NOx removal from flue gas by an integrated physicochemical absorption and biological denitrification process

An integrated physicochemical and biological technique for NO(x) removal from flue gas, the so-called BioDeNO(x) process, combines the principles of wet absorption of NO in an aqueous Fe(II)EDTA(2-) solution with biological reduction of the sorbed NO in a bioreactor. The biological reduction of NO to di-nitrogen gas (N(2)) takes place under thermophilic conditions (55 degrees C). This study demonstrates the technical feasibility of this BioDeNO(x) concept in a bench-scale installation with a continuous flue gas flow of 650 l.h(-1) (70-500 ppm NO; 0.8-3.3% O(2)). Stable NO removal with an efficiency of at least 70% was obtained in case the artificial flue gas contained 300 ppm NO and 1% O(2) when the bioreactor was inoculated with a denitrifying sludge. An increase of the O(2) concentration of only 0.3% resulted in a rapid elevation of the redox potential (ORP) in the bioreactor, accompanied by a drastic decline of the NO removal efficiency. This was not due to a limitation or inhibition of the NO reduction, but to a limited biological iron reduction capacity. The latter leads to a depletion of the NO absorption capacity of the scrubber liquor, and thus to a poor NO removal efficiency. Bio-augmentation of the reactor mixed liquor with an anaerobic granular sludge with a high Fe(III) reduction capacity successfully improved the bioreactor efficiency and enabled to treat a flue gas containing at least 3.3% O(2) and 500 ppm NO with an NO removal efficiency of over 80%. The ORP in the bioreactor was found to be a proper parameter for the control of the ethanol supply, needed as electron donor for the biological regeneration process. The NO removal efficiency as well as the Fe(III)EDTA(-) reduction rate were found to decline at ORP values higher than -140 mV (pH 7.0). For stable BioDeNO(x) operation, the supply of electron donor (ethanol) can be used to control the ORP below that critical value.     

Soil acidity in relation to groundnut-Bradyrhizobium symbiotic performance

Effects of soil acidity on groundnut-Bradyrhizobium symbiotic performance were studied in a potted, sandy soil in a glasshouse in Zimbabwe. The soil was limed to soil-pH levels of 5.0 and 6.5. Soil acidity negatively affected plant development, measured as leaf area and plant dry weight, while nodulation was enhanced. This acidity-enhanced nodulation was most evident when nodulation was caused by the indigenousBradyrhizobium population. Effects of soil acidity differed between groundnut cultivars andBradyrhizobium spp. strains, the former having greater importance. TwoArachis hypogaea L. Spanish-type cultivars, Falcon and Plover, performed equally well at neutral soil pH, but Falcon was more acid tolerant. Comparison of the symbiotic performance in neutral versus acid soil of twoBradyrhizobium spp. strains, MAR 411 (3G4b20) and MAR 1510 (CB 756), showed that MAR 411 performed superiorly in neutral soil, but MAR 1510 in acid soil. The indigenousBradyrhizobium population was more effective than was inoculation with strains MAR 411 or MAR 1510. Comparison of twelveBradyrhizobium spp. strains for their symbiotic performance in acid soil showed that some strains were totally ineffective under acidity stress (MAR 253, MAR 967 and MAR 1506), while others performed well.Bradyrhizobium spp. strain MAR 1576 (32 H1) ranked highest for nitrogen accumulation, plant dry weight and leaf area, with strains MAR 1555 (TAL 11) and MAR 1510 following closely. Nitrate fertilisation of groundnut plants led to soil alkalinisation, while nitrogen fixation resulted in soil acidification. Soil acidity in combination with soil sterilisation gave rise to symptoms associated with Al and Mn toxicity.     

