The large-scale spatial distribution of bacteria across boreal networks differentiates the adaptive core versus accidental components of lake bacterioplankton. Adaptative core vs accidental components of lake bacterioplankton

Aquatic bacterial communities are composed of thousands of coexisting taxa, and a major challenge in microbial ecology has been to discriminate the core active from the passive, accidental component. We explored the abundance distributions of individual bacterioplankton taxa across 198 northern lakes, and we identified four distinct categories of spatial behaviour amongst lake bacteria using model distributions (normal-like, bimodal, logistic, lognormal). Their dynamics across lakes and along the associated riverine network showed that lake communities are composed of a core of ubiquitous abundant taxa whose spatial distribution is linked to active recruitment and in-lake environmental filtering (normal-like and bimodal categories), and a large fraction of rare bacteria (94% total OTUs) whose presence seems largely accidental and linked to hydrologically-mediated transport (logistic and lognormal categories). Whereas the adaptive core component likely drives community function, this vast rare component represents the spatial history of lake bacterioplankton assemblages within these complex aquatic networks.