Green Synthesis of Silver Nano-Particle from Cyanobacteria and Effect on Microalgal Growth and Production of Exopolysaccharide (EPS)

Abstract

Cyanobacterial exopolysaccharides (EPS) are heteropolysaccharides with significant biological importance in various industries. Investigating nanoparticles is gaining interest due to their great potential in improving cyanobacterial growth and co-products accumulation. Nevertheless, green synthesis of nanoparticles offers an alternative, eco-friendly and cost-effective approach to available chemical methods of nanoparticle synthesis. Thus, this study illustrates a novel approach to green synthesizing Ag nanoparticles (AgNPs) from marine cyanobacterium Phormidium tenue and investigates their effect on the enhancement of biomass and exopolysaccharide accumulation in the same cyanobacterium by incorporating previously synthesized AgNPs. Firstly, the AgNPs were synthesized from P. teneue by adding 1 mM silver sulfate into the culture medium, and the obtained AgNPs were characterized by using UV-VIS spectroscopy, XRD, SEM, and FTIR. In order to increase the biomass yield and EPS accumulation, P. tenue culture was subjected to different concentrations of AgNPs. Under different concentrations of AgNPs, the biomass yield and exopolysaccharides increased compared to the control condition on the 28th and 35th day of incubation, respectively. The characterization of the obtained EPS was studied by using FTIR which showed a specific absorbance of OH, weak aliphatic C-H stretching, sulfur-containing functional groups, and carboxylic acids, revealing the characteristic feature of EPS.

1. Introduction

1.1 Polysaccharides

Polysaccharides are biopolymers that are widely distributed in nature. Certain microorganisms have the ability to produce a large amount of polysaccharides in the presence of a surplus carbon source. Some of these polysaccharides (e.g. glycogen) serve as storage compounds while others are excreted by the cell. Different monosaccharides (hexoses and pentoses) including some complex sugars are linked glycosidically to form long chains of the polymer. These polysaccharides exhibit a wide range of chemical structures with greatly differing physical properties. A considerable expenditure of energy is incurred by the microbial cell to synthesize these biopolymers.

Microorganisms produce a diverse range of biopolymers with varied chemical properties by using both simple as well as complex substrates. These biopolymers could be either intracellular or extracellular depending upon their cellular location. Though the intracellular biopolymers are limited, nevertheless, the range of the extracellular biopolymers is vast and may be categorized into four major classes; polysaccharides, inorganic polyanhydrides (such as polyphosphates), polyesters, and polyamides to be collectively termed as extracellular polymeric substances or exopolysaccharides (EPS).

1.2 Exopolysaccharides

Exopolysaccharides are high-molecular-weight polymers that are synthesized and secreted by the microorganisms into the surrounding environment. These exopolysaccharides are mainly polysaccharidic in nature, that is, they are generally composed of monosaccharides and some non-carbohydrate substituents such as acetate, pyruvate, succinate, and phosphate. They are either covalently linked or loosely attached to the cell surface or can be released into the surrounding environment [1]. These exopolysaccharides are categorized into two groups: homopolysaccharides and heteropolysaccharides [2]. The homopolysaccharides consist of only one type of single structural unit whereas the heteropolysaccharides are composed of high-molecular-mass hydrated molecules made up of different sugar residues [3]. The composition of the EPS, however, varies with the type of microorganisms.

1.3 Cyanobacteria

In recent years, there has been a continuous search for new water-soluble polysaccharides, particularly those produced by microorganisms including cyanobacteria [4]. Cyanobacteria or blue-green algae are Gram-negative prokaryotes that perform oxygenic photosynthesis and are unicellular or filamentous. They are capable of movement by gliding when in contact with the substrate [5] and also possess the ability to survive desiccation, extremes of temperatures, high pH, and salinity [6]. They are widely distributed in diverse habitats. During their life cycle, cyanobacteria exocellularly secrete outer investments mostly constituted by heteropolysaccharides, which are frequently associated with small amounts of non-carbohydrate substituents, such as peptide, DNA, and fatty acids [7]. These exopolysaccharidic secretions are metabolites that accumulate on the surface of microbial cells. Their presence is considered as a boundary between the microbial cell and its immediate environment serving as a barrier to successfully cope with environmental constraints against high or low temperature and salinity or against possible predators and desiccation. The production of exopolysaccharides from cyanobacteria is considered to be a good alternative for polysaccharides produced by other organisms including higher plants, bacteria, fungi etc. This is owing to the versatile nature of cyanobacteria which are able to grow in any adverse environmental conditions. Their photosynthetic mode of nutrition and simple cultural requirements further add to the convenient growth of these organisms for large-scale production. In addition, the yield of the products obtained from these organisms can be enhanced by manipulating the culture conditions [8].

