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CO 2 fixation by phototrophic microalgae and cyanobacteria is seen as a possible global carbon emissions reducer; however, novel microalgae and cyanobacterial strains with tolerance to elevated temperatures and CO 2 concentrations are essential for further development of algae-based carbon capture. Four novel strains isolated from the Arabian Gulf were investigated for their thermotolerance and CO 2-tolerance, as well as their carbon capture capability. Two strains, Leptolyngbya sp. and Picochlorum sp., grew well at 40°C, with productivities of 106.6 ± 10.0 and 87.5 ± 2.1 mg biomass L −1 d −1 , respectively. Tetraselmis sp. isolate showed the highest biomass productivity and carbon capture rate of 157.7 ± 10.3 mg biomass L −1 d −1 and 270.8 ± 23.9 mg CO 2 L −1 d −1 , respectively, both at 30°C. Under 20% CO 2 , the biomass productivity increased over 2-fold for both Tetraselmis and Picochlorum isolates, to 333.8 ± 41.1 and 244.7 ± 29.5 mg biomass L −1 d −1. These two isolates also presented significant amounts of lipids, up to 25.6 ± 0.9% and 28.0 ± 2.0% (w/w), as well as presence of EPA and DHA. Picochlorum sp. was found to have a suitable FAME profile for biodiesel production. Both Tetraselmis and Picochlorum isolates showed promising characteristics, making them valuable strains for further investigation towards commercial applications and CO 2 capture.

Microalgae are photosynthetic microorganisms that can grow in different environments (sea water, fresh water, waste water soil, rocks….) and under various conditions (Light, pH, temperature, salinity….). During their phases of growth, they produce a variety of metabolites such as lipids, proteins and carbohydrates in large amounts over a short period of time. These metabolites can be processed into both biofuels and other useful bioproducts. Microalgal lipids can be converted to biodiesel via process called transesterification. The use of biodiesel will decrease the emission of harmful gases, which can help in reducing the greenhouse effects and global warming. It is nontoxic, biodegradable and has the potential to replace the conventional diesel fuel. The isolation of autochthonous microalgae, with high lipid-contents and biomass productivities, is a crucial aspect of the development of commercial production of microalgae-based biodiesel as well as food security. This is especially important for deployments in climates such as are found in Qatar, a peninsula in the west Arabian Gulf, which is characterized by an extreme desert climate. 53 autochthonous strains of microalgae were isolated from various freshwater, marine and terrestrial environments in Qatar that led to the establishment of the Qatar University Culture Collection of Cyanobacteria and Microalgae (QUCCCM). Strains were identified via ribotyping and characterized in terms of growth rate and lipid production. The molecular identification of the isolated strains showed a biodiversity and 13 different known genera were identified. Among them, Chlorella is the most abundant freshwater known genus (22.64%), followed by Chlorocystis (13.21%). Growth rate study evidenced a thermo and halotolerant Nannochloris isolate QUCCCM31. The strain is able to tolerate 45°C and wide salinity range 35–100 ppt. Determination of lipid content and lipid profiling indicated the presence of promising strains for biodiesel production such as Nannochloris sp. (strain QUCCCM31) with a promising FAME profile for biodiesel production. This study proved a biodiversity inside the Qatar University Culture collection with strains having different applications such as Biofuel as an environmental friendly alternative to the fossil fuel, and/or source of food and feed.

The effect of light intensity and inoculum volume on the occurrence of photooxidation for Leptolyngbya sp. QUCCCM 56 was investigated, to facilitate the transition from small-scale laboratory experiments to large-scale outdoor cultivation. Indoor, the strain was capable of growing at light intensities of up to 5600 µmol photons/m 2 /s, at inoculation densities as low as 0.1 g/L (10% inoculation volume vol/vol). Levels of chlorophyll and phycocyanin showed a significant decrease within the first 24 h, indicating some level of photooxidation, however, both were able to recover within 72 h. When cultivated under outdoor conditions in Qatar during summer, with average peak light intensities 1981 ± 41 μmol photons/m 2 /s, the strain had difficulties growing. The culture recovered after an initial adaptation period, and clear morphological differences were observed, such as an increase in trichome length, as well as coiling of multiple trichomes in tightly packed strands. It was hypothesized that the morphological changes were induced by UV-radiation as an adaptation mechanism for increased self-shading. Furthermore, the presence of contaminating ciliates could have also affected the outdoor culture. Both UV and contaminants are generally not simulated under laboratory environments, causing a mismatch between indoor optimizations and outdoor realizations.

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