scholarly journals Mechanisms for Accessing Insoluble Fe(III) Oxide during Dissimilatory Fe(III) Reduction by Geothrix fermentans

2002 ◽  
Vol 68 (5) ◽  
pp. 2294-2299 ◽  
Author(s):  
Kelly P. Nevin ◽  
Derek R. Lovley
Keyword(s):  
Defined Medium ◽  
Alginate Beads ◽  
Water Soluble ◽  
Oxide Reduction ◽  
Geobacter Metallireducens ◽  
Electron Shuttling ◽  
Electron Shuttles ◽  
Culture Filtrates ◽  
Subsurface Environments ◽  
Geothrix Fermentans

ABSTRACT Mechanisms for Fe(III) oxide reduction were investigated in Geothrix fermentans, a dissimilatory Fe(III)-reducing microorganism found within the Fe(III) reduction zone of subsurface environments. Culture filtrates of G. fermentans stimulated the reduction of poorly crystalline Fe(III) oxide by washed cell suspensions, suggesting that G. fermentans released one or more extracellular compounds that promoted Fe(III) oxide reduction. In order to determine if G. fermentans released electron-shuttling compounds, poorly crystalline Fe(III) oxide was incorporated into microporous alginate beads, which prevented contact between G. fermentans and the Fe(III) oxide. G. fermentans reduced the Fe(III) within the beads, suggesting that one of the compounds that G. fermentans releases is an electron-shuttling compound that can transfer electrons from the cell to Fe(III) oxide that is not in contact with the organism. Analysis of culture filtrates by thin-layer chromatography suggested that the electron shuttle has characteristics similar to those of a water-soluble quinone. Analysis of filtrates by ion chromatography demonstrated that there was as much as 250 μM dissolved Fe(III) in cultures of G. fermentans growing with Fe(III) oxide as the electron acceptor, suggesting that G. fermentans released one or more compounds capable of chelating and solubilizing Fe(III). Solubilizing Fe(III) is another strategy for alleviating the need for contact between cells and Fe(III) oxide for Fe(III) reduction. This is the first demonstration of a microorganism that, in defined medium without added electron shuttles or chelators, can reduce Fe(III) derived from Fe(III) oxide without directly contacting the Fe(III) oxide. These results are in marked contrast to those with Geobacter metallireducens, which does not produce electron shuttles or Fe(III) chelators. These results demonstrate that phylogenetically distinct Fe(III)-reducing microorganisms may use significantly different strategies for Fe(III) reduction. Thus, it is important to know which Fe(III)-reducing microorganisms predominate in a given environment in order to understand the mechanisms for Fe(III) reduction in the environment of interest.

scholarly journals Lack of Production of Electron-Shuttling Compounds or Solubilization of Fe(III) during Reduction of Insoluble Fe(III) Oxide by Geobacter metallireducens

2000 ◽  
Vol 66 (5) ◽  
pp. 2248-2251 ◽  
Author(s):  
Kelly P. Nevin ◽  
Derek R. Lovley
Keyword(s):  
Oxide Reduction ◽  
Semipermeable Membranes ◽  
Geobacter Metallireducens ◽  
Electron Shuttling ◽  
Common Technique ◽  
Experimental Approaches ◽  
The Common

ABSTRACT Studies with the dissimilatory Fe(III)-reducing microorganismGeobacter metallireducens demonstrated that the common technique of separating Fe(III)-reducing microorganisms and Fe(III) oxides with semipermeable membranes in order to determine whether the Fe(III) reducers release electron-shuttling compounds and/or Fe(III) chelators is invalid. This raised doubts about the mechanisms for Fe(III) oxide reduction by this organism. However, several experimental approaches indicated that G. metallireducens does not release electron-shuttling compounds and does not significantly solubilize Fe(III) during Fe(III) oxide reduction. These results suggest that G. metallireducens directly reduces insoluble Fe(III) oxide.

scholarly journals Microbially Mediated Biodegradation of Hexahydro-1,3,5-Trinitro-1,3,5- Triazine by Extracellular Electron Shuttling Compounds

