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1. INTRODUCTION The dried cells of microorganisms such as bacteria, fungi, yeasts and algae that are grown in large-scale culture systems as proteins, for human or animal consumption are collectively known as single cell proteins (Sasson, 1997). Single cell proteins (SCP) are characterized by fast growth rate, high protein content (43-85%) compared to field crops, require less water, land and independent of climate, grow on wastewater, can be genetically modified for desirable characters such as amino acid composition and temperature tolerance (Tri-Panji and Suharyanto. 2001). Microorganisms used to produce biomass and the choice of a microorganism depends on numerous criteria, the most important of which is the nature of the raw material available. The ideal microorganism should possess the following technological characteristics like high specific growth rate, biomass yield, low nutritional requirements, ability to develop high cell density, stability during multiplication, capacity for genetic modification and good tolerance to temperature and pH. In addition, it should have a balanced protein and lipid composition. It must have a low nucleic acid content, good digestibility and to be non-toxic. Nowadays, food industries need new food ingredients obtained from natural sources and nutraceuticals. Microalgae developed now combine novel the functional traditional foods and or new biotechnologies where microalgal biomass can be used as a source of proteins, biochemicals, lipids, polysaccharides and colorants (Athukorala et al., 2006). Among microalgal species, Spirulina utilized as food in the area around Lake Chad for long time ago and marketed as a healthy aliment in the United States and Japan (Borowizka, 1998). Spirulina (Arthrospira) is a blue-green algae found in alkaline Lakes around the world. The name “Spirulina” is derived from the Latin word for “helix” or “spiral”, referring to the physical structure of the organism. It is motile multicellular filamentous blue-green algae and reproduces by binary fission. Spirulina is a non nitrogen-fixing blue-green alga and cell wall made of mucopolysaccharide its soft and easily digestible nature, which makes it safe for human consumption. Spirulina is capable of growing in high alkalinity with the presence of carbonate, bicarbonates and inorganic nitrogen (Aiba and Ogawa, 1977; Yang et al., 2010). The ability of Spirulina to grow in hot and alkaline environments ensures its hygienic status, as no other organisms can survive to pollute the waters in which this alga thrives. Spirulina is one of the cleanest, most naturally sterile foods found in nature. It has been used as feed for fish, poultry and farm animals (Tragut et al., 1995; Abdulqader et al., 2000). Microalgal species are an important alternative material to extract natural antioxidant compounds to delay or prevent the oxidative damage caused by Reactive Oxygen Species (ROS) molecules (El-Baz et al., 2002). Spirulina has reported to prevent oxidative damage and hence can indirectly reduce cancer formation in human body. In this respect, the increased consumption of foods characterized by free radical scavenging activity, leads up to a doubling of protection against many common types of cancer formation (Cooke et al., 2002; Romay et al., 2003; Anbarasan et al., 2011). The United Nations world food conference declared Spirulina as “the best for tomorrow” and it is gaining popularity in recent years as a food supplement (Kapoor and Mehta, 1993). Arthrospira (Spirulina) is an economically important filamentous cyanobacterium. The annual production of the microalga is about 10,000 tons which makes it the largest microalgal cultivation industry in the world (Zhang and Skolnick, 2005). The Spirulina platensis was recognized a “wonderful food for health” since it contain high proteins (55-70%), (Umesh and Sheshagiri, 1984; Sanchez and Bernal, 2006), bioactive compounds such as, essential fatty acids (4-7%) like, linolenic and DŽ-Linolenic acid (Borowitzka, 1998; Othes and Pire, 2001; Sanchez and Bernal, 2006; Kumar et al., 2012), vitamins like, provitamin A, vitamin B complex, B1 (thiamine), B2 (riboflavin), B3 (nicotinamide), B6 (pyridoxine), B9 (folic acid), B12 (cyanocobalamin), vitamin C, vitamin D and vitamin E (Richmond, 1992; Belay, 1997), bio-pigments like phycocyanin and chlorophyll-a (Achmadi and Tri-Panji, 2000; Manojkumar