Changes in respiratory mitochondrial machinery and cytochrome and alternative pathway activities in response to energy demand underlie the acclimation of respiration to elevated CO2 in the invasive Opuntia ficus-indica

Studies on long-term effects of plants grown at elevated CO(2) are scarce and mechanisms of such responses are largely unknown. To gain mechanistic understanding on respiratory acclimation to elevated CO(2), the Crassulacean acid metabolism Mediterranean invasive Opuntia ficus-indica Miller was grown at various CO(2) concentrations. Respiration rates, maximum activity of cytochrome c oxidase, and active mitochondrial number consistently decreased in plants grown at elevated CO(2) during the 9 months of the study when compared to ambient plants. Plant growth at elevated CO(2) also reduced cytochrome pathway activity, but increased the activity of the alternative pathway. Despite all these effects seen in plants grown at high CO(2), the specific oxygen uptake rate per unit of active mitochondria was the same for plants grown at ambient and elevated CO(2). Although decreases in photorespiration activity have been pointed out as a factor contributing to the long-term acclimation of plant respiration to growth at elevated CO(2), the homeostatic maintenance of specific respiratory rate per unit of mitochondria in response to high CO(2) suggests that photorespiratory activity may play a small role on the long-term acclimation of respiration to elevated CO(2). However, despite growth enhancement and as a result of the inhibition in cytochrome pathway activity by elevated CO(2), total mitochondrial ATP production was decreased by plant growth at elevated CO(2) when compared to ambient-grown plants. Because plant growth at elevated CO(2) increased biomass but reduced respiratory machinery, activity, and ATP yields while maintaining O(2) consumption rates per unit of mitochondria, we suggest that acclimation to elevated CO(2) results from physiological adjustment of respiration to tissue ATP demand, which may not be entirely driven by nitrogen metabolism as previously suggested.     

Effect of Polyphenols on the Growth and Enzymes of Some Animal Cells

The effect was investigated of some polyphenol compounds on the growth and intracellular enzyme activity of human-derived cells and Chinese hamster ovary (CHO) cells. Quercetin, a mutagen, inhibited the growth of serum-free cultured human-human hybridomas (SI102 and HB4C5) and a human histiocytic lymphoma cell line (U-937), but did not affect the growth of CHO cells. Glycosides of quercetin such as quercetin-4′-glucoside (Q-4′-G), quercetin-3,4′-glucoside (Q-3,4′-G) and rutin, and other polyphenol compounds (catechin and epicatechin) had no significant inhibiting effect on the growth of human-derived cells or CHO cells. These compounds slightly promoted the growth of human-derived cells. Most of the polyphenols used increased the activity of a drug-metabolizing enzyme, NADPH-cytochrome C reductase, in the U-937 cells and CHO cells, this effect being more marked in the CHO cells than in the U-937 cells. Quercetin markedly reduced the activity of catalase in the human-derived cell lines, while it slightly activated catalase in the CHO cells. Rutin, Q-4′-G, Q-3,4′-G, catechin and epicatechin produced no significant change in catalase activity. Quercetin also reduced the activity of glutamic oxaloacetic transaminase in the U-937 cells.     

Pollutant degradation by a Methylocystis strain SB2 grown on ethanol: bioremediation via facultative methanotrophy

