Bacterial Organic Matter Research Articles

Decomposition process of organic matter derived from freshwater phytoplankton

We investigated the biodegradation process of freshwater phytoplanktonic organic matter using incubation experiments, with special reference to changes in three major biomolecules: neutral aldoses, amino acids and fatty acids. The concentration of neutral aldoses decreased drastically relative to amino acids and fatty acids during the early decomposition phase (days 0–7), owing largely to the rapid decomposition of storage carbohydrate. This resulted in a temporary decrease in the C/N ratio of organic matter. During the late phase (days 7–60), however, the rate of decrease in neutral aldoses slowed, while the considerable decrease in amino acids and fatty acids continued. The inconspicuous change in amino acid composition was probably due to the fact that no protein and/or peptide is composed of a limited species of amino acid. Although the compositional variety of organic matter among the phytoplankton was clearly observed at the start of decomposition, it became obscure in the course of 60 days. This indicates that while the organic composition of the labile fraction of phytoplanktonic organic matter varies depending on the phytoplankton groups, the refractory fraction has similar composition. The addition of bacterial organic matter is likely another reason for the similar composition of the remaining organic matter at day 60.

Major bacterial contribution to the ocean reservoir of detrital organic carbon and nitrogen

Bacterial biomarkers (D‐amino acids and muramic acid) were measured in various organic matter size fractions collected in the North Pacific and North Atlantic, and they were used to quantitatively estimate bacterial contributions to particulate and dissolved organic carbon and nitrogen reservoirs. The origins and yields of biomarkers were determined in cultured marine bacteria, and the results indicated that D‐amino acids are derived from numerous macromolecules in addition to peptidoglycan and are not solely from peptidoglycan. Bacterial detritus was a major component of particulate organic matter (POM) and is an important source of submicronsize particles and colloids in the ocean. Peptidoglycan was a substantial component of POM but not of dissolved organic matter (DOM). Compositional differences between POM and DOM primarily reflected the selective incorporation of specific bacterial components into these reservoirs. Autotrophic and heterotrophic bacterial sources were not quantified separately, but the presence of D‐aspartic acid (D‐Asx) and D‐serine (D‐Ser) suggested that heterotrophic sources were substantial. The average reactivity of bacterial organic matter was comparable to that of the bulk organic carbon pool. Bacteria were important sources of labile, semilabile, and refractory dissolved organic carbon. Bacterial organic matter accounted for ~25% of particulate and dissolved organic carbon and ~50% of particulate and dissolved organic nitrogen. These results demonstrate the importance of bacteria in regulating the ocean carbon and nitrogen cycles.

Depth Distribution of Freshwater Microorganisms and Physicochemical Characteristics in Iskar Reservoir

ABSTRACTThe depth distribution of different physiological and taxonomical groups of freshwater bacteria in Iskar reservoir—the main drinking water source for Sofia city, was studied. Samples were taken from several depth layers in the area of intake water tower of the reservoir and studied for presence of aerobic, anaerobic heterotrophs, oligotrophs, ammonifiers, nitrifiers and denitrifiers, genera Aeromonas and Pseudomonas and coliform bacteria with cultivation methods. We found close distribution of observed microbial groups according to the correlation coefficients of their numbers in different water layers. Two zones with similar distributions were presented—upper zone in the upper layers from the surface down to the fifth meter, and another zone under 10 meters depth. Exception was the observed distribution of microbial groups in the water layer at 25 meters, which showed closer correlation with the upper zones than with the contiguous layers. We determined also some physicochemical, chlorophyll a and phaeophytin concentration, chemical oxygen demand (COD), nitrogen forms and phosphate concentration. Correlation was presented also between the bacterial numbers, chlorophyll a and organic matter (COD). The dominating groups are aerobic heterotrophs and oligotrophs through the whole water column representing up to 31.34% respectively 48.58% from all culturable bacteria.

