Effects Of Light Conditions On Inhibition Of Microcystis Aeruginosa By Berberine And Its Mechanism Involved

Microcystis aeruginosa was the main species causing cyanobacterial bloom.Berberine could inhibit M.aeruginosa growth effectively,and be used as algicidal substance in the control of cyanobacterial bloom in aquaculture pond.Inhibitory effects of berberie on M.aeruginosa might be realized via affecting algal photosynthesis.Light conditions,as the essential environment factor invovled in photosynthesis,might affect the inhibitory effects of berberine.To declare the inhibitory mechanism of berberine on M.aeruginosa,effects of different light conditions on the growth and chlorophyll fluorescence parameters(Fv/Fm??PS??ETR?Yield')of M.aeruginosa exposed to berberine were investigated.The main results were presented as follows:1 Comparative effects of berberine on toxic M.aeruginosa(FACHB905)and non-toxic M.aeruginosa(FACHB469)Both toxic and non-toxic M.aeruginosa growth could be inhibited by berberine effectively under light(70 ?mol·m-2·s-1,12 light: 12 dark cycle).Inhibitory activity of berberine on toxic M.aeruginosa was stronger than that on non-toxic M.aeruginosa;Chlorophyll fluorescence parameters in the controls were constant.As compared to toxic M.aeruginosa,these parameters of non-toxic M.aeruginosa were much higher;Berberine could decrease chlorophyll fluorescence parameters of toxic and non-toxic M.aeruginosa significantly(P > 0.05),and these parameters of toxic M.aeruginosa decreased more quickly than those of non-toxic M.aeruginosa.2 Effects of ligt intensity on inhibitory activity of berberine on M.aeruginosa4 mg/L berberine could inhibit M.aeruginosa growth effectively under different light intensities(50,100,150 ?mol·m-2·s-1).Cell densities in berberine-added treatment decreased with the increasing light intensities,and there were no significant differences between treatments under different ligt intensities(P > 0.05);All chlorophyll fluorescence parameters in berberine-added treatments decreased to 0 at 1d and remained stable at 0 throughout the experiment under different light intensities.No differences in cell density and chlorophyll fluorescence parameters were observed between the control and berberine-added treatment under continuous darkness.Berberine had no inhibitory effects on M.aeruginosa growth under continuous darkness.3 Effects of darkness stress on the inhibitory activity of berberine on M.aeruginosa after lightrecoveryInhibitory effects of berberine on M.aeruginosa were weakened after light recovery from darkness as compared to those suffered no darkness stress.After light recovery(70 ?mol·m-2·s-1)from 2 d darkness,cell densities in 2 mg/L berberine-added treatment increased with the increasing culture time,and chlorophyll fluorescence parameters decreased to the lowest value at 1 d and then increased to the stable value.Under light(70 ?mol·m-2·s-1)without darkness stress,cell densities in 2 mg/L berberine-added treatment decreased first and then increased,and chlorophyll fluorescence parameters decreased to 0 at 1 d and then increased to the stable value with the increasing culture time;After light recovery from 2 d darkness,cell densities in 5 and 8 mg/L berberine-added treatments decreased with the increasing culture time,and algal cells were all killed at 8 d and 6 d,respectively.Under light(70 ?mol·m-2·s-1)without darkness stress,cell densities in 5 and 8 mg/L berberine-added treatments decreased with the increasing culture time,and algal cells were all killed at 4 d and 3 d,respectively.After light recovery from 2 d darkness,chlorophyll fluorescence parameters decreased to 0 at 1 d and remained stable at 0in 5 and 8 mg/L berberine-added treatments,which changed in the same manner as those suffered no darkness stress.After light recovery(50,100 and 150 ?mol·m-2·s-1)from 2 d darkness,cell densities in 4mg/L berberine-added treatment decreased first and then increased with the increasing culture time,decreased with the increasing light intensities.Chlorophyll fluorescence parameters decreased to the lowest value at 1 d and then increased with the increasing culture time.Under light(50,100 and 150 ?mol·m-2·s-1)without darkness stress,with the increasing culture time,cell densities in 4 mg/L berberine-added treatment decreased.It reached to 0 at 5 d and remained stable at 0.Chlorophyll fluorescence parameters decreased to 0 at 1 d and remained stable at 0.After light recovery(45 ?mol·m-2·s-1)from different durations(4 d,8 d and 12d)of darkness,cell densities in 4 mg/L berberine-added treatment remained stable first and then increased with the increasing culture time.Cell densities after light recovery from 12 d darkness were lower than those after light recovery from 4 d and 8 d darkness.Chlorophyll fluorescence parameters decreased first and then increased to the stable value.4 Effects of darkness stress before berberine exposure on inhibitory activity of berberine on M.aeruginosaM.aeruginosa cultured in light(40 ?mol·m-2·s-1)and darkness for 8 d were reinoculated to same initial cell density,respectively.Berebeine were added to different concentrations(0,2and 4 mg/L)and algae were cultured in light for 6 d.2 mg/L berberine could not inhibit M.aeruginosa growth effectively,and cell densities and chlorophyll fluorescence parameters decreased first and then increased.Cell densities of algae cultured in darkness before berberine exposure were significantly higher than those cultured in light at 6 d(P < 0.05);4mg/L berberine inhibited M.aeruginosa growth effectively,and algal cells were killed at 6 d.No differences in cell densities and chlorophyll fluorescence parameters were observed between algal cells cultured in light and darkness before berberine exposure.In conclusion,inhibitory effects of berberine on M.aeruginosa was light-dependent.Berberine could inhibit M.aeruginosa growth under light.However,berberine had no inhibitory activity under darkness.After light recovery from darkness,berberine could inhibit M.aeruginosa growth again and its inhibitory activity decreased.It was indicated that berberine was photosynthesis inhibitor which implemented inhibitory activity via participating in photosynthesis of M.aeruginosa.Changes in chlorophyll fluorescence parameters suggested that the target of berberine on M.aeruginosa might electron transport in PS?.