Photoacclimation strategies in the toxic cyanobacterium Nodularia spumigena (Nostocales, Cyanobacteria)

Abstract

Jodłowska S. and Latała A. 2010. Photoacclimation strategies in the toxic cyanobacterium Nodularia spumigena (Nostocales, Cyanobacteria). Phycologia 49: 203–211. DOI: 10.2216/08-14.1.This ecophysiological study of the planktonic cyanobacterium strain Nodularia spumigena (BA-15) was conducted at three photosynthetic active radiation (PAR) irradiances (10, 150, and 290 µmol photons m−2 s−1) and two temperatures (15 and 30°C). The filament concentration, pigment composition, and photosynthetic performance of N. spumigena depended on culture conditions. The cyanobacterium was very tolerant of the highest irradiance at the lower temperature (15°C). Filament concentration, however, was lower at the higher temperature and the highest irradiance compared with other culture conditions. The efficiency (α) and maximum rates of photosynthesis (Pm) were both affected negatively at 30°C under irradiances of 150 and 290 µmol photons m−2 s−1. The photoacclimation capacity of the cyanobacterium was evaluated by analysing pigment concentration (chlorophyll, carotenoids, phycobilins), the photosynthetic light response curves (P-E), and chlorophyll a fluorescence. The highest concentrations of phycobilins and chlorophyll a per 100 µm of filament were observed at 10 µmol photons m−2 s−1 and the lowest at 290 µmol photons m−2 s−1. Two photoacclimation mechanisms were identified in N. spumigena based on P-E, namely, changes in the number of photosynthetic units and changes in size. The minimum value of Pc (about 5 µmol photons m−2 s−1) and Ps (about 150 µmol photons m−2 s−1) is close to those reported for shade-tolerant plants, while the maximum value of Pc (about 100 µmol photons m−2 s−1) and Ps (about 400 µmol photons m−2 s−1) is close to those noted in heliophylous plants. Fluorescence measurements of N. spumigena indicated that high irradiance had a negative effect on both Fv/Fm and ΦPSII, but the effect was more pronounced in the case of ΦPSII. The tolerance of this planktonic cyanobacterium to elevated light levels explains to some degree why it occurs regularly in marine waters worldwide in summer and often forms toxic blooms.