The Mechanisms Of Enhanced Microalgal Growth And Lipid Accumulation By Nanoparticle Addition

At present,the shortage of energy is a crucial issue in the world.Microalgae biodiesel and other renewable energy is an important way to solve energy problems.Improving lipid accumulation of microalgae is still one of the most urgent problems in the field of bioenergy.In this study,microalgae were treated by photocatalytic nanoparticles in order to achieve the objective of effective promotion of lipid accumulation and its mechanism of action,meanwhile,was explored.In order to provide theoretical guidance and technical support for further research.A rapidly growing oil-rich Scenedesmus sp.H-1 plant preserved in the laboratory was selected as the research object,were dealt with different conditions(including light source,nanoparticles,particle concentration,light intensity and light duration)and its laws of lipid accumulation and biomass were studied.The results showed that the optimal conditions of promoting lipid accumulation were that the light source was xenon lamp,SiC nanoparticles,particle concentration was 150mg/L,light intensity was5000 Lux,and light duration was 8h.Also,in the optimal condition the effect of nanoparticles treatment on microalgae and lipid accumulation was investigated.In the best condition,at the stable phase of the microalgae its biomass increased from 2.6g/L to 3.18g/L,and lipid accumulation increased from 0.9g/L to 1.28g/L,and lipid content creased from 34.62% to 40.25% compared to control group.After determining the best parameters of nanoparticles treatment,the mechanism of nanoparticles stimulation on microalgae for lipid accumulation was explored.Variations including cells of utilization rate of substrate,structure,element content,permeability,cellular component,cytopigment,pH and redox potential,content of key enzymes and lipid composition were studied.The results indicated that after nanoparticles treatment the cell volume of microalgae increased,it is possible that photocatalysis stimulates cell growth,enhances metabolism,and improves substrate utilization.On the fourth day,the difference in carbon source concentration was 1.83g/L,and on the second day,the difference in nitrogen source concentration was 23.77mg/L.At the same time,stress resistance was enhanced.During the apoptotic period when nutrients were exhausted and toxic substances accumulated in large amounts,microalgae cells remained relatively active.In addition,during the growth process,the REDOX potential was reduced,and the contents of chlorophyll a and chlorophyll b were 1.88 and 2.02 times of the original content,respectively.These factors jointly led to the increase of microalgae biomass.We found that due to the use of xenon lamps and magnetic agitators,the surface of the microalgae became rough,presumably secreting more exopolysaccharides.Intracellular proteins and polysaccharides decreased by 28.3% and 13.61%,respectively.It also increased the pH during the growth of microalgae,which tended to accumulate oil at a higher pH.Most significantly,the enzyme activity of acetyl-coa carboxylase,A key enzyme for oil synthesis,increased by 11.01%,which may be the most important reason for the enhanced oil production of microalgae.This research provides a new strategy for improving lipid accumulation of microalgae and lays a foundation for industrialization of lipid production of microalgae.