Physiological and biochemical responses of bloom-forming Pseudanabaena spp. against the cyanolytic bacterium Pseudomonas fluorescens BG-E

The antagonistic interaction between heterotrophic bacteria and cyanobacteria plays a key role in terminating harmful cyanobacterial blooms. The cyanolytic bacterium Pseudomonas fluorescens BG-E has been reported to exhibit efficient cyanolytic activities against Pseudanabaena lonchoides LW1 and Pseudanabaena sp. LW2 via its cell-free supernatant and whole bacterial culture. Therefore, this study aimed to investigate the physiological and biochemical responses of two bloom-forming Pseudanabaena species following exposure to BG-E and its secreted metabolites. Time-course bioassays showed increased H2O2 levels in both LW2 and LW1 exposed to the whole BG-E culture and its cell-free supernatant, respectively, indicating treatment-induced oxidative stress. Changes in antioxidant enzyme activities and proline accumulation over time further indicated activation of the antioxidant defence system in both species as a cellular response mechanism. Concurrently, a time-dependent, significant reduction in photosynthetic and accessory pigment contents suggests that the bacterium BG-E and its secreted metabolites may have impaired photosynthesis and inhibited growth. Changes in protein and carbohydrate content over time further indicate treatment-induced physiological responses in both species. Consistent with these biochemical and physiological changes, scanning electron microscopy revealed pronounced alterations in filament morphology and structural integrity in two Pseudanabaena species after 10 days of exposure. Overall, the findings demonstrate that P. fluorescens BG-E induces substantial growth inhibition, physiological stress and structural damage in Pseudanabaena. Further investigation of BG-E and its bioactive metabolites as potential biological agents to control freshwater blooms associated with Pseudanabaena is necessary. Pseudomonas fluorescens BG-E strain inhibited growth of two Pseudanabaena species.BG-E strain exposure induced marked physiological and biochemical stress responses.SEM revealed structural damage and deformation in Pseudanabaena. Pseudomonas fluorescens BG-E strain inhibited growth of two Pseudanabaena species. BG-E strain exposure induced marked physiological and biochemical stress responses. SEM revealed structural damage and deformation in Pseudanabaena.