et al., 2011) and antioxidant compounds, carotenoids (Cohen, 1997; Kawata et al., 2004; Chen et al., 2006). Based on these effects, Spirulina was approved in Russia as “medicine food” for treating radiation sickness (Becker, 1984) The large-scale production of Spirulina biomass depends on many factors, the most important of which are nutrient availability, pH, temperature and light. These factors can influence the growth of Spirulina and the composition of the biomass produced by causing changes in metabolism, which considerably modify the time course of the accumulation of the main biomass components. In 1950, the United States and Japan began the experimental cultivations of Spirulina investigated its chemical composition and industrial applications. The commercial production of Spirulina started in the early 1960s in Japan, in the early 1970s at Lake Texcoco, Mexico and the third major microalgae industry was established in Australia in 1986. Currently, the commercial production of Spirulina is mainly oriented towards the health food market, utilizing a chemically defined medium (Belay et al., 1993). Spirulina is marketed and consumed in Germany, Brazil, Chile, Spain, France, Canada, Belgium, Egypt, United States, Ireland, Argentina, Philippines, India, Africa, and other countries, where public administration, sanitary organizations and associations have approved for human consumption. The first commercial plant for cultivation of Spirulina in seawater was set up at the Tropic Sanya area in 1992. The total area of seawater Spirulina cultivation is about 40000 m2 for production capacity of above 80 tons. Commercial products of seawater Spirulina including algal powder, tablet, natural blue colorant phycocyanin and highly purified phycobiliproteins were developed. The former two products are already in the market (Wu et al., 1993; Wu and Xiang, 1996; Xiang et al., 1995). Lower cost of production by the use of a low-cost medium could be a key factor in developing a competitive process for the production of Spirulina as a feed and as a source of added-value products. Development of seawater medium for culture of Spirulina is inevitable for propagating outdoor cultivation of these cyanobacteria in many tropical arid areas, where climatic conditions are favourable but freshwater is scarce (Materassi et al., 1980). The use of seawater as an alternative medium, after being pretreated (Faucher et al., 1979) or after being supplemented with specific nutrients (Materassi et al., 1980) or supplemented with animal waste (Olguin et al., 1994) under laboratory conditions or in outdoor raceways would reduce the cost of the production of Spirulina (Tredici et al., 1986; Wu et al., 1993). The advantages of Spirulina cultivation in seawater medium (compared to freshwater medium) are (1) lower fertilizer cost, (2) the medium after harvest can be repeatly used, (3) the pH of the seawater medium constantly remains at 9- 10 and need not be adjusted, (4) seawater culture is not easily polluted by heavy metals and contaminants. Hence, the both growth and quality of S. platensis were improved in seawater medium (Wu et al., 1993). The aim of the present study is to develop multi-stress tolerant mutant Spirulina platensis strain for mass cultivation in low cost seawater enriched medium. The study was therefore contemplated with the following objectives. 1. Isolation and characterization of Spirulina isolates from aquatic habitats. 2. Studies on the effect of temperature, pH, light intensity and salinity on the growth of Spirulina platensis. 3. Collection and physico-chemical characterization of seawater, to formulate new low-cost seawater enriched medium with various nutrients. 4. Improvement of stress tolerant Spirulina platensis strains using chemical mutagen, Ethyl Methane Sulfonate (EMS) and selection of multi stress (salinity and temperature) tolerant mutant strains. 5. Studies on growth parameters and biochemical (protein, lipid, chlorophyll-a, total phycobiliproteins and carotenoid) contents of mutant strains compared to wild strains in the seawater medium under laboratory condition. 6. Studies on identification of biochemical constituents in mutant Spirulina platensis strains by TLC, HPLC methods and their antioxidant activities. 7. Mass production of multi-stress tolerant Spirulina platensis mutant strain in seawater enriched medium during summer season in outdoor artificial cement tank.