To understand the effect of the hydrostatic pressure on Pseudanabaena galeata Böcher cells in both stratified and frequently mixed lakes, separate laboratory-scale models were developed. The pressure conditions in the stratified and mixed lakes were simulated in those models, and the variations of the cell and chlorophyll-a (Chl-a) concentration were analyzed. It was observed that an increase in pressure and darkness significantly reduced the cell concentration and pigmentation in P. galeata (p < 0.01, n = 3). After 10 days, the cell concentrations of P. galeata that were grown under conditions of a water depth of 30 m were reduced by 7.0%, per day, while the cell concentration rate after 10 days in atmospheric conditions was increased by 2.53% per day. During the experiment, cells were subjected to the prolonged darkness under 0.3 MPa pressure for 10 days and then exposed to the white light under atmospheric pressure for 5 days. Even after running this cycle for 60 days, 19.5% of the initial cells could survive. This rate exceeded the cell concentration-increasing rate in the control. These findings indicate that P. galeata has an adequate tolerance to pressure and fluctuating light irradiance and that the cells are able to propagate after escaping from those stress conditions.
Keywords: Cell concentration; Chlorophyll-a; Cyanobacteria; Hydrostatic pressure; Prolonged darkness; Pseudanabaena galeata Böcher.