In　aquatic　ecosystems,　water　microbial　communities　can　trigger　the　outbreak　or　decline　of　cyanobacterial　blooms.　However,　the　microbiological　drivers　of　Microcystis　decomposition　in　reservoirs　remain　unclear.　Here,　we　explored　the　bacterial　community　metabolic　profile　and　co-occurrence　dynamics　during　Microcystis　decomposition.　The　results　showed　that　the　decomposition　of　Microcystis　greatly　altered　the　metabolic　characteristics　and　composition　of　the　water　bacterial　community.　Significant　variations　in　bacterial　community　composition　were　observed:　the　bacterial　community　was　mainly　dominated　by　Proteobacteria,　Actinobacteria,　Planctomycetes,　and　Bacteroidetes　during　Microcystis　decomposition.　Additionally,　members　of　Exiguobacterium,　Rhodobacter,　and　Stenotrophomonas　significantly　increased　during　the　terminal　stages.　Dissolved　organic　matters　(DOM)　primarily　composed　of　fulvic-like,　humic　acid-like,　and　tryptophan-like　components,　which　varied　distinctly　during　Microcystis　decomposition.　Additionally,　the　metabolic　activity　of　the　bacterial　community　showed　a　continuous　decrease　during　Microcystis　decomposition.　Functional　prediction　showed　a　sharp　increase　in　the　cell　communication　and　sensory　systems　of　the　bacterial　communities　from　day　12　to　day　22.　Co-occurrence　networks　showed　that　bacteria　responded　significantly　to　variations　in　the　dynamics　of　Microcystis　decomposition　through　close　interactions　between　each　other.　Redundancy　analysis　(RDA)　indicated　that　Chlorophyll　a,　nitrate　nitrogen　(NO3−-N),　dissolved　oxygen　(DO),　and　dissolved　organic　carbon　(DOC)　were　crucial　drivers　for　shaping　the　bacterial　community　structure.　Taken　together,　these　findings　highlight　the　dynamics　of　the　water　bacterial　community　during　Microcystis　decomposition　from　the　perspective　of　metabolism　and　community　composition,　however,　further　studies　are　needed　to　understand　the　algal　degradation　process　associated　with　bacteria.　©　2020