A facultative methanotroph, Methylocystis strain SB2, was examined for its ability to degrade chlorinated hydrocarbons when grown on methane or ethanol. Strain SB2 grown on methane degraded vinyl chloride (VC), trans-dichloroethylene (t-DCE), trichloroethylene (TCE), 1,1,1-trichloroethane (1,1,1-TCA), and chloroform (CF), but not dichloromethane (DCM). Growth on methane was reduced in the presence of any chlorinated hydrocarbon. Strain SB2 grown on ethanol degraded VC, t-DCE, and TCE, and 1,1,1-TCA, but not DCM or CF. With the exception of 1,1,1-TCA, the growth of strain SB2 on ethanol was not affected by any individual chlorinated hydrocarbon. No degradation of any chlorinated hydrocarbon was observed when acetylene was added to ethanol-grown cultures, indicating that this degradation was due to particulate methane monooxygenase (pMMO) activity. When mixtures of chlorinated alkanes or alkenes were added to cultures growing on methane or ethanol, chlorinated alkene degradation occurred, but chlorinated alkanes were not, and growth was reduced on both methane and ethanol. Collectively, these data indicate that competitive inhibition of pMMO activity limits methanotrophic growth and pollutant degradation. Facultative methanotrophy may thus be useful to extend the utility of methanotrophs for bioremediation as the use of alternative growth substrates allows for pMMO activity to be focused on pollutant degradation.     

Differential Effects of Insulin on Choline Acetyltransferase and Glutamic Acid Decarboxylase Activities in Neuron-Rich Striatal Cultures

We studied the effects of insulin, nerve growth factor (NGF), and tetrodotoxin (TTX) on cellular metabolism and the activity of glutamic acid decarboxylase (GAD) and choline acetyltransferase (ChAT) in neuron-rich cultures prepared from embryonic day 15 rat striatum. Insulin (5 micrograms/ml) increased glucose utilization, protein synthesis, and GAD activity in cultures plated over a range of cell densities (2,800-8,400 cells/mm2). TTX reduced GAD activity; NGF had no effect on GAD activity. Insulin treatment reversibly reduced ChAT activity in cultures plated at densities of greater than 4,000 cells/mm2, and the extent of this reduction increased with increasing cell density. The number of acetylcholinesterase-positive neurons was not reduced by insulin, suggesting that insulin acts by down-regulating ChAT rather than by killing cholinergic neurons. Insulin-like growth factor-1 (IGF-1) reduced ChAT activity at concentrations 10-fold lower than insulin, suggesting that insulin's effect on ChAT may involve the IGF-1 receptor. NGF increased ChAT activity; TTX had no effect on ChAT activity. These results suggest that striatal cholinergic and GABAergic neurons are subject to differential trophic control.     

Dimethyl sulfoxide reductase activity by anaerobically grown Escherichia coli HB101.

Escherichia coli grew anaerobically on a minimal medium with glycerol as the carbon and energy source and dimethyl sulfoxide (DMSO) as the terminal electron acceptor. DMSO reductase activity, measured with an artificial electron donor (reduced benzyl viologen), was preferentially associated with the membrane fraction (77 +/- 10% total cellular activity). A Km for DMSO reduction of 170 +/- 60 microM was determined for the membrane-bound activity. Methyl viologen, reduced flavin mononucleotide, and reduced flavin adenine dinucleotide also served as electron donors for DMSO reduction. Methionine sulfoxide, a DMSO analog, could substitute for DMSO in both the growth medium and in the benzyl viologen assay. DMSO reductase activity was present in cells grown anaerobically on DMSO but was repressed by the presence of nitrate or by aerobic growth. Anaerobic growth on DMSO coinduced nitrate, fumarate, and and trimethylamine-N-oxide reductase activities. The requirement of a molybdenum cofactor for DMSO reduction was suggested by the inhibition of growth and a 60% reduction in DMSO reductase activity in the presence of 10 mM sodium tungstate. Furthermore, chlorate-resistant mutants chlA, chlB, chlE, and chlG were unable to grow anaerobically on DMSO. DMSO reduction appears to be under the control of the fnr gene.     

