Harmful algal blooms (HABs) have detrimental impacts on marine ecosystems and coastal zones. Despite the importance of interactions between microalgae and bacteria to marine ecosystems, the role of these interactions during HAB events is not yet fully understood. In this study, we isolated and characterized thirty bacterial strains from the 2021 Karenia brevis bloom in the Gulf of Mexico, and examined their effects on K. brevis growth. Results showed that the bacterium Mameliella alba CE5 significantly promoted K. brevis culture growth relative to controls, while Croceibacter atlanticus CE21 lysed K. brevis and inhibited its growth, which was coupled to strong cell aggregation. Genome sequencing of M. alba revealed genes responsible for aerobic anoxygenic photosynthesis, gene transfer agents, dimethylsulfoniopropionate metabolism, cofactors and vitamins (B₁₂), and secondary metabolites (e.g., terpenes). In contrast, C. atlanticus possessed genes for biosynthesis of polyketide algicides. Incubation experiments with blooming and terminating K. brevis water samples from a 2023 bloom showed that M. alba inhibited K. brevis cell decline and reduced stress during the termination phase of the bloom, while C. atlanticus promoted the demise of K. brevis cells relative to controls in the K. brevis-rich water samples. These findings shed light on the complex role that bacteria play in K. brevis blooms and suggest that different bacterial strategies modulate K. brevis growth during a bloom. Ongoing work is underway to identify the molecular mechanisms controlling these interactions, which may inform future management strategies for mitigating the impact of HABs.

Primary Presenter: Cong Fei, New York University Abu Dhabi (cf2290@nyu.edu)

Authors:

Cong Fei, New York University Abu Dhabi  (cf2290@nyu.edu)

Joaquίn Martίnez, Bigelow Laboratory for Ocean Sciences  (jmartinez@bigelow.org)

Anne Booker, Bigelow Laboratory for Ocean Sciences  (abooker@bigelow.org)

Cynthia Heil, Mote Marine Laboratory & Aquarium  (cheil@mote.org)

Sarah Klass, Mote Marine Laboratory & Aquarium  (sklass@mote.org)

Patrica Glibert, university of maryland  (glibert@umces.edu)

Sophia Ahn, university of maryland  (sahn@umces.edu)

Shady Amin, New York University Abu Dhabi   (samin@nyu.edu)