Hydrological changes in southern Africa over the last 200 Ka as recorded in lake sediments from the Tswaing impact crater

Sediments from Lake Tswaing (25°24′30″ S, 28°04′59″ E) document hydrological changes in southern Africa over the last 200 Ka. Using high-resolution XRF- scanning, basic geochemistry (TIC, TOC, TN), organic petrology and rock-eval pyrolysis, we identify intervals of decreased carbonate precipitation, increased detrital input, decreased salinity and decreased autochthonous (algal and bacterial) organic matter content that represent periods of less stable water column stratification and increased rainfall. Between 200 and 80 Ka BP, these intervals appear to be contemporaneous with local summer insolation maxima, indicating a strong influence of precessional variability (~23 Ka) on African subtropical climate. This influence weakens during the last glacial period (~80 to 10 Ka BP), when humid intervals at 73 to 68 Ka, 54 to 50 Ka, 37 to 35 Ka and 15 to 10 Ka BP are largely out of phase with insolation changes, and presumably reflect southward displacement of the ITCZ (Inter Tropical Convergence Zone) and/or changes in ocean circulation.

Geochemical study of crude oils from the Xifeng oilfield of the Ordos basin, China

The Xifeng oilfield is the largest newly-discovered oilfield in the Ordos basin. In order to determine the possible source, crude oils collected systematically from the oilfield and an adjacent oilfield have been examined isotopically and molecularly. The predominance of long-chain n-alkanes, high abundance of C 29 sterane, lower ratios of C 25/C 26 tricyclic terpane and C 25 tricyclic terpane/C 24 tetracyclic terpane and high C 24 tetracyclic terpane/(C 24 tetracyclic terpane + C 26 tricyclic terpanes ratio in the studied oils suggest generation from a source with mixed terrigenous and algal–bacterial organic matter. The presence of diterpenoid hydrocarbon with abietane skeletons is characteristic of the main contribution of higher land plants to the oils. The biomarker distributions in the oils show that they were formed under a weakly reducing freshwater environment. Molecular maturity parameters indicate that the crude oils are mature. The oil–source rock correlation and oil migration investigation suggest that the oils in the Xifeng oilfield originated from the source rocks of the Yanchang formation deposited in a shallow to deep freshwater lacustrine environment, especially Chang-7 source rocks. The data from the distribution of pyrrolic nitrogen compounds indicate that the charging direction of the Chang-8 crude oils is mainly from the Zhuang 12 well northeast of the oilfield toward the southwest. This direction of oil migration is consistent with that indicated by regional geological data.

Copper effects on bacterial activity of estuarine silty sediments

Bacteria of silty estuarine sediments were spiked with copper to 200 μg Cu g −1 dry weight sediment in order to assess the impact of copper on bacterial degradation of organic matter and on bacterial biomass production. Bacterial density was determined by direct counting under epifluorescence microscopy and bacterial production by the incorporation of 3H-Leucine. Leucine turnover rate was evaluated by 14C-leucine incorporation and ectoenzymatic activities were estimated as the hydrolysis rate of model substrates for β-glucosidase and leucine-aminopeptidase. The presence of added copper in the microcosms elicited, after 21 days of incubation, generalised anoxia and a decrease in organic matter content. The non-eroded surface of the copper-spiked sediment showed, when compared to the control, a decrease in bacterial abundance and significant lower levels of bacterial production and of leucine turnover rate. Bacterial production and leucine turnover rate decreased to 1.4% and 13% of the control values, respectively. Ectoenzymatic activities were also negatively affected but by smaller factors. After erosion by the water current in laboratory flume conditions, the eroded surface of the control sediment showed a generalised decline in all bacterial activities. The erosion of the copper-spiked sediment showed, however, two types of responses with respect to bacterial activities at the exposed surface: positive responses of bacterial production and leucine turnover rate contrasting with slight negative responses of ectoenzymatic activities. The effects of experimental erosion in the suspended cells were also different in the control and in the copper-spiked sediment. Bacterial cells in the control microcosm exhibited, when compared to the non-eroded sediment cells, decreases in all activities after the 6-h suspension. The response of the average suspended copper-spiked sediment cell differed from the control by a less sharp decrease in ectoenzymatic activities and, mainly, by the great intensification of bacterial biomass production and leucine turnover rate. We conclude that the bacterial community of silty estuarine sediments seems to withstand considerable concentrations of copper at the cost of reduced bacterial organic matter degradation and of the almost halting of bacterial production. The toxic effects elicited by copper on protein and carbohydrate degradation were not rapidly repaired by erosion and oxygenation of the sediment cells but, in contrast, bacterial biomass production and leucine turnover were rapidly and efficiently reactivated.

