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

01/2007; DOI: 10.5194/bgd-4-4261-2007
Source: OAI

ABSTRACT 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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    ABSTRACT: Ice nuclei impact clouds, but their sources and distribution in the atmosphere are still not well known. Par-ticularly little attention has been paid to IN sources in ma-rine environments, although evidence from field studies sug-gests that IN populations in remote marine regions may be dominated by primary biogenic particles associated with sea spray. In this exploratory model study, we aim to bring at-tention to this long-neglected topic and identify promising target regions for future field campaigns. We assess the likely global distribution of marine biogenic ice nuclei using a com-bination of historical observations, satellite data and model output. By comparing simulated marine biogenic immersion IN distributions and dust immersion IN distributions, we pre-dict strong regional differences in the importance of marine biogenic IN relative to dust IN. Our analysis suggests that marine biogenic IN are most likely to play a dominant role in determining IN concentrations in near-surface-air over the Southern Ocean, so future field campaigns aimed at investi-gating marine biogenic IN should target that region. Climate-related changes in the abundance and emission of biogenic marine IN could affect marine cloud properties, thereby in-troducing previously unconsidered feedbacks that influence the hydrological cycle and the Earth's energy balance. Fur-thermore, marine biogenic IN may be an important aspect to consider in proposals for marine cloud brightening by artifi-cial sea spray production.
    Atmospheric Chemistry and Physics 01/2013; 13:245-267. · 4.88 Impact Factor
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    ABSTRACT: Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions.
    Scientifica. 01/2014; 2014:976895.
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