Jeffrey C. Steiner

BACTERIA-CLAY INTERACTION: STRUCTURAL CHANGES IN SMECTITE INDUCED DURING BIOFILM FORMATION

Bacteria play an important role in determining the properties and behavior of clay minerals in natural environments and such interactions have great potential for creating stable biofilms and carbon storage sites in soils, but our knowledge of these interactions are far from complete. The purpose of this study was to understand better the effects of bacteria-generated biofilms on clay interlayer expansion. Mixtures of a colloidal, 2-water hectorite clay and Pseudomonas syringae in a minimal media suspension evolve into a polysaccharide-rich biofilm aggregate in time-series experiments lasting up to 1 week. X-ray diffraction analysis reveals that upon aggregation, the clay undergoes an initial interlayer contraction. Short-duration experiments, up to 72 h, result in a decrease in the d001 value from 1.50 to 1.26 nm. The initial interlayer contraction is followed in long-duration (up to 1 week) experiments by an expansion of the d001 value of 1.84 nm. The expansion is probably a result of large, biofilm-produced, polymeric molecules being emplaced in the interlayer site. The resultant organo-clay could provide a possible storage medium for carbon in a microbial colony setting.

In situ determination of refractive index and size of Bacillus spores by light transmission

Light-extinction measurements in the wavelength range of 400 to 1000 nm are performed in situ on Bacillus subtilis endospores during heat-shock-induced activation. Simultaneous information on particle size and refractive indices during activation is calculated from the transmission spectra by use of the Gaussian ray approximation of anomalous diffraction theory. During activation the refractive index of the core decreases from 1.51 to 1.39, and the size increases from 0.38 to 0.6 microm.

Transmission of Flood Basalts through a Shallow Crustal Sill and the Correlation of Sill Layers with Extrusive Flows: The Palisades Intrusive System and the Basalts of the Newark Basin, New Jersey, U.S.A.

The Palisades Intrusive System consists of a 350-m-thick early Jurassic sill together with thinner comagmatic sills and dikes exposed within the Newark Basin of New Jersey and New York. The Palisades System is overlain by flood basalt that is interbedded with early Jurassic redbed formations. New and recently published data indicate that some of the basalt flows correlate with geochemically defined layers within a central well-exposed sill portion of the Palisades System at Fort Lee, New Jersey. Our interpretation views the sill as a progressively inflated conduit through which huge volumes of flood basalt flowed. The geochemical data are consistent with a Palisades sill fed by three compositionally distinct intrusion events. The first magma flowed through the sill and broke out near the northern end as three Orange Mountain basalt flows. Each of the three extrusive pulses is identified within the lower 150 m of the sill on the basis of distinct geochemical reversals. The end stage of each pulse was characterized by pyroxene phenocryst accumulation within the sill. Magma from a second source inflated the sill by an additional 170 m after approximately 260 k.yr. of minor intermittent igneous activity interbedded with sediments deposited above the Orange Mountain basalt. The second magma extruded as a highly fractionated 150-m-thick Preakness basalt flow and crystallized as a central layer of Palisades diabase of similar composition. Subsequent extrusions of relatively thin Preakness flows (magma 3) correlate with upper layers of the Palisades sill. We interpret the distinct layering of the Palisades sill as injections of magmas that were largely prefractionated at deeper levels and then modified to varying degrees by in situ processes.

Effects of smectite clay on biofilm formation by microorganisms

We have investigated the role of smectite clay particles in biofilm formation by several different species of bacteria ( Pseudomonas syringae, Escherichia coli , Staphylococcus aureus and Bacillus subtilis ). We observed that the presence of clay particles enhances the formation of biofilms and, after 24 h, the bacterial populations in the clay mixtures were greater than the respective populations in media without clay. Smectite-bearing clay slurries uniformly develop bacteria–clay aggregates with a substantial biofilm component within 24 h, while the exclusively bacterial suspensions do not develop any observable biofilm component. The biofilm–clay aggregates vary in size from tens of micrometers to several millimeters. Biofilm formation was evaluated by phase contrast microscopy and fluorescence staining. Biofilm promotion by smectite clays may indicate the importance of transport of bacteria by aerosol dust particles.

