Do exposures to aerosols pose a risk to dental professionals?

BACKGROUND: Dental care professionals are exposed to aerosols from the oral cavity of patients containing several pathogenic microorganisms. Bioaerosols generated during dental treatment are a potential hazard to dental staff, and there have been growing concerns about their role in transmission of various airborne infections and about reducing the risk of contamination. AIMS: To investigate qualitatively and quantitatively the bacterial and fungal aerosols before and during clinical sessions in two dental offices compared with controls. METHODS: An extra-oral evacuator system was used to measure bacterial and fungal aerosols. Macroscopic and microscopic analysis of bacterial species and fungal strains was performed and strains of bacteria and fungi were identified based on their metabolic properties using biochemical tests. RESULTS: Thirty-three bioaerosol samples were obtained. Quantitative and qualitative evaluation showed that during treatment, there is a significant increase in airborne concentration of bacteria and fungi. The microflora included mainly gram-positive organisms (Staphylococcus epidermidis and Micrococcus spp.), gram-positive rod-shaped bacteria and those creating endospores as well as non-porous bacteria and mould fungi (Cladosporium and Penicillium). CONCLUSIONS: Exposure to the microorganisms identified is not a significant occupational hazard for dental care professionals; however, evidence-based prevention measures are recommended.

PAH-pools in soils along a PAH-deposition gradient.

The objectives of this study are to characterize different PAH-pools (soil horizons, microsites influenced by stem flow, aggregate core and surface fractions, particle size fractions) in soils affected by depositions. Three forest soils affected by the emissions of an aluminium plant near Ziar/Central Slovakia were sampled to analyze 20 PAHs. The organic layers have high concentrations of PAHs (40-200 mg kg(-1)), decreasing as soil depth and distance from the aluminium plant increases. At the two sites nearest to the plant PAH-concentrations are higher in microsites affected by stem flow than in microsites not influenced by stem flow. They are also higher in aggregate surface fractions than in aggregate core fractions and in bulk soil samples than in aggregates. Sand- and siltsize particles contain decreasing percentages of the sum PAH-concentrations as distance from the plant increases. This microscale heterogeneity affects PAH-availability and has to be considered when assessing environmental risks.

Soil monitoring system in Slovakia.

It can be said that the quality of the environment has become of increasing interest for many developed countries especially during the last one or two decades. It is important to know what has been the influence of human activity (especially industry, agriculture, etc.) upon the quality of the main components of the environment.Soil as one important part of the environment is more complicated as it includes organic and inorganic components and which involves comparing the monitoring with other environment components (i.e. monitoring of air, water, etc.).

Identification and levels of 2'-carboxyarabinitol in leaves.

2'-Carboxyarabinitol 1-phosphate (CA1P) is a naturally occurring inhibitor of ribulose-1,5 bisphosphate carboxylase/oxygenase activity. A chloroplast phosphatase has previously been identified that degrades CA1P in vitro to carboxyarabinitol (CA) plus phosphate, but CA has not yet been detected in plants. Here, we detail procedures to isolate and assay CA from leaves and utilize mass spectrometry to demonstrate for the first time that CA is present in plants. CA was present in leaves of all 13 species examined, including those of C(3), C(4), and Crassulacean acid metabolism photosynthetic subgroups. CA was present both in species with high levels of CA1P (e.g. Phaseolus vulgaris, Lycopersicon esculentum, Beta vulgaris) as well as in species with low levels of CA1P (e.g. Spinacea oleracea, Triticum aestivum). CA levels in the light were sometimes greater than those in the dark. Bean leaves had the most CA of any species tested, with levels in the light approaching 1 micromole per milligram of chlorophyll. In illuminated bean leaves, about 63% of the CA is located outside the chloroplast. CA is one of only a few branched chain sugar acids to be identified from plants.

Measurement of 2-carboxyarabinitol 1-phosphate in plant leaves by isotope dilution.