Galactoglucomannan oligosaccharides inhibition of elongation growth is in pea epicotyls coupled with peroxidase activity

The effect of galactoglucomannan oligosaccharides — GGMOs, GGMOs-r (GGMOs with reduced reducing ends), and GGMOs-g (GGMOs with reduced number of d-galactose units) on peroxidase activity was determined in pea epicotyls. GGMOs didn’t significantly modify the activity of soluble peroxidases. However, cell wall-associated peroxidases activity increased after GGMOs and GGMOs-r treatment, while in the presence of GGMOs-g this activity was significantly lower. These results are inversely related to the GGMOs, GGMOs-r, and GGMOs-g effect on elongation growth induced by 2,4-D (2,4-dichlorophenoxyacetic acid) in pea epicotyls. It can be concluded that GGMOs evoked inhibition of the elongation growth induced by auxin is probably associated with cell wall modifications catalysed by peroxidase.     

Changes in the lymphoid cells of DNA and purine nucleotide synthesis and sensitivity to glucocorticoids associated with impairment of differentiation and immune function during tumor growth in mice. Thymocytes

Some biochemical mechanisms underlying the impairments of cellular immunity were studied in C3Ha mice in the course of growth of transplantable and induced (ortoaminoazotoluol) solid hepatomas. During intensive hepatoma growth, the adenosine deaminase activity in host thymocytes was shown to be drastically (6 times) reduced, resulting in the elevation of dATP and dGTP concentrations (6- and 7-fold, respectively), the potential inhibitors of ribonucleoside diphosphate reductase. Consequently, the rate of DNA synthesis was reduced as can be evidenced by the decrease of (a) thymidine kinase activity, (b) 14C-thymidine incorporation into DNA, and (c) dTTP and dCTP pools. By the terminal period of hepatoma growth (both transplantable and induced one), the serum corticosterone content increased 3- and 8-fold, respectively. At the same time, specific binding of [3H]triamsinolone acetonide by thymocytes was augmented and the activity of terminal deoxynucleotidyl transferase increased the latter alterations, which can be regarded as a reflection (including other parameters mentioned) of the arrest of T-lymphocyte differentiation at the level of immature cortex thymocytes.     

Alpha tocopheryl succinate inhibits melanocyte-stimulating hormone (MSH)-sensitive adenylate cyclase activity in melanoma cells

D-alpha tocopheryl succinate (vitamin E succinate), which is known to induce differentiation and growth inhibition in murine B-16 melanoma cells, reduced basal and melanocyte-stimulating hormone (MSH)-stimulated adenylate cyclase (AC) activity in vitro. Vitamin E succinate treatment also reduced sodium fluoride- and forskoline-stimulated AC activity of melanoma cells in vitro. Treatment of cells with vitamin E succinate (6 micrograms/ml] for a period of 24 hours was sufficient to reduce MSH-stimulated AC activity. Other forms of vitamin E, such as d1-alpha tocopheryl nicotinate, d1-alpha tocopheryl acetate, and d1-alpha tocopherol, which did not affect growth or morphology of melanoma cells, were relatively less effective in altering basal and MSH-stimulated AC activity. Retinoic acid, which inhibited the growth of B-16 melanoma cells, also reduced basal and MSH-, NaF-, and forskolin-stimulated AC activity in vitro. Prostaglandin A2, which inhibited growth and altered morphology, did not change basal or MSH-stimulated AC activity. These results show that one of the mechanisms of action of vitamin E succinate and retinoic acid on melanoma cells may involve reduction of basal and MSH-sensitive AC activity, and this vitamin effect is not necessarily related to growth inhibition.     

稀土元素铈对花生幼苗生长与抗氧化保护酶系统的影响

采用溶液培养方法,研究不同浓度硝酸铈对花生(Arachis hypogaea)幼苗生长、开花数目及抗氧化酶过氧化物酶(POD)、超氧化物歧化酶(SOD)活性与丙二醛(MDA)含量的影响。结果表明,与对照相比,铈浓度低于20.0 mg·L–1能促进花生幼苗生长及开花,其中以10.0 mg·L–1铈的效果最为明显,其生物量和开花数分别约为对照的1.3倍和2.8倍;但高于20.0 mg·L–1则抑制花生幼苗生长,降低花朵数目;同时,低于20.0 mg/L铈可抑制花生幼苗过氧化物酶(POD)活性和降低其丙二醛(MDA)含量,其中以10.0 mg·L–1铈的抑制效果最明显,其POD活性和MDA含量约为对照的47.51%和20.76%;而低于20.0 mg·L–1铈能提高花生幼苗的超氧化物歧化酶(SOD)活性,其中以5.0 mg·L–1铈的促进效果最明显,其SOD活性约为对照的2.0倍。     

