Dispersion and Transport of Cryptosporidium Oocysts from Fecal Pats under Simulated Rainfall Events

The dispersion and initial transport of Cryptosporidium oocysts from fecal pats were investigated during artificial rainfall events on intact soil blocks (1,500 by 900 by 300 mm). Rainfall events of 55 mm h⁻¹ for 30 min and 25 mm h⁻¹ for 180 min were applied to soil plots with artificial fecal pats seeded with approximately 10⁷ oocysts. The soil plots were divided in two, with one side devoid of vegetation and the other left with natural vegetation cover. Each combination of event intensity and duration, vegetation status, and degree of slope (5° and 10°) was evaluated twice. Generally, a fivefold increase (P < 0.05) in runoff volume was generated on bare soil compared to vegetated soil, and significantly more infiltration, although highly variable, occurred through the vegetated soil blocks (P < 0.05). Runoff volume, event conditions (intensity and duration), vegetation status, degree of slope, and their interactions significantly affected the load of oocysts in the runoff. Surface runoff transported from 10^0.2 oocysts from vegetated loam soil (25-mm h⁻¹, 180-min event on 10° slope) to up to 10^4.5 oocysts from unvegetated soil (55-mm h⁻¹, 30-min event on 10° slope) over a 1-m distance. Surface soil samples downhill of the fecal pat contained significantly higher concentrations of oocysts on devegetated blocks than on vegetated blocks. Based on these results, there is a need to account for surface soil vegetation coverage as well as slope and rainfall runoff in future assessments of Cryptosporidium transport and when managing pathogen loads from stock grazing near streams within drinking water watersheds.     

Inhibition of glucose phosphate isomerase by metabolic intermediates of fructose

1. Purified rabbit-muscle and -liver glucose phosphate isomerase, free of contaminating enzyme activities that could interfere with the assay procedures, were tested for inhibition by fructose, fructose 1-phosphate and fructose 1,6-diphosphate. 2. Fructose 1-phosphate and fructose 1,6-diphosphate are both competitive with fructose 6-phosphate in the enzymic reaction, the apparent K_i values being 1·37×10⁻³−1·67×10⁻³m for fructose 1-phosphate and 7·2×10⁻³−7·9×10⁻³m for fructose 1,6-diphosphate; fructose and inorganic phosphate were without effect. 3. The apparent K_m values for both liver and muscle enzymes at pH7·4 and 30° were 1·11×10⁻⁴−1·29×10⁻⁴m for fructose 6-phosphate, determined under the conditions in this paper. 4. In the reverse reaction, fructose, fructose 1-phosphate and fructose 1,6-diphosphate did not significantly inhibit the conversion of glucose 6-phosphate into fructose 6-phosphate. 5. The apparent K_m values for glucose 6-phosphate were in the range 5·6×10⁻⁴−8·5×10⁻⁴m. 6. The competitive inhibition of hepatic glucose phosphate isomerase by fructose 1-phosphate is discussed in relation to the mechanism of fructose-induced hypoglycaemia in hereditary fructose intolerance.     

Protozoan Bacterivory and Escherichia coli Survival in Drinking Water Distribution Systems

The development of bacterial communities in drinking water distribution systems leads to a food chain which supports the growth of macroorganisms incompatible with water quality requirements and esthetics. Nevertheless, very few studies have examined the microbial communities in drinking water distribution systems and their trophic relationships. This study was done to quantify the microbial communities (especially bacteria and protozoa) and obtain direct and indirect proof of protozoan feeding on bacteria in two distribution networks, one of GAC water (i.e., water filtered on granular activated carbon) and the other of nanofiltered water. The nanofiltered water-supplied network contained no organisms larger than bacteria, either in the water phase (on average, 5 × 10⁷ bacterial cells liter⁻¹) or in the biofilm (on average, 7 × 10⁶ bacterial cells cm⁻²). No protozoa were detected in the whole nanofiltered water-supplied network (water plus biofilm). In contrast, the GAC water-supplied network contained bacteria (on average, 3 × 10⁸ cells liter⁻¹ in water and 4 × 10⁷ cells cm⁻² in biofilm) and protozoa (on average, 10⁵ cells liter⁻¹ in water and 10³ cells cm⁻² in biofilm). The water contained mostly flagellates (93%), ciliates (1.8%), thecamoebae (1.6%), and naked amoebae (1.1%). The biofilm had only ciliates (52%) and thecamoebae (48%). Only the ciliates at the solid-liquid interface of the GAC water-supplied network had a measurable grazing activity in laboratory test (estimated at 2 bacteria per ciliate per h). Protozoan ingestion of bacteria was indirectly shown by adding Escherichia coli to the experimental distribution systems. Unexpectedly, E. coli was lost from the GAC water-supplied network more rapidly than from the nanofiltered water-supplied network, perhaps because of the grazing activity of protozoa in GAC water but not in nanofiltered water. Thus, the GAC water-supplied network contained a functional ecosystem with well-established and structured microbial communities, while the nanofiltered water-supplied system did not. The presence of protozoa in drinking water distribution systems must not be neglected because these populations may regulate the autochthonous and allochthonous bacterial populations.     

