الفهرس 
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Abstract
Microalgae are autotrophic organisms that are widespread, not only in aquatic media, but are also common and abundant in diverse terrestrial media. Soil microalgae are photosynthetic microorganisms found on the soil surface and within soil particles. Recently, microalgae have attracted attention as a potential candidate for the sustainable production of several highly valuable and bioactive compounds such as vitamins, proteins, lipids, carbohydrates, polyphenols and polyunsaturated or saturated fatty acids with antiviral, antibacterial, antifungal and anticancer activities. Hence, it can be applied in a lot of food and pharmaceutical industries. So, this study included two main approaches:
The first approach:
• Isolation and purification of microalgae from soil, where different soil samples were collected from the agricultural lands around Banha city, Qalyubia governorate, Egypt.
• Identification of the isolated species of algae through examination with a light microscope, where 11 isolates of algae were obtained: -
Nine species of green algae, which are as follows:
Asterarcys quadricellulare, Chlamydomonas sp., Chlorella vulgaris, , Chlorococcum oleofaciens, Chlorolobion lunulatum, Monoraphidium minutum, Protosiphon botryoides, Pseudococcomyxa chodatii and Tetradesmus obliquus
Two species of blue-green algae (Nostoc punctiforme f. populorum and Leptolyngbya cf. foveolarum) in a pure form.
• Determining the growth stages of all isolated algae, as some of the growth measurements were estimated, such as: optical density, algal cells count, chlorophyll a and dry weight.
The second approach:
Cultivation of purely isolated algae strains in different growth media (Bold medium for green algae isolates, BG-11 medium for blue-green algae isolates) with an appropriate temperature, aeration and lighting for algae growth to obtain the appropriate biomass to test the ability of the isolated algae to produce biologically active natural compounds. After that, the following experiments were carried out:
1st experiment:
Preparation of methanol extracts from all isolated algae to evaluate the antioxidants of these extracts which include the total antioxidant content (TAC) in addition to the total content of (phenolics, flavonoids and carotenoids).
2nd experiment:
Preparation of aqueous extracts of all isolated species of algae, and study their effect on the growth of broad bean, fenugreek, squash and sunflower seeds, where the heights of growing seedlings were measured.
3rd experiment:
Estimation of biomass productivity by measuring dry weight, as well as evaluation the lipid productivity of all isolated algal strains to determine their ability to produce high biomass and lipids under suitable conditions for growth, then select the most four lipid productive species of the isolated microalgae to perform gas chromatography analysis of lipids extracted from their biomass to characterize the fatty acids profile of them in terms of lipid content percentage.
Through the results of fatty acids profiles, the following were evaluated for the most four lipid productive microalgae:
• Predicted physical and chemical properties of biofuels, to assess their ability to produce biodiesel.
• Percentages of omega fatty acids, to assess their role as natural nutrients.
4th experiment:
Efficiency test of the four selected algal extracts (chloroform and methanol) to act as antibiotics against pathogenic bacteria, Staphylococcus aureus (Staph. aureus), an example of Gram-positive bacteria and Escherichia coli (E. coli), as an example of Gram-negative bacteria.
The following results were obtained:
1- The results of the first experiment showed that the total antioxidant content of the methanol extract of algae isolates ranged between (220.8-4755.8 µg ascorbic acid equivalent /1 ml of the extract), the highest value was achieved as a result of applying the extract of Monoraphidium minutum, which also recorded the highest value of the total content of flavonoids (215.5 µg equivalent catechin/ml), in addition to the total content of phenolics, the highest values (1769.9 and 1692.5 µg gallic acid equivalent/ml) were recorded for the algal extracts of Chlorella vulgaris and Pseudococcomyxa chodatii, respectively. On the other hand, the values of the total carotenoids content ranged between 1.1 and 4.1 µg mL-1, as the algal extracts, Monoraphidium minutum, Leptolyngbya cf. foveolarum and Pseudococcomyxa chodatii recorded the highest values (4.1, 3.7 and 3.6 µg mL-1, respectively), while the lowest value was achieved by Asterarcys quadricellulare extract (0.5 µg mL-1).
