Unlike other bioaerosols, bacteria are able to complete full reproductive cycles within the days or weeks that they survive in the atmosphere, making them a major component of the air biota ecosystem. These reproductive cycles support a currently unproven theory that bacteria bioaerosols form communities in an atmospheric ecosystem. The survival of bacteria depends on water droplets from fog and clouds that provide bacteria with nutrients and protection from UV light. The four known bacterial groupings that are abundant in aeromicrobial environments around the world include Bacillota, Actinomycetota, Pseudomonadota, and Bacteroidota.