Study On Enhancing Lipid Accumulation By Co-culture System Of Rhodotorula Glutinis And Chlorella Vulgaris

Microbial oil is the most potential raw material for biodiesel production.Microalgae has many remarkable advantages,such as fast growth rate and strong environmental adaptability.Chlorella vulgaris can not only convert inorganic carbon source into microbial oil and store it in cells through photosynthesis,but also can grow with organic carbon source.Rhodotorula glutinis is an oil-rich yeast in oleaginous microorganisms.Its growth cycle is short and can use waste water of factories such as molasses and glycerol.And the components of lipid are rich in polyunsaturated fatty acids.In this study,Chlorella vulgaris(UTEX2714) and Rhodotorula glutinis were selected as the research objects to establish the co-culture system to produce microbial lipid,and enhancd lipid accumulation by optimizing carbon source and culture method.Firstly,the biomass and lipid production of co-culture and single culture of microalgae and yeast were compared.This research studied the changes of metabolites in the co-culture system.Then the effects of initial concentration of different carbon sources(glucose: 2 g/L,5 g/L,7 g/L,10 g/L;glycerol: 1 g/L,3 g/L,5 g/L,7 g/L;sodium acetate: 2 g/L,5 g/L,7 g/L g/L,10 g/L) on co-culture growth and lipid accumulation were also investigated and determined the best carbon source concentration;Finally,lipid production increased by environmental pressure such as nitrogen limitation,salt stress and two-stage culture method.The main findings of this study are as follows:(1)When added 5 g/L of glucose,the biomass and lipid content of co-culture of Chlorella vulgaris and Rhodotorula glutinis were 3.40 g/L and 25.30% respectively.The biomass and lipid content of single culture of Chlorella vulgaris were 2.80 g/L and 26.60% respectively.The biomass and lipid content of single culture of Rhodotorula glutinis were 2.92 g/L and 23.20%.Co-culture of yeast and algae had little effect on lipid content,which could effectively increase biomass and lipid production.There is a symbiotic relationship during mixed culture of the two microorganisms gas and substance exchange,which has synergistic effect on cell growth and lipid accumulation.(2)When glucose was added as the carbon source,the optimum concentration was 7 g/L.And the lipid content was 25.01%.The lipid production was 1.05 g/L.The lipid production efficiency was 14.60 mg/(L·h);when glycerol was added as the carbon source,the optimum concentration was 5 g/L.And the lipid content was 21.51%.The lipid production was 0.63 g/L.The lipid production efficiency is 5.86 mg/(L·h);when sodium acetate was added as the carbon source,the optimum concentration was 10 g/L.And the lipid content was 18.85%.The lipid production was 0.74 g/L.The lipid production efficiency was 8.80 mg/(L·h).The optimum carbon source concentration was 7 g/L glucose.In addition,the fatty acids composition of lipid was analyzed by gas chromatography.It was found that the fatty acid composition ranged from C16 to C18 which met the requirements of biodiesel for carbon chain length.(3)The microorganisms of co-culture could grow in a nitrogen-deficient environment with a biomass of 1.20 g/L and a lipid content of 24.00%.In addition to nitrogen deficiency conditions,the biomass obtained by co-culture decreased with the increase of C/N,and the lipid content increased with the increase of C/N ratio.The maximum biomass was 4.10 g/L at the C/N of 5.The maximum lipid content was 31.00% at the C/N of 40.The maximum lipid production was 0.90 g/L at C/N of 10.(4)When added 2,5,10 and 20 g/L NaCl,the biomass of co-culture was 4.16,4.20,4.12 and 3.98 g/L,respectively.The biomass of co-culture was not significantly different from that of the group without NaCl(3.98 g/L).With the increase of NaCl,the lipid content of co-cultured increased.The maximum lipid content reached 40.90% at 20 g/L NaCl,and the lipid production was 1.67 g/L.The growth of co-culture was inhibited at 30 g/L NaCl,and the biomass was 3.78 g/L.Therefore,proper addition of NaCl in co-culture system could effectively improve microbial lipid production.(5)The maximum biomass was 7.50 g/L by co-culture of bacteria and algae in two-stage culture.The lipid content was increased by 50.00% and the lipid production was 3.75 g/L.Therefore,two-stage culture is an effective method to improve microbial lipid production.