Addition Of Ferrihydrite Research Articles

Influence of Microbially Reducible Fe(III) on the Bacterial Community Structure of Estuarine Surface Sediments

We analyzed PCR-amplified 16S rRNA genes from native and Fe(III)-enriched surface sediments of a major tidal channel in the Tijuana River Estuary, California, USA. Clones from native sediments were most closely affiliated with photosynthetic taxa (Cyanobacteria, Chloroflexi, and Halochromatium) and microorganisms known to reduce (Desulfatibacillus, Desulfobacterium, and Desulfuromusa) or oxidize (Microcoleus, Phormidium, and Halochromatium) various sulfur species, reflective of the fluctuating redox conditions in the tidal zone. Fe(III) was rapidly reduced in anaerobic microcosms amended with 2-line ferrihydrite, with or without the sulfate reduction inhibitor sodium molybdate. The addition of ferrihydrite without molybdate caused a major shift in community structure to a dominance of the Fe(III)-reducing genus Shewanella, while at the same time the sulfate-reducing and sulfide-oxidizing populations were replaced by taxa known to cycle elemental sulfur. Sediments amended with both ferrihydrite and molybdate were again populated by Shewanella clones, but also numerically important were clones most similar to Marinobacterium, Pseudomonas, and Bacillus, suggesting a role for these taxa in Fe(III) reduction in marine habitats.

Effects of sediment iron mineral composition on microbially mediated changes in divalent metal speciation: Importance of ferrihydrite

Dissimilatory metal reducing bacteria (DMRB) can influence geochemical processes that affect the speciation and mobility of metallic contaminants within natural environments. Most investigations into the effect of DMRB on sediment geochemistry utilize various synthetic oxides as the Fe III source (e.g., ferrihydrite, goethite, hematite). These synthetic materials do not represent the mineralogical composition of natural systems, and do not account for the effect of sediment mineral composition on microbially mediated processes. Our experiments with a DMRB ( Shewanella putrefaciens 200) and a divalent metal (Zn II) indicate that, while complexity in sediment mineral composition may not strongly impact the degree of “microbial iron reducibility,” it does alter the geochemical consequences of such microbial activity. The ferrihydrite and clay mineral content are key factors. Microbial reduction of a synthetic blend of goethite and ferrihydrite (VHSA-G) carrying previously adsorbed Zn II increased both [Zn II-aq] and the proportion of adsorbed Zn II that is insoluble in 0.5 M HCl. Microbial reduction of Fe III in similarly treated iron-bearing clayey sediment (Fe-K-Q) and hematite sand, which contained minimal amounts of ferrihydrite, had no similar effect. Addition of ferrihydrite increased the effect of microbial Fe III reduction on Zn II association with a 0.5 M HCl insoluble phase in all sediment treatments, but the effect was inconsequential in the Fe-K-Q. Zinc k-edge X-ray absorption spectroscopy (XAS) data indicate that microbial Fe III reduction altered Zn II bonding in fundamentally different ways for VHSA-G and Fe-K-Q. In VHSA-G, ZnO 6 octahedra were present in both sterile and reduced samples; with a slightly increased average Zn-O coordination number and a slightly higher degree of long-range order in the reduced sample. This result may be consistent with enhanced Zn II substitution within goethite in the microbially reduced sample, though these data do not show the large increase in the degree of Zn-O-metal interactions expected to accompany this change. In Fe-K-Q, microbial Fe III reduction transforms Zn-O polyhedra from octahedral to tetrahedral coordination and leads to the formation of a ZnCl 2 moiety and an increased degree of multiple scattering. This study indicates that, while many sedimentary iron minerals are easily reduced by DMRB, the effects of microbial Fe III reduction on trace metal geochemistry are dependent on sediment mineral composition.

Kaolinite, Halloysite, and Iron Oxide Influence on Physical Behavior of Formulated Soils

Soils of some tropical regions have low bulk density, high permeability, and resistance to erosion even under high rainfall. Soils with this combination of characteristics frequently contain halloysite and Fe oxides. We hypothesized that platy kaolinite particles form a more compact mass than tubular halloysite particles, and that Fe oxides promote porous aggregation. To test this hypothesis the settling densities were determined for soil analogs constructed of kaolinite and halloysite clays with ferrihydrite and nonionic, anionic, and cationic organic surfactants as organic matter proxies. The samples were mixed in water and compacted by centrifugation. The hydraulic conductivity of each kaolinite‐ and halloysite‐based mixture was determined with a falling head permeameter. Halloysite samples had lower bulk densities than kaolinite samples with the same centrifugation. The addition of ferrihydrite decreased bulk density of sets of both mineral mixtures. Numerous small particles of ferrihydrite adhered to halloysite tubes in contrast to larger oxide masses formed among clean kaolinite plates, as shown in transmission electron micrographs. The greater frequency of ferrihydrite particles associated with halloysite than kaolinite crystals provided more sites for inter‐particle bonding and clay aggregation. Cationic and neutral organic polymers decreased the bulk density of halloysite soil analogs. The kaolinite analog response to polymer treatment varied. Anionic polymers appeared to increase the bulk density of both mineral mixtures that is attributed to increased particle dispersion. These results support the hypothesis that clay morphology and bonding agents influence soil bulk density and hydraulic conductivity of fabricated clay soils.