Microbial reduction of hexavalent chromium by landfill leachate

The reduction of hexavalent chromium (Cr(VI)) in municipal landfill leachates (MLL) and a non-putrescible landfill leachate (NPLL) was investigated. Complete Cr(VI) reduction was achieved within 17 days in a MLL when spiked with 100 mg l −1 Cr(VI) or less. In the same period, negligible Cr(VI) reduction was observed in NPLL. In MLL, Cr(VI) reduction was demonstrated to be a function of initial Cr(VI) concentration and bacterial biomass and organic matter concentrations. The bacteria were observed to tolerate 250 mg l −1 Cr(VI) in MLL and had an optimal growth activity at pH 7.4 in a growth medium. The MLL also possessed an ability to sequentially reduce Cr(VI) over three consecutive spiking cycles.

Ozonation of a secondary effluent both for fresh water protection and re-use

49 trials were carried out at pilot scale to evaluate ozonation for polishing a nitrified and filtered effluent discharged in a brook, lying in a recreational protected area whose low and irregular flow provides a negligible dilution. Four ozone doses (3, 5, 7.5 and 10 mg O3/L) were tested and contact time was set at 10 minutes for each of the three contact columns. In most cases, at 3 mg O3/L, residual ozone concentration was below detection limit after 10 minutes contact time. For faecal coliforms and E. coli, log reduction increased from 3 mg O3/L to higher ozone doses, among which no appreciable difference was observed. No improvement in disinfection efficiency was seen for contact times over 10 minutes. Complete disinfection was obtained only in few cases, but final counts complying with the limits for discharge were always met. COD removal was low, while colour removal was significant and clearly increasing from 3 mg O3/L to higher doses. The removal of surfactants slightly increased with increasing dose for non ionic compounds, but not for anionic ones. Data confirmed that slight increases in ozone dose involve the release of bacterial organic matter which partially counterbalance the removal of COD.

Biohydrogenation of Fatty Acids and Digestibility of Fresh Alfalfa or Alfalfa Hay Plus Sucrose in Continuous Culture

The pattern of biohydrogenation of fatty acids from fresh alfalfa or alfalfa hay supplemented with 3 concentrations (0, 4, and 8%) of sucrose was studied at a constant pH of 6.2. Four continuous culture fermenters were used in a 4×4 Latin square design to test the hypothesis that fresh forage would increase flow of vaccenic acid (VA) from the fermenters compared with the same forage in hay form and that this difference would be diminished by adding sucrose to the hay diet by changing the bacterial community profile. Effluent was collected from each of the 4 fermenters during the last 3 d of each 10-d period. Nutrient digestibility, volatile fatty acids (VFA), and fatty acids in the effluent were measured. Flow of bacterial organic matter (OM) and neutral and acid detergent fiber and acid detergent fiber digestibilities were higher for fresh alfalfa than alfalfa hay. True OM digestibility of alfalfa hay tended to linearly decrease with sucrose supplementation. However, microbial efficiency and flow of bacterial OM (g/d) linearly increased with sucrose addition. There was no change in total VFA concentration; however, proportion of acetate linearly decreased and proportion of butyrate linearly increased with sucrose addition. Fresh alfalfa increased total biohydrogenation of fatty acids compared with than hay. Vaccenic acid flow (mg/d) was much higher for fresh alfalfa compared with alfalfa hay (216 vs. 41) and VA was the predominant 18:1 isomer, followed by trans-13 18:1; however, sucrose had no effect on VA flow. The percentage of VA (of total trans-18:1) was not different between fresh alfalfa and hay, whereas percentage of trans-10 18:1 was much lower for fresh alfalfa. Therefore, the ratio of VA to trans-10 18:1 was higher for fresh alfalfa. Flow of trans-12 18:1 linearly increased, whereas flows of cis-12 and total cis-18:1 had quadratic responses to sucrose supplementation. Total biohydrogenation and biohydrogenation of linoleic and linolenic acids linearly decreased with sucrose; however, there was no effect of sucrose on total trans fatty acid flow. Sucrose may be more detrimental to the last step of biohydrogenation of VA. The effects of sucrose on biohydrogenation and concentration of VFA may have been caused by a shift in microbial population by mechanisms that are independent of pH.

