Effects Of Exogenous Organic Carbon On The Relationship Between Cyanobacteria And Bacteria

Water bloom is a natural phenomenon in which phytoplankton proliferate rapidly in water.A large quantity of Microcystins and odorous substances will be produced in the water during the cyanobacteria blooms,which will seriously affect the structure of the aquatic ecosystem and cause the disorder of the function of the aquatic ecosystem.Moreover,when the polluted water is ingested by humans or mammals by accident,it will lead to diseases of the liver,nervous system or digestive system,which could seriously endanger human health.Cyanobacteria will interact with other bacteria in their living habitat,and the interactions will be affected by biological or non-biological factors.The interaction may be negative when they are competing for nutrients and living space or positive when exchanging each other's nutrition.Carbon source plays an important role in the growth and competition of microorganisms.However,we do not know much about how carbon source and other conditions affect the relationship between bacteria and cyanobacteria,which is worthy of further study.As a potential biological control material,algicidal bacteria have attracted the attention of many scholars all over the world.It is of great significance to study the influence of enviroumental factors on the interaction between cyanobacteria and algicidal bacteria in order to gain further understanding of their complex interactions in aquatic ecosystems and improving the competitiveness of algicidal bacteria in the natural environment.In our previous study,we isolated an algicidal bacteria WR11 and other many strains of bacteria,from the eutrophic water sample of the Nan-Lake in Wuhan during the period of water bloom.In this study,we combined the technology of microbiology and biochemical analysis,to explore the relationship between the bacterial strains and cyanobacteria species(Anabaena sp.PCC 7120;Synechocystis sp.PCC6803;Microcystis aeruginosa 7753)under different carbon source condition.The main results of this study are as follows:(1)Carbon sources can generally affect the relationship between bacteria and cyanobacteria.The isolated bacteria were co-cultured with Synechocystis sp.PCC6803 or Anabaena sp.PCC 7120 with different carbon source.The exogenous carbon species had a significant effect on the strong algicidal effect of WR11,among which glucose and sucrose could promote the rapid growth of cyanobacteria and improve the inhibitive ability of WR11,while glucose could also improve the strong algicidal effect of most bacteria.(2)Carbon source perturbing the effects of light cycle on the algicidal ability of WR11.Previous studies have shown that light cycle has an effect on the algal inhibition activity of algicidal bacteria WR11.In this study,we use glucose as exogenous organic carbon to explore the effect of light cycle on the interaction between cyanobacteria and bacteria.The results showed that the addition of carbon source would disturb the effect of light cycle on the ability of bacteria to inhibit algae,and lead the mutant M20 to inhibit cyanobacteria in the later stage of co-culture.By analyzing the changes of bacterial and cyanobacterial biomass under different conditions,we speculate that the improvement of the inhibition ability of M20 by carbon source may be through promoting the growth of bacterial M20 in the co-cultures.(3)Effects of carbon sources on inhibition substances.The results of HPLC show that the secretion of yellow extracellular pigment in WR11 medium supplemented with glucose were significantly increased,and the biomass of WR11 was also increased to a certain extent.However,in previous studies,we believed that this pigment was related to the inhibitive ability of WR11,suggesting that the improvement of the inhibitive ability of WR11 by carbon source may be through promoting the increase of bacterial biomass,on the other hand,it also increased the secretion of bacterial active substances.In summary,based on the microbiological method,we preliminarily explored the influence of carbon sources on the relationship between cyanobacteria and bacteria in water.Our study should be helpful in deepen people's understanding of cyanobacteria blooms and the interaction between algicidal bacteria cyanobacteria in nature condition.