1.4 Cyanobacterial EPS

There are two categories in which cyanobacterial EPS can be grouped, the first one being those which are associated with the cell surface known as cell-bound or capsular polysaccharides (CPS) and the other being the released polysaccharides (RPS) referring to those that are discharged into the surrounding environment. Depending on the thickness, consistency, and appearance, the EPS associated with the cell surface can be termed sheaths and slimes [1]. The sheath is a thin, dense layer loosely surrounding the cells or cell groups usually visible in light microscopy without staining. The slime, on the other hand, refers to the mucilaginous material dispersed around the organism but does not reflect the shape of the cells. On the contrary, the RPS is soluble aliquots of polysaccharidic material released into the medium, either from the external layer(s) or derived biosynthetically which can be easily recovered from liquid cultures.

The cyanobacterial EPS are high molecular weight complex hetero-biopolymer of 10 kDa–2 MDa. This complexity is due to the presence of branching among the monomers and frequently with other macromolecules [9]. These high molecular weight heteropolysaccharides are made up of linear or branched repeating units comprised of 2–10 monosaccharides such as hexoses, pentoses, uronic acids, and deoxy-sugars. While other important substituents include phosphate, sulfhate, acetate, pyruvate, proteins and lipids form the side chains. EPS are attached to the cell surface via hydrogen bonds, hydrophobic and electrostatic interactions.

Certain characteristic features are exhibited by the cyanobacterial EPS which are rarely found in the EPS produced by other microbial groups. For instance, the presence of uronic acid and sulfhate groups contribute to the anionic nature of the cyanobacterial EPS, conferring a negative charge and a “sticky” behavior to the overall macromolecule [1, 10]. The anionic charge plays an important role in building the affinity of these EPS towards cations, notably metal ions. Furthermore, many cyanobacterial EPS are also characterized by a significant level of hydrophobicity due to the presence of ester-linked acetyl groups, peptidic moieties and deoxysugars such as fucose and rhamnose. In the past decades, several factors controlling the production of cyanobacterial EPS have been identified. These include energy availability and the C: N ratio [11]. However, other important factors such as the effect of other nutrients as well as growth conditions such as light intensity, salinity, and temperature have not been much focused. Hence, EPS production by variation of different growth parameters becomes an important area of study.

1.5 Role of cyanobacterial EPS

Cyanobacterial EPS plays a major role in protecting cells from various stress conditions in extreme habitat by serving as boundary between the cell and the surrounding environment. EPS are considered to maintain the structure and function of the biological membrane, hence, protecting them from irreversible and lethal changes during desiccation. They possess hydrophobic/hydrophilic characteristics, owing to which they are able to trap and accumulate water; thus creating a gelatinous layer around the cell that regulates water uptake and loss and stabilizes the cell membrane during the periods of desiccation. Cyanobacterial sheath formed by EPS protects the cells from the detrimental process of biomineralization [12].

Polysaccharidic layer around the cell, in addition, prevent the cell from direct contact with toxic heavy metal present in the surrounding. Being negatively charged, these cyanobacterial EPS plays an important role in sequestration of metal cations and also create a microenvironment enriched in those metals that are essential for the growth of the cell which is otherwise present in low concentration in certain environments. The slime layer surrounding the cyanobacterial cell prevents the inactivation of nitrogenase enzyme, an enzyme responsible for nitrogen fixation which otherwise gets inhibited in presence of atmospheric oxygen. Cyanobacterial sheath also contains some UV absorbing substances such as scytonemim and mycosporine-like amino acid which protects the cell from the harmful effect of UV rays. Another important role of exopolysaccharides is that it helps in the gliding movement of cyanobacteria and also acts as an adhesive for cyanobacterial cell that lives in association or symbiosis with higher plant.

1.6 Applications of cyanobacterial EPS

Cyanobacterial exopolysaccharides possess potential applications in various fields such as food, cosmetics, environmental improvement, pharmaceutical, and water treatment industries [13, 14]. Due to the presence of both hydrophilic and hydrophobic groups in the macromolecules these exopolysaccharides act as emulsifying agent or biofloculant. Another interesting industrial application is that they have the ability to bind with the water molecules due to the presence of charged groups, finding their application in the cosmetic industry for product formulations [10]. These charged RPSs also have the capability to trap metal ions which may be used in the removal of toxic metal from polluted waters.

