Aeromicrobiology

The atmosphere presents one of the most challenging environments on Earth with extreme psychrophilic and oligotrophic conditions. Cloud temperatures are typically below 0 °C, and stratospheric temperatures have been measured as low as -100 °C, colder than any other environment in the biosphere. Despite these challenges, the diversity of microbial life in the atmosphere has been found to be high, with over 100 bacterial genera recorded. Viable bacteria have been found in the stratosphere at altitudes of 77 km and bacteria collected from cloud water have been shown to be capable of both growth and reproduction at 0 °C suggesting the existence of psychrophilic bioaerosols. The role that microorganisms perform in processes such as ice nucleation, cloud formation, nitrogen processing, and the degradation of organic carbon-based compounds is becoming progressively clearer. However, the lack of a consensus on the most suitable bioaerosol sampling techniques makes progress challenging. Hence, although aerobiological studies date back as far as the mid nineteenth century, our understanding of microbial life in the atmosphere is still relatively limited. As the importance of understanding microbial biogeography continues to grow, particularly with regard to biogeography, long- range atmospheric dispersal, human health, and agriculture, more research is required to better understand the functional role of psychrophiles in the atmosphere.