Effects of a nitric oxide donor, the substratum of NO-synthase, and an inhibitor of NO-synthase on the ROS-generation activity of phagocytes in the course of ascites tumor growth

Experiments in vitro were performed to investigate the effects of the nitric oxide donor (SNP), the substratum of NO-synthase (L-arginine), and the inhibitor of NO-synthase (nitroarginine) on the ROS-generating activity of blood plasma polymorphonuclear leucocytes and ascitic fluid macrophages isolated at different times of tumor (Zaidel hepatoma) growth in animal organism. It was found that in the initial period of tumor growth the nitric oxide donor at a concentration of 8 x 10(-5) M reduced the potential ROS-generating activity of macrophages by 38.5 +/- 9.0% and that of polymorphic-nuclear leucocytes of plasma by 27.6 +/- 7.0 %. However, the dynamics of this process during tumor growth was conservative: variations in the production of ROS by phagocytes were 10 +/- 3.0%. L-arginine induced a decrease in the ROS-generating activity of granulocytes and mononucleares by 25-30%. This fact points to an inducible inhibiting effect of NO-synthase on the ROS-generating activity of NADPH-oxidase in the course of tumor growth. The inhibitor of NO-synthase, nitroarginine, produced a monotonous increase in the ROS-generating activity of phagocytes isolated from the tumor at different periods of its growth. The use NO-synthase inhibitors for increasing ROS levels in the region of tumor growth may favor the suppression of tumor cell growth in vivo.     

Influence of nitric oxide donor,NO-synthase substrate,and inhibitor on leucocyte ROS-generating activity during ascites tumor growth

The influence of nitric oxide (NO) donor, NO-synthase substrate (L-arginine), and inhibitor (nitroarginine) on the reactive oxygen species (ROS)-generating activity of blood plasma polymorphonuclear leucocytes and ascitic fluid macrophages was studied during tumor growth in animal organisms. It was found that, in the initial period of tumor growth, 8 × 10⁻⁵ M sodium nitroprusside (SNP), which is an NO donor, reduced the potential ROS-generating activity of macrophages by 38.5 ± 9% and plasma polymorphicnuclear leucocytes by 27.6 ± 7%. However, the dynamics of this process during the tumor growth was conservative and variations in ROS production by phagocytes were 10 ± 3%. L-arginine induced a decrease in the ROS-generating activity of granulocytes and mononucleares by 25–30%. The results point to inducible inhibition effect of NO-synthase on the ROS-generating activity of NADPH-oxidase in the course of tumor growth. Nitroarginine, an inhibitor of NO-synthase, produced stable increase in the ROS-generating activity of phagocytes isolated from the tumor at different periods of its growth. The use NO-synthase inhibitors to increase the ROS level in the area of tumor growth may favor the suppression of tumor-cell growth in vivo.     

Cinnamic acid induced changes in reactive oxygen species scavenging enzymes and protein profile in maize (Zea mays L.) plants grown under salt stress

