Study On The Bacterial Composition And Difference Of Euglena Under Different Culture Systems

Euglena(Euglena gracilis)is a kind of microalga with various high value bioproducts,including cosmetics,health drugs to the sustainable development of energy and other fields,lyophilized powder of Euglena also contains vitamins,unsaturated fatty acids,amino acids,and other essential nutrients,its unique paramylon also helps to eliminate fat and cholesterol in our body and can boost our immunity systems.However,the large scale cultivation of Euglena is still very difficult.One of the reasons is that contaminated bacteria during the cultivation process prevents the growth of Euglena.Therefore,the study of the composition and distribution of microbial populations in the Euglena culture system has become pre-prevention and improvement of Euglena quantity as vital scientific issues.In this study,16 S rDNA high-throughput sequencing technology was used to study the composition and distribution of bacteria in the culture system,analyzed the changes of bacterial abundance and diversity,and provide a theoretical basis for optimizing the cultivation method of Euglena.The effects of penicillin,lactic acid bacteria,yeast,and photosynthetic bacteria on Euglena culture were also preliminarily discussed.The specific research results are as follows:1)Composition and identification of bacteria.The 16 S rDNA high-throughput sequencing technology was used to analyze the five widely used photobioreactors(15L,500 L glass cylinder,15 L plastic barrel,60 L column,and 500 L pipeline photobioreactor)suitable for large-scale cultivation of microalgae.The investigation with the composition of bacteria and bacterial community structure in the culture system indicated the major type species mainly as cyanobacteria and proteobacteria;analysis of different photobioreactors shows that the 15 L glass tank,15 L plastic barrel,500 L glass cylinder culture systems shared high similarity in bacterial composition,with cyanobacteria accounting as the vast majority;while 60 L column photobioreactors have a certain proportion of various bacteria,indicating they might be more susceptible to diverse bacteria contamination.Similar to other bioreactors,in the 500 L pipeline,bacteria are majorly composed of cyanobacteria andproteobacteria.2)Distribution and source of bacteria in different photobioreactors were also studied.According to the characteristics of selected photobioreactors,from three parts of the bioreactors,the wall,algae liquid surface,and algae liquid,water samples were used forDNA extraction.The results showed that the bacteria in different parts were similar in species composition,and the more air they were exposed to,the more diverse composition was observed.At the same time,we performed DNA extraction and sequencing of pure culture medium and tap water used for large scale culture medium.We found that it is seldom to detect bacteria in the pure medium,and the tap water contains a small number of bacteria.Interestingly,the major bacterial species,cyanobacteria,was not detected in the culture medium.and the culture medium is therefore not the main cause of Euglena contamination.Instead,the airborne cyanobacteria from the culture environment may account for the always happening bacterial contamination during cultivation.3)The effects of penicillin,lactic acid bacteria,yeast,photosynthetic bacteria,and open culture on the growth of Euglena were initially investigated.Penicillin was found to increase the biomass of Euglena at 25 μg/ml.The addition of lactic acid bacteria,yeasts,and photosynthetic bacteria to the algal broth also increased the biomass of the Euglena.The open culture of Euglena greatly affects the development of Euglena,which may be contaminated by bacteria in the air.In summary,the bacterial composition,distribution,location,and source of a green microalgal culture system were obtained by using 16 S rDNA high-throughput sequencing technology,which provided a theoretical basis for quality and bacteria control for Euglena large scale cultivation.Preliminary experiments with penicillin,lactic acid bacteria,yeast,photosynthetic bacteria,and open culture were also conducted to show the way for subsequent practice.