الفهرس 
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Abstract
Cyanophycea is primitive, prokaryotic, photosynthetic microorganisms belonging to algae which might be appeared during the precambrian age producing the environmental oxygen that maintained the present life. According to their genetic capability to grow in various environmental stresses, they have promoted distinguishable adaptability and developed effective protective strategies to face this changes in environmental conditions. This study indicated that A. platensis and S. mundulus are radio-resistant cyanobacterium candidates that have the ability to tolerate acute gamma irradiation doses (1.0 and 2.0 kGy), whereas both of the cyanobacteria are able to recover viability and grow after irradiation process. Growth curves in irradiated cultures displayed decline in growth by measuring culture density and dry biomass. Results revealed non-significant positive effect on total carbohydrate for A. platensis and S. mundulus, total free amino acids while, a significant increment in case of A. platensis and S. mundulus content were recorded. Protein content illustrated a significant decrease in response to gamma irradiation in A. platensis meanwhile, S. mundulus illustrated non-significant decrease. Super oxide dismutase (SOD) illustrated a significant increment in both A. platensis and S. mundulus. Chlorophyll-a exhibited a non-significant decrease, meanwhile carotenoids content illustrated significant increment in response to acute gamma irradiation doses. Both Extracellular polysaccharides (EPS) and phycobiliproteins exhibited a significant increment in both A. platensis and S. mundulus at the two irradiation doses. Results indicated significant increases in EPS for both alga whereas, gamma irradiation enhanced EPS secretion and modified its biochemical composition. Saccharide-protein nature of EPSs was confirmed via chemical, UV Visible spectrophotometer, and Fourier-transform infrared spectroscopy (FT-IR), revealed an increment of protein content in EPS from irradiated cultures. HPLC analysis revealed the hetero-polymeric nature of the EPS comprised seven monomers in the saccharide portion from irradiated cultures. EPS solution of A. platensis was used for AgNPs biosynthesis whereas EPS from A. platensis irradiated cultured mediated AgNPs (IEPS-AgNPs) exhibited a stronger UV absorbance than EPS from A. platensis non-irradiated cultured mediated AgNPs (EPS-AgNPs) at pH 9.0 and 2.0 mg L-1. Synthesized AgNPs displayed the difference in coating nature and its aggregation under Transmission Electron Microscope (TEM) IEPS-AgNPs displayed mono-dispersed nanoparticles capped by protein layers meanwhile EPS-AgNPs exhibited poly-dispersed ones capped with a faint sheath of EPS. FT-IR analysis illustrated the capping mechanism for both EPS-AgNPs and IEPS-AgNPs. EPS from S. mundulus irradiated cultures (R-EPS) demonstrated seven monosaccharides, two uronic acids and several chemical functional groups: O–H, N–H, =C–H, C=C, C=O, COO–, O–SO3, C–O–C and a newly formed peak at 1593 cm-1 (secondary imide). The roughness of EPS was quantified as 96.71 nm as revealed by Atomic Force Microscope (AFM). Thermal Gravimetric Analysis (TGA) analysis exhibited its thermo stable nature whereas, only 28.4% total loss in weight was observed till 800 °C. A high degree of crystallinity was quantified as CIDSC (0.722) using Differential Scanning calorimetric (DSC) and CIXRD (0.718) using X-ray Diffraction (XRD) analysis. Preliminary comparative analyses of EPS exhibited high protein content in the radiologically modified (R- EPS) than control (C-EPS). Modified EPS were characterized with a high biosorption efficiency, which could be attributed to its high content of uronic acids, protein and sulfates as well as various saccharide monomers. Data revealed that 0.0213 mg L-1 h-1 is the maximum biosorption rate (SBRmax) of Cr(VI) for R-EPS, whereas 0.0204 mg L-1 h-1 SBRmax for the C-EPS respectively. This study recognized the importance of irradiated EPS in synthesis of silver nanoparticles and bio-removal of heavy metal as Cr (VI).