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PubMed1996

Heparan sulfate proteoglycans play a dual role in regulating fibroblast growth factor-2 mitogenic activity in human breast cancer cells.

The human breast cancer cell lines MCF-7 and MDA-MB-231 differ in their responsiveness to fibroblast growth factor-2 (FGF-2). This growth factor stimulates proliferation in well-differentiated MCF-7 cells, whereas the less well-differentiated MDA-MB-231 cells are insensitive to this molecule. To investigate the potential regulation of FGF-2 mitogenic activity by heparan sulfate proteoglycans (HSPG), we have treated human breast cancer cells by glycosaminoglycan degrading enzymes or a metabolic inhibitor of proteoglycan sulfation: sodium chlorate. The interaction between FGF-2 and proteoglycans was assayed by examining the binding of 125I-FGF-2 to breast cancer cell cultures as well as to cationic membranes loaded with HSPG. Using MCF-7 cells, we showed that heparinase treatment inhibited FGF-2 binding to HSPG and completely abolished FGF-2 induced growth; chlorate treatment of MCF-7 cells decreased FGF-2 binding to HSPG and cell responsiveness in a dose-dependent manner. This demonstrates a requirement of adequately sulfated HSPG for FGF-2 growth-promoting activity on MCF-7 cells. In highly invasive MDA-MB-231 cells which produce twice as much HSPG as MCF-7 cells and which are not normally responsive to exogenously added FGF-2, chlorate treatment decreased FGF-2 binding to HSPG and induced FGF-2 mitogenic effect. This chlorate effect was dose dependent and observed at concentrations of 10-30 mM; higher chlorate concentrations completely abolished the FGF-2 effect. This shows that the HSPG level of sulfation can also negatively regulate the biological activity of FGF-2. Taken together, these results demonstrate a crucial role for HSPG in both positive and negative control of FGF-2 mitogenic activity in breast cancer cell proliferation.

Breast Neoplasms↗
PubMed1993

Heparin-binding EGF-like growth factor stimulation of smooth muscle cell migration: dependence on interactions with cell surface heparan sulfate.

Heparin-binding EGF-like growth factor (HB-EGF), but not EGF, binds to cell surface heparan sulfate proteoglycan (HSPG). This was demonstrated in (a) the binding of 125I-HB-EGF to mutant CHO cells deficient in HS production was diminished by 70% compared to wild-type CHO cells, (b) the binding of 125I-HB-EGF to CHO cells and bovine aortic smooth muscle cells (BASMC) was diminished 80% by heparitinase or chlorate treatment, and (c) 125I-EGF did not bind to CHO cells and its binding to BASMC was not diminished at all by heparitinase and only slightly by chlorate treatment. Accordingly, the role of HB-EGF interactions with HSPG in modulating bioactivity was examined. Heparitinase or chlorate treatment of BASMC diminished the ability of HB-EGF to stimulate BASMC migration by 60-80%. A similar inhibition of migration occurred when BASMC were treated with a synthetic peptide (P21) corresponding to the sequence of the putative heparin-binding domain of HB-EGF. As a control for BASMC viability, and for specificity, it was found that heparitinase and P21 did not inhibit at all and chlorate inhibited only slightly the stimulation of BASMC migration by PDGF AB. Since heparitinase, chlorate, and P21 treatment also diminished by 70-80% the cross-linking of 125I-HB-EGF to the EGF receptor, it was concluded that the interaction of HB-EGF, via its heparin-binding domain, with cell surface HSPG was essential for its optimal binding to the EGF receptor on BASMC and hence for its optimal ability to stimulate migration.

Amino Acid Sequence↗
PubMed2006

Differences in the apical and basolateral pathways for glycosaminoglycan biosynthesis in Madin-Darby canine kidney cells.