The level of 2-carboxyarabinitol 1-phosphate (CA1P) in leaves of 12 species was determined by an isotope dilution assay. (14)C-labeled standard was synthesized from [2-(14)C]carboxyarabinitol 1,5-bisphosphate using acid phosphatase, and was added at the initial point of leaf extraction. Leaf CA1P was purified and its specific activity determined. CA1P was found in dark-treated leaves of all species examined, including spinach (Spinacea oleracea), wheat (Triticum aestivum), Arabidopsis thaliana, and maize (Zea mays). The highest amounts were found in bean (Phaseolus vulgaris) and petunia (Petunia hybrida), which had 1.5 to 1.8 moles CA1P per mole ribulose 1,5-bisphosphate carboxylase catalytic sites. Most species had intermediate amounts of CA1P (0.2 to 0.8 mole CA1P per mole catalytic sites). Such intermediate to high levels of CA1P support the hypothesis that CA1P functions in many species as a light-dependent regulator of ribulose 1,5-bisphosphate carboxylase activity and whole leaf photosynthetic CO(2) assimilation. However, CA1P levels in spinach, wheat, and A. thaliana were particularly low (less than 0.09 mole CA1P per mole catalytic sites). In such species, CA1P does not likely have a significant role in regulating ribulose 1,5-bisphosphate carboxylase activity, but could have a different physiological role.

Metabolism of 2-carboxyarabinitol 1-phosphate and regulation of ribulose-1,5-bisphosphate carboxylase activity.

Metabolism of 2'-carboxy-D-arabinitol 1-phosphate (CA1P) is an important component in the light-dependent regulation of ribulose-1,5-bisphosphate carboxylase (Rubisco) activity and whole leaf photosynthetic CO2 assimilation in many species, and functions as one mechanism for regulating Rubisco activity when photosynthesis is light-limited. Species differ in their capacity to accumulate CA1P, ranging from those which can synthesize levels of this compound approaching or in excess of the Rubisco catalytic site concentration, to those which apparently lack the capacity for CA1P synthesis. CA1P is structurally related to the six carbon transition state intermediate of the carboxylation reaction and binds tightly to the carbamylated catalytic site of Rubisco, making that site unavailable for catalysis. Under steady-state, the concentration of CA1P in the leaf is highest at low photon flux density (PFD) or in the dark. Degradation of CA1P and recovery of Rubisco activity requires light and is stimulated by increasing PFD. The initial degradation reaction is catalyzed by an enzyme located in the chloroplast stroma, CA1P phosphatase, which yields carboxyarabinitol (CA) and inorganic phosphate as its products. The pathway of CA metabolism in the plant remains to be determined. Synthesis of CA1P occurs in the dark, and in Phaseolus vulgaris this process has been shown to be stimulated by low PFD. The pathway of CA1P synthesis and its relationship to the degradative pathway remains unknown at the present time. The discovery of the existence of this previously unknown carbon pathway in photosynthesis indicates that we still have much to learn concerning the regulation of Rubisco activity and photosynthesis.

Regulation of ribulose-1,5-bisphosphate carboxylase activity in response to diurnal changes in irradiance.

The regulation of ribulose-1,5-bisphosphate (RuBP) carboxylase (Rubisco) activity and metabolite pool sizes in response to natural diurnal changes in photon flux density (PFD) was examined in three species (Phaseolus vulgaris, Beta vulgaris, and Spinacia oleracea) known to differ in the mechanisms used for this regulation. Diurnal regulation of Rubisco activity in P. vulgaris was primarily the result of metabolism of the naturally occurring tight-binding inhibitor of Rubisco, 2-carboxyarabinitol 1-phosphate (CA1P). In B. vulgaris, the regulation of Rubisco activity was the result of both changes in activation state and CA1P metabolism. In S. oleracea, Rubisco activity was regulated by a combination of changes in activation state and the binding/release of another tight binding inhibitor, probably RuBP. Despite these different mechanisms for the light regulation of Rubisco activity, the relationship between the in vivo activity of Rubisco and the PFD was the same for all three species. Rates of CA1P metabolism were thus sufficient to allow this mechanism to participate in the diurnal regulation of Rubisco activity as PFD changed at its normal rate. Furthermore, under natural conditions this regulatory mechanism was found to be important in controlling Rubisco activity over approximately the same range of PFD as did changes in activation state of the enzyme. Finally, this regulation of Rubisco activity resulted in relatively similar and saturating RuBP pool sizes for photosynthesis at all but the lowest PFD values in all three species.

