Post-Sampling Changes in Microbial Community Composition and Activity in a Subsurface Paleosol

Abstract Laboratory storage of deep vadose zone sediments has previously resulted in an increase in the abundance of cultured microorganisms by as much as 10,000-fold, without concomitant increases in total microscopic counts. In the present study, factors contributing to the time-dependent stimulation of various microbiological parameters were examined during a 224 d post-sampling period, using a factorial-design experiment that partitioned the effects of storage time, sediment condition (intact blocks or homogenized) during storage, and O₂ concentration (0.5, 4.5, and 21%) during storage at 15°C. Stored samples were analyzed at selected intervals, to determine direct microscopic counts, viable biomass, lipid biomarker profiles, cultured aerobic heterotrophic microorganisms, and microbial activity. Time of storage prior to analysis of the samples was the most important factor affecting the microbiological response. Sediment condition influenced the stimulation response: microbial activity and the population of cultured microorganisms increased faster, and reached slightly higher values, in the homogenized samples, although maximum values were reached at similar times in the homogenized and intact samples. O₂ concentration also influenced the response, but was the least important of the factors evaluated. Total cells and viable biomass, measured as total phospholipid fatty acids, changed little during storage. Maximum cultured populations and activity were attained at 63 to 112 d, with culture counts approximating the total numbers of microscopically counted cells. At approximately the same time, unbalanced growth (evidenced by high ratios of polyhydroxybutyrate to phospholipid fatty acid) indicated that inorganic nutrients became limiting. Lipid biomarkers indicative of Gram-positive bacteria, including actinomycetes, became dominant components of the community profiles in samples maintained at 0.5% and 4.5% O₂. The shift in the microbial community from relatively inactive, predominantly uncultured microorganisms to metabolically active populations that were nearly all cultured highlights the need for rapid initiation of analyses after sample acquisition, if measurement of in situ microbiological properties is desired. The fact that these processes also occur in intact sediment blocks suggests that minor perturbations in the chemical or physical properties of subsurface sediments can result in major changes in the activity and composition of the microbial community. Revised: 22 October 1997; Accepted 20 November 1997     

Distribution of protozoa in subsurface sediments of a pristine groundwater study site in oklahoma

Sediment core samples were obtained at a groundwater study site in Oklahoma in January and June 1985. Most-probable-number estimates showed that protozoan numbers declined steeply with depth in subsoil. Flagellates and amoebae dominated the protozoan population, which declined to a most probable number of 28 . g (dry weight) in a clay loam layer at the bottom of the unsaturated zone. Samples from a texturally variable interface zone between 3 and 4 m down also were variable in their content of protozoa. Four contiguous clay loam samples in a single core from this zone contained variable numbers of amoebae ranging from 0.2 to 44 . g (dry weight). However, a sandy clay loam layer at the bottom of the core contained a mixture of flagellates and amoebae with a combined population density of 67 . g (dry weight). A slow-growing filose amoeba was isolated from interface zone samples and was tentatively classified in a new family in the order Aconchulinida. Protozoa were not detected in the saturated zone except in a very permeable gravelly, loamy sand layer at a depth of approximately 7.5 m. Low numbers (4 to 6 . g [dry weight]) of surface-type flagellates and amoebae, as well as the filose amoeba seen in the interface zone, were observed in this layer. Acid-treated and untreated samples contained equivalent numbers of protozoa, showing that the majority of protozoa in the layer at 7.5 m and the interface zone samples were encysted. Increased numbers of bacteria also were found in the layer at 7.5 m, indicating that it was biologically more active than other saturated-zone layers. Cyanobacteria grew in illuminated samples from this layer, suggesting that it may be connected hydrologically to a nearby river.     

Distribution of aerobic bacteria,protozoa, algae,and fungi in deep subsurface sediments