Purification and properties of adenosine diphosphoglucose pyrophosphorylase from sweet corn

A 40-fold purification of adenosine diphosphoglucose pyrophosphorylase from sweet corn (Zea mays var. Golden Beauty) revealed the enzyme to be specific for adenosine triphosphate. The enzyme has an absolute requirement for Mg²⁺ and is activated by 3-phosphoglycerate and to a lesser extent by ribose-5-phosphate and fructose-6-phosphate. The apparent Km values of the enzyme for glucose-1-phosphate, adenosine triphosphate, pyrophosphate, and adenosine diphosphoglucose are 1.9 × 10⁻⁴, 3.2 × 10⁻⁵, 3.3 × 10⁻⁵, and 6.2 × 10⁻⁴m, respectively. Pyrophosphate inhibits adenosine diphosphoglucose synthesis competitively (Ki = 3.8 × 10⁻⁷m), while orthophosphate and sulfate appear to inhibit the reacion noncompetitively. These results show that the production of this sugar nucleotide can be controlled by the concentration of pyrophosphate.     

Purification and Characterization of a Secreted Laccase of Gaeumannomyces graminis var. tritici

We purified a secreted fungal laccase from filtrates of Gaeumannomyces graminis var. tritici cultures induced with copper and xylidine. The active protein had an apparent molecular mass of 190 kDa and yielded subunits with molecular masses of 60 kDa when denatured and deglycosylated. This laccase had a pI of 5.6 and an optimal pH of 4.5 with 2,6-dimethoxyphenol as its substrate. Like other, previously purified laccases, this one contained several copper atoms in each subunit, as determined by inductively coupled plasma spectroscopy. The active enzyme catalyzed the oxidation of 2,6-dimethoxyphenol (K_m = 2.6 × 10⁻⁵ ± 7 × 10⁻⁶ M), catechol (K_m = 2.5 × 10⁻⁴ ± 1 × 10⁻⁵ M), pyrogallol (K_m = 3.1 × 10⁻⁴ ± 4 × 10⁻⁵ M), and guaiacol (K_m = 5.1 × 10⁻⁴ ± 2 × 10⁻⁵ M). In addition, the laccase catalyzed the polymerization of 1,8-dihydroxynaphthalene, a natural fungal melanin precursor, into a high-molecular-weight melanin and catalyzed the oxidation, or decolorization, of the dye poly B-411, a lignin-like polymer. These findings indicate that this laccase may be involved in melanin polymerization in this phytopathogen’s hyphae and/or in lignin depolymerization in its infected plant host.     

Rates of Microbial Transformation of Polycyclic Aromatic Hydrocarbons in Water and Sediments in the Vicinity of a Coal-Coking Wastewater Discharge

