot of attention recently. The physical, chemical, biological, and other hybrid methods are used to create the nanoparticles. The physical and chemical methods are very useful for production of mono dispersed nanoparticles. Because the chemicals used in these procedures are toxic, flammable, and difficult to remove from the environment, they are harmful in one way or another. These techniques cause harmful substances to become adsorbed on the exterior of nanoparticles, which could be harmful in medical applications. Thus, it is worthwhile to develop safe, biocompatible, non-toxic, and environmentally friendly processes in order to create nanoparticles. Biological methods are considered to be safe, economical, environmentally friendly, and sustainable processes. Prokaryotes and eukaryotes are the principal biological components used in green approaches   in order to create nanoparticles. Numerous biological processes involve the direct or indirect participation of microbes [1]. The process of creating NPs can include done in two main ways. First, NPs are made chemically, which includes physiochemical (c-radiation), photochemical (using light's photons), chemical reduction, electrochemical, micro emulsion, microwave radiation, and laser ablation. All of these techniques produce a large number of NPs with limitations because of their expensive, labor-intensive equipment, and toxic ingredients. The method of chemical reduction is one of these techniques that is frequently used to create NPs. In an aqueous medium, a variety of substances, including tollens, polyethylene glycol, sodium borohydride, sodium citrate, and elemental hydrogen, function as reducing agents. Clusters of NPs, or nanoparticles are created when these reducing compounds convert metal ions (M+) into their metallic form (M0) Second, green, or biosynthesis, is a productive process that substitutes affordable, hazardous chemicals with natural compounds as capping, stabilizing, and reducing agents. Because of this, researchers Adapt techniques for biosynthesis. This preference has multiple justifications. First off, NPs produced biologically have different physicochemical characteristics from NPs produced chemically. Second, compared to the chemical method, which uses pricey chemicals, this method is relatively less expensive and more human. These substances are hazardous to people, pets, and the environment in particular. As a result, the majority of experts refer to the bottom-up strategy of green synthesis, which substituted plant extract for chemicals [2]. The morphology, size, and shape of the nanoparticles are used to categorize them into various types. This article mentions a few significant classes of nanoparticles.

Classification of Nanoparticles:

1] Organic nanoparticles:

Ferritin, micelles, dendrimers, and liposome’s are among the organic nanoparticles depicted in Figure. The organic nanoparticles are biodegradable, non-toxic, and some Micelles and liposome's are two examples of organic nanoparticles with hollow spheres.

2] Inorganic nanoparticles:    

Inorganic nanoparticles do not contain carbon. It is safe to handle the inorganic nanoparticles. The inorganic nanoparticles exhibit hydrophilicity and biocompatibility.

a] Metal nanoparticles:          

Metallica nanoparticles are synthesized from metals through either constructive or destructive methods. The pure metal is created using the metal precursors, tiny particles.

b] Metal oxide nanoparticles:

The goal of creating metal oxide nanoparticles is to alter the characteristics of the corresponding metals. For example, iron nanoparticles are oxidized to oxide nanoparticles of iron. When compared to iron nanoparticles, iron oxide nanoparticles exhibit higher reactivity [3].

Fig 1. Classification of Nanoparticles [3]

Sources of nanoparticles:

Nanomaterials can generally be grouped into three primary categories based on their origin: (i) incidental nanomaterials, which are unintentionally generated as byproducts of various industrial activities—such as particles released from vehicle exhaust, welding operations, combustion, or even natural events like forest fires; (ii) engineered nanomaterials, which are intentionally created by humans to exhibit specific properties for particular applications; and (iii) naturally occurring nanomaterials, which are present in nature and can be found within living organisms, including plants, animals, insects, and humans. However, the boundaries between these categories natural, incidental, and engineered are not always clearly defined. In fact, incidental nanomaterials are sometimes regarded as a subset of naturally occurring ones [4].