2- According to the results of the second experiment; most of algal extracts had a positive effect on the growth of plants seeds compared to the effect of control, where Chlorobion lunulatum extract achieved the highest increase in seedling height of squash by 114%, and the use of Protosiphon botryoides extract led to the highest increase in the seedling length of fenugreek plant by 34%, while the highest value in the length of sunflower plant (64%) was recorded as a result of using Leptolyngbya cf. foveolarum extract. Finally, for the broad bean plant, Monoraphidium minutum extract achieved the highest value of seedling height by 160% as compared to the control.
3- Based on the third experiment results, the four algae with the highest lipid productivity were selected for fatty acids analysis. The four algae were Monoraphidium minutum at a value of 29.17 mg L-1 day-1, Tetradesmus obliquus of 27.64 mg L-1 day-1, Chlorolobion lunulatum of 19.17 mg L-1 day-1 in addition to Asterarcys quadricellulare of 18.61 mg L-1 day-1.
By analyzing the fatty acids of the four previously selected isolates, the results were as follows:
• The percentages of saturated fatty acids ranged between 24.44% and 39.75%, monounsaturated fatty acids from 23.76% to 32.5% and polyunsaturated fatty acids from 31.91% to 46.39%
• The saturated fatty acids values of the four algal isolates revealed that the highest content was that of palmitic acid (C16:0) with percentages ranging between 16.75% and 25.98%, followed by the monounsaturated fatty acids, oleic acid (C18:1 ω9) between 7.21% and 16.43%. Among the polyunsaturated fatty acids, linoleic acid (C18:2 3) “ALA” with an approximate percentage of 3.68% and 16.7% and alpha-linoleic acid (C18:2 ω3) ALA between 6.5% and 24.32%.
• In general, the proportions of unsaturated fatty acids are significantly higher than saturated fatty acids in the four algal species, which in turn has an important effect on the properties of biodiesel derived from these algae.
The results of the expected physical and chemical properties of biodiesel fuel for the four selected algae, obtained by mathematical equations, were as follows: specific gravity (0.8 g cm-3), kinematic viscosity (4.12-4.46 mm2 s-1), cetane number (51.45-54.99), iodine value (100.57-140.16 g I2 100 g-1), higher heating value (40.61 - 41.55 MJ kg-1), oxidative stability (6.46 - 7.58 h), cold filter plugging point (-16.41: -16.30 °C) and these results are in accordance with American specifications, European and Egyptian biofuels.
Fatty acids analysis results revealed that the fats extracted from the four selected algae contain omega 3, 6, 7 and 9 fatty acids. Omega-3 fatty acids were the highest among the others (10.0-34.4%). The percentage of omega-6 fatty acids was (4.3-19.46%), in addition to omega-9 fatty acids (20.3-26.3%), while omega-7 fatty acids achieved the lowest values (3.3-6.0%). These results are compatible when compared with the values of omega fatty acids found in some other oil sources recorded in some published scientific references, such as fish oil, palm oil, soybean oil and coconut oil.
4- The results of the fourth experiment revealed that
• Chloroform and methanol extracts of Chlorolobion lunulatum and Tetradesmus obliquus have antibacterial activity against Staph. aureus and E. coli. However, extracts of Asterarcys quadricellulare have an inhibitory effect only on E. coli, while Staph.aureus was resistant to their effect. On the other hand, the two extracts of Monoraphidium minutum had no effect on either of the two species of bacteria.
• Methanol extracts have a greater inhibitory effect on both of the used pathogenic bacteria than chloroform extracts.
It is clear from the current study results that microalgae, including soil algae, contain high-value materials that can be used in many fields such as the production of biofertilizers, pharmaceuticals nutraceuticals, as well as biofuels. Therefore, the study recommends further exploration of new species of algae in different environments and work to reduce the production obstacles of such organisms.