To facilitate predictions of the transport and fate of contaminants at future coal conversion facilities, rates of microbial transformation of polycyclic aromatic hydrocarbons were measured in stream water and sediment samples collected in the vicinity of a coal-coking treated wastewater discharge from November 1977 through August 1979. Six radiolabeled polycyclic aromatic hydrocarbons were incubated with sediment and water samples; ¹⁴CO₂, cell-bound ¹⁴C, and polar transformation products were isolated and quantified. Whereas ¹⁴CO₂ and bound ¹⁴C were major transformation products in sediment assays, soluble polar ¹⁴C dominated transformation in water samples. Mean rate constants (measured at 20°C) in sediments collected downstream from the effluent outfall were 7.8 × 10⁻² h⁻¹ (naphthalene), 1.6 × 10⁻² h⁻¹ (anthracene), and 3.3 × 10⁻³ h⁻¹ [benz(a)anthracene], which corresponded to turnover times of 13, 62, and 300 h, respectively. No unequivocal evidence for transformation of benzo(a)pyrene or dibenz(a,h)anthracene was obtained. Only naphthalene and anthracene transformations were observed in water samples; rate constants were consistently 5- and 20-fold lower, respectively, than in the corresponding sediment samples. The measured rate constants for anthracene transformation in July 1978 sediment samples were not related to total heterotroph numbers. In late July 1978, the effluent was diverted from the primary study area; however, no differences were observed either in transformation rate constants or in the downstream/upstream sediment rate constant ratio. These results are consistent with the hypothesis that continuous inputs of polycyclic aromatic hydrocarbons result in an increased ability within a microbial community to utilize certain polycyclic aromatic hydrocarbons. However, because transformation rates remained elevated for more than 1 year after removal of the polycyclic aromatic hydrocarbon source, microbial communities may shift only slowly in response to changes in polycyclic aromatic hydrocarbon concentrations.     

Distribution of Sulfate-Reducing and Methanogenic Bacteria in Anaerobic Aggregates Determined by Microsensor and Molecular Analyses

Using molecular techniques and microsensors for H₂S and CH₄, we studied the population structure of and the activity distribution in anaerobic aggregates. The aggregates originated from three different types of reactors: a methanogenic reactor, a methanogenic-sulfidogenic reactor, and a sulfidogenic reactor. Microsensor measurements in methanogenic-sulfidogenic aggregates revealed that the activity of sulfate-reducing bacteria (2 to 3 mmol of S²⁻ m⁻³ s⁻¹ or 2 × 10⁻⁹ mmol s⁻¹ per aggregate) was located in a surface layer of 50 to 100 μm thick. The sulfidogenic aggregates contained a wider sulfate-reducing zone (the first 200 to 300 μm from the aggregate surface) with a higher activity (1 to 6 mmol of S²⁻ m⁻³ s⁻¹ or 7 × 10⁻⁹ mol s⁻¹ per aggregate). The methanogenic aggregates did not show significant sulfate-reducing activity. Methanogenic activity in the methanogenic-sulfidogenic aggregates (1 to 2 mmol of CH₄ m⁻³ s⁻¹ or 10⁻⁹ mmol s⁻¹ per aggregate) and the methanogenic aggregates (2 to 4 mmol of CH₄ m⁻³ s⁻¹ or 5 × 10⁻⁹ mmol s⁻¹ per aggregate) was located more inward, starting at ca. 100 μm from the aggregate surface. The methanogenic activity was not affected by 10 mM sulfate during a 1-day incubation. The sulfidogenic and methanogenic activities were independent of the type of electron donor (acetate, propionate, ethanol, or H₂), but the substrates were metabolized in different zones. The localization of the populations corresponded to the microsensor data. A distinct layered structure was found in the methanogenic-sulfidogenic aggregates, with sulfate-reducing bacteria in the outer 50 to 100 μm, methanogens in the inner part, and Eubacteria spp. (partly syntrophic bacteria) filling the gap between sulfate-reducing and methanogenic bacteria. In methanogenic aggregates, few sulfate-reducing bacteria were detected, while methanogens were found in the core. In the sulfidogenic aggregates, sulfate-reducing bacteria were present in the outer 300 μm, and methanogens were distributed over the inner part in clusters with syntrophic bacteria.     