Microbial manganese and sulfate reduction in Black Sea shelf sediments.

The microbial ecology of anaerobic carbon oxidation processes was investigated in Black Sea shelf sediments from mid-shelf with well-oxygenated bottom water to the oxic-anoxic chemocline at the shelf-break. At all stations, organic carbon (C(org)) oxidation rates were rapidly attenuated with depth in anoxically incubated sediment. Dissimilatory Mn reduction was the most important terminal electron-accepting process in the active surface layer to a depth of approximately 1 cm, while SO(4)(2-) reduction accounted for the entire C(org) oxidation below. Manganese reduction was supported by moderately high Mn oxide concentrations. A contribution from microbial Fe reduction could not be discerned, and the process was not stimulated by addition of ferrihydrite. Manganese reduction resulted in carbonate precipitation, which complicated the quantification of C(org) oxidation rates. The relative contribution of Mn reduction to C(org) oxidation in the anaerobic incubations was 25 to 73% at the stations with oxic bottom water. In situ, where Mn reduction must compete with oxygen respiration, the contribution of the process will vary in response to fluctuations in bottom water oxygen concentrations. Total bacterial numbers as well as the detection frequency of bacteria with fluorescent in situ hybridization scaled to the mineralization rates. Most-probable-number enumerations yielded up to 10(5) cells of acetate-oxidizing Mn-reducing bacteria (MnRB) cm(-3), while counts of Fe reducers were <10(2) cm(-3). At two stations, organisms affiliated with Arcobacter were the only types identified from 16S rRNA clone libraries from the highest positive MPN dilutions for MnRB. At the third station, a clone type affiliated with Pelobacter was also observed. Our results delineate a niche for dissimilatory Mn-reducing bacteria in sediments with Mn oxide concentrations greater than approximately 10 micromol cm(-3) and indicate that bacteria that are specialized in Mn reduction, rather than known Mn and Fe reducers, are important in this niche.

Turnover of glucose and acetate coupled to reduction of nitrate, ferric iron and sulfate and to methanogenesis in anoxic rice field soil.

Turnover of glucose and acetate in the presence of active reduction of nitrate, ferric iron and sulfate was investigated in anoxic rice field soil by using [U-(14)C]glucose and [2-(14)C]acetate. The turnover of glucose was not much affected by addition of ferrihydrite or sulfate, but was partially inhibited (60%) by addition of nitrate. Nitrate addition also strongly reduced acetate production from glucose while ferrihydrite and sulfate addition did not. These results demonstrate that ferric iron and sulfate reducers did not outcompete fermenting bacteria for glucose at endogenous concentrations. Nitrate reducers may have done so, but glucose fermentation may also have been inhibited by accumulation of toxic denitrification intermediates (nitrite, NO, N(2)O). Addition of nitrate resulted in complete inhibition of CH(4) production from [U-(14)C]glucose and [2-(14)C]acetate. However, addition of ferrihydrite or sulfate decreased the production of (14)CH(4) from [U-(14)C]glucose by only 70 and 65%, respectively. None of the electron acceptors significantly increased the production of (14)CO(2) from [U-(14)C]glucose, but all increased the production of (14)CO(2) from [2-(14)C]acetate. Uptake of acetate was faster in the presence of either nitrate, ferrihydrite or sulfate than in the unamended control. Addition of ferrihydrite and sulfate reduced (14)CH(4) production from [2-(14)C]acetate by 83 and 92%, respectively. Chloroform completely inhibited the methanogenic consumption of acetate. It also inhibited the oxidation of acetate, completely in the presence of sulfate, but not in the presence of nitrate or ferrihydrite. Our results show that, besides the possible toxic effect of products of nitrate reduction (NO, NO(2)(-) and N(2)O) on methanogens, nitrate reducers, ferric iron reducers and sulfate reducers were active enough to outcompete methanogens for acetate and channeling the flow of electrons away from CH(4) towards CO(2) production.

