Isolation And Identification Of Interalgal Bacteria And Nitrogen Uptake Characteristics And Omics Analysis Of Algal-Bacterial Systems

Shrimp aquaculture is an important part of aquaculture industry in China.Excessive accumulation of nitrogen salts during aquaculture will cause eutrophication of aquaculture water,which is one of the main reasons for the deterioration of shrimp aquaculture water environment.Therefore,how to effectively control the concentration of nitrogen in the aquaculture ponds to maintain the health of water quality is an important issue of water treatment in the aquaculture industry.Bacteria and microalgae are the main microorganisms in aquaculture water,and are of great significance in removing nutrients,purifying water,and maintaining ecosystem stability.However,different microalgae and bacteria have great differences in adaptability in different water quality environments.Therefore,selecting suitable microalgae and bacteria to construct an algal-bacteria system can realize its value and application.Oocystis borgei is a common alga in subtropical shrimp culture ponds,and has a good effect on regulating the water environment of shrimp culture ponds.The main research content of this paper is to isolate culturable interalgal bacteria from the algal microbial community of Oocystis borgei,verify the effect of bacteria on algal growth through algal-bacterial co-culture experiments,and then select suitable bacteria to construct algal-bacterial system.Then,the absorption characteristics of the algal-bacterial system for dissolved nitrogen in water were explored.In addition,the differences in transcriptome and micro RNA of Oocystis borgei were analyze under different nitrogen concentration or different culture system conditions.Finnaly,the response mechanism of Oocystis borgei and algal-bacterial system to nitrogen concentration and were preliminarily explained.The main results are as follows:1.After separation,purification and identification,5 strains of culturable bacteria were obtained,which were:Enterobacter hormaechei、Pseudoalteromonas sp.、Staphylococcus pasteuri、Algoriphagus marincola and Marinobacter hydrocarbonoclasticus.The 5 strains bacteria were co-cultured with O.borgei respectively,and the A.marincola showed significantly promoted the growth of chlorophyll a of Oocystis borgei（P<0.05）,which was 45.74%higher than that in the control group2.Compared with the pure algae system and the pure bacterial system,the nitrogen absorption rate of the algal bacterial system constructed by Oocystis borgei and Algoriphagus marincola was significantly increased（P<0.05）.When sodium nitrite or ammonium chloride was used as the nitrogen source,the synergistic effect of algae and bacteria is more obvious.The algal-bacterial system has a"saturation effect"on the absorption rate of nitrogen.When urea or ammonium chloride is the nitrogen source,the absorption inflection point occurs when the nitrogen concentration is greater than 5 mmol·L^-1,and when sodium nitrite is the nitrogen source,the absorption inflection point is greater than 3 mmol·L^-11 has an absorption inflection point.Too high nitrogen co ncentration will inhibit the absorption of nitrogen by the algae system.3.The transcriptomes of O.borgei in pure algal systems and algal-bacterial systems cultured under low and high nitrogen conditions were analyzed.A total of28956 Unigenes were assembled and annotated under the four experimental conditions,the N50 length was 2323 bp,and the GC content was 59.53%.Under high nitrogen concentration conditions,nitrogen content was sufficient,and algal cells in both culture systems enhanced the utilization of ammonia nitrogen by upregulating gln A and GLT1 genes related to glutamate synthesis.Compared with the algal-bacterial system,the genes related to glutamine synthase/glutamate synthase（GS/GOGAT）were up-regulated in the two nitrogen concentrations,and the nitrogen metabolism in algal cells was more active.Under the condition of high nitrogen concentration,it is not limited by nitrogen.Compared with the condition of low nitrogen concentration,Psa,Pet and Psb genes related to photosynthesis in pure algae system.are significantly up-regulated,and the photosynthesis ability is enhanced;while in the algal-bacterial system,these three genes appeared significantly Down-regulation,the addition of bacteria,hinders the photosynthesis of algal cells to a certain extent.4.A total of 274 differentially expressed mi RNAs were detected in all treatment groups,and some differentially expressed mi RN As acted on target genes of nitrogen metabolism,photosynthesis and other pathways,and promoted the significant up-regulation of related gene expression.To sum up,the A.marincola obtained by isolating algal culturable bacteria had the best effect on promoting the growth of O.borgei,and the algal-bacterial system constructed by the two could effectively absorb dissolved nitrogen in water;Transcriptome and mi RN A sequencing data show that the algal-bacterial system can effectively regulate nitrogen metabolism,photosynthesis and other life activities by regulating its own gene expression in different environmental changes.