Mitochondrial Networks in Cardiac Myocytes Reveal Dynamic Coupling Behavior

Oscillatory behavior of mitochondrial inner membrane potential (ΔΨ_m) is commonly observed in cells subjected to oxidative or metabolic stress. In cardiac myocytes, the activation of inner membrane pores by reactive oxygen species (ROS) is a major factor mediating intermitochondrial coupling, and ROS-induced ROS release has been shown to underlie propagated waves of ΔΨ_m depolarization as well as synchronized limit cycle oscillations of ΔΨ_m in the network. The functional impact of ΔΨ_m instability on cardiac electrophysiology, Ca²⁺ handling, and even cell survival, is strongly affected by the extent of such intermitochondrial coupling. Here, we employ a recently developed wavelet-based analytical approach to examine how different substrates affect mitochondrial coupling in cardiac cells, and we also determine the oscillatory coupling properties of mitochondria in ventricular cells in intact perfused hearts. The results show that the frequency of ΔΨ_m oscillations varies inversely with the size of the oscillating mitochondrial cluster, and depends on the strength of local intermitochondrial coupling. Time-varying coupling constants could be quantitatively determined by applying a stochastic phase model based on extension of the well-known Kuramoto model for networks of coupled oscillators. Cluster size-frequency relationships varied with different substrates, as did mitochondrial coupling constants, which were significantly larger for glucose (7.78 × 10⁻² ± 0.98 × 10⁻² s⁻¹) and pyruvate (7.49 × 10⁻² ± 1.65 × 10⁻² s⁻¹) than lactate (4.83 × 10⁻² ± 1.25 × 10⁻² s⁻¹) or β-hydroxybutyrate (4.11 × 10⁻² ± 0.62 × 10⁻² s⁻¹). The findings indicate that mitochondrial spatiotemporal coupling and oscillatory behavior is influenced by substrate selection, perhaps through differing effects on ROS/redox balance. In particular, glucose-perfusion generates strong intermitochondrial coupling and temporal oscillatory stability. Pathological changes in specific catabolic pathways, which are known to occur during the progression of cardiovascular disease, could therefore contribute to altered sensitivity of the mitochondrial network to oxidative stress and emergent ΔΨ_m instability, ultimately scaling to produce organ level dysfunction.     

Thickness and Surface Density of Extracellular Polymers on Acidithiobacillus ferrooxidans

In vivo force microscopy measurements of Acidithiobacillus ferrooxidans revealed a repulsive force that was due to the presence of extracellular polymers on the bacterium's surface. Measured force-distance profiles were fit to steric force theory to estimate the density and thickness values of these exopolymers. The polymer densities were 3.4 × 10¹⁶ to 7.1 × 10¹⁶ molecules m⁻², and the equilibrium thickness was 29 nm.     

The Influence of Sulphate Deposition on the Seasonal Variation of Peat Pore Water Methyl Hg in a Boreal Mire

In this paper we investigate the hypothesis that long-term sulphate (SO₄ ²⁻) deposition has made peatlands a larger source of methyl mercury (MeHg) to remote boreal lakes. This was done on experimental plots at a boreal, low sedge mire where the effect of long-term addition of SO₄ ²⁻ on peat pore water MeHg concentrations was observed weekly throughout the snow-free portion of 1999. The additions of SO₄ ²⁻ started in 1995. The seasonal mean of the pore water MeHg concentrations on the plots with 17 kg ha⁻¹ yr⁻¹ of sulphur (S) addition (1.3±0.08 ng L⁻¹, SE; n = 44) was significantly (p<0.0001) higher than the mean MeHg concentration on the plots with 3 kg ha⁻¹ yr⁻¹ of ambient S deposition (0.6±0.02 ng L⁻¹, SE; n = 44). The temporal variation in pore water MeHg concentrations during the snow free season was larger in the S-addition plots, with an amplitude of >2 ng L⁻¹ compared to +/−0.5 ng L⁻¹ in the ambient S deposition plots. The concentrations of pore water MeHg in the S-addition plots were positively correlated (r² = 0.21; p = 0.001) to the groundwater level, with the lowest concentrations of MeHg during the period with the lowest groundwater levels. The pore water MeHg concentrations were not correlated to total Hg, DOC concentration or pH. The results from this study indicate that the persistently higher pore water concentrations of MeHg in the S-addition plots are caused by the long-term additions of SO₄ ²⁻ to the mire surface. Since these waters are an important source of runoff, the results support the hypothesis that SO₄ ²⁻ deposition has increased the contribution of peatlands to MeHg in downstream aquatic systems. This would mean that the increased deposition of SO₄ ²⁻ in acid rain has contributed to the modern increase in the MeHg burdens of remote lakes hydrologically connected to peatlands.     

