Abstract
The toxigenic cyanobacterium Cylindrospermopsis raciborskii previously restricted to tropical latitudes, has been increasingly reported in temperate lakes in recent decades. The causes of its biogeographical expansion are under investigation, but efficient physiological adaptation to changes in temperature and light regimes are likely to be involved. The present study evaluated the morpho-physiological responses of a strain of C. raciborskii from southern Brazil to nine light intensities, from 9 to 250 µmol photons m-2 s-1. Blooms of this cyanobacterium are regularly recorded in the region. Morpho-physiological responses were measured based on growth rate and trichome length. Cylindrospermopsis raciborskii showed slow growth at low light intensities, 9 and 20 µmol photons m-2 s-1, and responded morphologically by increasing the length of trichomes. In turn, the strain displayed constant maximum growth rates at light intensities higher than 50 µmol photons m-2 s-1. These results support the hypothesis that C. raciborskii can survive under low light conditions and continue to produce viable trichomes. Moreover, the strain achieved high growth rates under a relatively wide range of light intensities, a physiological adaptation that can potentially be a competitive advantage in the phytoplankton community.
Highlights
Cylindrospermopsis raciborskii is a toxigenic cyanobacterium initially ascribed as a tropical to subtropical species (Padisák 1997)
The present study evaluated the morpho-physiological responses of a strain of C. raciborskii from southern Brazil to nine light intensities, from 9 to 250 μmol photons m-2 s-1
Growth of C. raciborskii strain was influenced by light intensity (F8.171 = 5.71, P = 0.02), two main distinct trends in the curves were recorded: slower growth at 9 and 20 μmol photons m-2 s-1, and faster ones at 50 μmol photons m-2 s-1 and above (Fig. 1)
Summary
Cylindrospermopsis raciborskii is a toxigenic cyanobacterium initially ascribed as a tropical to subtropical species (Padisák 1997). Blooms of this species have increased over the past two decades in many lakes and reservoirs around the world, including temperate latitudes, leading researchers to reclassify the species as cosmopolite (Briand et al 2004). Wide ranges of environmental preferences and tolerance to variable light intensity have been referred to as factors that promote the expansion of C. raciborskii (Briand et al 2004; Piccini et al 2011)
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