Wastewater Culture And Transcriptome Analysis Of Navicula Sp.N6

Algal contamination is a major problem in the open cultivation of microalgae for biofuel production. Silicon plays an important role in the growth of diatom.Algal contamination in open-scale diatom cultivation can be controlled by regulating the sodium silicate concentration. This research is a comprehensive study on the selection and culture optimization of microalgae strain, culture in wastewater and heavy metal removal,inhibition of algal contamination by silicon stress, transcriptome analyses. The main works are as follow:In this study, a unicellular microalga strain was selected and named as Navicula sp.N6. The strain can grow well with sodium nitrate and urea, but not ammonium. CO2 was chosen as carbon source, while adding different organic carbon sources could not promote the growth and lipid accumulation of the strain.The stain can grow fast between p H 6-9 and temperatures of 20-30°C with optimal conditions at p H 8 and 22°C, and prolonging the harvest time is beneficial to the accumulation of lipid in cells. The biomass increased from 0.73g/L to 1.43g/L and lipid content decreased from 23.18% to14.11% as the sodium nitrate concentration increased.The effect of Na2 Si O3·9H2O on the growth and lipid content of Navicula sp. N6 was larger,and the concentration of 50~100mg/L was suitable for the growth. VB1 and biotin were beneficial to the growth and accumulation, while the effect of VB12 was not obvious. The optimization of the culture conditions of the microalgae for biofuel production was p H 8.86,Na NO3 88.45 mg/L, Na2 Si O3 70.78mg/L with RSM(response surface methodology), and the biomass and lipid increased from 1.01 g/L 、10.98% to 1.33 g/L、20.04% respectively.Growth curves of Navicula sp. N6, Chaetoceros gracilis, Nitzschia closterium,Isochrysis galbana 3011, Dunaliella salina, Chlorella sp. under different concentration of sodium silicate showed that the diatom strains can grow well while the other three strains were inhibited to grow under Na2 Si O3 concentration excess 150mg/L. Unde separate culture, as the Na2 Si O3 concentration increased, the biomass of Navicula sp. N6,Chaetoceros gracilis, Nitzschia closterium increased while lipid content decreased. High Na2 Si O3 concentration not only effects the growth of Isochrysis galbana 3011, Dunaliella salina, Chlorella sp., but also the lipid metabolism process inhibitied. Mixed culture test showed that the diatoms(Navicula sp. N6, Chaetoceros gracilis, Nitzschia closterium) and Isochrysis galbana 3011, Dunaliella salina, Chlorella sp.grew well under low Na2 Si O3concentration condition. As the Na2 Si O3 concentration excessed 100mg/Lor 150mg/L,Isochrysis galbana 3011, Dunaliella salina, Chlorella sp. can not utilize the nutrient, but Navicula sp. N6, Chaetoceros gracilis, Nitzschia closterium can untilize the silicon,nitrogen and phosphorus to grow fast, and become the dominant strain in medium. The result indicated the important role played by silicon in the growth and metabolism of diatom In contrast, under the osmotic pressure caused by high concentration of Na2 Si O3,diatom had a competitive advantage of absorbing nutrients compared to I. galbana 3011, D.salina, and Chlorella sp..The biomass of Navicula sp. N6 were 0.97g/L(municipal wastewater), 0.68 g/L(dairy wash wastewater) and 1.21 g/L(meliorative municipal wastewater). The strain grew better in meliorative municipal wastewater than single wastewater.The removal rate of N and P in meliorative municipal wastewater(90% of municipal wastewater and 10% of dairy wash wastewater) were 80%、60% respectively. The removal rate of N and P in meliorative municipal wastewater(85% of municipal wastewater and 15% of biogas fermentation wastewater) were 80% 、 60% respectively. In contract of F/2, carbohydrate increased,protein content remained unchanged, oil content slightly decreased. The result of absorbing Ni2+、Cd2+showed that the absorbance effect of Ni2+、Cd2+was better in its log growth middle phase, the higher concentration of Ni2+、Cd2+, the higher absorbance rate was.The transcriptome sequencing and analysis with Navicula sp. N6 nitrogen sufficient and nitrogen limited were carried out. In this transcriptome sequencing, about 45 million raw reads were obtained, about 5.5 Gb bases. With the Fast QC software detection, the base which has Qphred score more than or equal to 20 occupies above 93%, all the single location base Qphred score are qualified, the content of GC are about 50%, and the base distribution curves are close to each other. This result show that this transcriptome sequencing isreliable, building high quality uniform. Through Trinity software, about 59863 transcrips with the length in the range of 201 bp to17616bp, mean length 858 bp were get. From the transcript length, long fragment transcript(above 1000bp) accounted for 26.71%, short fragment transcript(above 1000bp) accounted for 73.29%, N50 for 1501 bp. With NCBI blast, Hmmscan, Blast2 GO and KAAS software, the unigenes blast with Nr, Nt, Swiss Prot,KOG, GO, Pfam, KEGG database, and a total of 36127 unigene has been annotated.The pathway of lipid biosynthesis, elongation and metabolism were described for the genetic engineering of improving lipid yield in microalgae. Meanwile, identification of genes involved in cell growth and death provides theoretical basis for further study on Navicula sp. N6.