High-resolution ice nucleation spectra of sea-ice bacteria: Implications for cloud formation and life in frozen environments

Biogeosciences (Impact Factor: 3.98). 11/2007; 5(3). DOI: 10.5194/bgd-4-4261-2007
Source: OAI


Even though studies of Arctic ice forming particles suggest that a bacterial or viral source derived from open leads could be important for cloud formation in the Arctic (Bigg and Leck, 2001), the ice nucleation potential of most polar marine psychrophiles or viruses has not been examined under conditions more closely resembling those in the atmosphere. In this paper, we examined the ice nucleation activity (INA) of several representative Arctic and Antarctic sea-ice bacterial isolates and a polar Colwellia phage virus. High-resolution ice nucleation spectra were obtained for droplets containing bacterial cells or virus particles using a free-fall freezing tube technique. The fraction of frozen droplets at a particular droplet temperature was determined by measuring the depolarized light scattering intensity from solution droplets in free-fall. Our experiments revealed that all sea-ice isolates and the virus nucleated ice at temperatures very close to the homogeneous nucleation temperature for the nucleation medium ? which for artificial seawater was ?42.2±0.3°C. Our results indicated that these marine psychro-active bacteria and viruses are not important for heterogeneous ice nucleation processes in sea ice or polar clouds. These results also suggested that avoidance of ice formation in close proximity to cell surfaces might be one of the cold-adaptation and survival strategies for sea-ice bacteria. The fact that INA occurs at such low temperature could constitute one factor that explains the persistence of metabolic activities at temperatures far below the freezing point of seawater.

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    • "A través de cientos de millones de años de emisiones volcánicas, se arrojaron elementos volátiles los cuales quedaron retenidos gracias a la gravedad del planeta, y originaron la primera atmósfera primitiva compuesta por dióxido de carbono (CO 2 ), nitrógeno y vapor de agua como elementos mayoritarios, y monóxido de carbono y gases de azufre como componentes minoritarios; además de una pequeña proporción de ácido clorhídrico e hidrógeno (Pérez, 2006); sin embargo, aún se discute si el proceso de nucleación requerido para la formación de nubes es semejante al actual, en el cual las cenizas funcionan como núcleos higroscópicos, entre otras cinco nucleaciones que son arena, polvo, cenizas volcánicas, polen, bacterias y virus, entre otros (Schaefer y Day, 1981; Junge y Swanson, 2008). De igual forma, la baja masa del hidrógeno facilitó su evasión hacia el espacio y, paralelamente, el bombardeo de los cometas aportó amoniaco, metano y agua, los cuales se incorporaron gradualmente a la atmósfera. "

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    • "This nucleation surface is usually composed of ice splinters, clay particles, or other water-insoluble substances (Kuhn, 2001). Indeed, cloud condensation and ice nucleation within the atmosphere can also be catalyzed by biological agents, such as bacteria or fungal spores (see Jayaweera and Flanagan, 1982; Morris et al., 2007; Christner et al., 2008; Delort et al., 2010), even though the significance of these processes might be of minor importance when other nuclei are abundant (Junge and Swanson, 2008; Diehl and Wurzler, 2010; Hoose et al., 2010). After deposition from the atmosphere (via dry and wet deposition), snowpack microbial communities may start thriving when the conditions become favorable (Christner, 2002; Segawa et al., 2005; Bakermans and Skidmore, 2011). "
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