Photoinactivation of virus on iron-oxide coated sand: enhancing inactivation in sunlit waters

Adsorption onto iron oxides can enhance the removal of waterborne viruses in constructed wetlands and soils. If reversible adsorption is not coupled with inactivation, however, infective viruses may be released when changes in solution conditions cause desorption. The goals of this study were to investigate the release of infective bacteriophages MS2 and ΦX174 (two human viral indicators) after adsorption onto an iron oxide coated sand (IOCS), and to promote viral inactivation by exploiting the photoreactive properties of the IOCS. The iron oxide coating greatly enhanced viral adsorption (adsorption densities up to ∼10⁹ infective viruses/g IOCS) onto the sand, but had no affect on infectivity. Viruses that were adsorbed onto IOCS under control conditions (pH 7.5, 10 mM Tris, 1250 μS/cm) were released into solution in an infective state with increases in pH and humic acid concentrations. The exposure of IOCS-adsorbed MS2 to sunlight irradiation caused significant inactivation via a photocatalytic mechanism in both buffered solutions and in wastewater samples (4.9 log₁₀ and 3.3 log₁₀ inactivation after 24-h exposure, respectively). Unlike MS2, ΦX174 inactivation was not enhanced by photocatalysis. In summary, IOCS enhanced the separation of viruses from the water column, and additionally provided a photocatalytic mechanism to promote inactivation of one of the surrogates studied. These qualities make it an attractive option for improving viral control strategies in constructed wetlands.     

Contribution of coexisting sulfate and iron reducing bacteria to methylmercury production in freshwater river sediments

We investigated microbial methylmercury (CH(3)Hg) production in sediments from the South River (SR), VA, an ecosystem contaminated with industrial mercury (Hg). Potential Hg methylation rates in samples collected at nine sites were low in late spring and significantly higher in late summer. Demethylation of (14)CH(3)Hg was dominated by (14)CH(4) production in spring, but switched to producing mostly (14)CO(2) in the summer. Fine-grained sediments originating from the erosion of river banks had the highest CH(3)Hg concentrations and were potential hot spots for both methylation and demethylation activities. Sequencing of 16S rRNA genes of cDNA recovered from sediment RNA extracts indicated that at least three groups of sulfate-reducing bacteria (SRB) and one group of iron-reducing bacteria (IRB), potential Hg methylators, were active in SR sediments. SRB were confirmed as a methylating guild by amendment experiments showing significant sulfate stimulation and molybdate inhibition of methylation in SR sediments. The addition of low levels of amorphous iron(III) oxyhydroxide significantly stimulated methylation rates, suggesting a role for IRB in CH(3)Hg synthesis. Overall, our studies suggest that coexisting SRB and IRB populations in river sediments contribute to Hg methylation, possibly by temporally and spatially separated processes.     

Temporal analysis of net fluvial methylmercury loading in a dystrophic and a clear water lake

The concentration of methylmercury (MeHg) in aquatic ecosystems is the net result of the highly dynamic abiotic and biotic processes of mercury methylation and demethylation. In this study, we conduct an examination of the net fluvial loading of methylmercury (MeHg_Net = MeHg_Watershed − MeHg_{Lake outflow}) across a 3 year time frame in both a dystrophic lake and an oligotrophic lake. A significant portion of MeHg_Net variance in both lakes could be attributed to a seasonal pattern (11.4%, p = 0.009; oligotrophic, and 27.0%, p < 0.0001; dystrophic) which in both cases, was most correlated with air temperature. The dystrophic lake appeared to be a net source of methylmercury (MeHg_Net = − 1.9 ± 0.3 mg MeHg d^− 1) while the oligotrophic lake appeared to be a net sink (MeHg_Net = 0.4 ± 0.2 mg MeHg d^− 1), indicating that there was net methylation in the dystrophic lake and net demethylation in the oligotrophic lake. Higher MeHg loading to the lakes occurred during the summer and between seasons there was a difference in MeHg_Net of 1.1 ±0.3 mg MeHg d^− 1 and 3.1 ± 0.6 mg MeHg d^− 1. Seasonal patterns of MeHg_Net in the oligotrophic lake lagged behind the dystrophic lake by 39 days. The short term variation in MeHg_Net was dominated by precipitation (t = 2.73, p = 0.008; dystrophic, t = 2.53, p = 0.017; oligotrophic).     