Serglycin with a green fluorescent protein tag (SG-GFP) expressed in epithelial Madin-Darby canine kidney cells is secreted mainly (85%) into the apical medium, but the glycosaminoglycan (GAG) chains on the SG-GFP protein core secreted basolaterally (15%) carry most of the sulfate added during biosynthesis (Tveit et al. (2005) J. Biol. Chem., 280, 29596-29603). Here we report further differences in apical and basolateral GAG synthesis. The less intensely sulfated chondroitin sulfate (CS) chains on apically secreted SG-GFP are longer than CS chains attached to basolateral SG-GFP, whereas the heparan sulfate (HS) chains are of similar lengths. When the supply of 3'-phosphoadenosine-5'-phosphosulfate (PAPS) is limited by chlorate treatment, the synthesis machinery maintains sulfation of HS chains on basolateral SG-GFP until it is inhibited at 50 mM chlorate, whereas basolateral CS chains lose sulfate already at 12.5 mM chlorate and become longer. Apically, incorporation of 35S-sulfate into CS is reduced to a lesser extent at higher chlorate concentrations than basolateral CS, although apical CS is less intensely sulfated than basolateral CS in control cells. Similar to what was found for basolateral HS, sulfation of apical HS was not reduced at chlorate concentrations below 50 mM. Also, protein-free, xyloside-based GAG chains secreted basolaterally are more intensely sulfated than their apical counterpart, supporting the view that separate apical and basolateral pathways exist for GAG synthesis and sulfation. Introduction of benzyl beta-d-xyloside (BX) to the GAG synthesis machinery reduces the apical secretion of SG-GFP dramatically and also the modification of SG-GFP by HS.

Animals↗
PubMed1996

Sulfate moieties in the subendothelial extracellular matrix are involved in basic fibroblast growth factor sequestration, dimerization, and stimulation of cell proliferation.

The growth promoting activity of the subendothelial extracellular matrix (ECM) is attributed to sequestration of basic fibroblast growth factor (bFGF) by heparan sulfate proteoglycans and its regulated release by heparin-like molecules and heparan sulfate (HS) degrading enzymes. HS is also involved in bFGF receptor binding and activation. The present study focuses on the growth promoting activity and bFGF binding capacity of sulfate-depleted ECM. Corneal endothelial cells (EC) maintained in the presence of chlorate, an inhibitor of phosphoadenosine phosphosulfate synthesis, produced ECM containing 10-15% of the sulfate normally present in ECM. Incorporation of sulfate into HS was reduced by more than 90%. Binding of 125I-bFGF to sulfate-depleted ECM was reduced by 50-60% and only about 10% of the ECM-bound bFGF was accessible to release by heparin. Incubation of 125I-bFGF on top of native ECM resulted in dimerization of the ECM-bound bFGF, but there was a markedly reduced binding and dimerization of bFGF on sulfate-depleted ECM. ECM produced in the presence of chlorate contained a nearly 10-fold less endogenous bFGF as compared to native ECM and exerted little or no mitogenic activity toward vascular EC and 3T3 fibroblasts. In other studies, we investigated the interaction between chlorate-treated vascular EC and either native or sulfate-depleted ECM. Exogenous heparin stimulated the proliferation of chlorate-treated EC seeded on native ECM, suggesting its interaction with ECM-bound bFGF and subsequent presentation to high affinity cell surface receptors. On the other hand, heparin had no effect on chlorate-treated cells seeded in contact with sulfate-depleted ECM or regular tissue culture plastic. Altogether, the present experiments indicate that heparan sulfate proteoglycans associated with the cell surface and ECM act in concert to regulate the bioavailability and growth promoting activity of bFGF. While HS in the subendothelial ECM functions primarily in sequestration of bFGF in the vicinity of responsive cells, HS on cell surfaces is playing a more active role in displacing the ECM-bound bFGF and its subsequent presentation to high affinity signal transducing receptors.

3T3 Cells↗
PubMed1981

Nitrate Utilization by Nitrate Reductase-deficient Barley Mutants.

