Autoaggregation Of The Bacteria Associated With Microcystis

Bacterial aggregation is a common phenomenon wordwide,which has important influence on bacterial colonization,biofilm formation and stress tolerance.We found that some of the cyanobacterium Microcystis-associated bacteria have autoaggregation ability.In this paper,six Microcystis-associated bacteria including Staphylococcus caprae 54D4,Blastomonas natatoria 159D1,Methylobacterium aminovorans 159D2,Sphingomonas wittichii 159D5,Nocardioides 159D7,and Rhizobium 177D6 were selected,and their autoaggregation properties and mechanisms were studied.The results showed that bacterial isolates 54D4,159D2 and 159D5 had strong autoaggregation ability.In the aggregation test at 24 h,the autoaggregation ability of bacterial isolate 54D4,159D2 and 159D5 reached 82.03%,92.40%and 90.05%,respectively;177D6 reached 50.19%;159D1 and 159D7 reached 21.07%and 31.94%,respectively.The aggregation ability was influenced by the growth phases.The autoaggregation ability of the bacterium 54D4 was significantly different in the exponential phase,early stationary phase and late stationary phase,and was the strongest in the exponential phase.The autoaggregation ability of the bacteria 159D1,159D2 and 177D6 in the stationary phase were significantly higher than that of exponential phase.For the bacteria 159D5 and 159D7,the aggregation ability at stationary phase was significantly lower than exponential phase and early stationary phase.The effect of metal ions on bacterial autoaggregation ability was strain-specific.Metal ions(Na+,K+,Ca2+and Mg2+)can inhibit aggregation of 159D2 and 159D5,while promoted aggregation of 159D1 and 159D7.In the aggregation test at 24 h,Metal ions(Na+,K+,Ca2+and Mg2+)promoted aggregation of 177D6;Metal ions Na+and K+ at the concentrations of 0.5mM,1 mM and 10 mM,and Ca2+and Mg2+at the concentrations of 0.5 mM and 1 mM can promote the aggregation ability of 54D4.The aggregation ability of 54D4 was inhibited by Na+and K+at the concentrations of 50 mM and 100 mM,and Ca2+and Mg2+at the concentrations of 10 mM,50 mM and 100 mM.In the aggregation test at 24 h,the aggregation ability of bacteria 54D4 and 177D6 were not affected significantly by the metal ions.The effect of pH on bacterial aggregation ability was also strain-specific.pH 3 and 11 can promote the aggregation ability of 54D4 and 159D2.pH 11 inhibited the aggregation ability of 159D5.For the bacteria 159D1,159D7 and 177D6,the aggregation ability was inhibited at pH 3,while was promoted at pH 11.The analyses of the cell surface hydrophobicity showed that the bacteria 54D4,159D1 and 159D7 had high hydrophobicity,reaching 79.65%,60.27%and 48.59%,respectively.The hydrophobicity of bacteria 159D2 and 159D5 was 18.68%and 24.87%,respectively.The bacterial isolate 177D6 was hydrophilic.Removal of extracellular polysaccharides(EPS)decreased significantly the aggregation ability of all bacterial isolates.Protease(proteinase K,trypsin)treatment inhibited the aggregation ability of 159D5,and did not affect autoaggregation of other bacteria.For the selected three kinds of amino acids,lysine inhibited the aggregation ability of 159D5,promoted aggregation of 159D1 and 159D7,and glutamate inhibited the aggregation ability of 159D7,promoted aggregation of 159D1.In the aggregation test at 4 h,galactose and arabinose inhibited the aggregation ability of 54D4.Galactose,mannose and rhamnose inhibited the aggregation ability of 54D4 at 24 h.Galactose,mannose,arabinose and rhamnose promoted aggregation of 159D2 at 1 h.The selected amino acids and monosaccharides promoted the aggregation ability of 177D6 at 4 h.In concludion,the selected six strains of Microcystis-associated bacteria had strong autoaggregation ability.Autoaggregation of bacteria were growth phase-dependent.Metal ions and pH influence the bacterial autoaggregation abilities.There was no significant correlation between the autoaggregation ability and the surface hydrophobicity of the bacteria.EPS may be the main factor that affecting the bacterial aggregation ability.The results on autoaggregation ability of Microcystis-associated bacteria could provide reference for exploring the effect of bacteria on formation of Microcystis colony.