Light-dependent kinetics of 2-carboxyarabinitol 1-phosphate metabolism and ribulose-1,5-bisphosphate carboxylase activity in vivo.

The light-dependent kinetics of the apparent in vivo synthesis and degradation of 2-carboxyarabinitol 1-phosphate (CA1P) were studied in three species of higher plants which differ in the extent to which this compound is involved in the light-dependent regulation of ribulose-1,5-bisphosphate carboxylase (Rubisco) activity. Detailed studies with Phaseolus vulgaris indicate that both the degradation and synthesis of this compound are light-stimulated, although light is absolutely required only for CA1P degradation. We hypothesize that the steady state level of CAIP at any particular photon flux density (PFD) represents a pseudo-steady state balance between ongoing synthesis and degradation of this compound. The rate of CA1P synthesis in P. vulgaris and the resultant reduction in the total catalytic constant of Rubisco were maximal at 200 micromoles quanta per square meter per second following a step decrease from a saturating PFD, and substantially faster than the rate of synthesis in the dark. Under these conditions an amount of CA1P equivalent to approximately 25% of the Rubisco catalytic site content was synthesized in less than 1 minute. The rate of synthesis was reduced at higher or lower PFDs. In Beta vulgaris, the rate of CA1P synthesis at 200 micromoles quanta per square meter per second was substantially slower than in P. vulgaris. In Spinacea oleracea, an apparent noncatalytic tight-binding of RuBP to deactivated sites on the enzyme was found to occur following a step decrease in PFD. When dark acclimated leaves of P. vulgaris were exposed to a step increase in PFD, the initial rate of CA1P degradation was also found to be dependent on PFD up to a maximum of approximately 300 to 400 micromoles quanta per square meter per second. The rate of degradation of this compound was similar in B. vulgaris. In S. oleracea, a step increase in PFD resulted in noncatalytic RuBP binding to Rubisco followed by an apparent release of RuBP and activation of the enzyme. The in vivo rate of change of Rubisco activity in response to an increase or decrease in PFD was similar between species despite the differences between species in the mechanisms used for the regulation of this enzyme's activity.

Mechanisms for light-dependent regulation of ribulose-1,5-bisphosphate carboxylase activity and photosynthesis in intact leaves.

The mechanisms involved in the in vivo light-dependent regulation of ribulose-1,5-bisphosphate (RbuP(2)) carboxylase [3-phospho-D-glycerate carboxy-lyase (dimerizing), EC 4.1.1.39] activity in intact leaves were studied. In the three species examined, Phaseolus vulgaris, Beta vulgaris, and Spinacea oleracea, the regulated level of RbuP(2) carboxylase activity (assayed in vitro with saturating substrate) was highly correlated (r = 0.96) with the rate of net CO(2) uptake of the corresponding leaves measured over a wide range of photosynthetic photon flux density (PPFD). However, the mechanisms by which the enzyme was regulated differed between these species. In Phaseolus, the inhibitor 2-carboxyarabinitol 1-phosphate (CAP) accounted for all of the PPFD-dependent regulation of RbuP(2) carboxylase activity. A similar compound was detected in Beta, and changes in its concentration accounted for about half of the PPFD-dependent regulation of enzyme activity in this species. No CAP was detected in Spinacea, but evidence we obtained suggests that a different inhibitor (possibly RbuP(2)) accounts for a significant portion of the PPFD-dependent regulation of enzyme activity in this species. Changes in the activation state of the enzyme were observed with Beta and Spinacea, while in Phaseolus the enzyme was apparently fully activated at all PPFD levels. These results indicate that plant species may differ markedly in the mechanisms they use to regulate RbuP(2) carboxylase activity as PPFD changes. The results also suggest that tight binding inhibitors are a more widespread mechanism for regulation of this enzyme than previously thought. Furthermore, the results establish the importance of such inhibitors in regulating both the activity of RbuP(2) carboxylase and whole leaf photosynthesis over a range of PPFD.

