Heterogeneity of buoyancy in response to light between two buoyant types of cyanobacterium Microcystis
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Previous investigations suggested that buoyancy state in response to light differed between individuals within natural populations of cyanobacteria. To understand the mechanisms of heterogeneity of buoyancy in different species/strains in relation to light, two types of colonial Microcystis in different buoyancy behavior were selected and used to compare their photosynthetic activity, gas vesicle volume, ballast mass, and migration at varying light regime. The photosynthesis–irradiance curve and F v/F m examination indicated that negatively buoyant strains were more adapted at high irradiance than buoyant ones. Transcription levels of gvp gene and gas vesicle volume decreased in buoyant strains, but increased in negatively buoyant ones at high irradiance. The results indicated that the combination effect of decrease in gas vesicle buoyancy and increase in carbohydrate contributed to the downward migration of buoyant strains, while the significant increase of gas vesicles provided sufficient buoyancy to negate ballast mass, resulting in the upward migration of negatively buoyant ones at high irradiance. In addition, either sinking or floating velocities were elevated in buoyant and negatively buoyant strains, coincidently with the colony enlargement of all strains at high irradiance, respectively. These findings suggest that this heterogeneity was associated with the interplay between gas vesicles, ballast, and colony size. The fact that different species/strains of Microcystis respond diversely to light depending on their physiological conditions presents a good example to understand heterogeneity of buoyancy in the field, and the presence of heterogeneity of buoyancy may be implicated in the dominancy and persistence of Microcystis bloom in ever-changing environment.
KeywordsBuoyancy Colonial Microcystis Heterogeneity Light Vertical migration
This work was supported by grants from the National Key Project for Basic Research (2008CB418001, 2008CB418006); the National Natural Science Foundation of China (31070355); and the Natural Science Foundation of China-Yunnan Project (U0833604). We thank Dr. Zhaosheng Chu for his assistant in measurement of gas vesicle volume.
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