Clouds provide atmospheric oases for microbes

摘要

Although low in number compared to the 10 ~(29) microbes estimated in oceans, the 10 ~(19) microbial cells in clouds are sufficiently plentiful to affect the atmosphere. Bacteria in clouds actively metabolize nutrients-for example, about 1 million tons of organic carbon per year-but only about 1% of such cells can be cultured. Even though clouds play an important role dispersing microbes over long distances, they apparently do not serve as long-term microbial reservoirs. In theory, a single ice-nucleating bacterium within a cloud can induce precipitation and thus cause its own deposition. Little is known about rates of emission of bacteria from surfaces into the atmosphere, and such data are not easy to generate.