In-situ monitoring of Cryptosporidium parvum oocyst surface adhesion using ATR-FTIR spectroscopy
ABSTRACT Surface chemistry and molecular interaction mechanisms of Cryptosporidium parvum oocysts with a ZnSe internal reflection element (IRE) surface were investigated as a function of pH and ionic strength in NaCl and CaCl(2) background electrolyte using in-situ ATR-FTIR spectroscopy. Since the surface properties of oocysts play an important role in adhesion behavior, the effects of surface modifications that are commonly employed to inactivate the pathogen for laboratory studies, including viable (control), formalin-, and heat-inactivation, were also examined. The ATR-FTIR spectra of oocyst surfaces exhibit amide, carboxylate, phosphate, and polysaccharide functional groups. Results indicate that changes in solution chemistry strongly impact oocyst adhesion behavior in aqueous systems. Increasing ionic strength from 1 to 100 mM or decreasing pH from 9.0 to 3.0 resulted in an increase in oocyst adhesion to the IRE surface as measured by IR absorbance. For equivalent ionic strength, the adhesion rate was found to be independent of CaCl(2) versus NaCl electrolyte solution, but was increased following formalin and heat treatments. This latter effect correlated with molecular changes reflected in spectral data. The ratio of amide I:amide II band intensities increased, and sugar ring vibrations at 1023 cm(-1) became sharper and more intense following formalin treatment. Similar changes in the polysaccharide region were observed following heat treatment, and protein secondary structure was also altered from mainly parallel beta-sheet to anti-parallel beta-sheet conformation.
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ABSTRACT: Vibrational spectroscopy techniques provide a powerful approach to the study of environmental materials and processes. These multifunctional analytical tools can be used to probe molecular vibrations of solid, liquid, and gaseous samples for characterizing materials, elucidating reaction mechanisms, and examining kinetic processes. Although Fourier transform infrared (FTIR) spectroscopy is the most prominent type of vibrational spectroscopy used in the field of soil science, applications of Raman spectroscopy to study environmental samples continue to increase. The ability of FTIR and Raman spectroscopies to provide complementary information for organic and inorganic materials makes them ideal approaches for soil science research. In addition, the ability to conduct in situ, real time, vibrational spectroscopy experiments to probe biogeochemical processes at mineral interfaces offers unique and versatile methodologies for revealing a myriad of soil chemical phenomena. This review provides a comprehensive overview of vibrational spectroscopy techniques and highlights many of the applications of their use in soil chemistry research.Advances in Agronomy 05/2014; 126:1-148. DOI:10.1016/B978-0-12-800132-5.00001-8 · 5.02 Impact Factor
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ABSTRACT: Prior studies have indicated that the subsurface transport of Cryptosporidium parvum is diminished in sediments containing iron oxides, but the molecular mechanisms are poorly known, as are the impacts thereon of natural organic matter (NOM). Using in-situ attenuated total reflectance (ATR)-FTIR spectroscopy, we examined the molecular mechanisms of viable Cryptosporidium parvum öocyst adhesion at the hematite (α-Fe 2 O 3)-water interface over a wide range in solution chemistry. The anionic surfactant sodium dodecylsulfate (SDS) was used as a surrogate for NOM to examine the impacts of surfactant-type components on öocyst adhesion mechanisms. Results indicate that, in the absence of SDS, öocyst surface carboxylate groups form inner-sphere complexes with hematite Fe metal centres at low pH and outer-sphere complexes at high pH. Such direct chemical bonding is likely one mechanism whereby Fe oxides diminish öocyst transport. The presence of SDS significantly diminishes Fe-carboxylate complexation in the öocyst-SDS-hematite ternary system. Results suggest that the sulfate groups (OSO 3 -) of SDS compete effectively for α-Fe 2 O 3 surface sites, and this is likely the primary mechanism for decreasing Fe-carboxylate complexation. Sorptive competition with NOM may, therefore, increase the mobility of C. parvum öocysts in soils. Introduction Cryptosporidium parvum is a water-borne protozoan pathogen that is responsible for the gastrointestinal disease Cryptosporidiosis, which is potentially lethal for immuno-compromised individuals (Casemore et al. 1997). Öocysts, the encysted, environmental form of the obligate pathogen, exhibit a complex mixture of surface biomacromolecules consisting primarily of amide, carboxylate, phosphate, and polysaccharide functionalities (Gao and Chorover 2009). Ionizable functional groups, such as carboxylate and phosphate groups, may serve as reactive sites for direct bonding to mineral surfaces. In a previous spectroscopic study, we found that formation of inner-sphere versus outer-sphere complexes between öocyst surface carboxyls and hematite surface hydroxyls was dependent on solution chemistry (Gao et al. 2009). Such molecular-scale chemical bonding is likely to retard öocyst transport in Fe-rich tropical soils. Ionic surfactants are ubiquitous in the environment and may play important roles in mediating the fate and transport of pathogenic cells in the subsurface. For example, anionic surfactants can decrease or even reverse the positive surface charge on metal oxides by forming monolayer or bilayer surface patches (Fuerstenau and Colic 1999; Bai et al. 2004). This could diminish öocyst adhesion due to an increase in electrostatic repulsive force. However, it is also possible that surfactant coatings could enhance öocyst adhesion to mineral surfaces because of an increase in sorbent hydrophobicity. Furthermore, ionic surfactant compounds can form surface complexes at mineral surfaces (Bai et al. 2004; Gao and Chorover 2010), competing for the reactive surface sites with öocyst surface biomolecules. Despite the prevalence of naturally produced and synthetic surfactants in waters contaminated with C. parvum öocysts, their influence on öocyst fate and transport remains poorly understood. The main objective of this study was to use SDS as a model compound to examine the effect of surfactant-type NOM components on öocyst adhesion mechanisms using in-situ ATR-FTIR spectroscopy, and to explore the potential effect of anionic surfactant on pathogen transport in the subsurface. Specifically, we compared the ATR-FTIR spectra of öocysts at the aqueous solution – hematite interface in the presence and absence of SDS. By close examination of spectral changes, the molecular interaction mechanisms were determined.
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ABSTRACT: The role of collector surface charge heterogeneity on transport of Cryptosporidium parvum oocyst and carboxylate microsphere in 2-dimensional micromodels was studied. The cylindrical silica collectors within the micromodels were coated with 0, 10, 20, 50, and 100% Fe2O3 patches. The experimental values of average removal efficiencies (η) of the Fe2O3 patches and on the entire collectors were determined. In the presence of significant (>3500 kT) Derjaguin-Landau-Verwey-Overbeek (DLVO) energy barrier between the microspheres and the silica collectors at pH 5.8 and 8.1, η determined for Fe2O3 patches on the heterogeneous collectors were significantly less (p < 0.05, t-test) than those obtained for collectors coated entirely with Fe2O3. However, η calculated for Fe2O3 patches for microspheres at pH 4.4 and for oocysts at pH 5.8 and 8.1, where the DLVO energy barrier was relatively small (ca. 200-360 kT), were significantly greater (p < 0.05, t-test) than those for the collectors coated entirely with Fe2O3. The dependence of η for Fe2O3 patches on the DLVO energy barrier indicated the importance of periodic favorable and unfavorable electrostatic interactions between colloids and collectors with alternating Fe2O3 and silica patches. Differences between experimentally determined overall η for charged heterogeneous collectors and those predicted by a patchwise geochemical heterogeneous model were observed. These differences can be explained by the model's lack of consideration for the spatial distribution of charge heterogeneity on the collector surface.Environmental Science & Technology 02/2013; 47(6):2670. DOI:10.1021/es304075j · 5.48 Impact Factor