Differential responses of different phenotypes of Microcystis (Cyanophyceae) to UV-B radiation

Abstract:

Microcystis can be single celled or colonial under certain conditions, thereby possessing phenotypic plasticity. Differential physiological and biochemical responses of colonial Microcystis aeruginosa FACHB 939 and its single-celled strain to ultraviolet type B radiation (UV-B) exposure were investigated. Results suggested that UV-B exposure exerted a lower inhibitory effect on the growth of colonial Microcystis, and that the single-celled strain had higher ability to recover after exposure to UV-B. Carotenoids/chlorophyll a (Chl a) ratios were increased, whereas phycobilisome/Chl a ratios were decreased by UV-B exposure. The photosynthetic activities of both phenotypes were inhibited, but colonial Microcystis showed higher tolerance and recovery ability to UV-B exposure. The sheath and shading effect, as well as changes of pigments of colonial Microcystis, were believed to play roles in resisting UV-B exposure. UV-B radiation can increase the sinking rate of the single-celled Microcystis and cause colonial Microcystis to shift from a floating to a sinking state. The observed reduction of colony size and increase in total carbohydrate content induced by UV-B radiation presumably caused the decrease in buoyancy in Microcystis. However, the increase in sinking rate is also an important way for Microcystis to avoid damage inflicted by UV-B radiation.

Key Words::

• Chlorophyll fluorescence
• Cyanobacteria
• Migration rate
• Phenotypic plasticity
• Photosynthesis
• UV-B radiation

ACKNOWLEDGEMENTS

We thank anonymous reviewers for manuscript revising and good suggestions. We thank editors of Phycologia for manuscript revision. We thank native English speakers from the EasyStar Company for their excellent English language editing. The study was supported by the National Major Program of Water Body Pollution Control and Remediation (2012ZX07103003-02).