Biological Characterisation of Hailstones from Two Storms in South Brazil

Although studies focusing on the physicochemical properties of aerosols/clouds have not been performed extensively, even less attention has been given to hailstones and their biological composition. Here, we present the results of the physical and microbiological characterisation of 20 hailstones collected in Southern Brazil originating from two storms. Nearly half of the hailstones (9 out of 20, or 45%) did not contain any cultivable bacteria or fungi. A total of 18 bacterial species were found in hailstones from both storms, and the genus Bacillus was found in 5 out of the 11 hailstones, with Bacillus cereus being the most frequent bacterial species. Fungi, on the other hand, were only present in four hailstones derived from a single storm, with three fungal species identified and Epicoccum nigrum being the most frequent fungal species. HYSPLIT modelling indicated the different flow of air masses from the Amazon and Pacific Ocean that contributed to the loading of microorganisms found in the clouds at the time of the two storms. Our findings suggest that ca. 50% of hailstones have cultivable bacterial or fungal species, which came mainly from the local landscape with intrusions of air masses derived from the Amazon and the Pacific Ocean.