الفهرس 
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Abstract
Macroalgae (seaweeds) are multi-cellular, eukaryotic photosynthetic aquatic organisms. They grow abundantly in the intertidal, shallow and deep waters of sea areas up to 180 meter depth and also in estuaries and backwaters. Marine macroalgae are classified into three phyla: Phaeophyta, Chlorophyta, and Rhodophyta.
Survey of macroalgae from studied localities along the Egyptian Red Sea shore showed a total of 36 species of macroalgae belong to the three divisions of macroalgae. Phaeophyta was the most dominant division (50%), followed by Chlorophyta and Rhodophyta (25%) each. The green macroalga (Caulerpa prolifera), the red macroalga (A. spicifera) and the brown macroalgae (Cystoseira myrica, C. trinodis and Turbinaria ornata) were the most prominent species along various seasons at most of collection sites throughout the year. The composition and density of macroalgal communities in the studied sites were highly related to the physico-chemical different characteristics of seawater. This relation was confirmed by using CCA analysis.
Seasonal variations in macroalgal biochemical composition were observed, which affect the apt period for harvesting based on the nutritional requirements for commercial utilizations. In general, primary metabolites including total sugars, amino acids, and fatty acids in addition to phenolic compounds were higher in the summer season than in winter in all investigated macroalgae. Moreover minerals were more accumulated in macroalgae C. prolifera, A. spicifera and T. ornata in the winter season, but they were accumulated in both C. myrica and C. trinodis in the summer season. Macroalgae are considered an important source of proteins because their protein content is rich in essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine). Oleic acid (C18:1) followed by palmitic acid (C16:0) were the most abundant FA. Macroalgal lipid contents are directly affected by many variables, such as macroalgal species, location, sampling period and environmental conditions. The total phenolic content of macroalgae changes with seasonal variations in temperature, salinity, light intensity, geographical region and water depth, in addition to other biological factors, such as age and size.
The current work evaluated the potential of naturally grown macroalgae harvested from studied localities along the Egyptian Red Sea shore for production of biodiesel and bioethanol. Two main factors significantly impacted the lipids yield; the solvent used for lipids extraction and biomass/solvent ratio. The highest lipids yield was recorded by using chloroform/methanol 7.42 and 5.61 % (g/g) in C. prolifera and C. myrica respectively. In addition, the biomass/solvent ratio (1:10) showed higher lipids yield than that of ratio 1:7 from all tested macroalgae. Lipids from five macroalgae were converted into fatty acids methyl esters through base-catalyzed transesterification reaction using methanol and KOH as catalyst. Macroalga C. prolifera exhibited the greatest biodiesel yield of 90.5% followed by T. ornata (87.4) and (86.4) C. myrica, whereas C. trinodis and A. spicifera recorded the lowest yield of biodiesel of 78.5 and 75.03 % respectively. Therefore, seaweeds could be considered as obtainable feedstock for biodiesel production without any competition with human food sources.
After biodiesel production, lipid free macroalgal biomasses were subjected to hydrolysis to evaluate bioethanol production. Based on the obtained results, enzymatic hydrolysis using cellulase enzyme derived from A. niger produced the maximum concentration of glucose followed by acid hydrolysis using 4% H2SO4 (w/v) that achieved high amounts of glucose. The conversion of sugars into bioethanol was measured every 24 hrs for three days of fermentation. The content of glucose decreased gradually with the increase of fermentation time. The sugar content of C. prolifera, A. spicifera, C. myrica, C. trinodis and T. ornata biomass obtained from the enzymatic hydrolysis gradually reduced from the initial concentration of 4.01 to 0.78, 3.71 to 0.76, 3.64 to 0.72, 4.4 to 0.83, and 4.2 to 0.92 (g/g) during the fermentation process after 72 hrs using S. cerevisiae. The glucose conversion to bioethanol of macroalgae C. prolifera, A. spicifera, C. myrica, C. trinodis and T. ornata recorded 75.8, 69.5, 65.2, 83.5, 77.6 % respectively. Therefore, macroalgae have the potentiality to generate significant amount of liquid transportation fuels such as bioethanol due to their significant concentrations of carbohydrate.
Recently, biosynthesis of Au-NPs has been preferred over the chemical and physical fabrication of nanoparticles because of the eco-friendly and non-toxic nature of the produced nanoparticles, as well as high biocompatibility and sensitivity. Moreover, it is necessary to improve novel compounds with an antimicrobial action because of the increase in microbial infection rates, the rapid development of antibiotic resistance. Therefore, the present study proposed a rapid, convenient, and efficient biosynthesis of Au-NPs using the ethanolic extracts of five studied macroalgae. The reduction of Au ions and the fabrication of Au-NPs were validated using UV–Vis spectroscopy, XRD, FT-IR, TEM, and zeta potential analysis. The produced Au-NPs were tested for their antibacterial, antifungal activity. The obtained results revealed the biosynthesis of highly stable Au-NPs with an average size from 12.6 to 18.8 nm with pure crystalline nature. This result confirmed that macroalgal extract components can serve as a reducing, capping, and stabilizing agent for Au-NP fabrication.
Strong antibacterial activity against E. coli (inhibition zones 22 and 19 mm) was recorded by C. myrica, C. trinodis and A. spicifera based Au-NPs respectively followed by (inhibition zones 20.5 and 18 mm) recorded by C. trinodis and C. myrica based Au-NPs respectively against S. aureus. On the other hand, the high antifungal activity of C. trinodis Au-NPs against A. niger and A. alternate showed the inhibition zones of 18 and 17 mm, respectively. The high antifungal activity of T. ornata and C. trinodis Au-NPs against C. albicans (inhibition zone17 and 16 mm) was also recorded. Consequently, macroalgae based Au-NPs were proven to have significant antibacterial and antifungal activities against many pathogenic strains bacteria and fungi, particularly Au-NPs of C. myrica and C. trinodis.