Biological Ice Nucleators in Snow Samples from Greece

Dimitrios G Georgakopoulos

doi:10.3390/atmos12111461

Abstract

The formation of precipitation in clouds is initiated by inorganic and organic/biological ice nuclei. Certain species of bacteria and fungi are known to act as efficient biological ice nuclei at temperatures between −10 and 0 °C. Biological ice nuclei have been found and characterized in precipitation samples (snow, rain, and hail). We investigated the presence of warm temperature biological ice nuclei in 17 fresh snow samples from Greece and isolated and partially characterized ice nucleation active bacteria from these. All snow samples contained particles or other material active as ice nuclei at −9 °C in concentrations ranging from 3 to 943 nuclei/L. The numbers of this class of ice nuclei were reduced or eliminated after incubating snowmelt concentrates at 100 °C for 15 min and by treatment with lysozyme, a bacterial cell wall-degrading enzyme. These findings indicate the presence of microbial ice nuclei in snow samples from Greece. We also isolated ice nucleation active bacteria from some of the samples. These bacteria belong to genus Pseudomonas and are common on plants and soil. This is the first report on biological ice nuclei in precipitation samples from Greece.

Highlights

Biological ice nucleation was first discovered in the 1970s, almost simultaneously but independently, by atmospheric scientists investigating soil and plants as sources for atmospheric ice nuclei found in hail, and by plant pathologists investigating factors that enhance frost damage on crops [1]
The effects of lysozyme and heat on the concentration of ice nuclei in snow samples provide a good indication of the microbial nature of these ice nuclei
We investigated the presence of biological ice nuclei in 17 fresh samples of snow collected 24 h after snowfall from two high-altitude locations in Mt

Summary

Introduction

Biological ice nucleation was first discovered in the 1970s, almost simultaneously but independently, by atmospheric scientists investigating soil and plants as sources for atmospheric ice nuclei found in hail, and by plant pathologists investigating factors that enhance frost damage on crops [1]. The first characterized biological ice nuclei were bacteria from the aerial plant surface of the plant pathogenic species Pseudomonas syringae. The discovery of bacterial ice nucleation led scientists to speculate about the potential involvement of ice nucleation active microorganisms in atmospheric processes. Sands and colleagues proposed a “bioprecipitation” cycle, where crops harboring large populations of ice nucleation active bacteria serve as sources of aerial bacterial ice nuclei involved in the formation of precipitation in clouds, which enhances plant growth and crops, enabling in turn the development of new epiphytic bacterial populations acting as ice nuclei in the atmosphere [11,12]. Moore et al [13] showed a clear correlation between climatic and landscape changes and the frequency of rainfall in areas of the United States, a possible effect of several different biological processes on climate

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