Microalgae cultivation and intracellular lipid detection
Each microalgae can grow rapidly under specific cultivation condition and nutrients. Microalgae growth is directly affected by the availability of nutrients and suitability of the cultivation condition to microalgae isolate. In addition, initial inoculum density also leads better microalgae growth during cultivation time (Li et al., 2011). Five strains of microalgae were cultivated on AF6 medium and incubate at 12:12 (light:dark) condition. Measurements of the microalgae growth were measured as turbidity cells at OD (optical density) of lambda 680 nm wavelength. The specific growth rate (umax) of LIPI11-2-Al005; LIPI11-2-Al010; LIPI11-2-Al015; LIPI11-2-Al018; LIPI11-2 Al019 were 0.065; 0.097; 0.157; 0.088; and 0.062 respectively. The result exhibited LIPI11-2-Al015 have growth rate faster than other selected four (4) microalgae. As is faster growing algae LIPI11-2-Al015 reached the stationer phase earlier than other microalgae isolate.
Detection intracellular lipid were performed by staining of dye Nile red which have been use to evaluate the lipid content of animal cells and microorganism, such as mammalian cell, bacteria, yeasts, zooplankton and microalgae. Nile red is a lipid-soluble florescent dye. Nile red emits a yellow gold fluorescence when dissolved in neutral lipid which is the best substrate to produce biodiesel [20] and [21].
Fluorescence microscope observation of five microalgae strains shows all microalgae strain emit yellow glow fluorescence, but different intensity. Based on the fluorescence result, LIPI11-2-Al018 gives high and bright intensity of yellow gold. The lowest intensity of Nile red stain is isolate LIPI11-2-Al010 (Fig. 2). This result used as the preliminary lipid detection which all the strains have intracellular lipid but the yield of each strain were different one another. Nile red observation can used as early detection of lipid content in microalgae cell[22].