Microbes have a remarkable ability to adapt to a host of environmental stressors, including low temperature, high pressure and osmotic stresses. The adaptations of resistant microbes to low temperatures are varied, and may include the accumulation of solutes to maintain osmotic balance, the production of antifreeze proteins (AFPs) or ice nucleation proteins (INPs) to manipulate ice growth or formation. AFPs depress the freezing point, inhibit ice recrystallization, and have been reported to inhibit or delay the growth of gas hydrates. Conversely, INPs precipitate ice formation at relatively high subzero temperatures. Collectively, these activities can be described as ‘ice-association’ activities. Here, ice-affinity and/or freeze-thaw cycling were used to either select for isolates with ice association properties or to assess the low temperature resistance of microbial consortia derived from various environments. Ice-affinity successfully selected psychrotolerant microbes from cultured temperate and boreal soils, some of which had been previously reported in glaciers and Arctic/Antarctic sites. Many of the recovered microbes demonstrated ice-association activities. Freeze-thaw selection also greatly decreased the abundance and diversity of consortia from distinct sites, and allowed the recovery of individual isolates, many of which demonstrated ice-association. Freeze-thaw selection was also used to assess the role of cross-tolerance between osmotic and freeze-thaw stresses, based on the common challenge of desiccation. Microbial consortia from lakes with varying degrees of salinity were subjected to freeze-thaw stress, and the consortia from more saline lakes tended to show greater low temperature resistance. While few of the recovered microbes demonstrated ice-association activities, those from the more saline lakes tended to contain a higher intracellular solute concentration and were more likely to form biofilms. This underscores the diversity of resistance strategies and supports the notion of cross-tolerance. To determine if these selective regimes would have applications for hydrate growth inhibition, microbes derived from an oil well sample were subjected to freeze-thaw stress. Selection reduced microbial abundance, shifted the diversity, and resulted in the recovery of microbes with some ice-association activity. Taken together, this thesis demonstrates that the application of low temperature stress can be used to successfully investigate stress resistance mechanisms within microbial communities from distinct environments. / Thesis (Ph.D, Biology) -- Queen's University, 2010-09-21 15:58:14.932

Ice crystals in clouds frequently form upon a subset of aerosol particles called ice nuclei (IN). IN influence cloud ice crystal concentrations, consequently affecting cloud lifetime and reflectivity. The present understanding of these effects on climate is hindered by limited data on the global distribution of IN. This thesis presents measurements of deposition-mode IN concentrations under conditions relevant to mid-level clouds, 238 K and 138% RHi. at two Canadian sites: Toronto, a major city, and Whistler, a pristine coniferous rainforest. In Toronto, chemically-resolved surface areas were estimated by single-particle mass spectrometry and regressed against IN concentrations to identify a significant relationship between IN concentrations and both carbonaceous aerosols (EC and/or OC) and dust. In Whistler, IN concentrations during a biogenic secondary organic aerosol (SOA) event did not increase from background levels (0.1 /L), suggesting that biogenic SOA particles do not nucleate ice under these conditions.

The indirect aerosol effect contributes to major uncertainties in determining the radiation budget of the earth. A large uncertainty is due to the formation of ice clouds onto natural or anthropogenic aerosols. Field studies have shown that mineral type particles are often associated with ice crystals in the mid-upper troposphere and given the long residence time in the atmosphere of dust particles (~2 weeks in the absence of precipitation), their contribution to ice formation processes is not fully defined. In order to probe ice formation onto natural mineral dust in a setting where it could be suspended as aerosol, a new continuous flow diffusion chamber (CFDC) was built. This allowed investigations of the effects of total aerosol surface area and particle size. The CFDC was also used in an international inter-comparison of ice nucleation instrumentation to compare efficiencies of soot, biological aerosol (bacteria) and samples of natural desert dusts from different regions of the world. The laboratory observations were parameterized using nucleation rates (Jhet) and contact angles () as described by classical nucleation theory. For both this experimental technique and a static one developed during the candidate’s Masters degree, mineral dust particulate proved to be the most efficient ice nuclei (IN) activating at RH with respect to ice (RHi) as low as 105% at T = 233 K. The efficiency varied with particle size and aerosol surface area (SA). Large particles or higher SA activated at lower RHi than small particles or lower SA. The static chamber was sensitive to the first ice event out of a large SA and therefore gave true onset RHi, which was lower than the onset defined by the CFDC studies, which was not sensitive to a single ice event. In addition the static chamber used a broader size range of particulate matter, including super micron particles while the CFDC particles sizes were restricted to below 0.5 µm. Soot and organic coated dust particles were inefficient IN compared to pure dust. Soot aerosols showed some efficiency at T < 233K where deposition ice formation was apparent. The hygroscopic organics had intermediate ice activity between dusts and alkyl-organics and soot. Bacteria aerosols were active in the deposition mode for T as high as 247 K. Contact angles () computed for ice germs forming onto natural mineral dust were small, 7<  < 29, at 223 K for RH ranging from ice to water saturation. It was concluded that there is no single value for the onset of ice formation in the atmosphere via deposition freezing. The associated contact angles show that there is a distribution of active sites on IN and that not all active sites have the same affinity for initiation of ice formation even within the same aerosol type. This work provides evidence that deposition mode nucleation can be an alternate pathway to homogeneous nucleation when mineral aerosols are present in the troposphere since the high T - low RH conditions required for deposition mode nucleation are more easily encountered in the atmosphere than the low T - high RH required for homogeneous nucleation.

