| Biodiesel has attracted attention in recent years because of the increasing greenhouse effect and the emerging energy crisis.Microalgae has thus become a research hotspot owing its higher photosynthetic efficiency,quicker growth rate,shorter growth cycle,more controllable and renewable and greater compatibility with food crops compared with other biodiesel raw materials.In previous work,we isolated an oil-riched microalgae Monoraphidium sp.from plateau freshwater lake in Yunnan province.Using Monoraphidium sp.FXY-10 as the experimental subject,we studied the effects of six metal ion(Fe,Mg,Zn,Cu,Mn,Co)on the growth and lipid accumulation of Monoraphidium sp.;explore the effects of metal ions on algae gravity settling efficiency,provide references for harvesting microalgae;study the effect of different level of Mg2+ on the growth,lipid content and components of Monoraphidium sp.with Mg2+ once and twice addition on the basis of previous study result.The results are summarized as follows:1.Fe3+and Mg2+ are significantly affect the growth of Monoraphidium sp.FXY-10 under photoautotrophic condition.The biomass was 0.65 times compares to other group when 0μM Fe3+in the culture medium;the biomass only 1.5 times higher after 50days growth when cultured in the medium with the absence of Mg2+.From the perspective of the lipid content,the highest lipid content(52.74%)was gained in the presence of 200 μM Mg2+.The different concentrations of Zn2+,Cu2+,Mn2+,Co2+on the growth and lipid content of microalgae was not significant.2.It was found that the settling efficiency of different metal ions on the microalgae mostly above 90%after 12 h.The settling efficiency is 57.71%after 12 h when the concentration of Mg2+ was 0 μM.The settling efficiency is 63.24%after 12h when Fe3+ was absence in the medium while settling efficiency reached to 90%when Fe3+was presence in the medium.Additionally,the highest settling efficiency was obtained when 200μM Mn2+in the medium after 24 h settlement when added the metal ion in the medium in late exponential phrase,it showed that Mn2+could enhanced the settling efficiency of microalgae.3.After analysis the effect of the removal rate of Monoraphidium sp.FXY-10 on the different level of mental ion,it showed that the removal rate of low concentration of Mg2+、Fe3+、Zn2+、Mn2+by microalgae was 100%while low removal rate was observed at Co2+.The result showed that the growth was inhibited when the cetal ion was over-dosed.4.After study the effect of 7 different carbon source on the growth and lipid accumulation of microalgae,it showed that the final cell density was obtained at 2.626 g L-1 when use glucose as only carbon source which 1.43 times higher compared to sodium acetate(1.834 g L-1),far higher than sucrose(0.251 g L-1)and xylitol(0.471 g L-1),barely grow in other culture condition.Moreover,the highest lipid productivity(77.45 mg L-1 d-1)was gained when use 10 g L-1 glucose as only carbon source.5.The effect of six different metal ion on the growth of Monoraphidium sp.FXY-10 under mixtrophic condition showed that Fe3+and Mg2+ are significantly affect the growth of Monoraphidium sp.FXY-10.The growth was inhibited when the absence of Fe3+and Mg2+.The highest biomass productivity(219.78 mg L-1 d-1)was obtained when 20 μM Zn2+in the medium;the highest lipid content(51.58%)was gained with 40 Mn2+.Additionally,it showed that Fe3+and Mg2+ were the key factors which affect the biomass of microalgae based on the result of PB experiment.6.Effects of additional Mg2+ on the growth,lipid production,and fatty acid composition of Monoraphidium sp.FXY-10 were studied under photoautotrophic,heterotrophic and mixotrophic conditions.The final cell density was 1.25 times than that of the control group(2.98 g L-1)and the lipid content was higher than 50%after supplemented with 100 μM Mg2+ under photoautotrophic condition.The experimental group with Mg2+ supplement achieved 37.03%lipid content,far higher than that in the control group(28.47%)under heterotrophic condition.It was observed that the lipid content was gained 46.96%of dry cell weight after twice addition under mixtrophic condition,higher than control group(36.72%)and once addition(38.68%).It indicated that Mg2+ could enhanced the lipid accumulation of Monoraphidium sp.FXY-10. |
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