The most common industrial use of microbial polysaccharides is that they act as thickening agents because of their ability to modify rheological behavior of water, [15], and also to stabilize the flow properties of their aqueous solutions under drastic changes in temperature, ionic strength, and pH [1, 10]. These exopolysaccharides are water-soluble and can be used as swelling agents in the food industry due to the presence of cations such as Ca⁺², Fe⁺³, Al⁺³, Cu⁺², and Co⁺². The cyanobacterial exopolysaccharides also find their use as soil conditioners due to the N₂-fixing ability of some cyanobacterium colonies. Microbial exopolysaccharides can also be considered bioactive substances due to their possession of biological activities, such as antibacterial, anticoagulant, anti-oxidative, anticancer, and anti-inflammatory activities. This is because of the presence of sulfhate group in the molecules which interfere with the absorption and penetration of another microorganism thereby preventing or inhibiting the activity of that microorganism.

1.7 Extraction

As discussed above, whilst some EPS are tightly bound to the cell structure, others are free and directly released (RPS). Therefore, there exist some differences in their extraction methodologies. RPS can be separated using physical methods such as high-speed centrifugation and ultra-sonication whereas, firmly cells-associated EPS requires chemical methods for extraction. EPS cross-linked by divalent cations can be released from the biofilm matrix by complexing agents such as ethylenediamine tetraacetic acid (EDTA), cation-exchange resins such as Dowex or by formaldehyde treatment with or without sodium hydroxide [11].

1.8 Characterization

The monosaccharides forming the cyanobacterial biopolymers consist of many isomers and show limited absorption in UV-Vis regions making the analysis of polysaccharides very difficult in terms of detecting or identifying the macromolecule using absorbance or mass spectrometry. Total carbohydrates content can be determined by using the phenol-sulfuric method [16]. For analysis of carbohydrate composition, high-performance liquid chromatography (HPLC), however, remains the most widely used technique because of its high selectivity, sensitivity, and reliability compared to other analytical methods [7].

Though present in lower concentrations, other non-carbohydrate constituents (like protein, lipid, nucleic acid, etc.), also impart very important characteristics to the EPS due to their unique linkage to sugar moieties. Hence, the determination of these components is also of vital importance. In this regard, Fourier Transformed Infrared (FTIR) spectroscopy can be used to characterize the vibrationally active functional groups within polysaccharides.

1.9 Nanoparticles

A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nm in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. Nanotechnology is the technology of inventing, synthesizing, and applying materials on the nanoscale. Nanotechnology produces materials with some specific properties and functions, which are different types from their counterparts. Nanomaterials can be classified according to their size in the range of different dimensions [17] as mentioned in Table 1.

Types of nanoparticles dimensions	Key features
Zero dimensions	This category includes spherical particles with diameters ranging from 1 to 100 nm; Examples: nanoparticles, fuller and quantum dots
One dimensions	This category includes nanomaterials with two dimensions in the nanometer range; Examples: nanotubes, nanofibers, nanowires and nanobelts.
Two dimensions	This category includes the one-dimensional nanometer range and two nanomaterials larger than 100 nm; Examples: graphene, nanoscales
Three dimensions	This category, all three nanomaterial sizes are larger than 100 nm and exhibit nano-effects; Example: porous nanostructure

Table 1.

Various types of nanoparticles dimensions.

Nanoparticles have several advantages over their mass particles, such as surface-to-volume ratio, which results in more significant heat treatment, better mass transfer paths, dissolution rate, and catalytic activity. In addition, nanoparticles have different functions and they are easy to function. Surface active sites have increased electrical, optical properties and improved absorption capacity.

2. Applications of nanoparticles

As the most prevalent morphology of nanomaterials used in consumer products, nanoparticles have an enormous range of potential and actual applications in agriculture, cosmetics, environment, medicine, renewable energies, and petroleum.

There are two pathways for nanoparticles preparation Klaine, et al., [17],

• The direct synthetic route that produces particles in the nanosized range.

• Grinding or milling macroparticles to reduce the size.

Nanoparticles are classified in a broad spectrum according to their chemical composition, source, size, and morphology [18]. The classification of nanoparticles in the type of material, source, size, composition, and morphology.