Influence of algal and bacterial particulate organic matter on benzo[ a]pyrene bioaccumulation in Daphnia magna

In order to better asses the influence of organic matter on the bioavailability of hydrophobic organic contaminants, the effect of algae and POM of bacterial origin on the bioaccumulation of benzo[ a]pyrene in Daphnia magna was evaluated. The bioaccumulation was monitored with increasing concentrations of particulate organic matter (POM) and dissolved organic matter (DOM). In all experiments, the presence of POM greatly reduced the bioaccumulation of benzo[ a]pyrene. The reduction was more pronounced in the presence of algae, for which we observed a 99%-reduction effect in the presence of 6×10 5 cell/mL (equivalent to 5.3 mg C/L). The bioaccumulation of benzo[ a]pyrene was decreased by 49% by organic matter of bacterial origin at 4.7 mg C/L. Assuming that benzo[ a]pyrene was partitioned between water, DOM and POM and supposing that D. magna accumulated free benzo[ a]pyrene via respiration and POM-bond benzo[ a]pyrene via ingestion, bioaccumulation data allowed to estimate the dietary uptake rate of benzo[ a]pyrene as well as partitioning coefficients K POC and K DOC. Despite the ingestion of contaminated particles, we could not observe any dietary uptake of benzo[ a]pyrene in daphnids. We verified, as usually supposed, that the bioaccumulation of benzo[ a]pyrene to D. magna occurs mainly via direct contact. Very high partitioning coefficients (log K POC between 5.2 and 6.2) were estimated. This study pointed out the great influence of biogenic organic matter on the fate and the bioavailability of benzo[ a]pyrene in aquatic ecosystems.

Geochemical characteristics of crude oils from Zao-V oil measures in Shenjiapu oilfield

The geochemical characteristics of crude oils from Zao-V oil measures in the Shenjiapu oilfield are systematically described in terms of the fractional composition of crude oils, GC characteristics of saturated hydrocarbon fraction of crude oils and the characteristics of their bio-markers. The depositional environment, type and evolution of the biological source are also discussed. All pieces of evidence such as low saturated hydrocarbon fraction, high resin and asphalt, high isoprenoid alkane, weak odd-carbon number predominance ( CPI ranging from 1.23 to 1.29, OEP ranging from 1.14 to 1.16) and low sterane and terpane maturity parameters show these crude oils are immature oils. Low Pr/Ph ratios (0.66–0.88) and high gammacerance/C31 hopane ratios (0.59–0. 86) indicate the source rocks were formed in a slightly saline to brackish reducing lake depositional environment. Gas Chromatographic characteristics of the saturated hydrocarbon fraction and the predominance of C30 hopane in terpane series and C29 sterane in sterane series indicate the biological source of the crude oils is composed mainly of bacterial and algal organic matter, and some algae are perhaps the main contributor of organic matter to the source rocks.

Sediments, porewaters and diagenesis in an urban water body, Salford, UK: impacts of remediation

AbstractContaminated sediments deposited within urban water bodies commonly exert a significant negative effect on overlying water quality. However, our understanding of the processes operating within such anthropogenic sediments is currently poor. This paper describes the nature of the sediment and early diagenetic reactions in a highly polluted major urban water body (the Salford Quays of the Manchester Ship Canal) that has undergone remediation focused on the water column.The style of sedimentation within Salford Quays has been significantly changed as a result of remediation of the water column. Pre‐remediation sediments are composed of a range of natural detrital grains, predominantly quartz and clay, and anthropogenic detrital material dominated by industrial furnace‐derived metal‐rich slag grains. Post‐remediation sediments are composed of predominantly autochthonous material, including siliceous algal remains and clays. At the top of the pre‐remediation sediments and immediately beneath the post‐remediation sediments is a layer significantly enriched in furnace‐derived slag grains, input into the basin as a result of site clearance prior to water‐column remediation. These grains contain a high level of metals, resulting in a significantly enhanced metal concentration in the sediments at this depth.Porewater analysis reveals the importance of both bacterial organic matter oxidation reactions and the dissolution of industrial grains upon the mobility of nutrient and chemical species within Salford Quays. Minor release of iron and manganese at shallow depths is likely to be taking place as a result of bacterial Fe(III) and Mn(IV) reduction. Petrographic analysis reveals that the abundant authigenic mineral within the sediment is manganese‐rich vivianite, and thus Fe(II) and Mn(II) released by bacterial reactions may be being taken up through the precipitation of this mineral. Significant porewater peaks in iron, manganese and silicon deeper in the sediment column are most probably the result of dissolution of furnace‐derived grains in the sediments. These species have subsequently diffused into porewater above and below the metal‐enriched layer.This study illustrates that the remediation of water quality in anthropogenic water bodies can significantly impact upon the physical and chemical nature of sedimentation. Additionally, it also highlights how diagenetic processes in sediments derived from anthropogenic grains can be markedly different from those in sediments derived from natural detrital material. Copyright © 2003 John Wiley & Sons, Ltd.

