Bacterial abundance and viability in long-range transported dust

Transports of bacteria in the atmosphere relate to climate and global hydrological cycles by acting as nuclei of ice-cloud formation, and affect the ecosystems and public health in the downwind ecosystems. Here we present quantitative investigations of airborne bacterial cells coupled with LIVE/DEAD BacLight assay in southwestern Japan to show that airborne bacteria were widespread with Asian dust. Total bacterial cell concentrations in dust varied between 1.0 × 106 and 1.6 × 107 cells m−3, which were one to two orders higher than those in non-dusty air and were correlated with the concentrations of aerosol particles larger than 1 μm. The ratio of viable bacterial cells to total bacterial cells (viability) of bacteria in dust ranged from 16 to 40%, which was quite smaller than the viability in non-dusty air. However viable bacterial cell concentrations in dust, 2.5 × 105 – 3.8 × 106 cells m−3, were similar to or higher than those in non-dusty air. Dust is thus a substantial source of airborne bacterial cells as well as mineral particles. These quantitative results suggest Asian dust is one of the processes for dispersal of airborne bacteria in the global atmosphere.