The distribution of microorganisms in deep subsurface profiles was determined at three sites at the Savannah River Plant, Aiken, South Carolina. Acridine orange direct counts (AODC) of bacteria were highest in surface soil samples and declined to the 10⁶ to 10⁷ per gram range in the subsurface, but then did not decline further with depth. In the subsurface, AODC values varied from layer to layer, the highest being found in samples from sandy aquifer formations and the lowest in clayey interbed layers. Sandy aquifer sediments also contained the highest numbers of viable bacteria as determined by aerobic spread plate counts (CFU) on a dilute heterotrophic medium. In some of these samples bacterial CFU values approached 100% of the AODC values. Viable protozoa (amoebae and flagellates, but no ciliates) were found in samples with high bacterial CFU values. A variety of green algae, phytoflagellates, diatoms, and a few cyanobacteria were found at low population densities in samples from two of the three boreholes. Low numbers of fungi were evenly distributed throughout the profiles at all three sites. Microbial population density estimates correlated positively with sand content and pore‐water pH, and negatively with clay content and pore‐water metal concentration. A large diversity of prokaryotic and eukaryotic microorganisms was found in samples with high population densities. A survey of bacterial strains isolated from subsurface samples revealed associations of gram‐positive bacteria with high clay sediments and gram‐negative bacteria with sandy sediments. The ability to deposit lipophilic storage material (presumably poly‐ß‐hydroxybutyrate) was found in a high proportion of isolates from sandy sediments, but only rarely in isolates from high clay sediments.     

Adenosine Triphosphate and Deoxyribonucleic Acid in the Alimentary Tract of Cattle Fed Different Nitrogen Sources

Total microbial cell counts and the content of deoxyribonucleic acid (DNA) and adenosine triphosphate (ATP) were determined in ruminal and abomasal digesta and in faeces from heifers fed a basal diet of barley and straw supplemented with urea, casein, soybean-protein concentrate or feather meal. The concentration of ATP in the rumen content varied independently of the DNA content and total cell count, but dependently upon the nitrogen sources, the highest ATP/DNA ratio being obtained with casein. The ATP/DNA ratio in faeces was only one-tenth of that found in the digesta of the rumen and abomasum, indicating either an extremely low level of activity of the microbial cells or more probably a very large number of dead organisms. It is suggested that DNA and ATP might be useful indices of the microbial status in terms of biomass and metabolic activity. The total cell count should still be included in routine studies to determine the proportion of protozoa to bacteria.     

Spatial distribution of microbial biomass,activity, community structure,and the biodegradation of linear alkylbenzene sulfonate (LAS) and linear alcohol ethoxylate (LAE) in the subsurface

The vertical distribution of microbial biomass, activity, community structure and the mineralization of xenobiotic chemicals was examined in two soil profiles in northern Wisconsin. One profile was impacted by infiltrating wastewater from a laundromat, while the other served as a control. An unconfined aquifer was present 14 meters below the surface at both sites. Biomass and community structure were determined by acridine orange direct counts and measuring concentrations of phospholipid-derived fatty acids (PLFA). Microbial activity was estimated by measuring fluorescein diacetate (FDA) hydrolysis, thymidine incorporation into DNA, and mixed amino acid (MAA) mineralization. Mineralization kinetics of linear alkylbenzene sulfonate (LAS) and linear alcohol ethoxylate (LAE) were determined at each depth. Except for MAA mineralization rates, measures of microbial biomass and activity exhibited similar patterns with depth. PLFA concentration and rates of FDA hydrolysis and thymidine incorporation decreased 10–100 fold below 3 m and then exhibited little variation with depth. Fungal fatty acid markers were found at all depths and represented from 1 to 15% of the total PLFAs. The relative proportion of tuberculostearic acid (TBS), an actinomycete marker, declined with depth and was not detected in the saturated zone. The profile impacted by wastewater exhibited higher levels of PLFA but a lower proportion of TBS than the control profile. This profile also exhibited faster rates of FDA hydrolysis and amino acid mineralization at most depths. LAS was mineralized in the upper 2 m of the vadose zone and in the saturated zone of both profiles. Little or no LAS biodegradation occurred at depths between 2 and 14 m. LAE was mineralized at all depths in both profiles, and the mineralization rate exhibited a similar pattern with depth as biomass and activity measurements. In general, biomass and biodegradative activities were much lower in groundwater than in soil samples obtained from the same depth.     

Advances in detection of microbiologically induced corrosion

A number of recently developed techniques which may be used for rapid quantification of total microbial activity or of specific microorganisms involved in corrosion are reviewed. These include viable counts using dip slides, microscope methods (epifluorescence), analysis of cell components (ATP, ergosterol, phospholipids), immunological methods (fluorescent antibody staining, ELISA), activity measurements (respiration, esterases, sulphate reduction) and the use of gene probes. The methods are discussed with reference to their simplicity, sensitivity, economics and applications.     