Fig 2. Sources of Nanoparticles [4]

Bacteria used in Nanotechnology:

1] Pseudomonas:

The silver mine   Pseudomonas stutzeri AG259 is the bacterium produced silver-based single nanocrystals   in the space between cells of the bacterium. Moreover, P. stutzeri exhibited the capacity to aerobically reduce selenite into insoluble elemental selenium. As of late, cell Gold ions were reduced using P. aeruginosa supernatant, leading to the extracellular biosynthesis of gold nanoparticles.

2] Magnetotactic bacteria:

Particles known as magnetic (Fe3O4) and greigite (Fe3S4) nanoparticles are produced by magneto tactic bacteria, such as Magneto spirillum magneticum.

3] sulphate- reducing bacterium:

The sulphate-reducing bacteria NCIMB 8307 Desulfovibrio desulfuricans has been demonstrated to synthesize palladium nanoparticles on the exterior of cells in the presence of an exogenous electron donor.

4] Lactobacillus:

Frequent strains of Lactobacillus identified in Within the cell, buttermilk promoted the growth of microscopic crystals of gold, silver, and gold-silver alloys with distinct morphologies without compromising their viability.        

5] Bacillus:

Au3+ ions can be reduced by Bacillus subtilis 168 to create nanoscale octahedral gold particles (5–25 nm) Ag+ ions have also recently been found to be reduced to Ag0 by an airborne Bacillus species.   

6] Fe [III] reducing bacteria: 

Gold was precipitated intracellularly in the area around the periplasm of the Fe (III) reducing bacterium Geobacter ferrireducens.

7] Staphylococcus:

Within a few minutes of subjecting the S. aureus to AgNO3, the reaction began, and the solution's color changed to a yellowish-brown hue, signifying the extracellular formation of AgNPs.

8] Entrobacteriacea:

Silver nanoparticles were produced quickly by the supernatants of culture Enterobacteriaceae, which includes Enterobacter cloacae, Escherichia coli, and Klebsiella pneumonia, by reducing Ag+ to Ag0.There have been reports of E. coli DH5-mediated bioreduction of chloroauric acid to nanoparticles [5].

Applications of bacteria used in nanotechnology:

1) Applications of Magnetotactic bacteria:

Magnetotactic Bacteria (MTB) in Drug Delivery:

In a recent review, Martel (2017) explores the potential of using drug-loaded magnetotactic bacteria (MTB) as "smart therapeutic agents" for precise drug delivery to specific organs or tissues. A key advantage of employing MTB or their magnetosomes is the ability to guide them to target sites using an external magnetic field, thereby minimizing effects on healthy, non-target tissues. For instance, ‘Magnetococcus marinus’ strain MC-1 was used to transport drug-loaded nanoliposomes into oxygen-poor regions of colorectal tumors in mice. The results showed enhanced therapeutic efficiency when nanocarriers were combined with MTB. Remarkably, after being injected near the tumor, the ‘Mc. Marinus’ cells remained alive and motile, demonstrating characteristics that are both aerotactic and magnetotactic. This allowed them to penetrate deeper into the tumor compared to passive delivery agents like microspheres or dead ‘Mc. Marinus’ cells. Although ‘Mc. Marinus’ is a marine bacterium not naturally suited to survive inside mammals, it unexpectedly remained active in the host environment. Even more surprising were the findings by Felfoul and colleagues, who reported that Mc. marinus cells were clinically “safe” and did not trigger adverse effects in mice. This outcome was unanticipated given the usual immune responses elicited by Gram-negative bacteria due to their lipopolysaccharide (LPS)-rich outer membranes, which are known endotoxins [6].

Magnetotactic Bacteria (MTB) in Bioremediation:

Innovative strategies utilizing live magnetotactic bacteria (MTB) and their unique metabolic functions have been explored for advancing bioremediation technologies. For instance, Shimoshige et al. (2017) identified a novel strain of Magnetospirillum magneticum (RSS-1) that produces magnetite magnetosomes coated with a thin layer of samarium oxide [7]. The co-precipitation of additional minerals within the magnetosome vesicle indicates that magnetotactic bacteria (MTB) could be utilized for magnetic recovery of transition metals and for creating structures that combine magnetic particles with these metals. In a separate study, Zhou et al. employed genetic engineering techniques to enhance the ability of Magnetospirillum gryphiswaldense to accumulate phosphate, improving its effectiveness in wastewater treatment [8].

