铜绿微囊藻生长代谢的密度依赖性特征及分子机制

蓝藻水华是淡水湖库普遍面临的水环境问题，目前水华形成机制研究大多关注外界环境因素而忽略了藻类自身及群体的关键调节作用.因此，本文以初始细胞密度为单一变量，考察了不同初始细胞密度条件下蓝藻生长、营养物质利用、叶绿素、藻毒素、胞外分泌物随时间的变化情况.结果发现，初始细胞密度会影响铜绿微囊藻的环境适应性和生长情况，当接种密度≥1×10⁶ cell·mL^-1，铜绿微囊藻适应期消失，初始细胞密度从1×10⁵ cell·mL^-1增加至1×10⁷ cell·mL^-1，最高细胞密度增加了68%，生长速率提高了21%，并且叶绿素变化趋势与生长情况一致.胞外分泌物随初始细胞密度增加而逐渐增加，有利于蓝藻细胞聚集成膜.当初始细胞密度较低（1×10⁵ cell·mL^-1）时，单细胞藻毒素分泌量反而增加，以提高蓝藻的环境适应能力.在高初始密度（1×10⁷ cell·mL^-1）条件下，铜绿微囊藻主要通过上调丙酮酸代谢和碳代谢，促进细胞生长增殖.因此，细胞密度是影响铜绿微囊藻生长代谢的重要因素，在蓝藻水华形成过程中可能发挥重要作用，水华防治应当在细胞密度较低的阶段进行.

The growth and metabolism of Microcystis aeruginosa depend on cell density and its molecular mechanism

Cyanobacteria bloom is a common water environment problem in freshwater lakes. Most of the mechanisms of bloom formation focus on external environmental factors but ignore the key regulatory role of algae itself and its population. In this study, the initial cell density serve as a single variable, the cell growth, nutrient utilization, chlorophyll, microcystin and extracellular secretion of cyanobacteria under different initial cell densities were investigated over time. It was found that the initial cell density affected the environmental adaptability and the cell growth. When the initial cell density was higher than 1×10⁶ cell·mL^-1, the adaptive phase was disappeared. The initial cell density increased from 1×10⁵ cell·mL^-1 to 1×10⁷ cell·mL^-1, the maximum cell density increased by 68% and the growth rate increased by 21%. The variation tendency of chlorophyll were consistent with the cell growth results. The extracellular secretion increased gradually with the increase of initial cell density, which was conducive to the aggregation of cyanobacteria cells and biofilm formation. When the initial cell density was 1×10⁵ cell·mL^-1, the secretion of single cell microcystin was higher to improve the environmental adaptability. The high initial cell density(1×10⁷ cell·mL^-1) promoted the growth and proliferation of Microcystis aeruginosa by up-regulating pyruvate metabolism and carbon metabolism. Therefore, cell density is an important factor for the growth and metabolism of Microcystis aeruginosa and it maybe play a crucial role in the cyanobacterial blooms. The prevention and control of blooms should be started at the initial stage with low cell density.