Spatial-temporal dynamics of marine microorganisms in Kuroshio-Oyashio Extension.

Kuroshio-Oyashio Extension (KOE) region is an ideal natural laboratory for investigating microbial community dynamics due to its frequent nutrient exchanges. However, comprehensive spatiotemporal investigations of microbial communities in this region remain limited. We conducted a systematic research examining microbial community variations across space and time through integrated physicochemical analysis and high-throughput sequencing of 54 surface water samples collected from 33 stations during three consecutive summer seasons (2021-2023). The results demonstrated an increasing trend in species richness from Cold Water Area (CWA) to Warm Water Area (WWA), while species diversity showed no significant spatiotemporal trends. The nMDS analysis indicated that the microbial communities in mixed area were more similar to those in WWA during 2022 and 2023. There were significant spatial and temporal differences in the structure and composition of microbial communities, with spatial differences being particularly pronounced. Proteobacteria (range: 61.64%-76.39%), Bacteroidota (range: 8.09%-10.74%), Cyanobacteria (range: 5.51%-19.05%), and Verrucomicrobiota (range: 0.95%-7.24%) were the dominant phylum. Spatially and temporally, dominant genera such as Vibrio, Alteromonas, Pseudoalteromonas, Prochlorococcus_MIT9313, Alcanivorax, and Synechococcus_CC9902 exhibited dynamic shifts in abundance. Spearman correlation analysis and Mantel tests indicated that temperature, salinity, density and conductivity were key environmental factors. Co-occurrence network analysis showed that microbial interactions were dominated by positive correlations. The complex interplay of geographic location, environmental parameters, microbial interactions, and ocean current patterns collectively governed the microbial distribution within KOE region. This research significantly enhances our understanding of the mechanisms underlying microbial community construction and maintenance in KOE region.