Comparison of Point-of-Use Technologies for Emergency Disinfection of Sewage-Contaminated Drinking Water

Four point-of-use disinfection technologies for treating sewage-contaminated well water were compared. Three systems, based on flocculant-disinfectant packets and N-halamine chlorine and bromine contact disinfectants, provided a range of 4.0 to >6.6 log₁₀ reductions (LR) of naturally occurring fecal indicator and heterotrophic bacteria and a range of 0.9 to >1.9 LR of coliphage.Disasters and flooding can overwhelm sanitation infrastructure, leading to sewage contamination of potable waters. This may be routine during the wet season in many parts of the world and spreads numerous waterborne diseases (21). Point-of-use (POU) water treatment has reduced the incidence of diarrheal disease when used for household drinking water (3, 4, 6, 13) and is now being promoted for disaster relief. While POU systems have recently been reviewed (14), to our knowledge there has been no direct, experimental comparison for treating actual sewage-contaminated waters. In this study, the efficacies of four POU disinfection systems (based on sodium dichloroisocyanurate [NaDCC] tablets, a flocculent-disinfectant powder, and chlorine and bromine contact disinfectant cartridges) in reducing the concentrations of six microbial indicators in well water contaminated with raw sewage were compared.The NaDCC tablets (67 mg; Aquatabs; Medentech, Wexford, Ireland), used for disinfection in low-turbidity water, have shown preliminary efficacy for routine household drinking water treatment (3, 4). The flocculant-disinfectant packet (4 g; PUR; Procter & Gamble Co., Cincinnati, OH) includes Fe₂(SO₄)₃, bentonite, Na₂CO₃, chitosan, polyacrylamide, KMnO₄, and Ca(OCl)₂ (13). It achieved >7.3 log₁₀ reductions (LR) of 24 bacteria species; >4.6 LR of poliovirus and rotavirus in EPA no. 2 test water (turbidity, >30 nephelometric turbidity units [NTU]) (15); and reduced diarrheal illness in Guatemala, Liberia, Kenya, and Pakistan (6, 7, 11, 13).HaloPure canisters (Eureka Forbes, Mumbai, India) contain N-halamine polymer disinfectant beads, poly[1,2-dichloro-5-methyl-5-(4′-vinylphenyl)hydrantoin] for chlorine canisters, and poly[1,2-dibromo-5-methyl-5-(4′-vinylphenyl)hydrantoin] for bromine canisters. Seeded laboratory trials achieved >6.8 LR for Escherichia coli and Staphylococcus aureus as water was passed through the canisters (2). The Cl-contact (producing residuals ranging from 0 to 0.6 mg/liter) and Br-contact (with residuals of 0.68 to 1.8 mg/liter) disinfectants achieved 2.9 LR and 5.0 LR of the bacteriophage MS2, respectively, and 27.5% and 88.5% reductions of the algal toxin microcystin, respectively (5).Sewage-contaminated water was prepared by mixing 9 liters of potable, nonchlorinated well water (pH 7.8; turbidity, 0.33 NTU; Williamston, MI) with 1 liter of raw sewage (City of East Lansing Wastewater Treatment Plant, MI) with an average pH of 6.6 ± 0.1, a biochemical oxygen demand of 144 ± 36 mg/liter, a concentration of total suspended solids of 146 ± 31 mg/liter, and a turbidity of 132 ± 12 NTU. Three disinfection trials were conducted at room temperature for each POU system on three different days to allow for variance in sewage strength. The turbidities of 1:10 dilutions of raw sewage averaged 7.5 ± 2.0 NTU. Table ​Table11 lists the indicator microorganism concentrations in the influent and effluent for each system.

TABLE 1.

