טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentSharon Kulikovsky
SubjectPhotosynthesis in the Desert: The Search for an Organism for
Green Energy Production
DepartmentDepartment of Biology
Supervisor Full Professor Schuster Gadi
Full Thesis textFull thesis text - English Version


Abstract

With the increase in pollution caused by using fossil fuels, the need for developing new technologies to utilize alternative energy sources is more crucial than ever.

Sun energy is the most abundant, sustainable and clean source of energy available to humanity. The natural process which can use this energy and convert it to an available chemical energy is the photosynthesis process. In this process, special proteins complexes named Photosystems are utilizing the sun energy to induce electrons flow. The electron flow creates chemical energy and reducing agents which in turn helps the process of sugars production.  Few techniques have already been developed to use this electron flow to create electricity, and in some cases even hydrogen.

A main problem with these techniques is the short lifetime of the systems as a result of photo-damage to the photosynthetic proteins. In the presence of light, there is always a possibility that excess energy will generate radicals, which will damage the photosynthetic proteins.

D1 protein, a core protein of Photosystem II is considered the most vulnerable. In living organisms, damaged D1 proteins are continuously repaired via degradation and synthesis of newly D1 proteins in order to maintain the photosynthesis electron flow. When the rate of damage is faster than the repair rate, there is a reduction in the photosynthesis efficiency, a phenomenon known as photoinhibition.

Our motivation is to improve the biophotoelectic cell performance and extend its life span by using an organism which exhibits more resistance to photo-damage.

C. ohadii is a small green alga (2 microns) that inhabits one of the biological soil crusts area found in the North Western Negev, Israel. This habitat is characterized by daily dehydration, high temperature and light intensity. Recent studies have shown unique characteristics regarding this alga which may help it cope with excess light and maintain growth at extreme light intensities. In this work we want to further investigate whether C .ohadii developed a unique resistance to photo-damage.

In order to answer this question we examined its resistance to photodamage by exposing whole cells, isolated thylakoids and isolated PSII to photoinhibition conditions. In none of these forms, a difference in photoinhibition rate was found between C. ohadii and the control aquatic alga - C. Sorokiniana. We also found different mechanisms which may help both algae cope with excess light: antenna truncation and carotenoids accumulation. Following high light growth the photosynthetic antenna is reduced almost completely, thus preventing absorption of excess damaging energy to the system. Moreover, growth at high light results in accumulation of carotenoids. The carotenoids pigments have the ability to release the excess energy as heat and also act as anti-oxidants.

In this work we found that C. ohadii may be an important organism for green energy production, as may be C. Sorokiniana. Both the Chlorella strains maintain growth at extreme high light and exhibit efficient repair mechanism for the damaged proteins.

This fact may improve the biophotoelectic cell efficiency by extending its life span.