Screening Collagenase Activity in Bacterial Lysate for Directed Enzyme Applications

Collagenases are essential enzymes capable of digesting triple-helical collagen under physiological conditions. These enzymes play a key role in diverse physiological and pathophysiological processes. Collagenases are used for diverse biotechnological applications, and it is thus of major interest to identify new enzyme variants with improved characteristics such as expression yield, stability, or activity. The engineering of new enzyme variants often relies on either rational protein design or directed enzyme evolution. The latter includes screening of a large randomized or semirational genetic library, both of which require an assay that enables the identification of improved variants. Moreover, the assay should be tailored for microplates to allow the screening of hundreds or thousands of clones. Herein, we repurposed the previously reported fluorogenic assay using 3,4-dihydroxyphenylacetic acid for the quantitation of collagen, and applied it in the detection of bacterial collagenase activity in bacterial lysates. This enabled the screening of hundreds of E. coli colonies expressing an error-prone library of collagenase G from C. histolyticum, in 96-well deep-well plates, by measuring activity directly in lysates with collagen. As a proof-of-concept, a single variant exhibiting higher activity than the starting-point enzyme was expressed, purified, and characterized biochemically and computationally. This showed the feasibility of this method to support medium-high throughput screening based on direct evaluation of collagenase activity.     

Bounding theorems for stress intensity factors

Bounding theorems for the changes in elastic energy due to a crack in a finite body and crack tip Stress Intensity Factors are established by use of the variational principles of the theory of elasticity. It is shown that the change in elastic energy due to a crack in a finite body is larger than the change in energy due to the same crack in an infinite body with the same boundary conditions when stresses are prescribed on the external boundary, and smaller when displacements are prescribed. The energy changes can be expressed as functions of the crack tip Stress Intensity Factors and for special loadings, bounds for single mode Stress Intensity Factors are obtained. The obtained inequalities are in agreement with known numerical solutions of finite cracked bodies.     

Effect of water and bht on stability of cottonseed oil during frying

The behaviour was studied in cottonseed oil which had been exposed to frying under controlled conditions in a system in which only the oil, water and/or the antioxidant BHT were present. In the oils, changes which had been caused by heating were evaluated through determination of acid, hydroxyl, TBA and iodine values, extinctions at 232 nm and 460 nm, fatty acid composition, viscosity, amounts of “polymers” and non-urea-adduct-forming fatty acid methyl esters. All the changes were less pronounced when the frying was carried out in presence of either nitrogen or water. The latter protected the oil only if it was present in amounts sufficient to generate such a volume of vapours which could effectively act as an inert gas-blanket. BHT had no delaying effect on the deterioration of the oil during frying. When the oil was heated in the presence of air, the antioxidant's destruction was lessened by the presence of water in the system, but a large portion of BHT was lost through steam distillation.     

Mental capacity and cognitive functioning: Developmental and social class differences.

Hypothesized that social class performance differences of same-age children would be negligible on pure mental (M) capacity measures but would be greater on tasks that confound other variables with M capacity. This hypothesis is anchored in a neo-Piagetian theory of cognitive development (J. Pascual-Leone; see record 1971-07908-001), which gives a central role to an attentional mechanism of limited M capacity that grows monotonically with age. 268 Israeli 8-, 10-, and 12-yr-olds of low or high SES completed 10 cognitive developmental tasks that measured pure M capacity, short-term memory, verbal IQ, and spatial-analytic ability. Results show that M capacity developed similarly in same-age Ss, regardless of SES. Significant differences among the investigated populations were found only in performing tasks that confounded factors of learning and style. Results support the notion that a cognitive development process exists that is universal in stage sequences and in the rate and timing of development. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Studies of tocopherol dimers from soybean oil by reaction gas chromatography

Reaction gas chromatography was found to be helpful in elucidating structures of tocopherol dimers. By this method γ- and δ-tocopherols were determined as monomers derived from tocopherol dimers, after isolation of the latter compounds from soybean oil. It was shown that gas chromatographic determination of tocopherols, as performed by injection of total unsaponifiables from soybean oil, will give results too high; the eluted tocopherols will account for both tocopherol monomers and dimers.     

Conjunctive grammars and alternating pushdown automata

In this paper we introduce a variant of alternating pushdown automata, synchronized alternating pushdown automata, which accept the same class of languages as those generated by conjunctive grammars.