Concentrations of influent and 30-min-effluent microorganisms for POU disinfectant systems treating sewage-contaminated water

High-Frequency Phage-Mediated Gene Transfer among Escherichia coli Cells, Determined at the Single-Cell Level

Recent whole-genome analysis suggests that lateral gene transfer by bacteriophages has contributed significantly to the genetic diversity of bacteria. To accurately determine the frequency of phage-mediated gene transfer, we employed cycling primed in situ amplification-fluorescent in situ hybridization (CPRINS-FISH) and investigated the movement of the ampicillin resistance gene among Escherichia coli cells mediated by phage at the single-cell level. Phages P1 and T4 and the newly isolated E. coli phage EC10 were used as vectors. The transduction frequencies determined by conventional plating were 3 × 10⁻⁸ to 2 × 10⁻⁶, 1 × 10⁻⁸ to 4 × 10⁻⁸, and <4 × 10⁻⁹ to 4 × 10⁻⁸ per PFU for phages P1, T4, and EC10, respectively. The frequencies of DNA transfer determined by CPRINS-FISH were 7 × 10⁻⁴ to 1 × 10⁻³, 9 × 10⁻⁴ to 3 × 10⁻³, and 5 × 10⁻⁴ to 4 × 10⁻³ for phages P1, T4, and EC10, respectively. Direct viable counting combined with CPRINS-FISH revealed that more than 20% of the cells carrying the transferred gene retained their viabilities. These results revealed that the difference in the number of viable cells carrying the transferred gene and the number of cells capable of growth on the selective medium was 3 to 4 orders of magnitude, indicating that phage-mediated exchange of DNA sequences among bacteria occurs with unexpectedly high frequency.     

The Relationship between Inflammatory Biomarkers and Telomere Length in an Occupational Prospective Cohort Study

Background

Chronic inflammation from recurring trauma is an underlying pathophysiological basis of numerous diseases. Furthermore, it may result in cell death, scarring, fibrosis, and loss of tissue function. In states of inflammation, subsequent increases in oxidative stress and cellular division may lead to the accelerated erosion of telomeres, crucial genomic structures which protect chromosomes from decay. However, the association between plasma inflammatory marker concentrations and telomere length has been inconsistent in previous studies.

Objective

The purpose of this study was to determine the longitudinal association between telomere length and plasma inflammatory biomarker concentrations including: CRP, SAA, sICAM-1, sVCAM-1, VEGF, TNF-α, IL-1β, IL-2, IL-6, IL-8, and IL-10.

Methods

The longitudinal study population consisted of 87 subjects. The follow-up period was approximately 2 years. Plasma inflammatory biomarker concentrations were assessed using highly sensitive electrochemiluminescent assays. Leukocyte relative telomere length was assessed using Real-Time qPCR. Linear mixed effects regression models were used to analyze the association between repeated-measurements of relative telomere length as the outcome and each inflammatory biomarker concentration as continuous exposures separately. The analyses controlled for major potential confounders and white blood cell differentials.

Results

At any follow-up time, each incremental ng/mL increase in plasma CRP concentration was associated with a decrease in telomere length of −2.6×10⁻² (95%CI: −4.3×10⁻², −8.2×10⁻³, p = 0.004) units. Similarly, the estimate for the negative linear association between SAA and telomere length was −2.6×10⁻² (95%CI:−4.5×10⁻², −6.1×10⁻³, p = 0.011). No statistically significant associations were observed between telomere length and plasma concentrations of pro-inflammatory interleukins, TNF-α, and VEGF.

Conclusions

Findings from this study suggest that increased systemic inflammation, consistent with vascular injury, is associated with decreased leukocyte telomere length.     

Involvement of Abscisic Acid in Regulating Water Status in Phaseolus vulgaris L. during Chilling

During the first hours of chilling, bean (Phaseolus vulgaris L., cv Mondragone) seedlings suffer severe water stress and wilt without any significant increase in leaf abscisic acid (ABA) content (P. Vernieri, A. Pardossi, F. Tognoni [1991] Aust J Plant Physiol 18: 25-35). Plants regain turgor after 30 to 40 h. We hypothesized that inability to rapidly synthesize ABA at low temperatures contributes to chilling-induced water stress and that turgor recovery after 30 to 40 h is mediated by changes in endogenous ABA content. Entire bean seedlings were subjected to long-term (up to 6 d) chilling (3°C, 0.2-0.4 kPa vapor pressure deficit, 100 μmol·m⁻²·s⁻¹ photosynthetic photon flux density, continuous fluorescent light). During the first 24 h, stomata remained open, and plants rapidly wilted as leaf transpiration exceeded root water absorption. During this phase, ABA did not accumulate in leaves or in roots. After 24 h, ABA content increased in both tissues, leaf diffusion resistance increased, and plants rehydrated and regained turgor. No osmotic adjustment was associated with turgor recovery. Following turgor recovery, stomata remained closed, and ABA levels in both roots and leaves were elevated compared with controls. The application of ABA (0.1 mm) to the root system of the plants throughout exposure to 3°C prevented the chilling-induced water stress. Excised leaves fed 0.1 mm ABA via the transpiration stream had greater leaf diffusion resistance at 20 and 3°C compared with non-ABA fed controls, but the amount of ABA needed to elicit a given degree of stomatal closure was higher at 3°C compared with 20°C. These findings suggest that endogenous ABA may play a role in ameliorating plant water status during chilling.     

