The Co-culture Effects Of Microalgae And Regulatory Functions On Lipid Accumulation

Microalgae lipids(e.g.,palmitic,linoleic,EPA/DHA)are widely used in food,medicine,health care products,and bioenergy,among others.The high cost of microalgae cultivation and low lipid productivity are the primary factors that limit its industrialized application.At present,the cultivation of microalgae is principally based on monocultures,which has disadvantages such as low lipid productivity,susceptibility to contamination by miscellaneous bacteria,and delayed growth.The co-culturing of microalgae can improve the stability of the culture system through the beneficial interaction between the microalgae,thereby shortening the growth cycle,achieving the simultaneous increase of biomass and lipid,and improving the overall lipid productivity.In this paper,A.protothecoides and C.subellipsoidea were used as the subjects to establish a co-culture system of A.protothecoides and C.subellipsoidea,and with the monoculture of A.protothecoides and C.subellipsoidea as control group-1(CG-1)and control group-2(CG-2),respectively,the co-culture of A.protothecoides and C.subellipsoidea was used as the experimental group,to explore the effect of cocultivation on biomass and lipid accumulation,and revealing the interaction effect of A.protothecoides and C.subellipsoidea in co-cultivation and its functional role in the process of promoting lipid enrichment.The main findings obtained are as follows:1)Establish a co-culture system of A.protothecoides and C.subellipsoidea.The effects of three factors(inoculation ratio,inoculation time,carbon-nitrogen ratio)on the biomass and lipid accumulation of A.protothecoides and C.subellipsoidea cocultured were investigated.The results showed that the biomass and lipid productivity obtained by the co-culture of A.protothecoides and C.subellipsoidea were the highest at 7.91 g/L and 1.32 g/L/d,respectively,when the inoculation ratio of A.protothecoides and C.subellipsoidea was 3:7,the growth cycle was simultaneously inoculated with A.protothecoides and C.subellipsoidea,and the carbon-nitrogen ratio was 32.It was 1.74-3.21 and 2.57-2.98 times when CG-1 and CG-2 are monocultures.It is confirmed that the establishment of the co-cultivation can effectively promote the synthesis and accumulation of biomass and lipid,which provides a new idea for the industrialization of microalgae lipid.2)The co-culture effect of A.protothecoides and C.subellipsoidea was analyzed.Taking CG-1 and CG-2 as the control group,and taking the optimal co-culture of A.protothecoides and C.subellipsoidea as the experimental group(EG),It is found through metabolism and transcription analysis that during the interaction between A.protothecoides and C.subellipsoidea,a total of 2625 genes and 472 metabolites changed significantly compared with CG-1,and a total of 925 genes and 456 metabolites were differentially expressed compared with CG-2,and a total of 565 extracellular differential metabolites were compared with CG-1,CG-2 and EG.These significantly differentially expressed genes and metabolites were mainly involved in photosynthetic carbon fixation,glycolysis,TCA cycle,biosynthesis and degradation of fatty acids and glycerolipid.Meanwhile the intracellular/extracellular differential metabolites and differential genes of EG were enriched in hormone signaling and ROS oxidative stress.From the above,it was confirmed that the co-culture effect of A.protothecoides and C.subellipsoidea were quorum sensing effect and allelopathic effect.3)The co-culture effect of A.protothecoides and C.subellipsoidea on lipid enrichment was revealed.Compared with CG-1,EG integrates extracellular carbon sources into the intracellular carbon metabolism pathway,which significantly enhances the carbon metabolism pathways such as glycolysis and TCA cycle,providing sufficient energy and precursors for biomass and lipid synthesis and accumulation of the cocultivation.Meanwhile the fatty acid and glyceride synthesis pathways were strengthened,and the lipid degradation pathway was inhibited,which effectively promoted the biosynthesis and accumulation of co-cultured lipids.Using CG-2 as a control,it was found that glycolysis of co-cultivation was also significantly enhanced,while TCA cycle,fatty acid oxidation and triacylglycerol degradation of co-cultivation were all inhibited,allowing more acetyl Co A to flow to the lipid pathway,providing energy and precursors for lipid biosynthesis and accumulation,and facilitating the efficient enrichment of intracellular lipids.Further,EG also regulates the growth rate of co-cultured microalgae through exocrine plant hormones(e.g.,abscisic acid,transzeatin riboside,zeatin),and regulates the expression of related genes such as Sn RK2,MPK7-14 and CAT1 in the MAPK signaling pathway-plant pathway and the expression of related genes such as Sn RK2,PR-1 and GH3 in the plant hormone signal transduction pathway through intracellular signal transduction to promote the biosynthesis and accumulation of lipids.