An Assessment of the Effects of Light Intensities and Temperature Changes on Cyanobacteria’s Oxidative Stress via the Use of Hydrogen Peroxide as an Indicator
Mizanur Rahman | Takashi Asaeda | Helayaye Damitha Lakmali Abeynayaka | Kiyotaka Fukahori
Humans and other organisms are adversely affected by cyanobacterial blooming. This study aims to investigate the long-term effects of light intensities and different temperatures on <i>Phormidium ambiguum</i> and <i>Pseudanabaena foetida</i>. Enough <i>P. ambiguum</i> and <i>P. foetida</i> cells were acclimated for 24 days at 30 °C, 20 °C, and 10 °C in separate incubators. The starting day sample was collected after 24 days of acclimatization, and a second sample was collected seven days later at light intensities of 10, 30, 50, 200, and 600 µmol m<sup>−2</sup> s<sup>−1</sup> for each temperature. The optical density (OD<sub>730</sub>), hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) concentration, protein content, chlorophyll-a (Chl-a) concentration, and catalase (CAT) activity were measured. Light intensity changes soon after collection resulted in nearly identical starting day samples at each individual temperature. The H<sub>2</sub>O<sub>2</sub> concentration and algal biomass increased until a light intensity of 200 µmol m<sup>−2</sup> s<sup>−1</sup> was reached and decreased afterward in each temperature for both species after seven days. In association with an increasing H<sub>2</sub>O<sub>2</sub> concentration, the Chl-a concentration decreased after 50 µmol m<sup>−2</sup>s<sup>−1</sup> of light intensity, affecting the protein content. The algal biomass was significantly lower at 10 °C compared to 30 °C. The CAT activity increased proportionately with the H<sub>2</sub>O<sub>2</sub> concentration and algal biomass. Therefore, water bodies in the field can be illuminated with long-term high light intensities in different temperatures to reduce algal biomass.
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