Technology Study On Cultivation Of Oleaginous Microalgae Using The Saccharified Liquid Of Kelp Residue

Microalgae are distributed in the ocean and land,which are widely used in bioenergy,wastewater treatment,health care products and food industries.Some microalgae that grow fast and can accumulate oil and polyunsaturated fatty acids are also regarded as oleaginous microalgae with potential for development.At present,the cultivation of oleaginous microalgae is mainly autotrophic,which has the disadvantages of low biomass and relatively low oil and fatty acid content;while mixotrophic cultivation can obtain high biomass,but it is expensive.The cost of cultivation seriously hinders the large-scale development of oleaginous microalgae.Kelp residue is a kind of solid waste in kelp processing,which is rich in a large amount of cellulose.In this study,the saccharified liquid of kelp residue was used as the organic carbon source,and a process for efficiently culturing oleaginous microalgae using the hydrolyzed liquid of kelp residue was established.The main findings are as follows:(1)By comparing the effects of different pretreatment on the enzymatic hydrolysis of kelp residue,the results showed that under normal temperature and pressure,dilute sulfuric acid soaking kelp slag is an environmentally friendly pretreatment method.Under the optimized enzymolysis conditions,the concentration of total reducing sugar was 53.4 g/L and the yield of total reducing sugar was 98.9% under the conditions of50 UI/g cellulase dosage,36 h enzymolysis time and 1:5 solid-liquid ratio.(2)By comparing the autotrophic and mixotrophic biomass of 9 sterile oilproducing oleaginous microalgae,Chlorococcum sp.SCSIO-46880,which can grow with kelp residue saccharification solution.After optimizing the concentration of carbon and nitrogen sources,under the conditions of yeast at 1.0 g/L and kelp residue saccharification solution at 2.0 g/L,the biomass concentration of Chlorococcum sp.SCSIO-46880 was 1.4 g/L,the oil and oil yield were 21.1% DW and 29.2 mg/L/d,respectively.(3)Through the analysis of the differential genes of the transcriptome of Chlorococcum sp.SCSIO-46880 under autotrophic and mixotrophic conditions of saccharification solution,the following results are obtained:(1)The light capture ability of the algae was enhanced.(2)To provide more substrate for fatty acid synthesis.(3)The key genes for Sulfolipid synthesis,such as sulfur lipase(SQD1 and SQD2),were significantly expressed.(4)The results showed that mixotrophic-autotrophic two-stage culture the maximum biomass concentration was 7.1 g/L,and the lipid yield and lipid productivity were 2.3 g/L and 257.5 mg/L/d,respectively.This study showed that the enzymatic hydrolysis efficiency of kelp residue was improved,and biomass concentration,oil content and oil yield of oil-producing that Chlorococcum sp.SCSIO-46880 were significantly increased under the mixotrophicautotrophic two-stage culture.The expression of key genes for photosynthesis and fatty acid synthesis of Chlorococcum sp.SCSIO-46880 was changed in the saccharification solution of kelp residue,which affected the growth and biochemical composition of oleaginous microalgae.Therefore,using kelp residue saccharification liquid as the organic carbon source of oleaginous microalgae is of great significance to the development of kelp processing industry and the industrialization of oleaginous microalgae.