Growth Of Microalgae Promoted By Co-culturing With Cellvibrio Pealriver And Its Mechanism Research

With the depletion of fossil fuels,seeking renewable and sustainable fuels is becoming urgent at present.Microalgae,because of its fast growth,high oil content and strong adaptability,are an ideal feedstock for the biodiesel production.Beside the biodiesel,microalgae also produce many high-value materials,such as algal polysaccharide,algal protein,unsaturated fatty acids,etc.However,high cost of production of microalgal biomass limits its industrial application on the production of biodiesel and other high-value materials.Promoting the microalgal growth rate is an effective way to reduce the production cost.In this work,we constructed a PR1-microalgae co-cultivation model and used to promote the growth of microalgae by using xylan as feedstock.The possible reasons for the promotion of strain PR1 to microalgae growth was investigated by comparative transcriptomes and metabolomes.After that,the co-cultivation model that used to produce biomass and lipid were optimized.The main results are as follows:1)Physiological identification and phylogenetic analysis of 16 S rRNA gene sequences revealed that strain PR1 belonged to the genus Cellvibrio.The total genome size of strain PR1 is 4,427,922 bp with 3,986 coding sequences.Application of the Carbohydrate-Active enZyme(CAZy)database,strain PR1 were supposed to be the genetic basis for xylanolytic,amylolytic,mannanolytic,agarolytic and chitinolytic activities.In addition,strain PR1's main metabolic pathway of xylan are constructed on the genome-wide analysis,and verified by the comparative transcriptomes analysis.2)The growths of four microalgal species cultured by photoautotrophy,mixotrophy and co-cultivation with strain PR1 were compared,after 9 days of cultivation,the biomass concentrations of four microalgaes in co-cultivation were 1.9 to 3-fold higher than those in photoautotrophic cultivation.The neutral lipid content of Chlorella sacchrarophila,Chlamydomonas reinhardtii,Scenedesmus obliquusin in co-cultivation were 1.2-1.75-fold higher than those in other culture conditions.The biomass concentration of Dunaliella sp.in co-cultivation was 1.6-fold higher than those in mixotrophic growth on glucose as carbon source.The starch production of all tested strains in co-cultivation were notably enhanced in comparison with photoautotrophic cultures.By using hemicellulose as feedstock,co-cultivation model could also promote the growth of microalgaes.3)The promotion mechanism of co-cultivation model to Chlorella growth was investigated by comparative transcriptomes and metabolomes.A possible reason for the promotion was the strain PR1 could provide Chlorella with organic carbon.Besides that,co-cultivation model could promote the growth of Chlorella by provide Chlorella with CO2;promote folic acid,DNA,amino acid,chlorophyll synthesis of Chlorella;reduce Chlorella's photooxidative stress and reduce the consume of carotenoid.4)The co-cultivation model that used to produce biomass were optimized by plackett-burman assay,significant factor single factor experiments,and response surface centered combination experiment.The chlorophyll content(11.94 mg/L)in co-cultivation at optimization condition was 2.12-fold higher than those in co-cultivation at initial condition,and was 4.72-fold higher than those in photoautotrophic cultivation.In addition,the co-cultivation model that used to produce lipid were optimized.When nitrogen limitation,Chlorella reached the maximum lipid concentration in co-cultivation at BG-11-Xylan medium containing 200 mg/L NaNO3(192.63 mg/L).This lipid concentration was 2.12-fold higher than those in co-cultured at BG-11-Xylan medium(87.23 mg/L),and was 3.88-fold higher than those in photoautotrophic cultivation(49.54 mg/L).When phosphorus limitation,Chlorella reached the maximum lipid concentration in co-cultivation at BG-11-Xylan medium containing 8 mg/L K2HPO4(116.23 mg/L).This lipid concentration was 1.43-fold higher than those in co-cultivation at BG-11-Xylan medium(81.00 mg/L),and was 2.14-fold higher than those in photoautotrophic cultivation(48.46 mg/L).