Effect Of Iron On Growth And Lipid Accumulation In Several Microalgae With Different Metabolic Type

Due to the shortages of fossil fuels and the production of greenhouse gas carbon dioxide on their combustion,biodiesel is receiving considerable attention. Microalgae are one of the most promising feedstock owing to their higher oil yields and fast growth.Moreover,microalgae especially marine microalgae,can grow in places away from the farmlands and free from fresh water,thus minimizing the damages caused to the eco- and food-chain systems.However,the production of algae for biodiesel has not yet been undertaken on a commercial scale,and one of the key factors is the production of organisms.Lipids content and the dry matter yield of microalgae could be modified by environmental conditions.To optimize the cultural conditions for increasing lipids productivity in some microalgae,and to explore some metabolic controlled factors relevant to lipids accumulation,the effect of iron on growth and lipids accumulation in three microalgae species was investigated.Firstly,a simple and rapid method determining the lipid accumulation in microalgae with spectrofluorimetry was developed.Measurement conditions for lipids accumulation in Nile Red-stained algae Chlorella vulgaris C3 and C7, lsochrysis galbana,Phaeodactylum tricornutum and Chlamydomonas reinhardtii were optimized.Marine strain C vulgaris C7 is a kind of green algae which use starch as their primary storage component.Final cell densities of C.vulgaris C7 increased and the exponential growth phase was prolonged after Fe³⁺was added into media in the late growth phase.When cells in the late-exponential growth phase were collected by centrifugation and re-inoculated into new high-Fe³⁺media,total lipid content was stimulated up to 56.6%biomass by dry weight and was 3-7-fold that in other media supplemented with lower iron concentration.I.galbana is golden-brown alga and lipids are considered to be the major storage products.The exponential growth phase was prolonged and the final cell density increased when I.galbana culture supplemented with Fe³⁺in the late growth phase.When cells in the late-exponential growth phase were collected by centrifugation and re-inoculated into new media,both lipids content and cell densities in media with high Fe³⁺concentration were higher than that with lower Fe³⁺concentration.Lastly,effect of iron on growth and lipids accumulation in mixotrophic green microalage C.reinkardtii was studied.When cells in the late-exponential growth phase were collected by centrifugation and re-inoculated into iron depleted TAP media,neutral lipid accumulation determined with spectrofluorimetry increased and growth decreased.Inversely,neutral lipid accumulation decreased and growth increased when C.reinhardtii cells were re-inoculated into high- Fe³⁺media.Acetyl CoA Carboxylase catalyses the formation of malonyl CoA.The reaction is a potential regulatory step in lipid biosynthesis.However,in C reinhardtii cells exposed to different iron levels,positive correlation was not observed between ACCase mRNA levels and the neutral lipid.ACCase mRNA levels seemed related with cells division and growth in our study.