The Diversity And Characteristics Of The Cultivable Bacteria Associated With The Cyanobacterium Microcystis

In order study the diverisity and the characteristics of bacteria associated with colonial and unicellular Microcystis,and further explore the role of the associated bacteria in the transition of colonial Microcystis to unicellular Microcystis,twenty-eight bacterial isolates were isolated from colonial algae and unicellular algae of Microcystis wesenbergii(NJ-24),Microcystis Flos-aquae(NJ-159,NJ-72),Microcystis aeruginosa(NJ-177),Maicrocystis firma(NJ-54).The bacterial isolates belonged to Alpha proteobacterium,Beta proteobacterium,Gamma proteobacterium,Actinobacteria,Cytophagia,Bacilli and Flavobacteriia based on 16S rDNA gene fragment sequencing.43%of the bacterial isolates belonged to?-Proteobacteria,21%of the bacterial isolates belonged to Actinobacteria,11%of the bacterial isolates belonged to Cytophagia,and ?-Proteobacteria accounted for 11%.Among the bacterial isolates,the proportion of ?-Proteobacteria were highest,up to 55%,followed by Actinobacteria.The bacteria of Bacilli and ?-Proteobacteria bacteria were least.Among these 28 strains of associated bacteria,4 bacterial strains appeared in unicellular Microcystis,12 bacterial strains appeared in colonial Microcystis,the other 12 bacterial strains appeared in both unicellular Microcystis and colonial Microcystis.No regular pattern was found for the proportion of these bacteria in colonial and unicellular Microcystis.BIOLOG ECO plate analysis was used to investigate the utilization of different organic matters.Among the 28 bacterial isolates,17 strains utilized more than 20 kinds of carbon sources,including 7 isolates belonging to ?-Proteobacteria,4 isolates belonging to Actinobacteria,3 isolates belonging to Bacteroidete,and 3 isolates belonging to ?-Proteobacteria,?-Proteobacteria and Flavobacteriia.These bacteria appeared in colonial Microcystis or unicellular Microcystis.By MATH analysis,10 bacterial isolates exhibited hydrophobicity nature.Among the 10 bacterial isolates,the hydrophobicity of 54D-3(Rhodobacter sp.),54D-4(Staphylococcus caprae),177Q-1(Sphigomonas sp.)and 177Q-6(Aeromicrobium sp.)was more than 70%.Judged from the analysis of chemotaxis,chemotaxis diameters of 6 bacterial isolates reached more than 20 mm,and these bacteria appeared in colonial Microcystis or unicellular Microcystis.The experimental results of autoaggregation and coaggregation,8 bacterial isolates had the strong autoaggregation ability of which were very strong,but these bacteria had weak abilities of coaggregation with other bacteria.The bacterial isolates with the strong coaggregation ability also had the weak autoaggregation ability.It illustrated that there was no obvious correlation between the bacterial autoaggregation and the bacterial autoaggregation.With respect to the coaggregation and autoaggregation ability of bacteria,there was no obvious difference between colonial and unicellular Microcystis.These 28 bacterial isolates were able to grow in extracellular filtrates of colonial Microcystis and/or unicellular Microcystis,?OD600 of 5 bacterial isolates reached more than 0.1.Based on the above results on bacterial composition carbon source utilization,hydrophobicity,chemotaxis,autoaggregation,coaggregation and the growth in fltrates of Microcystis,it was suggested that the associated bacteria do not play important roles in the transition of colonial Microcystis to unicellular Microcystis.