Plant growth and development are greatly affected due to changes in environmental conditions and become a serious challenge to scientific people. Therefore, present study was conducted to determine the role of secondary metabolites on the growth and development of maize under abiotic stress conditions. Cinnamic acid (CA) is one of the basic phenylpropanoid with antioxidant activity, produced by plants in response to stressful conditions. Response of maize seeds to the presoaking treatment with 0.5 mM CA was studied under different concentrations of NaCl stress. Exogenous CA increased growth characteristics in saline and non-saline conditions, while effects of CA were more significant under saline conditions in comparison to non-saline conditions in maize plants. CA also reduced oxidative damage through the induction of ROS scavenging enzymes such as supperoxide dismutase (SOD) (EC 1.15.1.1), peroxidase (POD) (EC 1.11.1.7), while the activity of enzyme catalase (CAT) (EC 1.11.1.6) was decreased. The content of malondialdehyde (MDA) was reduced significantly in maize leaf under CA treatment. Changes in protein banding patterns in the maize leaves showed a wide variation in response to NaCl-stress, while in the presence of CA salt-induced expression of polypeptides was reduced significantly. Present study clearly reports the alleviative effects of CA in response to salinity stress on growth, metabolic activity and changes in protein profile of 21 days old maize plants.     

Identification and characterization of a second superoxide dismutase gene (sodM) from Staphylococcus aureus

A gene encoding superoxide dismutase (SOD), sodM, from S. aureus was cloned and characterized. The deduced amino acid sequence specifies a 187-amino-acid protein with 75% identity to the S. aureus SodA protein. Amino acid sequence comparisons with known SODs and relative insensitivity to hydrogen peroxide and potassium cyanide indicate that SodM most likely uses manganese (Mn) as a cofactor. The sodM gene expressed from a plasmid rescued an Escherichia coli double mutant (sodA sodB) under conditions that are otherwise lethal. SOD activity gels of S. aureus RN6390 whole-cell lysates revealed three closely migrating bands of activity. The two upper bands were absent in a sodM mutant, while the two lower bands were absent in a sodA mutant. Thus, the middle band of activity most likely represents a SodM-SodA hybrid protein. All three bands of activity increased as highly aerated cultures entered the late exponential phase of growth, SodM more so than SodA. Viability of the sodA and sodM sodA mutants but not the sodM mutant was drastically reduced under oxidative stress conditions generated by methyl viologen (MV) added during the early exponential phase of growth. However, only the viability of the sodM sodA mutant was reduced when MV was added during the late exponential and stationary phases of growth. These data indicate that while SodA may be the major SOD activity in S. aureus throughout all stages of growth, SodM, under oxidative stress, becomes a major source of activity during the late exponential and stationary phases of growth such that viability and growth of an S. aureus sodA mutant are maintained.     

Application of Bacillus megaterium MCR-8 improved phytoextraction and stress alleviation of nickel in Vinca rosea

The current research was performed to evaluate the effect of Bacillus megaterium MCR-8 on mitigation of nickel (Ni) stress in Vinca rosea grown on Ni-contaminated soil (50, 100, and 200 mg Ni kg^?1 soil). The treated plants exhibited reduced growth, biomass, gas exchange capacity, and chlorophyll (Chl) content under Ni stress. The inoculated plants growing in Ni-contaminated media exhibited relatively higher growth, total soluble protein, and proline contents. Similarly, bacterial inoculation improved the activity of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) under Ni stress. The Ni stress alleviation in inoculated plants was attributed to the reduced level of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), enhanced synthesis of protein, proline, phenols, and flavonides in conjunction with improved activity of antioxidant enzymes. The growth-promoting characteristics of microbe such as 1-aminocyclopropane-1-carboxylate deaminase (ACCD) and phosphate solubilization activity, siderophore, and auxin production capability also improved the growth and stress mitigation in inoculated plants. Furthermore, the inoculated plants exhibited higher value for bioconcentration factor (BCF), translocation factor (TF), and resulted in higher loss of Ni content from soil. The current results exhibited the beneficial role of B. megaterium MCR-8 regarding stress alleviation and Ni phytoextraction by V. rosea.     