Relationships between organic matter composition and methyl mercury content of offshore and carbon-rich littoral sediments in an oligotrophic lake

Relationships between organic matter (OM) compounds and methyl mercury concentrations ([MeHg]) have been examined in littoral and offshore sediments of Lake Lusignan (Québec). The highest [MeHg] were generally found at the sediment–water interface with exceptionally high concentrations at littoral sites (5.8 ± 1.3 ng·g dry weight–1), which were four times more elevated than at offshore sites (1.6 ± 0.77 ng·g dry weight–1). Source-specific fatty acid (FA) biomarkers identified that littoral sediments contained more than twice as much terrestrial and bacterial OM compounds than offshore sediments, whereas the amount of labile algal OM was three times higher at littoral sites. Results indicate that [MeHg] were higher in the presence of labile OM substrates, and the amount of terrestrial OM compounds could not predict [MeHg]. Correlations between [MeHg] and FA of Desulfovibrio desulfuricans (a sulfate-reducing bacterium producing MeHg) could significantly account for 36% of [MeHg] at offshore sites; however, no significant relationships were found at littoral sites. This study illustrates that the microbial dynamics involved in producing and degrading MeHg in lacustrine sediments are complex and cannot be predicted solely by the quantification of FA biomarkers in D. desulfuricans or by biomarkers in the OM itself.

Major shift in bacterioplankton utilization of enantiomeric amino acids between surfacewaters and the ocean's interior

The peptidoglycan layer of the bacterioplankton cell wall contains four major amino acids (alanine, Ala; serine, Ser; aspartic acid, Asp; and glutamic acid, Glu) in a characteristic enantiomeric ratio (D/L ratio). It is assumed that bacterioplankton are the only biological source of significance for these four specific D‐amino acid species in the ocean. The concentrations of these dissolved total enantiomeric amino acids were measured throughout the water column of the Faroe Shetland Channel (North Atlantic). Concurrently, the uptake of D‐ versus L‐Asp and of L‐leucine (as a measure of bacterial production) by bacterioplankton was determined. The D/L ratios of the dissolved total Ala, Asp, Glu, and Ser did not exhibit any particular trend with depth, averaging 0.49 for Ala, 0.42 for Asp, 0.15 for Glu, and 0.09 for Ser. The ratio of D‐/L‐Asp uptake by bacteria, however, increased from surface (D‐/LAsp uptake ratio of ~0.03) to deeper layers reaching a D‐/L‐Asp uptake ratio of close to 1 at 1,000 m depth, indicating that mesopelagic bacteria utilize D‐Asp almost as efficiently as L‐Asp. Subsequent laboratory experiments with surface‐water bacterioplankton assemblages incubated in nutrient‐amended artificial seawater confirmed that bacterioplankton, in the absence of other utilizable organic carbon, efficiently utilize D‐amino acids. In these laboratory experiments, the D‐/L‐Asp uptake ratio increased within 8 d to values similar to those obtained for mesopelagic bacteria. Furthermore, the presence of flagellates stimulated the uptake of D‐Asp probably via enhanced release of D‐amino acids during bacterivory. Thus, our results indicate that dissolved D‐amino acids might be an important substrate for mesopelagic bacterioplankton. The efficient uptake of D‐amino acids in the deeper layers of the ocean might indicate that mesopelagic bacterioplankton are utilizing bacterial cell wall‐derived organic matter efficiently.

