Effect of Salinity Stress on Lipid Accumulation in Scenedesmus sp. and Chlorella sp.: Feasibility of Stepwise Culturing.

The enhanced lipid accumulation in microalgae is envisioned under special stress conditions with the cost of algal growth, which in turn affects the overall lipid productivity. The selection of suitable stress conditions facilitates better lipid productivity without any harmful effect on microalgae growth and algal biomass production. In the present study, we have attempted to select the best salinity conditions towards better growth, biomass accumulation, and lipid productivity of microalgae. The study also envisaged testing the feasibility of the stepwise salinity stress-induced cultivation approach to minimize the growth penalty effect of microalgae. The highest specific growth rate (0.129, 0.133, 0.113 µday-1) and doubling per day (0.185, 0.193, 0.163 per day) were obtained at salinity concentration of 40 mM NaCl in BG-11 medium for Scenedesmus quadricauda (Sq19), Scenedesmus dimorphus (Sd12), and Chlorella sp. (Chl16), respectively. Maximal lipid content of 18.28, 30.70, and 32.19%, and lipid productivity of 8.59, 13.81, and 10.27 mg l-1 day-1 were achieved at 160 mM of NaCl in BG-11 media with the Sq19, Sd12, and Chl16 algal isolates, respectively. The utilization of stepwise salinity stress (160 mM) induced cultivation of Sd12 algal isolate results in higher lipid content (39.42%) and slightly improved lipid productivity than the control (without any stress, 20.4% lipid content). The results indicate the feasibility of enhancing the lipid content and productivity through the salinity-induced stepwise cultivation strategy.

Enhanced microalgal lipid production with media engineering of potassium nitrate as a nitrogen source.

Algal biofuels are far from a commercial reality due to the technical challenges associated with their growth and lipid extraction procedures. In this study, we investigated the effect of 4 different media and 5 different nitrogen sources at 5 levels on the growth, biomass and lipid productivity of Scenedesmus sp and Chlorella sp The hypothesis was that a nitrogen source can be identified that provides enough stress to accumulate lipids without compromising significantly on biomass and lipid productivity. A maximum specific growth rate and doubling per day have been observed with algal species using modified BG-11 medium. Among the tested nitrogen sources, 2.5 mM potassium nitrate as a nitrogen constituent of modified BG-11 medium resulted in higher lipid content and productivity in the case of S. dimorphus (29.15%, 15.449 mg L-1day-1). Another noteworthy outcome of the present study lies in the usage of a smaller amount of the nitrogen source, i.e., 2.5 mM, which is found to be 7 times less than the standard BG11 media (17.60 mM sodium nitrate).

Characterization and Screening of Native Scenedesmus sp. Isolates Suitable for Biofuel Feedstock.

In current study isolates of two native microalgae species were screened on the basis of growth kinetics and lipid accumulation potential. On the basis of data obtained on growth parameters and lipid accumulation, it is concluded that Scenedesmus dimorphus has better potential as biofuel feedstock. Two of the isolates of Scenedesmus dimorphus performed better than other isolates with respect to important growth parameters with lipid content of ~30% of dry biomass. Scenedesmus dimorphus was found to be more suitable as biodiesel feedstock candidate on the basis of cumulative occurrence of five important biodiesel fatty acids, relative occurrence of SFA (53.04%), MUFA (23.81%) and PUFA (19.69%), and more importantly that of oleic acid in its total lipids. The morphological observations using light and Scanning Electron Microscope and molecular characterization using amplified 18S rRNA gene sequences of microalgae species under study were also performed. Amplified 18S rRNA gene fragments of the microalgae species were sequenced, annotated at the NCBI website and phylogenetic analysis was done. We have published eight 18S rRNA gene sequences of microalgae species in NCBI GenBank.