Reduced Cytosolic Fructose-1,6-Bisphosphatase Activity Leads to Loss of O(2) Sensitivity in a Flaveria linearis Mutant.

The mutant plant of Flaveria linearis characterized by Brown et al. (Plant Physiol. 81: 212-215) was studied to determine the cause of the reduced sensitivity to O(2). Analysis of CO(2) assimilation metabolites of freeze clamped leaves revealed that both 3-phosphoglycerate and ribulose 1,5-bisphosphate were high in the mutant plant relative to F. linearis with normal O(2) sensitivity. The k(cat) of ribulose-1,5-bisphosphate carboxylase (RuBPCase) was equal in all plant material tested (range 18-22 s(-1)) indicating that no tight binding inhibitor was present. The degree of RuBPCase carbamylation was reduced in the mutant plant relative to the wild-type plant. Since 3-phosphoglycerate was high in the mutant plant and photosynthesis did not exhibit properties associated with RuBPCase limitations, we believe that the decarbamylation of RuBPCase was a consequence of another lesion in photosynthesis. Fructose 1,6-bisphosphate and its precursors, such as the triose phosphates, were in high concentration in the mutant plant relative to the wild type. The concentrations of the product of the fructose 1,6-bisphosphatase reaction, fructose 6-phosphate, and its isomer, glucose 6-phosphate, were the same in both plants. We found that the mutant plant had up to 75% less cytosolic fructose 1,6-bisphosphatase activity than the wild type but comparable levels of stromal fructose 1,6-bisphosphatase. We conclude that the reduced fructose-1,6-bisphosphatase activity restricts the mutant plant's capacity for sucrose synthesis and this leads to reduced or reversed O(2) sensitivity.

Influences of leaf temperature on photosynthetic carbon metabolism in wheat.

Net photosynthetic assimilation rate (A), extractable activities of three photosynthetic enzymes, and the concentrations of six metabolites were determined for wheat (Tricum aestivum L.) leaves as leaf temperature was varied under photorespiring (350 microliters per liter CO(2) and 21% O(2)) and under nonphotorespiring conditions (800 microliters per liter CO(2) and 2% O(2)). The extractable activity of ribulose-1,5-bisphosphate carboxylase (Rubisco) and fructose-1,6-bisphosphatase declined with increasing leaf temperature from 15 to 45 degrees C. Leaf concentrations of ribulose-1,5-bisphosphate (RuBP) declined slightly between 15 and 25 degrees C but increased to a level which is 4 to 5 times the binding site concentration of Rubisco at leaf temperatures of 35 and 45 degrees C. Leaf concentrations of 3-phosphoglycerate, fructose-6-phosphate, and glucose-6-phosphate all declined with increasing leaf temperature. Outside of the limitations imposed by photorespiration, it is proposed that under high light and at suboptimal temperatures, A is limited by rate of utilization of triose phosphate; at optimal temperatures, by the availability of substrate (CO(2) and RuBP) under photorespiring conditions or utilization of triose phosphate under nonphotorespiring conditions; and at supraoptimal temperatures, by the activation state of Rubisco.

The photosynthetic induction response in wheat leaves: net CO2 uptake, enzyme activation, and leaf metabolites.

