Abstract
It has been known for several decades that some bioaerosols, such as ice-nucleation-active (INA) bacteria, especially Pseudomonas syringae strains, may play a critical potential role in the formation of clouds and precipitation. We investigated bacterial and fungal ice nuclei (IN) in rainwater samples collected from the Hulunber temperate grasslands in North China. The median freezing temperatures (T50) for three years’ worth of unprocessed rain samples were greater than −10 °C based on immersion freezing testing. The heat and filtration treatments inactivated 7–54% and 2–89%, respectively, of the IN activity at temperatures warmer than −10 °C. We also determined the composition of the microbial community. The majority of observed Pseudomonas strains were distantly related to the verified ice-nucleating Pseudomonas strains, as revealed by phylogenetic analysis. Here, we show that there are submicron INA particles <220 nm in rainwater that are not identifiable as the known species of high-INA bacteria and fungi and there may be a new potential type of efficient submicroscale or nanoscale ice nucleator in the regional rainwater samplers. Our results suggest the need for a reinterpretation of the source of high-INA material in the formation of precipitation and contribute to the search for new methods of weather modification.
Highlights
It has been known for several decades that some bioaerosols, such as ice-nucleation-active (INA) bacteria, especially Pseudomonas syringae strains, may play a critical potential role in the formation of clouds and precipitation
Several works have attempted to investigate the quantities of INA genes[20], submicroscale INA bacterial fragments[16] and even nanoscale biological IN21–23 to demonstrate that biological ice nuclei (IN), especially the best-known efficient IN species from the genera Pseudomonas, Erwinia, Xanthomonas and Fusarium, are widespread in the atmosphere
In order to verify and interpret above noted phenomenon, rain samples collected from May to August in 2013 were further tested for nucleation abilities
Summary
It has been known for several decades that some bioaerosols, such as ice-nucleation-active (INA) bacteria, especially Pseudomonas syringae strains, may play a critical potential role in the formation of clouds and precipitation. Several works have elucidated the mechanism through which molecular biology influences the ability of known biological IN to initiate freezing at warmer temperatures in the laboratory[9,10,11] and isolated ice-nucleation-active (INA) bacteria from many different environments[12,13,14,15,16]. We applied immersion freezing tests to predict whether biological efficient IN are omnipresent in rainwater samples based on a comparison of the initial and median freezing temperature of droplets exposed to filtration and heat treatments. The microbial communities and phylogenetic relationship were determined using 16S RNA and 18S rRNA gene analysis to elucidate whether there are known ice-nucleating bacteria and fungi present in the samples collected from the Hulunber temperate grasslands in north China
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