Ascorbic acid improves the tolerance of wheat plants to lead toxicity

Among the heavy metals (HMs), lead (Pb) is considered as a toxic HM which adversely affects growth and development of crop plants. The present experiment was aimed to investigate the potential role of ascorbic acid (ASC) in the reversal of Pb-inhibited nitrogen and sulfur assimilation enzymes activity and activity of photosynthesis enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and growth response in wheat plants. Wheat seedlings were subjected to 0 mM (control) and 0.2 mM and 0.6 mM of ASC with and without 2 mM of Pb. Plants treated with Pb exhibited the following reduced growth characteristics (root length, shoot length, root fresh weight (FW), shoot FW, root dry weight (DW) and shoot DW). A decrease was also observed in the activity of Rubisco and ATP sulfurylase (ATP-S), relative water content (RWC), accumulation of total chlorophyll (Total Chl) and content of nutrients [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg)] in Pb-treated plants. However, an increase in Chl degradation and in the activity of O-acetylserine(thiol)lyase (OAS-TL) and accumulation of cysteine (Cys), malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) was observed in plants under Pb stress. On the contrary, exogenous application of ASC mitigated the Pb-toxicity-induced oxidative damage by enhancing the activities of antioxidant enzymes, such as superoxide dismutase, catalase and glutathione reductase. Improved activity of antioxidant enzymes suppressed the formation of MDA and H₂O₂, which was reflected in the form of improved growth characteristics. Moreover, ASC induced improvement in plants defense systems by reduced Chl degradation and improved the content of essential nutrients (N, P, K, Ca and Mg) and Cys, RWC and the activity of Rubisco, ATP-S, NR and OAS-TL.     

Role of group A p21-activated kinases in activation of extracellular-regulated kinase by growth factors

The canonical extracellular-regulated kinase (ERK) signaling cascade, consisting of the Ras-Raf-Mek-ERK module, is critically important to many cellular functions. Although the general mechanism of activation of the ERK cascade is well established, additional noncanonical components greatly influence the activity of this pathway. Here, we focus on the group A p21-activated kinases (Paks), which have previously been implicated in regulating both c-Raf and Mek1 activity, by phosphorylating these proteins at Ser(338) and Ser(298), respectively. In NIH-3T3 cells, expression of an inhibitor of all three group A Paks reduced activation of ERK in response to platelet-derived growth factor (PDGF) but not to epidermal growth factor (EGF). Similar results were obtained in HeLa cells using small interference RNA-mediated simultaneous knockdown of both Pak1 and Pak2 to reduce group A Pak function. Inhibition of Pak kinase activity dramatically decreased phosphorylation of Mek1 at Ser(298) in response to either PDGF or EGF, but this inhibition did not prevent Mek1 activation by EGF, suggesting that although Pak can phosphorylate Mek1 at Ser(298), this event is not required for Mek1 activation by growth factors. Inhibition of Pak reduced the Ser(338) phosphorylation of c-Raf in response to both PDGF and EGF; however, in the case of EGF, the reduction in Ser(338) phosphorylation was not accompanied by a significant decrease in c-Raf activity. These findings suggest that Paks are required for the phosphorylation of c-Raf at Ser(338) in response to either growth factor, but that the mechanisms by which EGF and PDGF activate c-Raf are fundamentally different.     

Salicylic acid and calcium-induced protection of wheat against salinity

Soil salinity is one of the important environmental factors that produce serious agricultural problems. The objective of the present study was to determine the interactive effect of salicylic acid (SA) and calcium (Ca) on plant growth, photosynthetic pigments, proline (Pro) concentration, carbonic anhydrase (CA) activity and activities of antioxidant enzymes of Triticum aestivum L. (cv. Samma) under salt stress. Application of 90 mM of NaCl reduced plant growth (plant height, fresh weight (FW) and dry weight (DW), chlorophyll (Chl) a, Chl b, CA activity) and enhanced malondialdehyde (MDA) and Pro concentration. However, the application of SA or Ca alone as well as in combination markedly improved plant growth, photosynthetic pigments, Pro concentration, CA activity and activities of antioxidant enzymes peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and ascorbate peroxidase (APX) under salt stress. It was, therefore, concluded that application of SA and Ca alone as well as in combination ameliorated the adverse effect of salinity, while combined application proved more effective to reduce the oxidative stress generated by NaCl through reduced MDA accumulation, Chl a/b ratio and Chls degradation and enhanced activities of antioxidant enzymes.     