2006 ◽  
Vol 72 (9) ◽  
pp. 5933-5941 ◽  
Author(s):  
Man Jae Kwon ◽  
Kevin T. Finneran
Keyword(s):  
Humic Substances ◽  
Electron Donor ◽  
Cell Suspensions ◽  
Electron Shuttle ◽  
Geobacter Metallireducens ◽  
Electron Shuttling ◽  
Resting Cell ◽  
Molar Basis ◽  
Novel Approach

ABSTRACT The potential for humic substances to stimulate the reduction of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was investigated. This study describes a novel approach for the remediation of RDX-contaminated environments using microbially mediated electron shuttling. Incubations without cells demonstrated that reduced AQDS transfers electrons directly to RDX, which was reduced without significant accumulation of the nitroso intermediates. Three times as much reduced AQDS (molar basis) was needed to completely reduce RDX. The rate and extent of RDX reduction differed greatly among electron shuttle/acceptor amendments for resting cell suspensions of Geobacter metallireducens and G. sulfurreducens with acetate as the sole electron donor. AQDS and purified humic substances stimulated the fastest rate of RDX reduction. The nitroso metabolites did not significantly accumulate in the presence of AQDS or humic substances. RDX reduction in the presence of poorly crystalline Fe(III) was relatively slow and metabolites transiently accumulated. However, adding humic substances or AQDS to Fe(III)-containing incubations increased the reduction rates. Cells of G. metallireducens alone reduced RDX; however, the rate of RDX reduction was slow relative to AQDS-amended incubations. These data suggest that extracellular electron shuttle-mediated RDX transformation is not organism specific but rather is catalyzed by multiple Fe(III)- and humic-reducing species. Electron shuttle-mediated RDX reduction may eventually become a rapid and effective cleanup strategy in both Fe(III)-rich and Fe(III)-poor environments.

Engineering Dense Connective Tissues via Anisotropic Nanofibrous Scaffolds With High Sacrificial Fiber Content

2010 ◽  
Author(s):  
Brendon M. Baker ◽  
Amy M. Silverstein ◽  
Robert L. Mauck
Keyword(s):  
Defined Medium ◽  
Fiber Content ◽  
Water Soluble ◽  
Cell Infiltration ◽  
Cell Alignment ◽  
Nanofibrous Scaffolds ◽  
Small Pore ◽  
Production And Distribution ◽  
Fiber Fractions ◽  
Poly Ethylene

Given their ability to dictate initial cell alignment and subsequent matrix organization, aligned electrospun scaffolds are a fitting means for engineering fiber-reinforced, anisotropic tissues such as tendon, ligament, the knee meniscus, and the annulus fibrosus [1–4]. However, one commonly observed limitation of such scaffolds is the relatively slow infiltration rates of surface-seeded cells, where the central thicknesses of constructs cultured for 10 weeks remain devoid of cells [3]. This limitation arises from the tight packing of fibers which yields small pore sizes, thereby hampering cell migration. Towards accelerating cell ingress, we have recently reported on two-polymer composite scaffolds containing both slow eroding poly(ε-caprolactone) (PCL) fibers as well as water-soluble poly(ethylene oxide) (PEO) fibers that serve as space holders during scaffold formation [5]. Removal of these PEO fibers prior to seeding resulted in improved cell infiltration after 3 weeks, but the long-term maturation of such constructs has yet to be characterized. To assess the effect of sacrificial PEO fiber content on construct growth, a triple-jet electrospinning device was employed to generate PCL/PEO scaffolds with PEO fiber fractions ranging from 0 to 60%. After seeding with human meniscus fibrochondrocytes (hMFCs), constructs were clamped in custom grips to maintain strip morphology. The mechanical and biochemical maturation of constructs was assessed over 12 weeks of free swelling culture in a chemically defined medium (CDM), along with cell infiltration and matrix distribution. We hypothesized that enhanced pore size in dual-fiber constructs would lead to not only to a better distribution of cells, but also to larger increases in stiffness resulting from enhanced matrix production and distribution.