Ice crystals in clouds frequently form upon a subset of aerosol particles called ice nuclei (IN). IN influence cloud ice crystal concentrations, consequently affecting cloud lifetime and reflectivity. The present understanding of these effects on climate is hindered by limited data on the global distribution of IN. This thesis presents measurements of deposition-mode IN concentrations under conditions relevant to mid-level clouds, 238 K and 138% RHi. at two Canadian sites: Toronto, a major city, and Whistler, a pristine coniferous rainforest. In Toronto, chemically-resolved surface areas were estimated by single-particle mass spectrometry and regressed against IN concentrations to identify a significant relationship between IN concentrations and both carbonaceous aerosols (EC and/or OC) and dust. In Whistler, IN concentrations during a biogenic secondary organic aerosol (SOA) event did not increase from background levels (0.1 /L), suggesting that biogenic SOA particles do not nucleate ice under these conditions.

Arctic clouds are poorly represented in numerical models due to the complex, small-scale interactions which occur within them. Modelled cloud fractions are often significantly less than observed in this region; therefore, the radiative budget is not accurately simulated and forecasts of the melting cryosphere are fraught with uncertainty. Our ability to accurately model Arctic clouds can be improved through observational studies. Recent in situ airborne measurements from the springtime Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign are presented in this thesis to improve our understanding of the cloud microphysical interactions unique to this region. Aerosol-cloud interactions - where aerosol particles act as ice nucleating particles (INPs) or cloud condensation nuclei (CCN) - are integral to the understanding of clouds on a global scale. In the Arctic, uncertainties caused by our poor understanding of these interactions are enhanced by strong feedbacks between clouds, the boundary layer, and the sea ice. In the Arctic spring, aerosol-cloud interactions are affected by the Arctic haze, where a stable boundary layer allows aerosol particles to remain in the atmosphere for long periods of time. This leads to a heightened state of mixing in the aerosol population, which affects the ability of particles to act as INPs or CCN. Aerosol particle compositional data are presented to indicate which particles are present during the ACCACIA campaign, and infer how they may participate in aerosol-cloud interactions. Mineral dusts (known INPs) are identified in all flights considered, and the dominating particle classes in each case vary with changing air mass history. Mixed particles, and an enhanced aerosol loading, are identified in the final case. Evidence is presented which suggests these characteristics may be attributed to biomass burning activities in Siberia and Scandinavia. Additionally, in situ airborne observations are presented to investigate the relationship between the Arctic atmosphere and the mixed-phase clouds - containing both liquid cloud droplets and ice crystals - common to this region. Cloud microphysical structure responds strongly to changing surface conditions, as strong heat and moisture fluxes from the comparatively-warm ocean promote more turbulent motion in the boundary layer than the minimal heat fluxes from the frozen sea ice. Observations over the transition from sea ice to ocean show that the cloud liquid water content increases four-fold, whilst ice crystal number concentrations, N_ice, remain consistent at ~0.5/L. Following from this study, large eddy simulations are used to illustrate the sensitivity of cloud structure, evolution, and lifetime to N_ice. To accurately model mixed-phase conditions over sea ice, marginal ice, and ocean, ice nucleation must occur under water-saturated conditions. Ocean-based clouds are found to be particularly sensitive to N_ice, as small decreases in N_ice allow glaciating clouds to be sustained, with mixed-phase conditions, for longer. Modelled N_ice also influences precipitation development over the ocean, with either snow or rain depleting the liquid phase of the simulated cloud.

