Isolation, identification, and algicidal characterization of the marine algicidal strain Pseudoalteromonas sp. J75

Abstract:

Objective This study isolated and identified an algicidal bacterium from the East China Sea near Wenzhou and investigated its algicidal characteristics and mechanisms, aiming to contribute a solid scientific basis to the microbial control against red tides.Methods The strain was identified by morphological observation, physiological and biochemical tests, and 16S rRNA gene sequence analysis. The algicidal characteristics such as algicidal activity, influences of environmental factors on the algicidal activity, and algicidal specificity were assessed. The algicidal mechanism was explored by electron microscopy, measurements of photosynthetic parameters, and determination of reactive oxygen species (ROS) and malondialdehyde levels and antioxidant enzyme activities.Results The algicidal strain J75 was identified as Pseudoalteromonas sp. The algicidal rate of strain J75 against Skeletonema costatum reached 95.97% within 36 h. Strain J75 induced lysis of algal cells indirectly by secreting extracellular algicidal substances, maintaining the algicidal activity across broad ranges of temperatures (-20 °C to 80 °C) and pH levels (5.0 to 9.0). In addition, strain J75 demonstrated algicidal activities against other harmful microalgae, including Karenia mikimotoi, Prorocentrum minimum, and Phaeocystis globosa. Under the stress of J75 cell-free supernatant, the algal cells showed morphological structure damage, a significant decrease in the photosynthetic activity, elevations in the levels of ROS, membrane lipid peroxidation, activities of superoxide dismutase, catalase, and peroxidase, and the level of glutathione. These results indicated that strain J75 caused oxidative damage to algal cells, ultimately leading to algal death.Conclusion The marine algicidal bacterium Pseudoalteromonas sp. J75, which holds significant potential for the control of red tides, demonstrates its efficacy by secreting algicidal compounds that inhibit the growth of diverse red tide microalgae. The exploration of the algicidal characteristics and mechanisms of this strain provides a theoretical basis for advancing red tide management strategies.