Influence of cations on aggregation rates in Mg-montmorillonite

Critical-zone reactions involve inorganic and biogenic colloids in a cation-rich environment. The present research defines the rates and structure of purified Mg-montmorillonite aggregates formed in the presence of monovalent (K+) and divalent (Ca2+, Mg 2+) cations using light-extinction measurements. Time evolution of turbidity was employed to determine early-stage aggregation rates. Turbidity spectra were used to measure the fractal dimension at later stages. The power law dependence of the stability ratios on cation concentration was found to vary with the reciprocal of the valence rather than the predicted reciprocal of valence-squared, indicating that the platelet structure may be a factor influencing aggregation rates. The critical coagulation concentrations (CCC) (3 mM for CaCl2, 4 mM for MgCl2, and 70 mM for KCl) were obtained from the stability ratios. At a later time and above a minimal cation concentration, turbidity reached a quasi-stable state, indicating the formation of large aggregates. Under this condition, an approximate turbidity forward-scattering correction factor was applied and the fractal dimension was determined from the extinction spectra. For the divalent cations, the fractal dimensions were 1.65 ± 0.3 for Ca2+ and 1.75 ± 0.3 for Mg2+ and independent of cation concentrations above the CCC. For the monovalent cation, the fractal dimension increased with K+ concentration from 1.35 to 1.95, indicating a transition to a face-to-face geometry from either an edge-to-edge or edge-to-face orientation.

Disassembly of the cystovirus ϕ6 envelope by montmorillonite clay

Prior studies of clay–virus interactions have focused on the stability and infectivity of nonenveloped viruses, yielding contradictory results. We hypothesize that the surface charge distribution of the clay and virus envelope dictates how the components react and affect aggregation, viral stability, and infectivity. The bacteriophage Cystoviridae species φ6 used in this study is a good model for enveloped pathogens. The interaction between φ6 and montmorillonite (MMT) clay (the primary component of bentonite) is explored by transmission electron microscopy. The analyses show that MMT–φ6 mixtures undergo heteroaggregation, forming structures in which virtually all the virions are either sequestered between MMT platelet layers or attached to platelet edges. The virions swell and undergo disassembly resulting in partial or total envelope loss. Edge‐attached viral envelopes distort to increase contact area with the positively charged platelet edges indicating that the virion surface is negatively charged. The nucleocapsid (NCs) remaining after envelope removal also exhibit distortion, in contrast to detergent‐produced NCs which exhibit no distortion. This visually discernible disassembly is a mechanism for loss of infectivity previously unreported by studies of nonenveloped viruses. The MMT‐mediated sequestration and disassembly result in reduced infectivity, suggesting that clays may reduce infectivity of enveloped pathogenic viruses in soils and sediments.

Broadband light scattering measurements of the time evolution of the fractal dimension of smectite clay aggregates

The characterization of the initial stages of complex aggregate flocculation is a central problem of colloidal science and environmental studies. A fast, white light scattering technique for monitoring aggregation kinetics is used to provide a unique probe of the changes that transpire during flocculation. The time evolution of an accreting smectite clay aggregate is monitored on the basis of changes in the fractal dimension (Df) initiated by the addition of an electrolyte (MgCl2). The evaluation of the Df change reveals for the first time three distinct stages in aggregate formation that characterize smectite flocculation: a rapid, initial jump; followed by a slow decrease; and a final gradual increase, eventually reaching a plateau. The three stages in the time evolution of Df correlate with (1) collapse of loosely packed face-to-edge structures and the formation of compact face-to-face composite structures; (2) the merging of the face-to-face composites; and (3) aggregation of the composites. Stage 3 eventually reaches a quasi-equilibrium condition. The quasi-equilibrium value of Df varies from 1.86 in 1 mM MgCl2—corresponding to diffusion-limited colloidal aggregation—to 2.20 in 57 mM MgCl2—corresponding to reaction-limited colloidal aggregation. These unexpected results originate from the formation of intermediate composite particles during aggregation and the increase in the compactness of the intermediate composite particles with electrolyte concentration. The new white light optical technique demonstrated here is non-invasive and has significant implications in the investigation of the growth dynamics of colloidal systems.

Microstructural study of tonalitic gneisses exposed by TBM-mining of New York City's third water tunnel

Abstract Regionally deformed tonalitic granites, associated foliated granulites (to 80% silica) and migmatitic granites (to 74% silica) are characterized by high densities of tangled dislocations, as estimated via x-ray diffraction line broadening and heat capacity data. The xenoblastic and sutured quartz grains create a grain-boundary-locking condition that is additionally hardened by strain within quartz. The combined effect of interlocking and strained quartz-plagioclase mosaics create increased uniaxial compressive strength in granites and produce conditions of slow TBM penetration rate. X-ray diffraction data show line broadening of 15 to 20 percent, and peak intensity decreases on annealing consistent with the release of strain within quartz grains. Decrease in peak height due to x-ray extinction is suggested as a useful index for strain-hardenning. These observations are supported by differential thermal calorimetry that show systematic decreases in heat effects at the alpha-beta quartz transition.

Changes in refractive index and size of Bacillus subtilis spores during activation, measured by light transmission

Refractive index and size changes in Bacillus subtilis spores were measured during heat shock activation by light scattering. The refractive index decreased from 1.51 to 1.38 while the size increased from 0.37 to 0.6 microns.