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.
"It exhibits much stronger asymmetric and symmetric COO -stretching bands, suggesting the formation of Fe-carboxylate complexes during öocyst adhesion. In addition, the separation in wavenumber (∆ν) of ν as and ν a COO -stretching bands (e.g., ∆ν > 200/cm for monodentate, 180 -150/cm for binuclear bidentate, and < 100/cm for mononuclear bidentate) (Deacon and Phillips 1980) allows the complexation mode (inner-versus outer-sphere) to be assigned (Gao et al. 2009). "
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: A series of miscible-displacement experiments was conducted to examine the retention and transport behavior of oocysts in natural porous media. Three soils and a model sand were used that differed in physical and geochemical properties. Transport behavior was examined under various treatment conditions to help evaluate retention mechanisms. Significant retention of oocysts was observed for all media despite the fact that conditions were unfavorable for physicochemical interactions with respect to DLVO theory. The magnitude of retention was not influenced significantly by alterations in solution chemistry (reduction in ionic strength) or soil surface properties (removal of soil organic matter and metal oxides). On the basis of the observed results, it appears that retention by secondary energy minima or geochemical microdomains was minimal for these systems. The porous media used for the experiments exhibited large magnitudes of surface roughness, and it is suggested that this surface roughness contributed significantly to oocyst retention.
[Show abstract][Hide abstract] ABSTRACT: The interaction of viable Cryptosporidium parvum oocysts at the hematite (alpha-Fe2O3)-water interface was examined over a wide range in solution chemistry using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Spectra for hematite-sorbed oocysts showed distinct changes in carboxylate group vibrations relative to spectra obtained in the absence of hematite, indicative of direct chemical bonding between carboxylate groups and Fe metal centers of the hematite surface. The data also indicate that complexation modes vary with solution chemistry. InNaCl solution, oocysts are bound to hematite via monodentate and binuclear bidentate complexes. The former predominates at low pH, whereas the latter becomes increasingly prevalent with increasing pH. In a CaCl2 solution, only binuclear bidentate complexes are observed. When solution pH is above the point of zero net proton charge (PZNPC) of hematite, oocyst surface carboxylate groups are bound to the mineral surface via outer-sphere complexes in both electrolyte solutions.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.