Succession of Particle-Attached and Free-Living Microbial Communities in Response to the Degradation of Algal Organic Matter in Lake Taihu, China

Decomposition of Cyanobacterial blooms frequently occurs in Lake Taihu, releasing various fractions of algal organic matter into the water through cell lysis. These fractions influence the production and consumption of dissolved organic matter, nutrient dynamics, and bacterial succession in the lake. However, the interactions between free-living and particle-attached bacterial communities with different algal organic matter fractions remain poorly understood. Herein, we investigated the effects of two distinct algal organic matter fractions, obtained through a fractionation procedure simulating cyanobacterial bloom collapse, on freshwater bacterial communities. The degradation of both fractions resulted in stage-specific changes in the chemical properties of lake water, which were divided into two distinct stages (labeled Stage I and Stage II). Flavobacteriaceae was dominant in Stage I, whereas Methylophilaceae dominated Stage II. Long-term ecological observations indicated that particle-attached bacteria responded more sensitively to different algal organic matter fractions than free-living bacteria. Compared to the degradation of algal-derived filtrate, the breakdown of algal residual exudative organic matter led to a more complex free-living bacterial community network. These findings provide new insights into the capacity of free-living and particle-attached bacterial communities to utilize different algal organic matter fractions and highlight their roles in aquatic ecosystems during the post-bloom stage.