Turnover of glucose and acetate coupled to reduction of nitrate, ferric iron and sulfate and to methanogenesis in anoxic rice field soil

Turnover of glucose and acetate in the presence of active reduction of nitrate, ferric iron and sulfate was investigated in anoxic rice field soil by using [U- 14C]glucose and [2- 14C]acetate. The turnover of glucose was not much affected by addition of ferrihydrite or sulfate, but was partially inhibited (60%) by addition of nitrate. Nitrate addition also strongly reduced acetate production from glucose while ferrihydrite and sulfate addition did not. These results demonstrate that ferric iron and sulfate reducers did not outcompete fermenting bacteria for glucose at endogenous concentrations. Nitrate reducers may have done so, but glucose fermentation may also have been inhibited by accumulation of toxic denitrification intermediates (nitrite, NO, N 2O). Addition of nitrate resulted in complete inhibition of CH 4 production from [U- 14C]glucose and [2- 14C]acetate. However, addition of ferrihydrite or sulfate decreased the production of 14CH 4 from [U- 14C]glucose by only 70 and 65%, respectively. None of the electron acceptors significantly increased the production of 14CO 2 from [U- 14C]glucose, but all increased the production of 14CO 2 from [2- 14C]acetate. Uptake of acetate was faster in the presence of either nitrate, ferrihydrite or sulfate than in the unamended control. Addition of ferrihydrite and sulfate reduced 14CH 4 production from [2- 14C]acetate by 83 and 92%, respectively. Chloroform completely inhibited the methanogenic consumption of acetate. It also inhibited the oxidation of acetate, completely in the presence of sulfate, but not in the presence of nitrate or ferrihydrite. Our results show that, besides the possible toxic effect of products of nitrate reduction (NO, NO 2 − and N 2O) on methanogens, nitrate reducers, ferric iron reducers and sulfate reducers were active enough to outcompete methanogens for acetate and channeling the flow of electrons away from CH 4 towards CO 2 production.

Role of interspecies H2 transfer to sulfate and ferric iron-reducing bacteria in acetate consumption in anoxic paddy soil

Addition of sulfate resulted in complete inhibition of methanogenesis in anoxic paddy soil. About 20% of the CH4 was produced from H2/14CO2, the rest from acetate. Inhibition of H2-dependent methanogenesis was explained by successful competition by sulfate reducers for H2, as the H2 partial pressures decreased upon addition of sulfate. However, acetate concentrations did not decrease. Sulfate reduction was stimulated by H2, but not by acetate. Counts of acetate-utilizing sulfate reducers were relatively low both in fresh and pasteurized soil indicating that the bacteria were only present as spores. Inhibition of methanogenesis by chloroform resulted in accumulation of both H2 and acetate. When sulfate was added in addition, H2 accumulation stopped, but acetate still accumulated indicating that the activity of the methanogens was necessary for acetate conversion and that acetate could not be utilized by the sulfate reducers directly. Conversion of [2-14C]acetate resulted in formation of relatively more 14CO2, when sulfate was added, indicating that the methyl group of acetate was now being oxidized instead of reduced. Addition of chloroform strongly inhibited the conversion of [2-14C]acetate, even in the presence of sulfate. A conceivable explanation is sulfate-dependent interspecies H2 transfer between acetate-utilizing methanogens and H2-utilizing sulfate reducers, changing the electron flow from CH4 production to sulfate reduction. Addition of ferrihydrite resulted only in incomplete inhibition of methanogenesis which could be explained by successful competition of ferric iron reducers for H2. The ferric iron reducers were able to use acetate directly, but did not outcompete the methanogens.

Role of interspecies H 2 transfer to sulfate and ferric iron-reducing bacteria in acetate consumption in anoxic paddy soil

Addition of sulfate resulted in complete inhibition of methanogenesis in anoxic paddy soil. About 20% of the CH 4 was produced from H 2 14 CO 2 , the rest from acetate. Inhibition of H 2-dependent methanogenesis was explained by successful competition by sulfate reducers for H 2, as the H 2 partial pressures decreased upon addition of sulfate. However, acetate concentrations did not decrease. Sulfate reduction was stimulated by H 2, but not by acetate. Counts of acetate-utilizing sulfate reducers were relatively low both in fresh and pasteurized soil indicating that the bacteria were only present as spores. Inhibition of methanogenesis by chloroform resulted in accumulation of both H 2 and acetate. When sulfate was added in addition, H 2 accumulation stopped, but acetate still accumulated indicating that the activity of the methanogens was necessary for acetate conversion and that acetate could not be utilized by the sulfate reducers directly. Conversion of [2- 14C]acetate resulted in formation of relatively more 14CO 2, when sulfate was added, indicating that the methyl group of acetate was now being oxidized instead of reduced. Addition of chloroform strongly inhibited the conversion of [2- 14C]acetate, even in the presence of sulfate. A conceivable explanation is sulfate-dependent interspecies H 2 transfer between acetate-utilizing methanogens and H 2-utilizing sulfate reducers, changing the electron flow from CH 4 production to sulfate reduction. Addition of ferrihydrite resulted only in incomplete inhibition of methanogenesis which could be explained by successful competition of ferric iron reducers for H 2. The ferric iron reducers were able to use acetate directly, but did not outcompete the methanogens.