The photosynthetic induction response was studied in whole leaves of wheat (Triticum aestivum L.) following 5-min, 30-min and 10-h dark periods. After the 5-min dark treatment there was a rapid burst in the rate of photosynthesis upon illumination (half of maximum after 30s), followed by a slight decrease after 1.5 more min and then a gradual rise to the maximum rate. During this initial burst in photosynthesis, there was a rapid rise in the level of 3-phosphoglycerate (PGA) and a high PGA/triose-phosphate (triose-P) ratio was obtained. In addition, after the 5-min dark treatment, ribulose-1,5-bisphosphate carboxylase (Rubisco, EC 4.1.1.39), ribulose-5-phosphate kinase (EC 2.7.1.19) and chloroplastic fructose-1,6-bisphosphatase (EC 3.1.3.11) maintained a relatively high state of activation, and maximum activation occurred within 1 min of illumination. The results indicate there is a high capacity for CO2 fixation in the cycle upon illumination but attaining maximum rates requires an increase in the ribulose-1,5-bisphosphate (RuBP) pool (adjustment in triose-P utilization for carbohydrate synthesis versus RuBP synthesis). With both the 30-min and 10-h dark pretreatments there was only a slight rise in photosynthesis upon illumination, followed by a lag, then a gradual increase to steady-state (half-maximum rate after 6 min). In contrast to the 5-min dark treatment, the level of PGA was low and actually decreased initially, whereas the level of RuBP increased and was high during induction, indicating that Rubisco is limiting. This regulation via the carboxylase was not reflected in the initial extractable activity, which reached a maximum by 1 min after illumination. The light activation of chloroplastic fructose-1,6-bisphosphatase in leaves darkened for 30 min and 10 h prior to illumination was relatively slow (reaching a maximum after 8 min). However, this was not considered to limit carbon flux through the carbon-fixation cycle during induction since RuBP was not limiting. When photosynthesis approached the maximum steady-state rate, a high PGA/triose-P ratio and a high PGA/RuBP ratio were obtained. This may allow a high rate of photosynthesis by producing a favorable mass-action ratio for the reductive phase (the conversion of PGA to triose phosphate) while stimulating starch and sucrose synthesis.

Temperature Dependence of Photosynthesis in Agropyron smithii Rydb. : III. Responses of Protoplasts and Intact Chloroplasts.

Protoplasts and intact chloroplasts isolated from Agropyron smithii Rybd. were utilized in an effort to determine the limiting factor(s) for photosynthesis at supraoptimal temperatures. Saturated CO(2)-dependent O(2) evolution had a temperature optimum of 35 degrees C for both protoplasts and intact chloroplasts. A sharp decline in activity was observed as assay temperature was increased above 35 degrees C, and at 45 degrees C only 20% of the maximal rate remained. The temperature optimum for 3-phosphoglycerate reduction by intact chloroplasts was 35 degrees C. Above this temperature, 3-phosphoglycerate reduction was more stable than CO(2)-dependent O(2) evolution. Reduction of nitrite in coupled intact chloroplasts had a temperature optimum of 40 degrees C with only slight variation in activity between 35 degrees C and 45 degrees C. Reduction of nitrite in uncoupled chloroplasts had a temperature optimum of 40 degrees C, but increasing the assay temperature to 45 degrees C resulted in a complete loss of activity. Reduction of p-benzoquinone by protoplasts and intact chloroplasts had a temperature optimum of 32 degrees C when measured in the presence of dibromothymoquinone. This photosystem II activity exhibited a strong inhibition of O(2) evolution as assay temperature increased above the optimum. It is concluded that, below the temperature optimum, ATP and reductant were not limiting photosynthesis in these systems or intact leaves. Above the temperature optimum, photosynthesis in these systems is limited in part by the phosphorylation potential of the stromal compartment and not by the available reductant.