Effects Of Symbiotic Bacteria Of Ochromonas On Growth And Metabolism Of Algal Cells

In recent years,improving the biomass of microalgae by constructing a symbiotic system of algal bacteria has become a research hotspot.However,previous research has mainly focused on the influence of some functional bacteria on the growth of microalgae,lacking systematic and in-depth understanding of the influence of symbiotic bacteria on the growth of microalgae in the naturally formed in the process of microalgae culture.In this study,the community structure difference of symbiotic bacteria from Ochromonas in domestic wastewater,BG11 and Glu+BG11(BG11 added with 10 g·L-1 glucose)were analyzed,and further isolated the symbiotic bacteria from the Ochromonas culture systems of BG111 and Glu+BG11,to study the influence of symbiotic bacteria on the growth of Ochromonas.The results show that:(1)There were significant differences in the community structure of the symbiotic bacteria among the three nutrient environments.By comparing alpha diversity,it was found that the highest diversity of symbiotic bacteria was found in domestic wastewater,with Shannon diversity index of 4.32,followed by BG11 and Glu+BG11 systems,with Shannon index of 2.13 and 1.54 respectively.The cluster analysis showed that the community structure of BG11 and Glu+BG11 was more similar than that of domestic wastewater.In terms of the composition of symbiotic bacterial community,the dominant bacteria were significantly different.The dominant bacteria in domestic wastewater were Gemmobacter,Sphingomonas and Roseococcus,accounting for 14.46%,14.9%and 14.54%of the total bacterial community respectively.In the BG11 culture system,the dominant symbiotic bacteria of Ochromonas mainly included Stenotrophomonas and Roseococcus,and the population abundance accounted for 26.86%and 51.03%,respectively.The dominant symbiotic bacteria in Glu+BG11 system was the same as that in BG11 system,but the abundance of Stenotrophomonas significantly increased,up to 82.41%,and the relative abundance of Rosecoccus decreased,only 6.2%.Compared with the three nutrient systems,it was found that Gemmobacter had a high abundance only in domestic wastewater,and was a typical indigenous bacteria in domestic wastewater.Rosecoccus was relatively abundant in the three trophic environments and was a good symbiotic bacterium of Ochromonas.(2)The results demonstrated that all the nine strains of symbiotic bacteria could enhance the growth of Ochromonas in the nutritional environment of BG11,but in BG11 medium containing glucose,the microalgae biomass promoting effect of bacteria was significantly reduced or even disappeared.Bacteria Porphyrobacter and Aneurinibacillus could increase the biomass accumulation of Ochromonas by 1.4 and 1.1 times in BG11 system respectively.And both bacterial species affected Ochromonas growth mainly though metabolites secreted into supernatant either in BG11 or BG11 system with glucose.Meanwhile,glucose concentration above 5 g·L-1 in culture system could significantly decline the algal growth-promoting effect of Aneurinibacillus,and 10 g·L-1 of glucose would cause the death of Ochromonas cells directly.Thus,the ecological relationship between algae and bacteria would be strongly affected by the organic nutrient in culture system,the effect of symbiotic bacteria on biomass accumulation of microalgae is regulated by glucose concentration in the system.(3)To further explore the mechanism of interaction between Porphyrobacter and Ochromonas,the results showed that the Porphyrobacter could promote the growth of Ochromonas cells by secreting IAA,and the growth rate of Ochromonas could be increased by 60%through 50 mL supernatant of Porphyrobacter.Meanwhile,the culture medium of Ochromonas also promoted the secretion of IAA by Porphyrobacter,and the concentration of IAA reached 6.29 mg/L/OD when the supernatant of Ochromonas with 50 mL Glu+BG11 system was added.Among them,the concentration of Zn2+ was the main factor affecting the IAA secretion of Porphyrogenia.When the concentration of Zn2+reached 22 mg·L-1,the specific growth rate of Ochromonas reached 0.55 D-1.(4).The transcriptome analysis showed that Aneurinibacillus affected the growth of Ochromonas cells by affecting the synthesis and transport of intracellular components,functional substances in Ochromonas.Glucose mainly affects the growth of Ochromonas from the aspects of energy synthesis,functional substance synthesis and metabolism.Such as the greatest effect on cytoplasmic structure.