Seasonal and diel relationships between the isotopic compositions of dissolved and particulate organic matter in freshwater ecosystems

A study of the isotopic composition of organic matter was conducted in a freshwater marsh over seasonal and diel time scales to determine the sources of dissolved organic matter (DOM) and the processes leading to its formation. Bulk C and N isotopic compositions of the bacterial fraction (0.2–0.7 μm) and particulate organic matter (POM; 0.7–10 μm) were compared on a seasonal basis with the change in δ13C of DOM. The bulk isotopic data support the idea that DOM was, in part, derived from the breakdown of larger organic matter fractions. The bacterial fraction and POM were compositionally similar throughout the year, based on a comparison of the δ13C of individual amino acids in each fraction. Annual variation in the δ13C of amino acids in DOM was greater relative to the variation in larger fractions indicating that microbial reworking was an important factor determining the proteinaceous component of DOM. The 13C enrichment of serine and leucine in each organic matter fraction suggested microbial reworking was an important factor determining organic matter composition during the most productive times of year. Changes in the bulk δ13C of DOM were more significant over daily, relative to seasonal, time scales where values ranged by 6‰ and followed changes in chlorophyll a concentrations. Although bulk δ13C values for POM ranged only from −29 to −28‰ during the same diel period, the δ13C of alanine in POM ranged from −30 to −22‰. Alanine is directly synthesized from pyruvate and is therefore a good metabolic indicator. The δ13C of individual amino acids in DOM revealed the diel change in the importance of autotrophic versus heterotrophic activity in influencing DOM composition. Diel changes in the δ13C of phenylalanine, synthesized by common pathways in phytoplankton and bacteria, were similar in both DOM and POM. The diel change in δ13C of isoleucine and valine, synthesized through different pathways in phytoplankton and bacteria, were distinctly different in DOM versus POM. This disparity indicated a decoupling of the POM and DOM pools, which suggests a greater source of bacterial-derived organic matter at night. The results of this study demonstrate the use of the isotopic composition of individual amino acids in determining the importance of microbial reworking and autotrophic versus heterotrophic contributions to DOM over both diel and seasonal time scales.

Small-Scale Distribution of Bacteria, Enzymatic Activities, and Organic Matter in Coastal Sediments.

The small-scale distribution of several structural (bacterial abundance, phytopigment, total and soluble protein, and carbohydrate content) and functional ecological variables (enzymatic activities, frequency of dividing cells) was investigated in coastal sediments during a spring bloom. For bacterial abundance, enzymatic activity, and organic matter determinations, samples were collected at 5-m depth from a sediment surface delimited by a 42 x 42-cm frame, divided into 49 squares. In order to test the influence of the bottom microtopography on the investigated variables, the size of this frame was defined to cover the distance between two subsequent ripples. As indicated by Fisher's index, benthic bacteria, enzymatic activities, proteins, carbohydrates, and their soluble fractions exhibited an aggregate distribution. Sampling size (i.e., sample unit of 36 cm2) was appropriate for all variables, except for chlorophyll a and frequency of dividing cells that displayed a contagious distribution. To estimate the reliability of the current sampling strategy, we compared the mean values from three randomly selected sample units with the average value of the entire sediment surface (i.e., 49 samples). For all variables reported in this study, the use of three replicates was representative of the mean values of the sampled area with a confidence limit within +/-20%. Bacterial population sizes did not correlate with their potential food sources (e.g., phytopigments, proteins, and carbohydrates), or with enzymatic activities, suggesting the presence of possible time lags between organic inputs and microbial response. Chlorophyll a during the spring bloom displayed much higher concentrations than phaeopigments and correlated with carbohydrates. Chlorophyll a distribution was autocorrelated and displayed a large patch size (1,134 cm2). Phaeopigments and proteins accumulated in the central depression of the ripple-mark structure, apparently depending upon a passive accumulation due to the reduced current action. In contrast, microphytobenthic biomass and bacterial numbers were highest in the two opposite ripples, suggesting that different driving forces operate selectively on the living components.

