A Test for Airborne Dispersal of Thermophilic Bacteria from Hot Springs

Physical and chemical barriers separate individual terrestrial hot springs and their affiliated communities of thermophilic bacteria. However, 16S rRNA gene sequence comparisons suggest that seemingly identical or closely related bacterial species are found in multiple hot springs that are separated by distances that range from a few meters to thousands of kilometers. To investigate whether this dispersal could result from airborne transport of bacteria on water vapor, steam was collected from multiple sites at approximately 1 meter above the flowing hot water of Spring AT-1, which is part of Angel Terrace in the Mammoth Hot Springs complex of Yellowstone National Park. The trapped steam was analyzed for the presence of bacterial 16s rRNA gene sequences and these were directly compared with sequences identified in Spring AT-1 itself. Of the 31 different sequences identified in the steam: 1 sequence is 100% identical to a sequence previously identified in Spring AT-1; 2 sequences are similar to Spring AT-1 sequences; and 3 more sequences are affiliated with thermophilic bacteria not observed in Spring AT-1. These findings indicate that that thermophilic bacteria are present in the steam, and suggest that aerosolization of hot spring thermophiles is a necessary first step for airborne transport.