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Growth and biosurfactant production of hydrocarbon-degrading consortia from the Eastern Mediterranean

Palatsidou Marianna

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Summary

Oil has become the world's most important source of energy and the present and future of the world economy depends on its production. However, in recent decades, thousands of oil spill accidents have been recorded that have caused huge ecological disasters due to the large amounts of oil released.The scope of this thesis was the growth and biosurfactant production of hydrocarbon-degrading consortia of deep and surface water from the Eastern Mediterranean.Specifically, were collected samples from depth (1500m depth) and surface water from Koufonisi Lassithi and 3 different cases were studied, consortia of deep water at 25°C, consortia of deep water at 14°C and consortia of surface water at 25°C. Initially, a total of two enrichments were performed for these 3 cases and then experimental cultures with nutrient ONR7 and crude oil were created (DEEP25, DEEP14 and SURF25). Their evolution was monitored for 50 days and the value of optical absorption was measured at 600nm so the growth curve for each community to be formed. At the same time, same cultures were developed with the isolated microorganisms Espa, Y, Yac, K and the microbial community E8, from a chronically polluted area with petroleum products, in order to compare the results. Finally, the cultures were tested for biosurfactants at specified intervals in three different ways, the oil spreading test, the emulsification test and the drop collapse test.Based on the growth curves for microbial communities, it was found that the SURF25 consortia does not show an increase in its development and the values of optical absorption are relatively stable and range between 0.3-0.5. The DEEP25 consortia shows fluctuations and at 18 days stabilizes at optical absorption of approximately 0.3. Finally, the DEEP14 consortia has low optical absorption values and the growth curve has decreasing trends. Test results for consortia of SURF25, DEEP14 and DEEP25 did not show presence of biosurfactants. The oil spreading test and the drop collapse test showed negative results, while the emulsification test showed evidence of biosurfactants with the DEEP14 consortia showing the best results.Isolated microorganisms and the E8 community showed better results than the SURF25, DEEP14 and DEEP25 consortia and their growth curves were increasing, with the E8 community having the best picture. Finally, as regards the tests, the emulsification test showed the presence of biosurfactants for the microorganisms K and Espa, the microorganism Y showed evidence of presence of biosurfactants, while the microorganism Yac had negative results.

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