Bacterial Buddies: A Tale of Two Lifestyles in the Jinsha River

In the rushing waters of the Jinsha River, two types of bacteria – free-living (FL) and particle-attached (PA) – play crucial roles in shaping the aquatic ecosystem. Despite their shared habitat, these bacteria have distinct ways of merging their communities, a process called coalescence. Scientists studied these bacteria at four hydropower stations along the river, focusing on tiny differences in their DNA, called 16S rRNA Amplicon Sequence Variants (ASVs). Surprisingly, the bacteria's communities didn't change much across different water layers – surface, middle, and bottom. But when it came to coalescence, the FL and PA bacteria had some stark differences. At the Xiangjiaba station, FL bacteria merged their communities more easily (31. 1% ± 2. 0%) compared to PA bacteria (27. 6% ± 2. 5%). This mixing in FL bacteria was mainly due to water layers blending together, while PA bacteria showed distinct geographical patterns and less merging.Using a special tool called the SourceTracker algorithm, researchers found that certain bacteria, called keystone species, were key to these coalescence patterns. There were 12 keystone species in PA bacteria and 7 in FL bacteria. Proteobacteria and Bacteroidetes were the most common groups among these species. Interestingly, the number of these key bacteria decreased with distance in PA bacteria, but increased in FL bacteria. Some bacteria, like Brevundimonas and Chryseobacterium, were important in both lifestyles. The study also showed that dam construction could affect these bacteria communities and their ability to merge. This is important because community coalescence can influence how stable these ecosystems are.