Effect Of Elevated CO₂ And Tempreture On The Toxigenicity And The Transcription Of Microcystin Biosynthesis Gene Of Microcystis Aeruginosa

In this study, Microcystis aeruginosa FACHB905 was grown in four different conditions:(1)25℃+400μmol/mol(control), (2)29℃+400μmol/mol (elevated temperature group), (3)25℃+800μmol/mol (elevated CO2 group),(4)29℃+800μmol/mol (greenhouse effect). After incubation, the biomass of each culture and the total content of microcystin were measured. The results showed that the number of algal cells of the control was significantly lower than the the elevated temperature group、the elevated CO2 group and the greenhouse effect group(P<0.05), and the number of algal cells of the greenhouse effect was significantly higher than the elevated temperature group、the elevated CO2 group, these rerults indicated that elevated temperature and elevated CO2 had a synergistic effect to stimulate the growth of M. aeruginosa. The total content of microcystin of the elevated CO2 group was significantly higher than the control (P<0.05), this indicated that elevated CO2 can increase the total content of microcystin and there was a significant positive correlation (P＜0.05) between the total toxin content and the algae biomass. The microcystin content in a single cell of the four group were significant difference in the logarithmic phase, but were no significant difference in the stationary phase. The results imply that the greenhouse effect (atmospheric temperature and the CO2 concentration increase synchronously) will increase the biomass of M. aeruginosa blooms, and the total amount of microcystin in the stationary phase will increase correspondingly.The M. aeruginosa FACHB905 was cultivated in the four different conditions. In the first and the third month, we measured the content of the microcystin of the 13th and the 15th and the transcription of mcyB and mcyD of the 14th. The results showed that: elevated temperature and elevated CO2 had no influence on the total content of microcystin in the logarithmic phase, but could reduce the average daily increment of the microcystin content in a single cell, these rerults indicated that greenhouse effect can slow the accumulation of the microcystin content in a single cell. The transcriptional variation of mcyB and mcyD in the four different conditions were similar, it showed that the transcriptional of mcyB and mcyD were synchronous, they did not affected by cultivation conditions and time. In addition, we found that the transcription of mcyB and mcyD in the four different conditions did not conform with the microcystin content accumulation in a single cell. These results suggest that global climate change (atmospheric temperature and the CO2 concentration increase synchronously) will slow the accumulation of the microcystin content in a single cell in the logarithmic phase, but it can increase the biomass of M. aeruginosa blooms, so the total amount of microcystin in the logarithmic phase will not increase, and there will not be linear relation between the toxin accumulation speed and the transcription efficiency of mcyB and mcyD.