INTRODUCTION

Water occupies most part of the Earth’s surface amounting to a volume of 1.38X109 km³ of which freshwater contributes to approximately 0.0013% of the global water^[1]. Freshwater ecosystems encompass an extensive range of habitats viz., rivers, lakes, and wetlands, with constant interaction of biotic with abiotic components. Studies have revealed that the use of freshwater in agricultural purposes is ~ 4000 km³ of water by 2050^[2], for domestic purposes (during 1987– 2003) is estimated to be 325 billion cubic meter^[3] while industrial consumption was 665 billion m³ during the same period^[4]. However, in the 21^st century, freshwater ecosystems are vulnerable to and by climate change^{[5, 6, 7]} increase in burgeoning human population coupled with growing food requirements, industrialization and urban sprawl^[8]. This turns fresh water into wastewater polluting the environment and creating health hazards to the aquatic life in the freshwater bodies making it unfit for human consumption. These polluted aquatic ecosystems are neglected owing to decline in water quality and quantity, nutrient and hence impeding species' diversity, photosynthesis, chlorophyll and the biochemical composition which includes lipids, carbohydrates and proteins. This has directed towards the threshold of water crisis and the urgent need for developing appropriate water management plans. Along with water management the utilization of biotic components like macrophytes^{[9, 10]}, micro^[11,12] and macrolage^[13] as sources of energy has gained prominence in recent years in an era of global warming in addressing production and utilization of renewable energy while  dealing with the social and ecological problems.

Biodiesel is a proven fuel and the technology for more than a decade now^[14]. Water is the primary factor in the development of biofuel feedstock production^[15]. Numerous researches have been carried out on the production of biodiesel through vegetable oils^[16] and other plant oils^{[17, 18]}. But due to the high cost of these oleaginous materials, the commercial production of biodiesel is hindered. Therefore, finding cheaper way of producing biodiesel is the need of the hour.

Lipids, the important secondary metabolite owing to specific cell functions and cell signaling pathways play a role in biodiesel production^[19]. Major feedstock of biodiesel include soybeans, canola oil, animal fat, palm oil, corn oil, waste cooking oil and jatropha oil^[20]. These crop based biofuels have limitations like low biomass productivity (Table 1), requirement of large land area and its non renewability^[21]. The other limitation includes the inadequacy of these crops and animal fats oil to meet the existing demand for fuels^[21]. Micro algae are efficient biological factories capable of taking zero-energy form of carbon and synthesize it into a high density liquid form of energy (natural oil) and are capable of storing carbon in the form of natural oils or as a polymer of carbohydrates^[22]. Microalgae as primary producers form the basis of the food web and play a significant role in the biotic and abitoic interactions of any aquatic ecosystem.  The variation in water chemistry and biotic components of an aquatic ecosystem consequent to anthropogenic stress attributes to changes in the structure of microalgae at community level. The concept of using microalgal lipid as a source of fuel is very mature, but its approach in benefiting multiple needs—both environmental and energy-related is an upcoming area of research. Hence characterizing the microalgal community is critical for better understanding of the ecological as well as biogeochemical processes^[23]. Over the past few decades, several thousand algae and cyanobacterial species have been screened for high lipid content of which several hundred oleaginous species have been isolated and characterized under laboratory and or outdoor conditions^{[12,21,24,25]}. The current investigation focuses on lipid characterization of the micro algal community in Bangalore collected from 4 wetlands with a wide range of environmental characteristics and an agricultural field.

TABLE 1. BIOFUEL SOURCE COMPARISON^{[21, 37]}

a= 70% oil (by wt) in biomass and b= 30 % oil (by wt) in biomass