2)Applications of Magnetosomes:

Magnetosomes in Cell Separation:

Magnetic cell separation has also been accomplished using magnetosomes in combination with specific antibodies. For instance, Yoshino (2008) engineered modified magnetosomes that displayed the antibody-binding protein A on their surface to facilitate cell separation [9].

Magnetosomes in Antigen recovery/detection assays and DNA:

Magnetosomes have been effectively utilized in tests for protein detection. By attaching biotin groups to their membranes, the magnetosomes were able to bind specifically to the protein streptavidin. These engineered composite particles, with their targeted biotin-binding ability, can serve as versatile platforms for attaching various Biotinylated antibodies and DNA oligonucleotides are examples of functional biomolecules.  [10].

Magnetosomes in Immobilization of Enzyme:

Magnetosomes' protein display system can be utilized to express catalytic components, making them well-suited for supporting enzymes that are immobilized, as previously stated.  Ginet and colleagues demonstrated this by expressing an organ phosphohydrolase enzyme from Flavobacterium species, fused to the magnetosome-associated protein MamC, for the purpose of breaking down paraoxon a widely used but toxic pesticide. The resulting protein-magnetosome complex exhibited paraoxon degradation activity similar to that of the purified enzyme. Furthermore, the study showed that the enzyme-magnetosome complex maintained 90% to 100% of its catalytic activity even after three reuse cycles, indicating high stability and reusability [11].

Fig 3. Applications of nanotechnology [12]

Methods of preparation of Nanoparticles:

Since the beginning of life on Earth, biological entities and inorganic materials have been in constant contact with each other. Because of these frequent interactions, life could continue to on this planet where the mineral deposits are orderedly. The relationship between inorganic molecules and biological species has drawn increasing attention from scientists recently. Numerous microbes have demonstrated themselves to be capable of producing inorganic nanoparticles through extracellular or intracellular pathways. This section covers the biological processes used to produce different types of nanoparticles. The categories covered are metallic nanoparticles, which include gold, silver, alloy, and other metal nanoparticles; oxide nanoparticles, which include sulfur dioxide, magnetic and nonmagnetic oxide nanoparticles; and other miscellaneous nanoparticles [13].

Common Methodologies for Metal Nanoparticle Synthesis using Microbes:

1] Extracellular Mechanism:

The test strain (culture) is raised in appropriate media and kept at 37°C in an orbital shaker set to 150 rpm. The broth is centrifuged after incubation, and the supernatant is utilized in the creation of nanoparticles. After being added to different reaction vessels that already contain the metal ions in the appropriate concentrations, the supernatant is incubated for a full 72 hours. The reaction mixture's color shift indicates the presence of nanoparticles, and a UV-visible spectrophotometer is used to sample the aqueous solution and measure the absorption spectrum to track the bioreduction of silver ions in the solution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to examine the shape and homogeneity of silver nanoparticles [14].

2] Intracellular Mechanism:

The culture is raised in suitable liquid media and kept at the ideal temperature in an incubator. The flask is left in a static position following incubation to allow the biomass to settle. After that, the supernatant is disposed of and sterile distilled water is added to wash the cells. After settling the biomass for thirty minutes, the flask is again sealed and the supernatant is thrown away. There are three iterations of this process. Centrifugation is subsequently employed for   ten minutes to separate the biomass from the sterile distilled water. The moist biomass is placed in a shaker at an appropriate temperature and exposed to 50 milliliters of sterile metal aqueous solution at different dilutions until a visible color shift is observed noted. The development of silver nanoparticles is indicated by a change in color from light yellow to brownish, the formation of gold nanoparticles by light yellow to pinkish, and the formation of manganese and zinc nanoparticles by Pale yellow to yellow [15]

Fig 4.  General scheme of synthesis of nanoparticles of metals by microorganisms [12]