No description available.

Aquatic environments contain a great diversity of microorganisms, some of which may be aerosolized and transported long distances through the atmosphere. The bacterium Pseudomonas syringae can be found in aquatic environments and in the atmosphere and may express an ice nucleation protein (bacteria expressing the protein are Ice+ and bacteria not expressing the protein are Ice-). Ice+ bacteria may be involved in cloud formation and precipitation processes due to their ability to freeze water at warmer temperatures. Freshwater aerosolization processes are not well understood, particularly the role the Ice+ phenotype may play. Water samples were collected from Claytor Lake, Virginia, USA and screened for Ice+ P. syringae. Results indicated that between 6% and 15% of Pseudomonas colonies assayed were Ice+. Preliminary phylogenetic analysis of cts (citrate synthase) sequences from strains of P. syringae showed a surprising diversity of phylogenetic subgroups present in the lake. A Collison nebulizer was used to aerosolize an Ice+ and an Ice- strain of P. syringae under artificial laboratory conditions. The aerosolization of P. syringae was not influenced by water temperature between 5° and 30°C. In general, the culturability (viability) of P. syringae in aerosols increased with temperature between 5 and 30°C. The Ice+ strain was aerosolized in greater numbers than the Ice- strain at all temperatures studied, suggesting a possible connection between the Ice+ phenotype and aerosol production. A quantitative empirical assessment of aerosolized droplets was generated using a laboratory flume and high-speed video. Droplet diameter and initial velocity upon leaving the water surface were examined at four wind speeds (3.5, 4.0, 4.5, and 5.0 m/s), and the results showed that droplet diameter and velocity had a gamma distribution and droplet mass flux increased exponentially with wind speed. An estimate of the potential amount of bacteria capable of aerosolizing was made for each wind speed. An interdisciplinary unit for advanced high school students has been developed presenting biological aerosolization and ice nucleation. This interdisciplinary work combines modeling and experimental approaches across biology and engineering interfaces, with the goal of increasing our understanding of microbial aerosols from aquatic environments that may impact our planet's water cycle. / Ph. D.

In the atmosphere, cloud droplets can remain in a supercooled liquid phase at temperatures as low as -40 °C. Above this temperature, cloud droplets freeze via heterogeneous ice nucleation whereby a rare and poorly understood subset of atmospheric particles catalyze the ice phase transition. As the phase state of clouds is critical in determining their radiative properties and lifetime, deficiencies in our understanding of heterogeneous ice nucleation poses a large uncertainty on our efforts to predict human induced global climate change. Experimental challenges in properly simulating particle-induced freezing processes under atmospherically relevant conditions have largely contributed to the absence of a well-established model and parameterizations that accurately predict heterogeneous ice nucleation. Conversely, the sparsity of reliable measurement techniques available struggle to be interpreted by a single consistent theoretical or empirical framework, which results in layers of uncertainty when attempting to extrapolate useful information regarding ice nucleation for use in atmospheric cloud models. In this dissertation a new framework for describing heterogeneous ice nucleation is developed. Starting from classical nucleation theory, the surface of an ice nucleating particle is treated as a continuum of heterogeneous ice nucleating activity and a particle specific distribution of this activity g is derived. It is hypothesized that an individual particle species exhibits a critical surface area. Above this critical area the ice nucleating activity of a particle species can be described by one g distribution, 𝑔, while below it 𝑔 expresses itself expresses externally resulting in particle to particle variability in ice nucleating activity. The framework is supported by cold plate droplet freezing measurements for dust and biological particles in which the total surface area of particle material available is varied. Freezing spectra above a certain surface area are shown to be successfully fitted with 𝑔 while a process of random sampling from 𝑔 can predict the freezing behavior below the identified critical surface area threshold. The framework is then extended to account for droplets composed of multiple particle species and successfully applied to predict the freezing spectra of a mixed proxy for an atmospheric dust-biological particle system. The contact freezing mode of ice nucleation, whereby a particle induces freezing upon collision with a droplet, is thought to be more efficient than particle initiated immersion freezing from within the droplet bulk. However, it has been a decades’ long challenge to accurately measure this ice nucleation mode, since it necessitates reliably measuring the rate at which particles hit a droplet surface combined with direct determination of freezing onset. In an effort to remedy this longstanding deficiency a temperature controlled chilled aerosol optical tweezers capable of stably isolating water droplets in air at subzero temperatures has been designed and implemented. The new temperature controlled system retains the powerful capabilities of traditional aerosol optical tweezers: retrieval of a cavity enhanced Raman spectrum which could be used to accurately determine the size and refractive index of a trapped droplet. With these capabilities, it is estimated that the design can achieve ice supersaturation conditions at the droplet surface. It was also found that a KCl aqueous droplet simultaneously cooling and evaporating exhibited a significantly higher measured refractive index at its surface than when it was held at a steady state temperature. This implies the potential of a “salting out” process. Sensitivity of the cavity enhanced Raman spectrum as well as the visual image of a trapped droplet to dust particle collisions is shown, an important step in measuring collision frequencies of dust particles with a trapped droplet. These results may pave the way for future experiments of the exceptionally poorly understood contact freezing mode of ice nucleation.