Two nitrate reductase-deficient barley mutants were studied for growth on nitrate and ammonium sources of nitrogen and for resistance to chlorate. Although nitrate reductase-deficient mutants in some species are chlorate-resistant (unable to reduce chlorate to chlorite), the barley mutants used in these studies when grown on nitrate and treated with chlorate were only slightly more resistant to chlorate than the control. When grown to maturity on vermiculite supplemented with either nitrate or ammonium nutrient solutions, the mutants produced as much dry weight and reduced nitrogen per plant as the control. The in vivo and in vitro nitrate reductase activities in the roots and shoots of the mutants grown on nitrate were consistently less than 10% of the control. To avoid the possibility that the mutants received reduced nitrogen from microbial sources, excised embryos were cultured under sterile conditions. Again the mutants were capable of growth and reduced nitrogen accumulation with nitrate as the sole source of nitrogen. In spite of the low apparent nitrate reductase activity, the nitrate reductase-deficient mutants are capable of substantial nitrate reduction.

Journal Article↗
PubMed1991

Identification of the Arabidopsis CHL3 gene as the nitrate reductase structural gene NIA2.

Chlorate, the chlorine analog of nitrate, is a herbicide that has been used to select mutants impaired in the process of nitrate assimilation. In Arabidopsis thaliana, mutations at any one of eight distinct loci confer resistance to chlorate. The molecular identities of the genes at these loci are not known; however, one of these loci--chl3--maps very near the nitrate reductase structural gene NIA2. Through the isolation, characterization, and genetic analysis of new chlorate-resistant mutants generated by gamma irradiation, we have been able to demonstrate that the CHL3 gene and the NIA2 gene are identical. Three new chlorate-resistant mutants were identified that had deletions of the entire NIA2 gene. These nia2 null mutants were viable and still retained 10% of wild-type nitrate reductase activity in the leaves of the plants. All three deletion mutations were found to be new alleles of chl3. Introduction of the NIA2 gene back into these chl3 mutants by Agrobacterium-mediated transformation partially complemented their mutant phenotype. From these data, we conclude that Arabidopsis has at least two functional nitrate reductase genes and that the NIA2 gene product accounts for the majority of the leaf nitrate reductase activity and chlorate sensitivity of Arabidopsis plants.

Arabidopsis↗
PubMedDate not supplied

[Exposure to water disinfection by-products and adverse pregnancy outcomes: results of a case-control study carried out in Modena (Italy)].

Chlorination By Products (CBPs) in drinking water have been associated with an increased risk of adverse pregnancy outcomes, such as small term birth (STB) and preterm delivery. Up to date epidemiological evidence is weakened by a generally inaccurate exposure assessment, often at an ecological level: in this study the exposure is evaluated at the individual level. A case control study with incident cases was performed in Modena between October 1999-September 2000. 332 subjects were enrolled: 93 preterm births (26th-37th week of pregnancy), 73 STB (from 38th week, and weight less than the lowest 10th percentile) and 166 controls. Exposure was assessed both by applying a questionnaire on personal habits and by personal water sampling directly at subjects' home. THMs were analysed in all samples, chlorite and chlorate in water samples treated with chlorine dioxide. Subjects usually drinking tap water were few (5.2%): most of them were living in areas supplied by water treated with chlorine dioxide (87%). Levels of THMs were low (mean: 0.73 microgram/l), while chlorite and chlorate concentrations were relatively high (mean: 217.8 microgram/l for chlorites and 95.2 microgram/l for chlorates). Preterm birth did not show any significant association with CBPs, while STB appeared significantly associated, after adjusting for many potential confounders, with CBPs induced by chlorine dioxide treatment, especially with levels of chlorate higher than 200 microgram/l (OR: 4.7; 95%CI: 1.15-19.72). The association between STB and chlorate must be investigated further as the number of water utilities applying chlorine dioxide as disinfection treatment is increasing.

Adult↗
PubMed1996

Extracellular matrix is required for skeletal muscle differentiation but not myogenin expression.

