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.