Title: Molecular simulations of ice nucleation Author: Eva Pluhařová Department: Department of Physical and Macromolecular Chemistry Faculty of Science UK Advisor: doc. Mgr. Pavel Jungwirth, DSc., IOCB AS CR, v.v.i. Advisor's e-mail address: pavel.jungwirth@uochb.cas.cz Abstract: By means of molecular dynamics simulations we have systematically investigated homogeneous ice nucleation in neat and surface contaminated water. As models of the adsorbates we have assumed pentanol and pentanoic acid. In neat water nucleation preferentially starts in the subsurface region, which accommodates better than the bulk the volume increase associated with freezing. Homogeneous ice nucleation is affected more by alcohol than by acid. Water slabs covered by a disordered layer of pentanol exhibit negligible preference for subsurface nucleation and longer nucleation times in comparison with neat water, while nucleation times are almost unaffected by the presence of pentanoic acid and the subsurface preference is only slightly decreased. We tried to rationalize the differences between the effects of different compounds by their ability to orient water molecules and to change their mobility. The fact that adsorbates differ in the influence on homogeneous ice nucleation has important implications for the microphysics of...

Pseudomonas syringae produz núcleos de gelo biológicos de grande eficiência. Bioaerossóis destas células tem potencial de participar na glaciação de nuvens, podendo influenciar a precipitação. Foram estudadas como as condições as quais P. syringae está sujeita em suspensão na atmosfera afetam sua sobrevivência e sua atividade de nucleação de gelo. Duas cepas foram testadas, e ambas apresentaram baixa tolerância ao UV-C e ao UV-B, mas exibiram uma maior resistência quando expostas a um espectro semelhante ao encontrado no ambiente. A atividade de congelamento de uma das cepas (pv. syringae) não foi afetada pelo UV, enquanto que para a outra (pv. garcae) houve uma redução moderada. Em resposta à dessecação, pv. garcae foi substancialmente mais resistente que pv. syringae. Isto também afetou a nucleação de gelo das cepas. Em ensaios adicionais, estas bactérias foram expostas em um voo de balão estratosférico, e a uma simulação em laboratório das condições no topo da troposfera. Nestes dois experimentos, sobreviventes protegidos do UV foram recuperados. / Pseudomonas syringae produces biological ice nuclei of great efficiency. Bioaerosols of these cells have the potential to take part in cloud glaciation, possibly influencing the precipitation. It was studied how the conditions to which P. syringae is subjected while in suspension in the atmosphere affect its survival and its ice nucleation activity. Two strains were tested, and both showed a low tolerance to UV-C and UV-B, but exhibited a higher resistance when exposed to a spectrum similar to the one found in the environment. The freezing activity of one of the strains (pv. syringae) was not affected by the UV, while that for the other (pv. garcae) there was a moderate reduction. In response to desiccation, pv. garcae was substantially more resistant than pv. syringae. This also affected the ice nucleation by the strains. In additional assays, these bacteria were exposed in a stratospheric balloon flight, and to a laboratory simulation of the conditions at the top of the troposphere. After these two experiments, survivors protected from the UV were recovered.