Introduction

Microalgae are found in both marine and freshwater ecosystems. They contribute to more than half of the total primary production at the base of the food chain (Gushina & Harwod, 2009). The ability of microalgae to survive or proliferate over a wide range of environmental conditions results in the production of an array of many secondary metabolites, which are of considerable value in biotechnology fields including aquaculture, health and food industries (Andersen, 1996). Lipids act as a secondary metabolite in microalgae, maintaining specific membrane functions and cell signaling pathways while responding to the environment changes.

Aquatic Species Program [National Renewable Energy Laboratory (NERL), Department of Energy (DOE), USA)], provided impetus to the global biofuel research. Important advances in microalgal strain are isolation and characterization, physiology and biochemistry, genetic engineering process development and microalgal culture piloting apart from establishing a collection of over 3000 algae gathered from various sites and they were screened for their tolerance to environmental conditions and their ability to produce neutral lipids (Sheehan et al., 1998). Major crop based feedstock for biodiesel are soybeans, canola oil, animal fat, palm oil, corn oil, waste cooking oil and jatropha oil (Demirbas, 2009). These feedstock’s have limitations such as low biomass productivity, requirements of large land area, non renewability and dissatisfaction towards meeting the existing demand for fuel (Chisti, 2007). In recent years, microalgae based biofuels are considered as viable alternative, in the context of food security and also requirement of large stocks to meet the growing fuel demand.

Triacylglycerol producing capabilities of microalgal cells are genetically controlled and the quantity and quality of oils produced by algal cells are directly proportional to the stimulus received from the surroundings. The major environmental factors include the nutrient deficit, light intensity, pH and temperature (Borowitzka, 1999). The optimization of these factors can maximize the oil production irrespective of the cultivation system. Production of algal oil need to be economically competitive and sufficient stock is required to meet the demand.  Therefore to reduce the cost, most of the cultivation systems use freely available sunlight and sea water, despite daily and seasonal variations in light levels. The growth for each algal species will depend on environment conditions- temperature 20-30^oC, essential medium of nitrogen, phosphorus, iron which are generally inexpensive. The convenient commercial scale production of microalgal biomass can be achieved by two methods, conventional open pond system and closed photo bioreactors. Open pond system: Algae cultivation in open pond production system has been used since1950’s (Borowitzka, 1999). Large scale cultivation of microalgae in open pond systems relies on natural light for illumination. The most common strains used for the open pond systems are Anabaena sp., Chlorella sp., Dunaliella sp., Haematococcus sp. and Nostoc sp. (Chisti, 2006). The open ponds have a variety of size and shapes depending upon the location of cultivation. The algal biomass productivity achieved in open pond systems range between 10 - 50 gm^-2d^-1(Verma et al., 2010), but they are economically more favorable due to lower establishment cost.

Closed photobioreactor: These are preferred over open ponds as they can be established and maintained either indoor or outdoor (Pulz, 2001). These bioreactors allow the cultivation of single microalgal species for prolonged duration under controlled conditions (Carvalho et al., 2005) with the enhanced productivity while operating cost serves as a major drawback. Open pond systems have certain advantages like low cost, low energy input requirement and large scale production but it has less efficiency, inefficient mixing and temperature fluctuation in the growth medium and less light availability compared to photobiorector.

Over the past few decades, several thousand algae and cyanobacterial species have been screened for high lipid content of which many species have been isolated and characterized under in situ and or outdoor conditions (Hu et al., 2008). Algae provide natural material in the form of a lipid rich feed stock and scope for manipulation for production of biofuel. However, understanding of lipid content and metabolism to enable the manipulation of the process physiologically and genetically is still in infant stage. Biofuel through algae provide sustainable gasoline while addressing the current energy crisis (Ramachandra et al., 2009). Beyond the level of lipid metabolism, the fundamental understanding of the regulatory mechanisms of lipid production and how it is related to the environmental control is required, which have been addressed in this work. The objectives of the study were: 1) to check the role of environmental parameters on the growth of the consortium in outdoor as well as indoor culture conditions; 2) lipid characterization of the consortium to understand the efficiency for biofuel production.