Molecular Mechanisms of Algicidal Bacteria in Controlling Harmful Algal Blooms: Advances in Bacteria-Algae Interactions.

The frequent occurrence of harmful algal blooms (HAB) poses severe threats to aquatic ecosystems, aquaculture industries and human health. Recently, algicidal bacteria have emerged as a promising biocontrol strategy. However, the precise mechanisms underlying their algicidal effects remain poorly understood, limiting their practical application in environmental management. This review systematically summarises the interactions between bacteria and algae, as well as the various algicidal modes employed by bacteria, with a particular focus on the mechanisms driving bacterial algicidal activity. Key bacterial behaviours such as chemotaxis, adhesion, quorum sensing and the release of extracellular vesicles have been identified as critical factors in the algicidal process, among which the role of bacterial extracellular vesicles warrants special attention. Furthermore, we elaborate on the death mechanisms of algal cells upon bacterial attack, including loss of cellular structural integrity, impairment of photosynthetic systems, oxidative stress responses and disruption of calcium ion homeostasis. Notably, advancements in detection technologies have increasingly highlighted the importance of calcium signalling regulation in algal cell death. This review not only elucidates the molecular mechanisms of bacterial algicidal activity, providing a theoretical foundation for the biocontrol of red tides, but also deepens our understanding of bacteria-algae interactions.