Although nanoparticles have always existed in the environment, for example, in volcanic ash and forest fires, they are considered discoveries in the 20th century. Nanotechnology has become popular, and a variety of nanomaterials have been developed and used in various research areas. In addition, the use of nanotechnology in many industrial applications has significantly advanced technical activities. Nanoparticles are widely used in commercial products, such as plastics, cosmetics, ultra-high-resolution displays, medical applications, pharmaceuticals, the environment, etc. The application of nanotechnology and nanoparticle technology has a significant impact on the economic viability of microalgae-based products (such as oils, lipids, bioactive compounds, EPS, and biofuels).

3. Materials and method

3.1 Green synthesis of silver nanoparticles

3.1.1 Preparation of algal biomass

The cyanobacterial biomass of P. tenue was harvested during their exponential phase. After that, the wet algal biomass of P. teneue was washed thoroughly with distilled water and ultrasonicated for the green synthesis of the nanoparticle. One gram of ultrasonicated wet biomass was resuspended in 100 mL of 1 mM silver sulfate aqueous solution at pH 7 and incubated in this mixture at 25°C for 24 hours [8, 19] (Figure 1).

Figure 1.

Sequential step for green synthesis of silver nanoparticle from P. tenue [8, 19].

3.2 Characterization of silver nanoparticles

3.2.1 UV-Vis spectrometry

The UV-visual spectra of the synthesized nanoparticles were recorded by a UV-Vis spectrophotometer. The developed color was examined at 220–600 nm in a UV-Vis spectrophotometer (Lambda 25 UV/Vis, Perkin Elmer, Shelton, CT, USA).

3.2.2 Fourier transformer infra-red spectrometry (FT-IR)

The FTIR spectra were measured using Thermonicolet Spectrometer, Nexus 870, Thermo Nicolet, Madison, USA instrument. The synthesized green silver nanoparticle was obtained from maximum biomass culture and was pressed into KBr pellets at a ratio of 1:100. The spectra were then recorded in transmittance mode over the wave range of 4000–400 cm⁻¹.

3.2.3 X-ray diffraction analysis

The XRD analysis of the sample was collected at room temperature on a Philips X’Pert Pro diffractometer, equipped with a Cu target X-ray tube with a step size of 0.020, 2θ, and time per step of 0.3 s.

The methods of Williamson and Hall were used to calculate the crystal size and strain. The simplest and most widely used method for estimating the mean crystal size is from the full width at half peak (FWHM) of the diffraction peak using the Scherrer equation as follows:

$${\text{d}}_{XRD}=K\lambda /\text{Bcos}\theta$$E1

Where d is the crystal size, λ diffraction wavelength, B is the corrected FWHM, is the diffraction angle, and K is the near-unit constant. The main assumption is that the sample is not deformed. B can be obtained from the observed FWHM by complicating a Gaussian configuration that models the expansion of the Br pattern, like this:

$${\text{B}}^2\text{r}={\text{B}}^2{}_0-{\text{B}}^2{}_{\text{i}}$$E2

Where B₀ is widely observed, and Bi is the instrument broadening. Williamson and Hall is a simplified integral width method to decipher the contributions of size and strain to line expansion as a function of 2θ [20].

3.2.4 Scanning electron microscopy (SEM) analysis

The surface morphology and characteristics of the synthesized nanoparticle were observed using Scanning Electron Microscopy (SEM) according to the protocol mentioned by [21]. Images were taken by the model ZEISS SEM and performed at a beam accelerating voltage of 20 kV.

3.3 Studies with the effect of silver nanoparticles

Silver nanoparticles synthesized from P. tenue were first filtered through a 0.22 μm membrane filter and then integrated into the control culture medium (ASN-III medium) of Phormidium tenue culture at different concentrations. The effects on the growth rate, biomass production, and EPS production were then monitored according to the protocol mentioned above. The total biomass yield and EPS yield were analyzed at regular intervals.

3.4 Extraction of EPS

3.4.1 Extracellular or released polysaccharides (RPS)

A known volume of culture was centrifuged at 10,000 rpm for 15 min. The supernatant so obtained was used for the extraction of released polysaccharides by addition of a measured volume of extraction solvent (acetone) followed by incubation at 4°C for 48 h. The released polysaccharide was then precipitated and collected by centrifugation at 10,000 rpm for 10 minutes. The pellet thus obtained was freeze drier (Figure 2).

Figure 2.

Sequential step for RPS extraction from P. tenue.

