Screening, Cultivation And Lipid Production Of Chlorella Sp.

Global energy shortage and environmental pollution are becoming increasingly serious,therefore, it is imperative to develop and exploit renewable and pollution-free bioenergy.Microalgal biodiesel is an attractive renewable bioenergy; meanwhile, microalgae canalleviate greenhouse effect as they were able to efficiently fix carbon dioxide throughphotosynthesis. Consequently, microalgae are becoming a research focus in many nations.Chlorella sp. is a kind of unicellular microalgae, and the intracellular lipid is a potentialmaterial for preparing biodiesel. Besides, with abundant protein, carbohydrate, vitamins andother bioactives, Chlorella sp. can be used as potential foods, feeds, medicines, health-careproducts, and so on.In this study, five strains of green algae were screened from the nature, and were initiallyidentified as Chlorella sp. on basis of their morphological characteristics. Cultured under lightfor ten days, the biomass yield and growth rate of these algal strains were compared, fromwhich strain G3was chosen out and identified as Chlorella vulgaris by18S rDNA analysis.This strain of C. vulgaris was further studied in this paper. The optimal medium type andculturing pattern for growth and lipid production were selected through experiments. Themedium composition was then optimized by response surface analysis. The effect ofphytohormones and vitamins on C. vulgaris was studied. The effect of carbon, nitrogensources and culturing condition on growth and lipid production of C. vulgaris was discussed.In a5-L fermentor, C. vulgaris was cultured by two steps, first to improve the biomass yieldthrough fed-batch cultivation, then to enrich the intracellular lipid by nitrogen deficiency.The optimal medium for growth and lipid production was BG11medium. The maximumspecific growth rate during logarithmic phase of C. vulgaris cultured by heterotrophy was twofolds of which cultured by autotrophy. The lipid content of C. vulgaris cultured byheterotrophy was1.5folds of which cultured by autotrophy. Cultivated for two days with themedium optimized by response surface analysis, the biomass yield of C. vulgaris reached10g/L which was improved by61%compared with the original medium. Besides, it was foundthat an appropriate amount of seaweed liquid fertilizer could significantly promote the growthof C. vulgaris, the stimulation effect of seaweed liquid fertilizer on the growth of algae wasfirstly stated in this paper.The effect of phytohormones and vitamins on C. vulgaris was as follows: With properamount, indole-3-acetic acid (IAA) could promote the growth of C. vulgaris; compared withthe control group, the biomass yield was raised by36%when the concentration of IAA was0.1mg/L. Triacontano l (TA) inhibited the growth of C. vulgaris, and high concentrations ofTA even caused the autolysis of C. vulgaris. Vitamin B1and Vitamin B12with proper amountpromoted the growth of C. vulgaris while biotin had no observable effect; compared with thecontrol group, the biomass yield was raised by39%and32%with5mg/L Vitamin B1and10μg/L Vitamin B12, respectively.The effect of carbon, nitrogen and culturing condition on growth and lipid accumulationof C. vulgaris was as follows: The optimal initial glucose concentration for growth was12g/L and the glucose utilization reached as high as91%; initial glucose of24g/L was conducive tolipid accumulation, however, when the concentration was over24g/L, the glucose utilizationdecreased, and glucose with higher concentrations restrained the growth of C. vulgaris. Thebiomass yield reached a maximum when the initial urea concentration was0.53g/L, and thelipid content reached a maximum when C. vulgaris was cultured without urea. The optimumtemperature, initial pH and inoculum size for lipid production were28℃,7.0and10%.After fed-batch cultivation for four times in a5-L fermentor, the biomass yield of C.vulgaris reached65g/L. C. vulgaris was then cultured by nitrogen deficiency for another12hours, the lipid content was raised from42.8%to63.8%, and the lipid yield reached43g/L.Both high cell density and high lipid production of C. vulgaris were achieved, consequentlylaying a good foundation for producing biodiesel.