Essential arginine residues in the nitrate uptake system from corn seedling roots

Three dicarbonyl reagents were used to demonstrate the presence of an essential arginine residue in the NO₃⁻ uptake system from corn seedling roots (Zea mays L., Golden Cross Bantam). Incubation of corn seedlings with 2,3-butanedione (0.125-1.0 millimolar) and 1,2-cyclohexanedione (0.5-4.0 millimolar) in the presence of borate or with phenylglyoxal (0.25-2.0 millimolar) at pH 7.0 and 30°C resulted in a time-dependent loss of NO₃⁻ uptake following pseudo-first-order kinetics. Second-order rate constants obtained from slopes of linear plots of pseudo-first-order rate constants versus reagent concentrations were 1.67 × 10⁻², 0.68 × 10⁻², and 1.00 × 10⁻² millimolar per minute for 2,3-butanedione, 1,2-cyclohexanedione, and phenylglyoxal, respectively, indicating the faster rate of inactivation with 2,3-butanedione at equimolar concentration. Double log plots of pseudo-first-order rate constants versus reagent concentrations yielded slope values of 1.031 (2,3-butanedione), 1.004 (1,2-cyclohexanedione), and 1.067 (phenylglyoxal), respectively, suggesting the modification of a single arginine residue. The effectiveness of the dicarbonyl reagents appeared to increase with increasing medium pH from 5.5 to 8.0. Unaltered K_m and decreased V_max in the presence of reagents indicate the inactivation of the modified carriers with unaltered properties. The results thus obtained indicate that the NO₃⁻ transport system possesses at least one essential arginine residue.     

Biological Instability in a Chlorinated Drinking Water Distribution Network

The purpose of a drinking water distribution system is to deliver drinking water to the consumer, preferably with the same quality as when it left the treatment plant. In this context, the maintenance of good microbiological quality is often referred to as biological stability, and the addition of sufficient chlorine residuals is regarded as one way to achieve this. The full-scale drinking water distribution system of Riga (Latvia) was investigated with respect to biological stability in chlorinated drinking water. Flow cytometric (FCM) intact cell concentrations, intracellular adenosine tri-phosphate (ATP), heterotrophic plate counts and residual chlorine measurements were performed to evaluate the drinking water quality and stability at 49 sampling points throughout the distribution network. Cell viability methods were compared and the importance of extracellular ATP measurements was examined as well. FCM intact cell concentrations varied from 5×10³ cells mL⁻¹ to 4.66×10⁵ cells mL⁻¹ in the network. While this parameter did not exceed 2.1×10⁴ cells mL⁻¹ in the effluent from any water treatment plant, 50% of all the network samples contained more than 1.06×10⁵ cells mL⁻¹. This indisputably demonstrates biological instability in this particular drinking water distribution system, which was ascribed to a loss of disinfectant residuals and concomitant bacterial growth. The study highlights the potential of using cultivation-independent methods for the assessment of chlorinated water samples. In addition, it underlines the complexity of full-scale drinking water distribution systems, and the resulting challenges to establish the causes of biological instability.     