Skeletal muscle cells are a useful model for studying cell differentiation. Muscle cell differentiation is marked by myoblast proliferation followed by progressive fusion to form large multinucleated myotubes that synthesize muscle-specific proteins and contract spontaneously. The molecular analysis of myogenesis has advanced with the identification of several myogenic regulatory factors, including myod1, myd, and myogenin. These factors regulate each other's expression and that of muscle-specific proteins such as the acetylcholine receptor and acetylcholinesterase (AChE). In order to investigate the role of extracellular matrix (ECM) in myogenesis we have cultured myoblasts (C2C12) in the presence or absence of an exogenous ECM (Matrigel). In addition, we have induced differentiation of myoblasts in the presence or absence of Matrigel and/or chlorate, a specific inhibitor of proteoglycan sulfation. Our results indicated that the formation of fused myotubes and expression of AChE was stimulated by Matrigel. Treatment of myoblasts induced to differentiate with chlorate resulted in an inhibition of cell fusion and AChE activity. Chlorate treatment was also found to inhibit the deposition and assembly of ECM components such fibronectin and laminin. The expression of myogenin mRNA was observed when myoblasts were induced to differentiate, but was unaffected by the presence of Matrigel or by culture of the cells in the presence of chlorate. These results suggest that the expression of myogenin is independent of the presence of ECM, but that the presence of ECM is essential for the formation of myotubes and the expression of later muscle-specific gene products.

Acetylcholinesterase↗
PubMed1995

Role of heparan sulfate in the terminal differentiation of growth plate chondrocytes.

Recent studies have demonstrated that basic fibroblast growth factor (bFGF) plays a key role in the terminal differentiation of growth plate chondrocytes during endochondral ossification. In this paper we examined the potential role of heparan sulfate in the regulation of the action of basic fibroblast growth factor (bFGF) in the terminal differentiation of rat growth plate chondrocytes. As rat growth plate chondrocytes differentiate in vitro, the percentage of heparitinase-sensitive material decreases. Treatment of growth plate chondrocytes with sodium chlorate, a reversible inhibitor of glycosaminoglycan sulfation, resulted in terminal differentiation of growth plate chondrocytes even in the presence of bFGF at concentrations that normally repress their differentiation. Chlorate treatment in the presence of bFGF resulted in an increase in alkaline phosphatase activity and a decrease in cellular proliferation, both characteristics of the differentiated state. Chlorate treatment also reduced the binding of bFGF to growth plate chondrocytes and this effect could be reversed in a dose-dependent manner by the simultaneous addition of sodium sulfate. The reduced binding was a function of a reduced number of receptors and not a reduced affinity for the receptor. Pretreatment of the growth plate chondrocytes with heparitinase significantly reduced the binding of bFGF to both low- and high-affinity receptors, while pretreatment with chondroitinase ABC had no effect. Finally, addition of exogenous heparin restored bFGF binding to chlorate-treated chondrocytes in a concentration-dependent manner. These results provide evidence that a cell surface heparan sulfate is involved in the binding of bFGF to high-affinity receptors and that a downregulation of this glycosaminoglycan is part of the pathway that leads to terminal differentiation of growth plate chondrocytes.

Animals↗
PubMed1996

Stress-induced rearrangement of Fusarium retrotransposon sequences.

Rearrangement of fusarium oxysporum retrotransposon skippy was induced by growth in the presence of potassium chlorate. Three fungal strains, one sensitive to chlorate (Co60) and two resistant to chlorate and deficient for nitrate reductase (Co65 and Co94), were studied by Southern analysis of their genomic DNA. Polymorphism was detected in their hybridization banding pattern, relative to the wild type grown in the absence of chlorate, using various enzymes with or without restriction sites within the retrotransposon. Results were consistent with the assumption that three different events had occurred in strain Co60: genomic amplification of skippy yielding tandem arrays of the element, generation of new skippy sequences, and deletion of skippy sequences. Amplification of Co60 genomic DNA using the polymerase chain reaction and divergent primers derived from the retrotransposon generated a new band, corresponding to one long terminal repeat plus flanking sequences, that was not present in the wild-type strain. Molecular analysis of nitrate reductase-deficient mutants showed that generation and deletion of skippy sequences, but not genomic amplification in tandem repeats, had occurred in their genomes.