3.4.2 Cell-bound or capsular polysaccharides (CPS)

A known amount of culture was centrifuged at 10,000 rpm for 10 min. The supernatant was discarded, and the pellet obtained was used to estimate capsular polysaccharides. It was carried out by the addition of 36.5% formaldehyde (0.06 mL) to the pellet, followed by incubation for 1 hour at 4°C [8], after which 60 mL of 1 N NaOH was introduced and further kept for incubation at 4°C for 3 hours. The treated sample was then centrifuged, and capsular polysaccharides in that supernatant were extracted by adding acetone (10 mL) and incubated for 48 hours at 4°C. The capsular polysaccharides were precipitated by centrifugation and freeze drier (Figure 3).

Figure 3.

Sequential step for CPS extraction from Phormidium tenue.

4. Results and discussion

4.1 Green synthesis silver nanoparticle from P. tenue

4.1.1 UV-Vis spectrometry analysis

In this study, green synthesis of AgNP has been demonstrated from a filamentous marine P. tenue. It is well known that AgNPs exhibit a yellow-brown color in aqueous solution due to excitation of surface layer oscillations in AgNP. The reduction of silver ions of Silver sulfhate to AgNPs upon exposure to P. tenue ultrasonic biomass was followed by changing the color of the culture medium. As shown in Figure 4A–D, the changing color of the reaction mixture from green to yellow and then dark brown, followed by precipitation of grayish-black particles, proved the bioconversion of silver ions and the formation of AgNPs in an aqueous medium. The silver sulfate solution with washed P. tenue biomass turned yellow indicating the formation of silver nanoparticles.

Figure 4.

(A) P. tenue culture (ASN-III medium),(B) Silver sulfate solution as the negative control, (C) Adding (1 g) ultrasonication wet biomass and Ag₂SO₄(1 Mm), the picture show the color change of silver sulfate solution by P. tenue in biomass and (D) The complete reduction of ionic silver (Ag+) and grayish black precipitation of AgNPs.

Figure 5 shows the UV-Vis spectrum of the synthesized nanoparticle from P. tenue. A clear peak was observed with a maximum absorbance at 380–420 nm with an absorbance of 1 mM of the silver sulfate solution. The occurrence of the peaks within shows the presence of silver nanoparticles in the solution. Agreeing Gray-black silver nanoparticle precipitation on P. tenue is observed in an experiment. They observed a characteristic protein coat at 270–275 nm in the ultraviolet spectrum. Ahmed et al. [22] shows that increasing the concentration of silver sulfate solution with 1 g of Phormidium tenue ultrasonic wet biomass causes the bioconversion of silver ions to silver nanoparticles. Furthermore, increasing the concentration of Silver sulfate solution with 1 g of P. tenue caused the ultrasonic wet biomass to induce the bioconversion of silver ions to silver to decrease, and the subsequent formation of SNPs in an aqueous medium. Regarding this concern, [18] observed a characteristic peak at 380–420 nm at 12 h. In principle, the wide plasma bonds with absorption at the longest wavelengths could be due to the size distribution of the nanoparticles. Silver ion reduction occurs either by an electron shuttle or by a reducing agent released by ultrasonicated P. tenue biomass into solution.

Figure 5.

UV-Vis spectrum was recorded after the reaction of 1Mm silver sulfhate solution with (1 g) P.tenue ultrasonication wet biomass at PH 7 and 25 °C and formation of AgNPs.

4.1.2 Fourier transformers infra-red spectrometry (FT-IR)

FTIR is used to identify the biomolecules in P. tenue responsible for the silver ions reduction and stabilization of reduced silver ions [22]. The FTIR spectrum of the AgNPs obtained from P. tenue, shows strong absorption peaks at 3390.90, 1634.19, 1419.41, 1111.25, 614.429, and 477.719 cm⁻¹ representing different functional groups such as fragments The stretching OH of the alcohol or phenol, the N-H (amino acid), the C-O carboxylic anion, the saturated C-O group, and the stretching N-O, respectively (Figure 6).

Figure 6.

FTIR analysis of Phormidium tenue show the presence of protein shell for the reduction of silver ions.

The absorption peak at 3390 cm⁻¹ indicates the presence of the N-H (amino acid). In agreement with this study [12] confirmed the presence of a protein coat responsible for the biosynthesis of nanoparticles. The presence of protein as a stabilizer surrounds silver nanoparticles. Protein molecule consisting of different functional groups in the amino acid chain such as amino group, carboxyl group, and sulfate group present in cyanobacterial protein promotes the formation of microscopic silver nanoparticles with narrow particle size distribution, and hydroxyl groups and sulfonic acid are beneficial for the synthesis of silver nanoparticles with slightly larger particle size in weakly reduced media.

