Biomedical subjects

Y A Gorby

Publications and source records attributed to Y A Gorby.

9 recordsLinked to original sources

PubMed2001

Microbial reduction of Fe(III) and sorption/precipitation of Fe(II) on Shewanella putrefaciens strain CN32.

The influence of Fe(II) on the dissimilatory bacterial reduction of an Fe(III) aqueous complex (Fe(III)-citrate(aq)) was investigated using Shewanella putrefaciens strain CN32. The sorption of Fe(II) on CN32 followed a Langmuir isotherm. Least-squares fitting gave a maximum sorption capacity of Qmax = 4.19 x 10(-3) mol/10(12) cells (1.19 mmol/m2 of cell surface area) and an affinity coefficient of log K = 3.29. The growth yield of CN32 with respect to Fe(III)aq reduction showed a linear trend with an average value of 5.24 (+/-0.12) x 10(9) cells/mmol of Fe(III). The reduction of Fe(III)aq by CN32 was described by Monod kinetics with respect to the electron acceptor concentration, Fe(III)aq, with a half-saturation constant (Ks) of 29 (+/-3) mM and maximum growth rate (micromax) of 0.32 (+/-0.02) h(-1). However, the pretreatment of CN32 with Fe(II)aq significantly inhibited the reduction of Fe(III)aq, resulting in a lag phase of about 3-30 h depending on initial cell concentrations. Lower initial cell concentration led to longer lag phase duration, and higher cell concentration led to a shorter one. Transmission electron microscopy and energy dispersive spectroscopy revealed that many cells carried surface precipitates of Fe mineral phases (valence unspecified) during the lag phase. These precipitates disappeared after the cells recovered from the lag phase. The cell inhibition and recovery mechanisms from Fe(II)-induced mineral precipitation were not identified by this study, but several alternatives were discussed. A modified Monod model incorporating a lag phase, Fe(II) adsorption, and aqueous complexation reactions was able to describe the experimental results of microbial Fe(III)aq reduction and cell growth when cells were pretreated with Fe(II)aq.

Adsorption↗

PubMed2001

Biotransformation of Ni-substituted hydrous ferric oxide by an Fe(III)-reducing bacterium.

The reductive biotransformation of a Ni(2+)-substituted (5 mol %) hydrous ferric oxide (NiHFO) by Shewanella putrefaciens, strain CN32, was investigated under anoxic conditions at circumneutral pH. Our objectives were to define the influence of Ni2+ substitution on the bioreducibility of the HFO and the biomineralization products formed and to identify biogeochemical factors controlling the phase distribution of Ni2+ during bioreduction. Incubations with CN32 and NiHFO were sampled after 14 and 32 d, and both aqueous chemistry and solid phases were characterized. By comparison of these results with a previous study (Fredrickson, J. K.; Zachara, J. M.; Kennedy, D. W.; Dong, H.; Onstott, T. C.; Hinman, N. W.; Li, S. W. Geochim. Cosmochim. Acta 1998, 62, 3239-3257), it was concluded that coprecipitated/sorbed Ni2+ inhibited the bioreduction of HFO through an undefined chemical mechanism. Mössbauer spectroscopy allowed analysis of the residual HFO phase and the identity and approximate mass percent of biogenic mineral phases. The presence of AQDS, a soluble electron shuttle that obviates need for cell--oxide contact, was found to counteract the inhibiting effect of Ni2+. Nickel was generally mobilized during bioreduction in a trend that correlated with final pH, except in cases where PO4(3-) was present and vivianite precipitation occurred. CN32 promoted the formation of Ni(2+)-substituted magnetite (Fe2IIIFe(1-x)IINixIIO4) in media with AQDS but without PO4(3-). The formation of this biogenic coprecipitate, however, had little discernible impact on final aqueous Ni2+ concentrations. These results demonstrate that coprecipitated Ni can inhibit dissimilatory microbial reduction of amorphous iron oxide, but the presence of humic acids may facilitate the immobilization of Ni within the crystal structure of biogenic magnetite.

Biotransformation↗

PubMed2001

Cell surface electrochemical heterogeneity of the Fe(III)-reducing bacteria Shewanella putrefaciens.