Chondrogenic Potential of in Vitro Multiplied Rabbit Perichondrium Cells Cultured in Alginate Beads in Defined Medium

2000 ◽  
Vol 6 (4) ◽  
pp. 321-330 ◽  
Author(s):  
Gerjo J. V. M. Van Osch ◽  
Simone W. Van Der Veen ◽  
Elisabeth H. Burger ◽  
Henriette L. Verwoerd-Verhoef
Keyword(s):  
Defined Medium ◽  
Alginate Beads ◽  
Chondrogenic Potential ◽  
Cells Cultured

scholarly journals Moorella humiferrea sp. nov., a thermophilic, anaerobic bacterium capable of growth via electron shuttling between humic acid and Fe(III)

2012 ◽  
Vol 62 (Pt_3) ◽  
pp. 613-617 ◽  
Author(s):  
Y. N. Nepomnyashchaya ◽  
G. B. Slobodkina ◽  
R. V. Baslerov ◽  
N. A. Chernyh ◽  
E. A. Bonch-Osmolovskaya ◽  
...  
Keyword(s):  
Humic Acid ◽  
Electron Acceptor ◽  
Type Strain ◽  
Kamchatka Peninsula ◽  
Alginate Beads ◽  
Rrna Gene ◽  
Electron Shuttling ◽  
Bacterium Strain ◽  
Hydrothermal Spring ◽  
Ph Range

An anaerobic, thermophilic, spore-forming bacterium (strain 64-FGQT) was isolated from a terrestrial hydrothermal spring from the Kamchatka peninsula, Russia. This strain utilized lactate as an electron donor, insoluble poorly crystalline Fe(III) oxide incorporated into alginate beads as a potential electron acceptor and 9,10-anthraquinone-2,6-disulfonate (AQDS) as an electron-shuttling compound. Vegetative cells of strain 64-FGQT were Gram-stain-positive, peritrichously flagellated, motile, straight rods, 0.3–0.5 µm in diameter and 2.0–5.0 µm long, growing singly or forming short chains. Cells formed round refractive endospores in terminal swollen sporangia. The temperature range for growth was 46–70 °C, with an optimum at 65 °C. The pH range for growth was 5.5–8.5, with an optimum at pH 7.0. The substrates utilized by strain 64-FGQT in the presence of AQDS as an electron acceptor included lactate, malate, succinate, glycerol and yeast extract. The strain fermented galactose, fructose, maltose, sucrose, pyruvate and peptone. Strain 64-FGQT used AQDS, humic acid, thiosulfate, nitrate and perchlorate as electron acceptors for growth. Fe(III) was not directly reduced, but strain 64-FGQT was able to grow and reduce Fe(III) oxide in the presence of small amounts of AQDS or humic acid as electron-shuttling compounds. The G+C content of the DNA of strain 64-FGQT was 51 mol%. 16S rRNA gene sequence analysis placed the isolate in the genus Moorella, with the type strain of Moorella glycerini as its closest relative (97.2 % similarity). Based on phylogenetic analysis and physiological characteristics, strain 64-FGQT is considered to represent a novel species of the genus Moorella, for which the name Moorella humiferrea sp. nov. is proposed; the type strain is 64-FGQT ( = DSM 23265T = VKM B-2603T).

scholarly journals Outer Cell Surface Components Essential for Fe(III) Oxide Reduction by Geobacter metallireducens

2012 ◽  
Vol 79 (3) ◽  
pp. 901-907 ◽  
Author(s):  
Jessica A. Smith ◽  
Derek R. Lovley ◽  
Pier-Luc Tremblay
Keyword(s):  
Outer Surface ◽  
Surface Protein ◽  
Transcript Abundance ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Outer Cell ◽  
Gene Transcript ◽  
Oxide Reduction ◽  
Geobacter Metallireducens ◽  
Content Type

