Fungi as a Critical Component of Lake Microbiota in Response to Cyanobacterial Harmful Algal Blooms

Cyanobacterial Harmful Algal Blooms (CyanoHABs) pose a growing threat to lake ecosystems. While microbial communities constitute the resilient power of lake ecosystems to CyanoHAB disturbances, the role of fungi remains underexplored. Here, the dynamics of size-fractionated fungal and associated bacterial communities were tracked across the peak and decline stages of a CyanoHAB event in shallow subtropical Lake Taihu. The results revealed that the composition of fungal and bacterial communities in separated size fractions varied between bloom stages, with enrichment patterns likely influenced by their reliance on algal-derived nutrients. Null model-based analysis revealed a shift in fungal community assembly, from dominance by dispersal limitation (44%) and drift (30%) at the peak stage to increased homogeneous selection (44%) at the early decline stage, whereas bacterial communities remained predominantly shaped by stochastic processes, highlighting their distinct responses to cyanobacterial biomass decomposition. Comparative topological analysis of microbial co-occurrence networks showed strengthened cross-kingdom fungi-bacteria interactions as the bloom declined, especially within decomposing cyanobacterial colonies, facilitating nutrient cycling and accelerating cyanobacterial biomass removal. These findings led to a conceptual model proposing fungi as critical members of the freshwater microbiome in eutrophic lakes, driving biogeochemical cycling and potentially contributing to the resilience of the lake ecosystem against CyanoHABs.