Suspended particulates mediate bacterial community coalescence in different habitats of a large sediment-laden river.

• A total of 267 water and sediment samples were taken from 45 sampling sites along the Yellow River in the spring and autumn. • The spatial patterns of bacterial community were explored with different habitats in the Yellow River. • Species sorting and dispersal limitation were key factors for water and sediment bacterial communities, respectively. • For community coalescence, the same and similar habitats had higher proportions of overlapped species. • Bacteria attached to suspended particles may facilitate community coalescence in a large sediment-laden river. Many studies have reported the influence of dispersal processes on aquatic bacterial communities, but the role of community coalescence is still unknown in sediment-laden rivers. Here, we examined the assembly of distinctive bacterial communities (free-living [FL], particle-attached [PA], and surface-sediment [SS]) with differing habitat preferences across different regions of the Yellow River (China) in the spring and autumn of 2019. We demonstrated that in both seasons SS bacteria featured the highest diversity, followed by PA bacteria, and then FL bacteria. Nonetheless, both FL and PA groups showed remarkable seasonal variation in water samples, while the SS group in sediment samples showed significant spatial variation. Furthermore, species sorting and dispersal limitation respectively governed the biogeographic patterns (strong distance–decay relationships) of water and sediment bacterial communities. With respect to community coalescence, not only the same habitats (i.e., water–water, particle–particle, and sediment–sediment) but also similar habitats (i.e., water–particle) had higher proportions of overlapped amplicon sequence variants (ASVs) compared with different habitats (i.e., water–sediment and particle–sediment). Moreover, the proportions of overlapped ASVs between PA and SS groups were higher than those between FL and SS groups. Network analysis revealed that the SS group harbored the highest network complexity, followed by PA and FL groups. Most connectors in the networks were identified as FL–PA–SS ASVs irrespective of the river reaches sampled. These findings demonstrate the biogeographic patterns of distinctive bacterial communities driven by species sorting and dispersal limitation, and provide evidence for bacterial community coalescence in the Yellow River's water and sediment. Bacteria attached to suspended particles may play a paramount role in the microbial ecology of different habitats in large sediment-laden rivers. [ABSTRACT FROM AUTHOR]