Recent Changes in Glacial Area and Volume on Tuanjiefeng Peak Region of Qilian Mountains,China

Glaciers'' runoff in the Qilian Mountains serves as a critical water resource in the northern sections of the Gansu province, the northeastern sections of the Qinghai province, and the northeastern fringe of the Tibetan Plateau. Changes in the glacial area and volume around the highest peak of the Qilian Mountains, i.e., Tuanjiefeng Peak, were estimated using multi-temporal remote-sensing images and digital elevation models, and all possible sources of uncertainty were considered in detail. The total glacier area decreased by 16.1±6.34 km² (9.9±3.9%) during 1966 to 2010. The average annual glacier shrinkage was −0.15% a⁻¹ from 1966 to 1995, −0.61% a⁻¹ from 1995 to 2000, −0.20% a⁻¹ from 2000 to 2006, and −0.45% a⁻¹ from 2006 to 2010. A comparison of glacier surface elevations using digital elevation models derived from topographic maps in 1966 and from the Shuttle Radar Topography Mission in 1999 suggests that 65% of the grid cells has decreased, thereby indicating that the glacier thickness has declined. The average change in glacier thickness was −7.3±1.5 m (−0.21±0.04 m·a⁻¹) from 1966 to 1999. Glaciers with northeastern aspects thinned by 8.3±1.4 m from 1966 to 1999, i.e., almost twice as much as those with southwestern aspects (4.3±1.3 m). The ice volume decreased by 11.72±2.38×10⁸ m³ from 1966 to 1999, which was about 17.4% more than the value calculated from the statistical relationship between glacier area and volume. The relationship between glacier area change and elevation zone indicates that glacier change is not only dominated by climate change but also affected by glacier dynamics, which are related to local topography. The varied response of a single glacier to climate change indicates that the glacier area change scheme used in some models must be improved.     

Phanerochaete chrysosporium β-Glucosidases: Induction, Cellular Localization, and Physical Characterization

Phanerochaete chrysosporium produces intracellular soluble and particulate β-glucosidases and an extracellular β-glucosidase. The extracellular enzyme is induced by cellulose but repressed in the presence of glucose. The molecular weight of this enzyme is 90,000. The K_m for p-nitrophenyl-β-glucoside is 1.6 × 10⁻⁴ M; the K_i for glucose, a competitive inhibitor, is 5.0 × 10⁻⁴ M. The K_m for cellobiose is 5.3 × 10⁻⁴ M. The intracellular soluble enzyme is induced by cellobiose; this induction is prevented by cycloheximide. The presence of 300 mM glucose in the medium, however, had no effect on induction. The K_m for p-nitrophenyl-β-glucoside is 1.1 × 10⁻⁴ M. The molecular weight of this enzyme is ~410,000. Both enzymes have an optimal temperature of 45°C and an E_act of 9.15 kcal (ca. 3.83 × 10⁴ J). The pH optima, however, were ~7.0 and 5.5 for the intracellular and extracellular enzymes, respectively.     

Effects of temperature on orthophosphate absorption by excised corn roots

The uptake of orthophosphate (³²P) by excised corn roots, Zea mays L. was studied using roots grown on 0.2 mm CaSO₄. Nine concentrations of KH₂PO₄ from 1 to 256 μm were used at temperatures of 20°, 30°, and 40°. Enzyme kinetic analysis was applied to the data obtained. Two apparent mechanisms (sites) of phosphate uptake were observed, 1 dominating at high P concentrations and 1 at low P concentrations. A Km of 1.36 × 10⁻⁴ and a Vmax of 177 × 10⁻⁹ moles per gram of roots per hour at 30° was calculated for the mechanism dominating at high P concentrations. Similar calculations gave a Km of 6.09 × 10⁻⁶ and a Vmax of 162 × 10⁻⁹ moles per gram of roots per hour at 30° for the mechanism dominating at low P concentrations. The Q₁₀ for both mechanisms was approximately 2. Calculation of thermodynamic values from the data gave ΔF of − 5200 cal, ΔH of − 950 to − 1400 cal, and a enthalpy of activation (A) of 10,300 to 13,800 cal per mole for the mechanism dominating at high P concentrations. Similar calculations from the data for the mechanism dominating at low P concentrations gave a ΔF of − 7300 cal, ΔH of − 10,700 to − 8200 cal, and a A of 9300 to 18,900 cal per mole. If the dual mechanism interpretation of this kind of data adequately describes this system, then both mechanisms of P absorption by corn roots involve chemical reactions.