Study On The Symbiotic Bacteria Of Three Energy Microalgae Species

Microalgae have a number of excellent characteristics such as fast growth,high photosynthetic efficiency,and short life cycle.They can synthesize and accumulate a variety of nutrients and physiologically-active substances.To date,microalgae have been widely used in many fields including food,medicine,feed,cosmetology,and bio-chemical engineering.The large-scale cultivation of economic microalgae for the commercial production of high-value biomass and products has been considered as new types of agriculture with great development potential.In particular,many oil-rich microalgae can be used to produce clean bienergy,benefiting the innovation of energy structure.It is of great significance to understand the dynamics of microalgae commensal bacteria during the microalgal cultivation and the mechanism underlying algae-bacteria symbiotic system.Study on such issues can provide scientific basis for green prevention of pests in alga cultivation and the establishment of high-efficiency and low-cost technology system of large-scale algal culture and algal biomass harvesting.Therefore,in this study,three new strains of microalgae were selected to use as test materials to systematically isolate and identify the symbiotic bacteria and their symbiosis and dynamic changes.The alga-bacterium symbiotic systems for the tested strains were artificially constructed to investigate the stability of the system under photoauto trophic conditions and its effects on the growth and oil accumulation of the three microalgae.The main results of this study are described as the followings:(1)In order to obtain microalgae strains with strong anti-pollution ability,good growth,and high oil content,the algal samples were collected from the water body near a coal chemical plant in Shanxi province.These algal samples were isolated,purified and screened,and finally obtained three strains of microalgae labelled as C1,C2 and C3.Thes three new strains can be used as energy microalgae.Morphological examination and 18S rDNA molecular identification reveraled that strain C1 is Ankistrodesmus gracilis which.This strain showed non-stick properties in the cultivation,and its biomass and oil content were up to 2.4 g/L and 18.32%,respectively,after 8 days of cultivation.Strain C2 was Scenedesmus obliquus whos biomass and oil content reached 3.1 g/L and 22.56%,respectively,after 8 days of cultivation.;Stain C3 was Chlorella emersonii,and after 8 days of cultivation,its biomass and oil content were increased to 2.8 g/L and 28.24%,respectively(2)Obtain algae samples from single algae cultures of Chlorella emersonii,Scenedesmus obliquus and Ankistrodesmus graciliswhich algae respectively,then separate bacteria using plate separation method,following with 16S rDNA molecular identification,we isolated 21 strains of bacteria.Three species of microalgae have different types of their symbiotic bacteria.Six strains of Chlorella emersonii belong to four bacterial genus:Enterococcus gallinarum,Escherichia coli,Pseudomonas and Pantoea;seven strains of Scenedesmus obliquus belong to four bacterial genus:Micrococcus yunnanensis,Staphylococcus sp,Exiguobacterium aurantiacumand Pseudomonas;eight strains of Ankistrodesmus graciliswhich belong to three bacterial genus:Pseudomonas,Staphylococcus sp and Brevundimonas Segers.(3)Three strains of microalgae were used to construct a symbiosis system of algae,and the effects of each symbiotic system of algae on the biomass,oil content and fatty acid composition accumulation of microalgae were tested.Compared with the sterile culture system,the algal symbiotic system can promote the growth of microalgae and oil accumulation.The symbiotic system constructed by Ankistrodesmus gracilisandand Brevundimonas with a ratio of 1:10 was cultivated for 8 days.The biomass of microalgae reached 3 g/L,the oil content reached 20%,and the content of oleic acid(18:1)reached 12%,significantly higher than the control.The symbiotic system constructed by Scenedesmus obliquus and Pseudomonas at a ratio of 1:5 was cultivated for 8 days.Microalgal biomass,total oil and oleic acid contents were 3.7 g/L,23.8%,and 12.2%,respectively.The symbiotic system of Chlorella emersonii and Pantoea ananatisthat was constructed with a ratio of 1:5 was cultivated for 8 days.The biomass,oil content and oleic acid content of Chlorella emersonii were 3.5 g/L,26.88%and 14.5%respectively.The symbiotic system of Chlorella emersoniiand and Pseudomonas was constructed with an ratio of I:1.After cultured for 8 days,the biomass,oil content,and oleic acid content of Chlorella emersonii were 3.29 g/L,29.5%and 12.3%respectively.The symbiotic system of algae also affects the sensitivity of microalgae to antibiotics,and it is beneficial to the stability of the microalgae culture system,meanwhile,it can resist the invasion of pests and microalgae flocculation and harvest.