Bacterial composition and survival on Sahara dust particles transported to the European Alps. Sequencing bacteria associated with Sahara dust in snow on high alpine site

The Sahara Desert is the primary source of wind-blown biological and mineral particles (aerosols) on Earth, 10% of which arrive to Europe. Aerosols that are deposited on high alpine snowfields in freezing conditions are well preserved and facilitate downstream biological analyses. As little is known about the structure and viability of bacteria transported during Saharan dust events (SDEs), the goal of this study was to characterize SDE-associated bacteria in snow using an interdisciplinary approach. We collected samples from a snow profile at the Jungfraujoch (Swiss Alps; 3621 m asl), where the presence of distinct ochre Sahara dust layers (SD-layers) could be ascribed to two SDEs reported in February and May 2014. Backward trajectories, physicochemical analyses of the snow, and dust particle concentrations of distinct geochemical compositions permitted us to determine the origin of the SDEs. Bacterial community structures were assessed using high throughput sequencing; distinct differences in bacterial community structures and metabolic activity associated with SD-layers as compared to clean snow layers were observed. Most striking was the exclusive presence in the SD-layers of bacteria that are adapted to hostile environments, and are hence well suited to survive the harsh conditions of long-distance airborne transport.