Effects of growth factors on an intestinal epithelial cell line: transforming growth factor beta inhibits proliferation and stimulates differentiation

The effects of epidermal growth factor transforming growth factor beta (TGF beta) and other growth factors on the proliferation and differentiation of a cell line derived from rat intestinal crypt epithelium (IEC-6) were defined. Incorporation of [3H]-thymidine was stimulated 1.4-2.4 fold by insulin, insulin like growth factor (IGF), platelet derived growth factor (PDGF), epidermal growth factor (EGF) and 2% fetal calf serum (FCS) respectively. Additive stimulation was observed when FCS was supplemented by insulin,IGF-I or PDGF but not EGF. Incorporation of [3H]-thymidine by IEC-6 was strongly inhibited by TGF beta with greater than 80% inhibition of incorporation at concentration approximately equal to 2.0 pM. IEC-6 cells bound 4.1 +/- 0.15 X 10(4) molecules TGF beta/cell and appeared to have only a single class of high affinity receptors (Kd approximately equal to 0.5 pM). TGF beta inhibition was unaffected by the presence of insulin or IGF-I suggesting it inhibits proliferation at a step subsequent to that at which these growth factors stimulate [3H]-thymidine incorporation. TGF beta also reduced the stimulation induced by FCS by 65%. In contrast EGF reduced TGF beta inhibition by 60%. IEC-6 cells demonstrated the appearance of sucrase activity after greater than 18 hours treatment with TGF beta. These findings suggest that TGF beta may inhibit proliferative activity and promote the development of differentiated function in intestinal epithelial cells.     

Modulation of glucan-binding protein activity in streptococci by fluoride

Glucan-binding lectin (GBL) activity of Streptococcus sobrinus was significantly reduced by fluoride in the growth medium. Approximately 1.5 mM fluoride was required for a 50% reduction in GBL activity. In addition to the GBL, several other glucan-binding proteins were reduced when the bacteria were grown in subinhibitory fluoride. Fluoride had no effect on glucosyltransferases (GTFs), enzymes capable of converting sucrose into alpha-1,6-glucans. All the proteins were detected by use of enhanced chemiluminescence (ECL of fluorescein-labeled dextran) and Western blotting of renatured SDS-PAGE gels. The effects of fluoride on the bacteria were abrogated when the manganous ion was included in the growth medium. It thus appears that one mechanism of action of fluoridated water is its effects on glucan-binding proteins. The fluoride may be reducing metabolism of the mangano aquo ion, essential for expression of the glucan-binding proteins.     

Ectomycorrhizal mycelia reduce bacterial activity in a sandy soil

Abstract: Bacterial activity was studied in a growth system containing Pinus contorta seedlings inoculated with different mycorrhizal fungi. Nylon nets enabled separation of soil compartments with extramatrical mycorrhizal hyphae from soil compartments with roots and mycelium. In three separate experiments bacterial activity, estimated as thymidine incorporation, was reduced in soils with Paxillus involutus hyphae compared to controls without mycorrhizal hyphae. This effect was found irrespective of compartments with and without roots were compared. Laccaria bicolor only reduced the activity in one of these three experiments. Thelephora terrestris (tested in two experiments), Laccaria proxima, Suillus variegatus and Hebeloma crustuliniforme (one experiment), also reduced the thymidine and leucine incorporation rates of bacteria. The reduction for these fungi varied between 20% and 50% in all experiments. Numbers of viable bacteria appeared to be reduced by T. terrestris, L. proxima, S. variegatus and H. crustuliniforme in one experiment, while no effect was seen in the other experiments.