Acid-base titration experiments and electrostatic force microscopy (EFM) were used to investigate the cell surface electrochemical heterogeneity of the Fe(III)-reducing bacteria, Shewanella putrefaciens. The acid-base titrations extended from pH 4 to 10, and the titration data were fit using a linear programming pKa spectrum approach. Overall, a five-site model accounted for the observed titration behavior with the most acidic sites corresponding to carboxylic groups and phosphodiester groups, intermediate sites phosphoryl groups, and two basic sites equivalent to amine or hydroxyl groups. The pH for the point of zero charge on the bacteria was 5.4. In EFM images of cells rinsed in solutions at pH 4.0, 7.0, and 8.0, a pronounced increase in small (< or = 100 nm diameter) high contrast patches was observed on the cells with increasing pH. The pH dependence of EFM image contrast paralleled the pattern of cell surface charge development inferred from the titration experiments; however, quantitative analysis of high contrast regions in the EFM images yielded lower surface charge values than those anticipated from the titration data. For example at pH 7, the calculated surface charge of high contrast regions in EFM images of the bacterial cells was -0.23 microC/cm2 versus -20.0 microC/cm2 based on the titration curve. The differences in surface charge estimates between the EFM images and titration data are consistent not only with charge development throughout the entire volume of the bacterial cell wall (i.e., in association with functional groups that are not directly exposed at the cell surface) but also with the presence of a thin structural layer of water containing charge-compensating counterions. In combination, the pKa spectra and EFM data demonstrate that a particularly high degree of electrochemical heterogeneity exists within the cell wall and at the cell surface of S. putrefaciens.

Cell Membrane↗

PubMed2000

Effect of electron donor and solution chemistry on products of dissimilatory reduction of technetium by Shewanella putrefaciens.

To help provide a fundamental basis for use of microbial dissimilatory reduction processes in separating or immobilizing (99)Tc in waste or groundwaters, the effects of electron donor and the presence of the bicarbonate ion on the rate and extent of pertechnetate ion [Tc(VII)O(4)(-)] enzymatic reduction by the subsurface metal-reducing bacterium Shewanella putrefaciens CN32 were determined, and the forms of aqueous and solid-phase reduction products were evaluated through a combination of high-resolution transmission electron microscopy, X-ray absorption spectroscopy, and thermodynamic calculations. When H(2) served as the electron donor, dissolved Tc(VII) was rapidly reduced to amorphous Tc(IV) hydrous oxide, which was largely associated with the cell in unbuffered 0. 85% NaCl and with extracellular particulates (0.2 to 0.001 microm) in bicarbonate buffer. Cell-associated Tc was present principally in the periplasm and outside the outer membrane. The reduction rate was much lower when lactate was the electron donor, with extracellular Tc(IV) hydrous oxide the dominant solid-phase reduction product, but in bicarbonate systems much less Tc(IV) was associated directly with the cell and solid-phase Tc(IV) carbonate may have been present. In the presence of carbonate, soluble (<0.001 microm) electronegative, Tc(IV) carbonate complexes were also formed that exceeded Tc(VII)O(4)(-) in electrophoretic mobility. Thermodynamic calculations indicate that the dominant reduced Tc species identified in the experiments would be stable over a range of E(h) and pH conditions typical of natural waters. Thus, carbonate complexes may represent an important pathway for Tc transport in anaerobic subsurface environments, where it has generally been assumed that Tc mobility is controlled by low-solubility Tc(IV) hydrous oxide and adsorptive, aqueous Tc(IV) hydrolysis products.

Carbonates↗

PubMed1999

Dissimilatory reduction of Fe(III) and other electron acceptors by a Thermus isolate.