ABSTRACTGeobacterspecies are important Fe(III) reducers in a diversity of soils and sediments. Mechanisms for Fe(III) oxide reduction have been studied in detail inGeobacter sulfurreducens, but a number of the most thoroughly studied outer surface components ofG. sulfurreducens, particularlyc-type cytochromes, are not well conserved amongGeobacterspecies. In order to identify cellular components potentially important for Fe(III) oxide reduction inGeobacter metallireducens, gene transcript abundance was compared in cells grown on Fe(III) oxide or soluble Fe(III) citrate with whole-genome microarrays. Outer-surface cytochromes were also identified. Deletion of genes forc-type cytochromes that had higher transcript abundance during growth on Fe(III) oxides and/or were detected in the outer-surface protein fraction identified sixc-type cytochrome genes, that when deleted removed the capacity for Fe(III) oxide reduction. Several of thec-type cytochromes which were essential for Fe(III) oxide reduction inG. metallireducenshave homologs inG. sulfurreducensthat are not important for Fe(III) oxide reduction. Other genes essential for Fe(III) oxide reduction included a gene predicted to encode an NHL (Ncl-1–HT2A–Lin-41) repeat-containing protein and a gene potentially involved in pili glycosylation. Genes associated with flagellum-based motility, chemotaxis, and pili had higher transcript abundance during growth on Fe(III) oxide, consistent with the previously proposed importance of these components in Fe(III) oxide reduction. These results demonstrate that there are similarities in extracellular electron transfer betweenG. metallireducensandG. sulfurreducensbut the outer-surfacec-type cytochromes involved in Fe(III) oxide reduction are different.

Endocytosis of Sugars in Embryonic Skeletal Tissues in Organ Culture

1969 ◽  
Vol 4 (1) ◽  
pp. 133-137
Author(s):  
T. C. APPLETON ◽  
S. R. PELC ◽  
J. T. DINGLE ◽  
HONOR B. FELL
Keyword(s):  
Organ Culture ◽  
Defined Medium ◽  
Water Soluble ◽  
Chemically Defined Medium ◽  
Limb Bone ◽  
Pinocytotic Vesicles ◽  
And Cartilage

Earlier experiments have shown that when limb-bone rudiments from 8½-day embryonic chicks are cultivated in medium containing an indigestible sugar, the perichondrial cells become intensely vacuolated, but this vacuolation does not appear in the chondrocytes, except in the articular region. Appleton's radioautographic method for demonstrating water-soluble materials was used to study the uptake, distribution and loss of 14C-labelled sucrose in 8½ limb-bone rudiments cultivated in a chemically defined medium (BGJ5). After 48 h exposure to [14C] sucrose, both perichondrium and cartilage were heavily labelled. When such explants were either washed for 1 h in BGJ5 or cultivated for a further 24 h in non-radioactive medium, labelling was almost unaffected in the perichondrial cells but was greatly reduced in the cartilage, the cells of which were almost devoid of radioactivity. The presence in the medium of 0.08 M ‘cold’ sucrose did not alter the perichondrial grain counts in the washed explants. This finding supports the view that in the perichondrial cells sucrose is taken up non-specifically by endocytosis, arid that the intense vacuolation of the cytoplasm is due to abnormal persistence of the pinocytotic vesicles in the presence of the sugar. It is concluded that failure of the chondrocytes to take up sucrose is due, not to lack of penetration of the sugar into the cartilage, but to a weak endocytotic activity of the cells.

Dimers of Altersolanol A from Alternaria solani

1988 ◽  
Vol 43 (11-12) ◽  
pp. 813-817 ◽  
Author(s):  
George Lazarovits ◽  
R. William ◽  
Albert Stoessl
Keyword(s):  
Early Blight ◽  
Alternaria Solani ◽  
Mass Spectrometric ◽  
Water Soluble ◽  
H Nmr ◽  
Culture Filtrates

Abstract Weakly phytotoxic, water-soluble pigments from culture filtrates of the potato early blight organism Alternaria solani have been identified by 1H NMR, UV, mass spectrometric, and acetylation studies as the pair of rotamers represented by structure 1a.