In the presence of Silver nanoparticles inside the cytoplasm, silver ions are reduced to AgNP, since Ag₂SO₄, a toxic reactant, is used in metabolism, it eventually kills the cells. When the cyanobacteria died, the silver nanoparticles produced inside the cell were released across the cell membrane into solution, as indicated by the precipitation of silver nanoparticles around the cell. The dead P. tenue also releases organic matter (proteins and other biochemicals), which causes silver to continue to precipitate from solution outside the cell. The protein molecules act as a reducing agent for the silver nanoparticles. Protein molecule consisting of different functional groups in the amino acid chain such as amino group, carboxyl group, and sulfate group present in cyanobacterial protein promotes the formation of silver nanoparticles. Silver ions are reduced in the presence of sulfate reductase, resulting in the formation of a stable silver hydrosol (1111.25 in cm⁻¹) and stabilized by a capping peptide [13].

4.1.3 XRD- size determination analysis

X-ray diffraction patterns have been widely used in nanoparticle research as the main characterization tool to obtain essential characteristics such as crystal structure, crystal size, and strain of nanoparticles. Randomly oriented crystals in nanocrystalline materials cause the widening of the diffraction peaks. In addition, homogeneous lattice distortion and structural defects lead to widening of peaks in diffraction patterns [23].

Figure 7 illustrates the XRD pattern of silver nanoparticles. The device apex width is obtained with standard silver powder-free from dimensional expansion, defects, and distortion. Using the Williamson and hall method and a Gaussian profile for the peak form, the average crystal sizes obtained at 60 nm and 88.18 nm for the peaks were 2θ = 32.40 and 2θ = 46.40, respectively.

Figure 7.

The XRD pattern of silver nanoparticle.

4.1.4 Scanning electron microscopy (SEM) analysis

The size and structure of nanoparticles were further characterized using SEM analysis. SEM image of obtained nanoparticles clearly distinguishes the difference between shape and size. The surface deposited silver nanoparticles are clearly seen at high magnification in the micrograph (Figure 8).

Figure 8.

SEM image of the silver nanoparticle produced by P. tenue.

4.2 Estimation of exopolysaccharides (EPS) yield from supernatant of phormidium tenue under varying concentration of extracting solvents

EPS yield in terms of released polysaccharides (RPS) in both the cyanobacterial species using different extraction solvents viz. acetone, ethanol, and EDTA respectively taken in varying ratios with respect to the supernatant. All the three solvents gave a higher yield of EPS under supernatant: solvent ratio of 1:2 with acetone emerging out to be the best extraction solvent for cyanobacteria the test organisms.

4.3 Studies with effects of silver nanoparticles

In terms of toxicity, conducted studies have shown that Ag nanoparticles are one of the most toxic nanoparticles for microalgae due to their high reactivity, fast adsorption, and its antimicrobial properties. Thus, research effort has been directed toward finding nanoparticles that can act as nutritional supplements to increase microalgae growth and enhance the accumulation of high-value exopolysaccharides (EPS) and some other products.

5. Conclusion

The natural ability of the cyanobacteria to produce high levels of exopolysaccharide (EPS) has made them potentially attractive hosts. The present study was focused on the extraction and characterization of exopolysaccharide from cyanobacterial species namely Phormidium tenue. The exopolysaccharides are nothing but polysaccharide which are present on outer surface of the cell or released into the surrounding environment. The preliminary study was focused on extraction methodologies using acetone. Once the best extracting solvent was known, the studies were emphasized on the time-course analysis of the exopolysaccharide yield (released and capsular polysaccharide) from the P. tenue (cyanobacterial species). Green synthesis of silver nanoparticle from P. tenue (Cyanobacteria). The study was to characterize the silver nanoparticle through XRD, FTIR, SEM and UV-VIS spectroscopy. Later, the enhancement in microalgae growth and exopolysaccharide from P. tenue was observed by applying various concentrations (0.1 mg) of silver nanoparticle. Thus, the conclusion that can be drawn from the present study are:

• P. tenue was found to be the efficient biomass and EPS production.

• Acetone was found to be the best EPS extracting solvent in P. tenue (Cyanobacteria)

• Green synthesis of silver nanoparticle from Phormidum tenue (Cyanobacteria).

• XRD analysis of silver nanoparticle confirmed size determination by X’Pert Pro diffractometer.

• The functional groups (O-H, C=O, N-H, S=O, C-H) present in the EPS were the characteristic feature revealed by FTIR.

• Application of silver nanoparticle in enhanced biomass and EPS (both RPS and CPS) production with showing the highest biomass and EPS content than the control.