Metagenomic insights into the impacts of Vulcanococcus proliferation on microbial communities in a coastal bay

Cyanobacterial blooms pose a major ecological challenge globally, with their outbreaks exerting profound effects on aquatic ecosystems. Vulcanococcus, a recently described cyanobacterial genus previously thought to be restricted to freshwater habitats, was documented in this study proliferation in seawater for the first time. Here, we reconstructed prokaryotic metagenome-assembled genomes (MAGs), including Vulcanococcus and the associated bacteria, enabling the assessment of their metabolic potential and influence of proliferation of Vulcanococcus on marine ecosystems. The proliferation of Vulcanococcus significantly altered the prokaryotic community compositions in the water, leading to a marked decline in the stability of prokaryotic co-occurrence networks. Comparative genomic analysis revealed that Vulcanococcus MAGs clustered within the freshwater Vulcanococcus clade, suggesting a possible freshwater origin. The high-quality Vulcanococcus MAG possess a complete set of urea transporter genes as well as urease genes, highlighting its potential for efficient urea utilization. The genome of Vulcanococcus encodes critical genes involved in vitamin B₁ biosynthesis and is capable for de novo vitamin B₁₂ synthesis, implying that proliferation of Vulcanococcus may serve as an important source of B vitamins for phytoplankton. Furthermore, Vulcanococcus exhibited significant correlations with eukaryotic phytoplankton, including diatoms and dinoflagellates, suggesting that Vulcanococcus may enhance B-vitamin availability for phytoplankton. Overall, these findings provide novel insights into the ecological roles and metabolic versatility of Vulcanococcus in marine environments, underscoring its potential impact on microbial community dynamics and nutrient cycling.