Effects of cholesterol oxidase on cultured vascular smooth muscle cells

Summary Cholesterol oxidase (3-hydroxy-steroid oxidase) catalyzes the oxidation of cholesterol to 4-cholesten-3 one and other oxidized cholesterol derivatives. The purpose of the present study was to investigate its effects on cultured vascular smooth muscle cells. Cultured rabbit aortic smooth muscle cells were morphologically altered after exposure to cholesterol oxidase in the presence of culture medium containing 10% fetal calf serum. If fetal calf serum was absent, cells were unaffected by the treatment. The extent of morphological change of the smooth muscle cells was dependent upon the time of exposure to the enzyme and the concentration of cholesterol oxidase employed. After moderate treatment with cholesterol oxidase, cells excluded trypan blue. Further, a specific mitochondrial marker DASPMI (dimethyl aminostyryl-methyl-pyridiniumiodine) which was used as a fluorescent index of cell viability, revealed that cell viability was unchanged after moderate cholesterol oxidase treatment. Nile red, a hydrophobic probe which selectively stains intracellular lipid droplets, was applied to detect the cellular lipid content after treatment with cholesterol oxidase. Cellular nile red fluorescence intensity increased linearly with the time and concentration of cholesterol oxidase treatment. These results demonstrate that cholesterol oxidase alters lipid deposition in the cell and changes cell morphology. The primary site of action of cholesterol oxidase appears to be independent of the cell membrane itself and instead is dependent upon the lipid content in the surrounding culture media. These changes occur prior to the cytotoxic effects of extensive oxidation. Because oxidized cholesterol may play an important role in the pathogenesis of atherosclerosis, our results have implications for intracellular accumulation of lipids in smooth muscle cells during the atherosclerotic lesion.     

Community structure and diversity of endophytic bacteria in seeds of three consecutive generations of <Emphasis Type="Italic">Crotalaria pumila</Emphasis> growing on metal mine residues

Aims

We investigated the possible transgenerational transfer of bacterial seed endophytes across three consecutive seed generations of Crotalaria pumila growing on a metal mining site in Mexico.

Methods

Seeds were collected during three successive years in the semi-arid region of Zimapan, Mexico. Total communities of seed endophytes were investigated using DNA extraction from surface sterilized seeds and 454 pyrosequencing of the V5-V7 hypervariable regions of the 16S rRNA gene.

Results

The communities consisted of an average of 75 operational taxonomic units (OTUs); richness and diversity did not change across years. Methylobacterium, Staphylococcus, Corynebacterium, Propionibacterium and eight other OTUs constituted >60% of the community in each generation. The microbiome was dominated by Methylobacterium (present in >80% of samples). Functions associated with the microbiome were C and N fixation, oxidative phosphorylation and photosynthesis activity.

Conclusions

The bacterial endophytic communities were similar across three consecutive seed generations. Among the core microbiome Methylobacterium strains were the most abundant and they can contribute to nutrient acquisition, plant growth promotion and stress resilience to their host in metal contaminated mine residues. Identification of the seed microbiome of C. pumila may lead to novel and more efficient inoculants for microbe-assisted phytoremediation.

     

Rapid Remodeling of Invadosomes by Gi-coupled Receptors: DISSECTING THE ROLE OF Rho GTPases*

Invadosomes are actin-rich membrane protrusions that degrade the extracellular matrix to drive tumor cell invasion. Key players in invadosome formation are c-Src and Rho family GTPases. Invadosomes can reassemble into circular rosette-like superstructures, but the underlying signaling mechanisms remain obscure. Here we show that Src-induced invadosomes in human melanoma cells (A375M and MDA-MB-435) undergo rapid remodeling into dynamic extracellular matrix-degrading rosettes by distinct G protein-coupled receptor agonists, notably lysophosphatidic acid (LPA; acting through the LPA₁ receptor) and endothelin. Agonist-induced rosette formation is blocked by pertussis toxin, dependent on PI3K activity and accompanied by localized production of phosphatidylinositol 3,4,5-trisphosphate, whereas MAPK and Ca²⁺ signaling are dispensable. Using FRET-based biosensors, we show that LPA and endothelin transiently activate Cdc42 through G_i, concurrent with a biphasic decrease in Rac activity and differential effects on RhoA. Cdc42 activity is essential for rosette formation, whereas G_12/13-mediated RhoA-ROCK signaling suppresses the remodeling process. Our results reveal a G_i-mediated Cdc42 signaling axis by which G protein-coupled receptors trigger invadosome remodeling, the degree of which is dictated by the Cdc42-RhoA activity balance.     

Newly created ponds complement natural waterbodies for restoration of macroinvertebrate assemblages

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