Stress induced lipid enhancement in microalgae: scenedesmus sp.

Abstract

Microalgae are the photosynthetic autotrophs that can survive in fresh as well as marine water. These photosynthetic organisms can be eukaryotic or prokaryotic (cyanobacteria) (Li et al., 2008). It is believed that approx. 50,000 species have been explored till-date which can survive in diverse environmental conditions (Richmond, 2004), confirming enormous diversity within the group. These organisms can capture sunlight and convert the solar energy into efficacious products such as lipids (glycerophospholipids and triacylglycerols), carbohydrates, proteins, etc. These are also defined as oleaginous microorganisms due to their lipid accumulation potential, which is almost 15-20% higher as compared land based oleaginous crops (Aratboni et al., 2019). Their lipid content under various environmental perturbations such as salinity, pH, light, and nutrients, can be increased upto 70% of algal dry cell weight (DCW) (Fan et al., 2014; Donot et al., 2014). Because of their speedy growth rate, high CO2 fixation rate, no competition for arable land, and less impact on freshwater resources, these can cement their position in the run of a suitable candidate to produce renewable energy and can be considered as a sustainable feedstock for energy demands. Moreover, the algal cultivation is not restricted to any climatic, seasonal or geographical variation and can be cultivated even in wastewater or saline water (Ochsenreitheri et al., 2016). Despite being a good storehouse of lipids, mass production of algal biodiesel is bounded because of high production cost, low yield of lipids, and lack of efficient harvesting and extraction steps (Zhao et al., 2019). Therefore, to make algal biodiesel commercially applicable and economically viable, it is indeed imperative to optimize certain crucial factors pertaining to algal lipid accumulation (Ruiz et al., 2016). In the recent decade, multiple studies have reported various strategies and approaches to incite lipid biosynthesis in microalgae cells. These strategies include harmonizing light intensity in cultures, CO2 concentration and temperature, coaxing nutrient starvation in the culture, implementing stress via potentially toxic metals or high salinity condition or peroxide addition. Also, the ongoing research have however provided a track advancing towards lipid accumulation but the specificity related with the strength of strain assortment and familiarization with the site-specific and other culture conditions often makes the process inappropriate specific to a location. In the current study, to understand the impact of chronic/acute stress factors such as salinity, nutrients, and hydrogen peroxide on Scenedesmus sp., the work was divided into two parts: (1) long-term study and (2) short-term study. The growth profile, pigment content, biomolecular transitions, biochemical composition, and fatty acid methyl ester profile are some of the important parameters evaluated to monitor the impact of strong and mild agents.