Retene in pyrolysates of algal and bacterial organic matter

Retene, dehydroabietin, and 1,2,3,4-tetrahydroretene have been identified by GC–MS in extractable aromatic hydrocarbon fractions produced by pyrolysis at 200 and 300°C of pure strains of the green alga Chlorella protothecoides and the cyanobacterium Synechocystis sp. The results suggest phytoplankton as a possible source of retene in Recent and ancient sediments.

Fossilized filamentous microbiota in volcanosedimentary deposits in iceland

The mineralization of bacterial organic matter in the groundwater of Iceland is discussed. Structural relationships between secondary minerals in cavities within a Pleistocene basaltic sill and the general sequence of their precipitation allowed us to recognize five stages of the secondary mineral formation. Two stages of layer silicate formation separated by a stage of zeolite and apophyllite formation were pointed out. The composition and structure of clay minerals formed at different stages as a result of the interaction between groundwater and basalt with an active participation of bacteria have been investigated. Clay minerals of the second stage are similar in composition and microstructure to biomorphic structures previously studied in Miocene plateau basalts. The last stage of mineralization is related to the fossilization of filamentous microbiota residing in open cavities and covering all older secondary minerals

Retention of strontium, cesium, lead and uranium by bacterial iron oxides from a subterranean environment

Bacteriogenic Fe oxides (BIOS) and groundwater samples were collected 195 m underground at the Stråssa Mine in central Sweden. Ferrous iron oxidizing bacteria, including stalked Gallionella ferruginea and filamenous Leptothrix sp., were prominent in the BIOS samples. The BIOS samples were found to contain only poorly ordered (amorphous) hydrous ferric oxide, as determined by X-ray diffraction. Inductively coupled plasma mass spectroscopy revealed hydroxylamine-reducible Fe and Mn oxide contents that ranged from 55 to 85% on a dry weight basis. Concentrations of Sr, Cs, Pb and U in filtered groundwater ranged from 0.002 to 1.8 μM. Solid phase concentrations of these heavy metals in the BIOS spanned the 0.04–2.23 mmol/kg range. Distribution coefficients ( K d values), calculated as the ratio between BIOS and dissolved heavy metal concentrations, revealed solid phase enrichments that, depending on the heavy metal and Fe oxide content of the sample, extended from 10 3.0 to 10 4.7. At the same time, however, a strong inverse linear relationship was found between log K d values and the corresponding mass fraction of reducible oxide in the samples, implying that metal uptake was strongly influenced by the relative proportion of bacterial organic matter in the composite solids. Based on the metal accumulation properties of the BIOS, an important role can be inferred for intermixed Fe oxides and bacterial organic matter in the transport and fate of dissolved metals in groundwater systems.

Bacterial Stimulation in Mixed Cultures of Bacteria and Organic Carbon from River and Lake Waters.

Abstract Interactions between natural bacterial assemblages and dissolved organic carbon (DOC) were investigated in two complementary batch experiments. In the first, a positive relationship was found between the proportion of electron transport system (ETS) active bacteria and the diversity of DOC in microcosms enriched with an increasing number of organic substrates. In a second experiment, bacterial and nutrient dynamics were measured in microcosms with natural bacterial populations and organic matter from rivers and lakes of different trophic levels. The interactions between the bacterial assemblages and DOC from different sources was investigated using source systems (rivers or lakes) and blended (different proportions of river and lake water) batch cultures. In each experiment, the number of total and ETS-active bacteria, the fluorescein diacetate (FDA)-hydrolytic activity, and the total (DOC), biodegradable (BDOC) and refractory (RDOC) dissolved organic carbon were measured four times during 5 days. The results suggested that the temperature, more than trophic level, controlled planktonic bacterial production. Furthermore, bacterial activity was stimulated in micrososms where river and lake waters were mixed. For the oligotrophic microcosms, this observation can be explained by a greater diversity of the organic nutrients ("qualitative" stimulation of bacteria), whereas for the meso-eutrophic microcosms, the production of new pools of dissolved organic carbon (both biodegradable and total) could account for the observed "quantitative" stimulation of the bacteria. These experiments suggest that the mixing of bacteria and organic matter from two different systems can give rise to novel nutrient and bacterial dynamics that are likely similar to those that occur in river-lake ecotones.http://link.springer-ny.com/link/service/journals/00248/bibs/38n3p285.html</hea