A thermophilic bacterium that can use O2, NO3-, Fe(III), and S0 as terminal electron acceptors for growth was isolated from groundwater sampled at a 3.2-km depth in a South African gold mine. This organism, designated SA-01, clustered most closely with members of the genus Thermus, as determined by 16S rRNA gene (rDNA) sequence analysis. The 16S rDNA sequence of SA-01 was >98% similar to that of Thermus strain NMX2 A.1, which was previously isolated by other investigators from a thermal spring in New Mexico. Strain NMX2 A.1 was also able to reduce Fe(III) and other electron acceptors. Neither SA-01 nor NMX2 A.1 grew fermentatively, i.e., addition of an external electron acceptor was required for anaerobic growth. Thermus strain SA-01 reduced soluble Fe(III) complexed with citrate or nitrilotriacetic acid (NTA); however, it could reduce only relatively small quantities (0.5 mM) of hydrous ferric oxide except when the humic acid analog 2,6-anthraquinone disulfonate was added as an electron shuttle, in which case 10 mM Fe(III) was reduced. Fe(III)-NTA was reduced quantitatively to Fe(II); reduction of Fe(III)-NTA was coupled to the oxidation of lactate and supported growth through three consecutive transfers. Suspensions of Thermus strain SA-01 cells also reduced Mn(IV), Co(III)-EDTA, Cr(VI), and U(VI). Mn(IV)-oxide was reduced in the presence of either lactate or H2. Both strains were also able to mineralize NTA to CO2 and to couple its oxidation to Fe(III) reduction and growth. The optimum temperature for growth and Fe(III) reduction by Thermus strains SA-01 and NMX2 A.1 is approximately 65 degrees C; their optimum pH is 6.5 to 7.0. This is the first report of a Thermus sp. being able to couple the oxidation of organic compounds to the reduction of Fe, Mn, or S.

Biodegradation, Environmental↗

PubMed1996

Environmental processes mediated by iron-reducing bacteria.

Considerable progress has been made towards enhancing our understanding of the phylogeny, ecology and biogeochemical role of dissimilatory iron-reducing bacteria. The known phylogenetic range of iron-reducing bacteria has expanded considerably, as has the known range of iron minerals that serve as a source of Fe(III) for anaerobic respiration. In addition, the number of biotechnological applications of iron-reducing bacteria, including remediation of soils and sediments contaminated with metals, radionuclides and organics, is rapidly expanding.

Bacteria↗

PubMed1993

Geobacter metallireducens gen. nov. sp. nov., a microorganism capable of coupling the complete oxidation of organic compounds to the reduction of iron and other metals.

The gram-negative metal-reducing microorganism, previously known as strain GS-15, was further characterized. This strict anaerobe oxidizes several short-chain fatty acids, alcohols, and monoaromatic compounds with Fe(III) as the sole electron acceptor. Furthermore, acetate is also oxidized with the reduction of Mn(IV), U(VI), and nitrate. In whole cell suspensions, the c-type cytochrome(s) of this organism was oxidized by physiological electron acceptors and also by gold, silver, mercury, and chromate. Menaquinone was recovered in concentrations comparable to those previously found in gram-negative sulfate reducers. Profiles of the phospholipid ester-linked fatty acids indicated that both the anaerobic desaturase and the branched pathways for fatty acid biosynthesis were operative. The organism contained three lipopolysaccharide hydroxy fatty acids which have not been previously reported in microorganisms, but have been observed in anaerobic freshwater sediments. The 16S rRNA sequence indicated that this organism belongs in the delta proteobacteria. Its closest known relative is Desulfuromonas acetoxidans. The name Geobacter metallireducens is proposed.

Cytochrome c Group↗

PubMed1991

Electron Transport in the Dissimilatory Iron Reducer, GS-15.

Mechanisms for electron transport to Fe(III) were investigated in GS-15, a novel anaerobic microorganism which can obtain energy for growth by coupling the complete oxidation of organic acids or aromatic compounds to the reduction of Fe(III) to Fe(II). The results indicate that Fe(III) reduction proceeds through a type b cytochrome and a membrane-bound Fe(III) reductase which is distinct from the nitrate reductase.

Journal Article↗

PubMed1988

Characterization of the bacterial magnetosome membrane.

Intact magnetosomes of Aquaspirillum magnetotacticum were purified from broken cells by a magnetic separation technique. Electron microscopic and chemical analyses revealed the magnetite to be enclosed by a lipid bilayer admixed with proteins. Lipids were recovered in fractions expected to contain (i) neutral lipids and free fatty acids, (ii) glycolipids and sulfolipids, and (iii) phospholipids (in a weight ratio of 1:4:6). Phospholipids included phosphatidylserine and phosphatidylethanolamine. Two of the numerous proteins detected in the magnetosome membrane were not found in other cell membranes or soluble fractions.

Bacteria↗