Blotting, Southern↗
PubMed1991

Role of sulphation in post-translational processing of rat salivary mucins.

Segments of rat submandibular salivary gland were incubated in MEM supplemented with 10-800 microM sulphate in the presence of [3H]-glucosamine, [3H]-proline and [35S]-Na2SO4, with 0-8 mM chlorate, an inhibitor of 3'-phosphoadenosine-5'-phosphosulphate formation. Incorporation of glucosamine and sulphate depended upon the sulphate content of the medium and reached a maximum at 400 microM sulphate. The introduction of chlorate into the medium, while having no effect on the protein synthesis as shown by [3H]-proline incorporation, caused, at its optimal concentration of 4 mM, a 90% decrease in mucin sulphation and a 29% drop in mucin glycosylation. At low sulphate content in the medium and in the presence of chlorate the incorporation of sulphate and glucosamine was mainly into the low molecular-weight form of mucin. An increase in sulphate in the medium caused an increase in the high molecular-weight form of mucin and in the extent of sulphation in its carbohydrate chain. This effect of sulphate was, however, inhibited by chlorate. The results suggest that sulphation takes place at an early stage of mucin assembly and that sulphate availability is essential for the formation of the high molecular-weight mucin.

Animals↗
PubMed1992

Repression of myogenic differentiation by aFGF, bFGF, and K-FGF is dependent on cellular heparan sulfate.

We have proposed a model in which fibroblast growth factor (FGF) signalling requires the interaction of FGF with at least two FGF receptors, a heparan sulfate proteoglycan (HSPG) and a tyrosine kinase. Since FGF may be a key mediator of skeletal muscle differentiation, we examined the synthesis of glycosaminoglycans in MM14 skeletal muscle myoblasts and their participation in FGF signalling. Proliferating and differentiated MM14 cells exhibit similar levels of HSPG, while differentiated cells exhibit reduced levels of chondroitin sulfate proteoglycans and heparan sulfate chains. HSPGs, including syndecan, present in proliferating cells bind bFGF, while the majority of chondroitin sulfate and heparan sulfate chains do not. Treatment of skeletal muscle cells with chlorate, a reversible inhibitor of glycosaminoglycan sulfation, was used to examine the requirement of sulfated proteoglycans for FGF signalling. Chlorate treatment reduced glycosaminoglycan sulfation by 90% and binding of FGF to high affinity sites by 80%. Chlorate treatment of MM14 myoblasts abrogated the biological activity of acidic, basic, and Kaposi's sarcoma FGFs resulting in terminal differentiation. Chlorate inhibition of FGF signalling was reversed by the simultaneous addition of sodium sulfate or heparin. Further support for a direct role of heparan sulfate proteoglycans in fibroblast growth factor signal transduction was demonstrated by the ability of heparitinase to inhibit basic FGF binding and biological activity. These results suggest that activation of FGF receptors by acidic, basic or Kaposi's sarcoma FGF requires simultaneous binding to a HSPG and the tyrosine kinase receptor. Skeletal muscle differentiation in vivo may be dependent on FGFs, FGF tyrosine kinase receptors, and HSPGs. The regulation of these molecules may then be expected to have important implications for skeletal muscle development and regeneration.

Animals↗
PubMed2004

Utilization of the nitrate reductase enzymatic pathway to reduce enteric pathogens in chickens.

