Dataset on bacterial community responses to light limitation in freshwater mesocosms of the Nakdonggang River.

This dataset describes bacterial community responses under light-limited conditions in freshwater mesocosms established in the Nakdonggang River, Republic of Korea. The Nakdonggang River frequently experiences cyanobacterial blooms during summer, making it a suitable system for examining microbial responses to altered light conditions. The dataset includes 30 samples collected from control and light-limited treatment mesocosms at five time points, with three biological replicates per condition at each time point. The V3-V4 region of the bacterial 16S rRNA gene was sequenced using the Illumina MiSeq platform. Sequence reads were processed using DADA2 to generate amplicon sequence variants (ASVs), followed by taxonomic assignment using the SILVA database. Raw sequence data and associated metadata are available in NCBI under BioProject accession number PRJNA1477286. After quality filtering, denoising, and chimera removal, a total of 4729 bacterial ASVs were identified across the mesocosm samples. Over the approximately 2-month mesocosm experiment, bacterial community composition differed clearly between the control and light-limited treatments. Cyanobacteria exhibited substantially lower relative abundance under light-limited conditions, showing a 15.5-fold lower relative abundance in the treatment than in the control at the end of the experiment. Since the Nakdonggang River frequently experiences seasonal cyanobacterial blooms, this dataset provides useful insights into both cyanobacterial responses and broader shifts in heterotrophic bacterial groups under light-limited conditions in freshwater environments.