The 24-kDa protein from Fusarium oxysporum f.sp. erythroxyli: occurrence in related fungi and the effect of growth medium on its production

1997 ◽  
Vol 43 (1) ◽  
pp. 45-55 ◽  
Author(s):  
Bryan A. Bailey ◽  
James C. Jennings ◽  
James D. Anderson
Keyword(s):  
Fusarium Oxysporum ◽  
Protein Production ◽  
Fusarium Species ◽  
Infected Plant ◽  
Water Soluble ◽  
Western Blots ◽  
Fungal Isolates ◽  
Culture Filtrates ◽  
Dicotyledonous Plants ◽  
Casamino Acids

A 24-kDa protein that elicits ethylene production and necrosis in leaves of dicotyledonous plants was previously purified from culture filtrates of Fusarium oxysporum Schlechtend:Fr. f.sp. erythroxyli. Antisera to the denatured 24-kDa protein detected 2.5 ng of the 24-kDa protein on Western blots at 100 000-fold dilutions. The antisera cross-reacted with a 24-kDa protein on Western blots of culture filtrates from three other F. oxysporum formae speciales. Of seven Fusarium species, only F. oxysporum, F. acuminatum Ellis and Kellerm., and F. avenaceum (Fr.:Fr.) Sacc. isolates produced an antigenically related 24-kDa protein. Although there were differences in the profiles of proteins extracted from stems of coca (Erythroxylum coca var. coca L. Lam.) infected with F. oxysporum f.sp. erythroxyli compared with uninfected stems, antisera to the 24-kDa protein did not cross-react with any proteins from the infected coca stems. For the fungal isolates studied, the best medium tested for production of the 24-kDa protein contained 1% sucrose and 1% asparagine. Biological activity of the F. oxysporum culture filtrates on sweet basil leaves was consistently correlated with the presence of the 24-kDa protein. Production of the 24-kDa protein was limited in cultures containing pectin or cellulose as the primary carbon source, or in cultures lacking sucrose or casamino acids. Water-soluble extracts from coca stems inhibited production of the 24-kDa protein, whereas cellulose and pectin did not. Components produced by the plant may limit production of the 24-kDa protein in infected plant tissue and thereby limit the response of the plant to the fungus. These results suggest the 24-kDa protein does not function in the symptomatic phase of the F. oxysporum f.sp. erythroxyli–coca disease interaction.Key words: Fusarium oxysporum, toxin, elicitor.

Removal of Sacrificial Fibers Enhances Long Term Cell and Matrix Distribution in Aligned Nanofibrous Scaffolds

2009 ◽  
Author(s):  
Brendon M. Baker ◽  
Giana Montero ◽  
Robert L. Mauck
Keyword(s):  
Defined Medium ◽  
Water Soluble ◽  
Cell Infiltration ◽  
Cell Alignment ◽  
Nanofibrous Scaffolds ◽  
Small Pore ◽  
Matrix Distribution ◽  
Production And Distribution ◽  
Fiber Fractions

Given their ability to dictate initial cell alignment and subsequent matrix organization, aligned electrospun scaffolds are a fitting means for engineering fiber-reinforced, anisotropic tissues such as tendon, ligament, the knee meniscus, and the annulus fibrosus [1–3]. However, one commonly observed limitation of such scaffolds is the relatively slow infiltration rates of surface-seeded cells, where the central thicknesses of constructs cultured for 10 weeks remain devoid of cells [2]. This limitation arises from the tight packing of fibers which yields small pore sizes, thereby hampering cell migration. Towards accelerating cell ingress, we have recently reported on two-polymer composite scaffolds containing both slow eroding poly(ε-caprolactone) (PCL) fibers as well as water-soluble poly(ethylene oxide) (PEO) fibers that serve as space holders during scaffold formation [4]. Removal of these PEO fibers prior to seeding resulted in improved cell infiltration after 3 weeks, but the long term maturation of such constructs has yet to be characterized. To assess the effect of sacrificial PEO fiber content on construct growth, a triple-jet electrospinning device was employed to generate PCL/PEO scaffolds with PEO fiber fractions ranging from 0 to 60%. After seeding with mesenchymal stem cells (MSCs), constructs were clamped in custom grips to maintain strip morphology. The mechanical and biochemical maturation of constructs was assessed over 9 weeks of free swelling culture in a chemically defined medium (CDM), along with cell infiltration and matrix distribution. We hypothesized that enhanced pore size in dual-fiber constructs would lead to not only a better distribution of cells, but also larger increases in stiffness resulting from enhanced matrix production and distribution.

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