Previous reports have shown that some bacteria, including Salmonella, use a dissimilatory nitrate reductase enzyme pathway (NREP) in anaerobic environments. This enzyme reduces nitrate to nitrite and has been shown to cometabolize chlorate to cytotoxic chlorite. The present investigations were performed to evaluate the susceptibility of a competitive exclusion culture (CE) to the experimental chlorate product (ECP). A commercially available CE product was evaluated for its nitrate reductase activity and therefore its chlorate sensitivity. Individual isolates (in triplicate) were cultured in 10 mL of Viande Levure broth containing 5 mM sodium nitrate or 10 mM sodium chlorate. Bacterial growth (optical density at 625 nm) was measured and 1-mL aliquots were removed concurrently for colorimetric determination of nitrate content at 0, 3, 6, and 24 h. Of the 15 different facultative strains, 11 had slight NREP utilization, 3 had moderate NREP utilization, and the remainder were NREP negative (with slight and moderate NREP utilization: >0.1 to <1.0 mM and >1.0 mM nitrate used within 6 h, respectively). Of the obligate anaerobes evaluated, 3 had slight NREP utilization and the remainder were NREP negative. In vivo studies utilizing both products (CE and ECP) in a horizontal transmission challenge model (seeders + contacts) showed significant reductions in Salmonella from 5.37 to 1.76 log10 cfu/g and 3.94 to 0.07 log10 cfu/g, respectively. The combined effect of the CE culture and an ECP are effective in killing these food-borne pathogens.

Animal Husbandry↗
PubMed1990

Concurrent reduction in the sulfation of heparan sulfate and basement membrane assembly in a cell model system.

Basement membranes (BMs) are specialized extracellular matrices that have important roles in cell attachment, migration, growth and differentiation. The murine teratocarcinoma cell line, M1536-B3, has been shown to produce a model BM composed of laminin, entactin and heparan sulfate proteoglycans but lacking collagen. Therefore, M1536-B3 cells are an excellent model system in which to study the role of non-collagenous components in BM assembly. We have used these cells to test for a requirement of mature heparan sulfate (HS) chains in BM assembly. Growth of M1536-B3 cells in the presence of chlorate, an inhibitor of activated sulfate synthesis, resulted in a dose-dependent decrease in the sulfation of glycosaminoglycans and reduction in the charge density of the isolated HS. The undersulfated HS from chlorate-treated cells had a decreased binding capacity for laminin when compared with control HS. Concurrent with these changes in sulfation, chlorate treatment of M1536-B3 cells resulted in the failure of BM assembly, which was restored upon removal of the chlorate from the growth medium. These results were not due to major alterations in cell attachment, spreading, growth, protein synthesis, or to an inability of the cells to synthesize and secrete laminin. These data suggest that the sulfation of HS and its subsequent ability to interact with other BM components play major roles in the assembly and structure of BMs.

Animals↗
PubMed2002

Role of sulfated O-linked glycoproteins in zymogen granule formation.

Packaging of proteins into regulated secretory granules is mediated by the mildly acidic pH of the trans Golgi network and immature secretory granules. This need for an acidic pH indicates that ionic interactions are important. The mouse pancreatic acinar cell contains four major sulfated glycoproteins, including the zymogen granule structural component Muclin. I tested the hypothesis that sulfation and the O-linked glycosylation to which the sulfates are attached are required for normal formation of zymogen granules in the exocrine pancreas. Post-translational processing was perturbed with two chemicals: sodium chlorate was used to inhibit sulfation and benzyl-N-acetyl-alpha-galactosaminide was used to inhibit O-linked oligosaccharide elongation. Both chemicals resulted in the accumulation in the Golgi region of the cell of large vacuoles that appear to be immature secretory granules, and the effect was much more extensive with benzyl-N-acetyl-alpha-galactosaminide than chlorate. Both chemical treatments inhibited basal secretion at prolonged chase times, and again benzyl-N-acetyl-alpha-galactosaminide had a greater effect than chlorate. In addition, benzyl-N-acetyl-alpha-galactosaminide, but not chlorate, totally inhibited stimulated secretion of newly synthesized proteins. These data provide evidence for a role of sulfated O-linked glycoproteins in protein condensation and maturation of zymogen granules. Under maximal inhibition of O-linked oligosaccharide biosynthesis, anterograde post-Golgi traffic in the regulated pathway is almost totally shut down, demonstrating the importance of these post-translational modifications in progression of secretory proteins through the regulated pathway and normal granule formation in the pancreatic acinar cell.

Acetylgalactosamine↗
PubMed1987

Molecular oxygen controls nitrate transport of Escherichia coli nitrate-respiring cells.

