Biological ice nucleators (IN) function as catalysts for freezing at relatively warm temperatures (warmer than ؊10°C).We examined the concentration (per volume of liquid) and nature of IN in precipitation collected from Montana and Louisiana, the Alps and Pyrenees (France), Ross Island (Antarctica), and Yukon (Canada). The temperature of detectable ice-nucleating activity for more than half of the samples was > ؊5°C based on immersion freezing testing. Digestion of the samples with lysozyme (i.e., to hydrolyze bacterial cell walls) led to reductions in the frequency of freezing (0 -100%); heat treatment greatly reduced (95% average) or completely eliminated ice nucleation at the measured conditions in every sample. These behaviors were consistent with the activity being bacterial and/or proteinaceous in origin. atmosphere ͉ climate ͉ microbial dissemination ͉ biological ice nuclei A t subzero temperatures warmer than Ϫ40°C, aerosol particles in clouds initiate freezing through the heterogeneous nucleation of ice directly from water vapor or by freezing droplets via several mechanisms: deposition, condensation, contact, and immersion freezing (1). These processes lead to ice formation in clouds that can trigger precipitation. A diverse range of natural and anthropogenic particles, referred to as ice-forming nuclei or ice nucleators (IN), are capable of initiating the ice phase (2). The maximum temperature at which an IN can initiate freezing is specific to that nucleator, but they function similarly by providing templates for the aggregation of individual water molecules in the configuration of an ice embryo, resulting in a subsequent phase change and the cascade of crystal formation (3). Consequently, knowledge of the nature and sources of IN in the atmosphere is important for understanding the meteorological processes responsible for precipitation. The most active naturally occurring IN are biological in origin and have the capacity to catalyze freezing at temperatures near Ϫ2°C (4). The most widespread and well-studied biological aerosols with icenucleating activity are comprised of certain species of plantassociated bacteria (Pseudomonas syringae, Pseudomonas viridiflava, Pseudomonas fluorescens, Pantoea agglomerans, and Xanthomonas campestris), but also fungi (e.g., Fusarium avenaceum), algae such as Chlorella minutissima, and birch pollen (5). P. syringae (6 -8) and F. avenaceum (7) in particular have been detected in atmospheric aerosols and clouds. Icenucleating strains of P. syringae possess a 120-to 180-kDa ice nucleation active protein in their outer membrane comprised of contiguous repeats of a consensus octapeptide; the protein binds water molecules in an ordered arrangement, providing a nucleating template that enhances ice crystal formation (9).Based on reports of ice-nucleating bacteria at altitudes of several kilometers (6, 10) and the warm temperatures at which they function as ice nuclei (Ϫ2°C to Ϫ7°C; ref. Our previous work on snowfall collected from a variety of midand high-latitude locations...

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Vibrio vulnificus is a Gram-negative bacterium found in estuaries and coastal waters and is associated with human disease caused by ingestion of raw shellfish. Pathogenesis is directly related to the presence of capsular polysaccharide (CPS). Encapsulated virulent strains exhibit an opaque colony phenotype, while unencapsulated attenuated strains appear translucent. A third colony type, rugose, is caused by expression of rugose extracellular polysaccharide (rEPS) and forms robust biofilms. Vibrio vulnificus undergoes phase variation associated with altered levels of CPS and rEPS, and we show here that calcium (Ca²(+) ) significantly increases the rate of CPS and rEPS phase variation in this species. Interestingly, multiple phenotypic responses to increased [Ca²(+) ] were observed among strains, which suggests the existence of underlying cognate genetic or epigenetic differences. Certain translucent isolates contained deletions at the group I CPS operon, inferring increased [Ca²(+) ] upregulates existing phase variation mechanisms. Expanding on a previous observation (Kierek and Watnick, Proc. Natl. Acad. Sci. USA 100: 14357-14362, 2003), increased [Ca²(+) ] also enhanced biofilm formation for all phase variants. Our results show that Ca²(+) promotes both polysaccharide phase variation and biofilm formation of the resulting phase variants, thereby likely serving a dual role in persistence of V. vulnificus in the environment.

Development of ionic liquid (IL)-based colorimetric sensor arrays for detection and identification of chemicals in both the aqueous and vapor phases is reported. These facile and inexpensive optoelectronic sensors were fabricated by using ionic liquids (ILs) derived from readily available pH indicator dyes. A series of 12 different chemosensory ILs were synthesized by pairing anionic pH indicator dyes with trihexyl(tetradecyl)phosphonium ([P 66614 ]) cation via an ion exchange reaction. The incorporation of the [P 66614 ] cation imparted hydrophobic characteristics to these ILs, and this induced hydrophobicity led to their desired low solubility in aqueous solutions, as well as eliminated the need for a specialized hydrophobic matrix/substrate for immobilization. In this manuscript, four different matrices, i.e. glass microfiber filter papers, cotton threads, silica thin layer chromatography (TLC) plates, and alumina TLC plates, were employed for fabrication of sensor arrays. These sensor arrays were used to analyze pH values of aqueous solutions as well as for detection of acidic and basic vapors. To further prove the applicability of these IL sensor arrays as tools to sense closely related complex materials, the arrays were applied to successful discrimination of aqueous solutions of smoke from three commercially available cigarettes. The digital data generated from these sensor arrays were used in developing predictive models for accurately identifying various analytes. Two approaches were used for developing the models, and two methods were applied for assessing the predictive accuracy of the models. Use of cotton threads as a matrix led to development of a more flexible, low volume, and lightweight array to estimate pH and detect a variety of vapors. These wearable arrays may possibly be incorporated into bandages, sweatbands, diapers, and similar systems. Overall, these IL-based sensor arrays should provide a new research direction in the development of advanced colorimetric sensor arrays for detection and identification of a range of analytes relevant to many different applications.

We studied the relationship between reading nutrition labels and percent calorie intake from fat. In adolescent boys, reading nutrition labels was associated with higher fat intake. In girls, fat intake did not differ by frequency of nutrition label reading. Nutrition label reading does not translate into healthier diet in adolescents.