Escherichia coli cells grown anaerobically in the presence of nitrate reduce the nitrate as a terminal electron acceptor in place of molecular oxygen by an induced respiratory-type electron transferring system residing in the inner membrane structure. When oxygen is introduced to a suspension of nitrate-respiring cells, the oxygen is immediately reduced preferentially and the cellular uptake of nitrate ceases abruptly. In contrast, we found that the cells exhibited no oxygen control on uptake of chlorate, a competitive substrate analogue, indicating operation of an oxygen-sensitive transport system specific to nitrate. This was further evidenced by the fact that chlorate inhibition of reduction of nitrate was brought about only when the transport of both chlorate and nitrate was facilitated by the aid of carrier-type chlorate (or nitrate) ionophore. We demonstrated that oxygen inhibition on reduction of nitrate was abolished within the cells treated by octyl glucoside resulting in a removal of permeability barrier specific to nitrate. We conclude that the transient control by molecular oxygen is primarily due to the inhibition of nitrate transport into the cytoplasmic side. Since nitrate induces the nitrate-respiring system, the repression of the nitrate reductase operon by molecular oxygen is consistently interpreted on the basis of the "inducer exclusion mechanism."

Aerobiosis↗
PubMed2004

Cometabolic reduction of bromate by a mixed culture of microorganisms using hydrogen gas in a gas-lift reactor.

The discharge of bromate, a suspected carcinogen, will be restricted in the near future. To assess the possibility of biotechnological treatment of bromate-containing wastewaters, the removal of bromate by chlorate-reducing microorganisms was studied. The removal of bromate and chlorate was studied in laboratory gas-lift bioreactors supplied with hydrogen gas as electron donor in the absence of molecular oxygen. In these reactors, bromate was reduced cometabolically by chlorate-respiring microorganisms. To allow the cometabolic reduction of bromate, a chlorate:bromate molar ratio of at least 3:1 was required. The cometabolic conversion permitted almost complete reduction of bromate into bromide at hydraulic retention times of at least 6 h. Optimal bromate reduction activity was observed at approximately 35 degrees C. The pH optimum was between 7 and 8. Bromate reduction in excess of 80% and a maximum bromate reduction rate of 2.3 g l(-1) day(-1) in a pilot-scale gas-lift bioreactor demonstrates that the process is sustainable.

Air Pollutants↗
PubMed2006

Identification of a respiratory-type nitrate reductase and its role for survival of Mycobacterium smegmatis in Wayne model.

Nitrate reductase (NR) is found to be expressed in certain mycobacterium sp. whose link with the development of persistence is yet to be resolved. The present study demonstrates the action of selective inhibitors on NR as well as in the survival of Mycobacterium smegmatis using Wayne's model. During gradual shift down to anaerobic stage in Wayne's model, conversion of nitrate to nitrite became apparent in M. smegmatis. More than 97 percent inhibition was observed for the conversion of nitrate to nitrite by azide (0.05 mM) and thiocyanate (20 mM) in both whole-cell as well as its cell-free lysate, respectively. Under identical condition, chlorate (20 mM) inhibited nitrate reduction by 67 and 10 percent, respectively. At these concentrations, neither of azide, thiocyanate nor chlorate had any significant effect on cell growth under aerobic condition. In Wayne's culture model, thiocyanate and chlorate inhibited the growth of M. smegmatis by almost 2 logs at the same concentrations whereas azide inhibited by almost 1.75 log when added at the time of inoculation. Exposure of same culture at 96 h after inoculation in Wayne's model to these inhibitors showed 1.74, 1.95 and 2.37 log inhibition of viable cells with respect to azide, thiocyanate and chlorate. These findings further indicated that NR inhibitors kill the bacilli at anaerobic stage under the experimental condition mentioned. Metronidazole (MTZ) (2 mM) and Nitrofurantoin (NIT) (0.3 mM) reduced the cell number at both stages by <0.7 log. They did not have any effect on NR. Altogether, the results clearly indicate that NR-specific inhibitors could become more promising in killing the bacilli at anaerobic stage than the available conventional drugs.

Anti-Infective Agents↗