洞庭湖湿地土壤碳、氮、磷及其与土壤物理性状的关系

以洞庭湖3类典型湿地的8个土壤剖面为代表,研究了土壤碳、氮、磷,微生物量碳、氮、磷和土壤物理性状的分布特征.结果表明,土壤表层有机碳含量为19.63～50.20 g·kg^-1,微生物量碳为424.63～1 597.36 mg·kg^-1,微生物量碳占有机碳的比例为3.17%～4.82%;土壤表层全氮1.85～4.45 g·kg^-1,微生物量氮5.90～259.47 mg·kg^-1,微生物量氮占全氮的比例3.13%～6.42%;土壤表层微生物量磷含量顺序为:湖草洲滩地(200.99 mg·kg^-1)＞垦殖水田(163.27 mg·kg^-1)＞芦苇洲滩地(24.16 mg·kg^-1),微生物量磷占全磷的比例为1.09%～11.20%;土壤表层容重0.65～1.04 g·cm^-3;土壤表层粘粒(＜0.001mm)26.24%～39.48%.土壤表层有机碳、全氮、微生物量氮、微生物量磷的含量,湖草洲滩地＞垦殖水田＞芦苇洲滩地.土壤表层微生物量碳,垦殖水田和湖草洲滩地接近,而大于芦苇湿地;土壤表层容重,芦苇洲滩地＞垦殖水田＞湖草洲滩地;土壤表层＜0.01 mm、＜0.001 mm粘粒,湖草洲滩地、芦苇洲滩地＞垦殖水田.湿地土壤剖面中有机碳、微生物量碳、全氮、微生物量氮、微生物量磷、容重以及微生物量碳占有机碳的比例、微生物量氮占全氮的比例、微生物量磷占全磷的比例均随深度的增加而降低,至一定深度稳定,而土壤全磷在剖面上下的差异很小.湿地土壤微生物量碳、氮、磷之间呈极显著的正相关关系;土壤容重与有机碳、全氮、微生物量碳、氮、磷之间呈极显著指数负相关关系.湿地土壤＜0.001 mm粘粒与有机碳、全氮、微生物量碳、氮、磷含量呈极显著对数正相关关系.     

Depth-Dependent Patterns of Bacterial Communities and Assembly Processes in a Typical Red Soil Critical Zone

Abstract

Depth patterns of soil microbial distribution have not been well characterized and little is known about the balance between stochastic and deterministic processes in shaping microbial community through soil profiles. We examined how the composition, diversity, and assembly processes of bacterial communities change to a depth of 4 m along three cores sampled through a typical upland red soil Critical Zone in subtropical China. The sampled soils at the center of the Critical Zone were acidic, highly weathered, and clay loam to clay in texture, and developed from Quaternary red clay. Bacterial richness and phylogenetic diversity decreased with depth in the upper soil zone (0–90?cm), but was constant in the deeper zone (90–420?cm). In both the upper and deeper zones, richness was strongly and positively correlated with total organic carbon, dissolved organic carbon and total nitrogen. Depth-dependent changes of community structure were observed above the upper but not deeper zones. Stochastic processes were more important in the upper zone, whereas deterministic processes were dominant in the deeper zone. The distinct depth-dependent patterns of bacterial communities and assembly processes exist through deep soil profiles and are influenced by both contemporary and historical pedogenetic factors and processes.     

Interactions in the microbial community of the marginal ice zone of the northwestern Weddell Sea through size distribution analysis

Summary Enumeration and identification of planktonic microorganisms (phytoplankton, bacteria, protozoa) were carried out for 16 stations sampled in the marginal ice zone of the northwestern Weddell Sea during sea-ice retreat in 1988 (EPOS Leg 2). From these data, carbon biomass distribution among various classes, chosen according to size and trophic mode, has been determined. This analysis reveals the general dominance of nano-phytoplankton (74 %), mainly Cryptomonas sp.. In two stations only, significant microphytoplanktonic biomass occurred. Bacterioplankton biomass was 16 % of the phytoplanktonic biomass. Protozooplankton appeared as a significant group whose biomass represented an average of 23 % of the total microbial biomass. Maximum phytoplankton and protozooplankton biomass was reached at about 100–150 km north of the receding ice edge whilst bacteria did not show marked spatial variations. From these results, indirect evidence for close relationships between protozoa and bacteria, as well as protozoa and autotrophs, is given. The size range of autotrophic prey and predators overlaps (equivalent spherical diameter range = 6 to 11 m). This size overlapping increases the complexity of the trophic organization of the microbial community. Our results thus support the idea of a flux of energy not always oriented towards an increasing particle size range. Potential ingestion rate, calculated from a mean clearance rate in the literature, indicated that protozooplankton might ingest as high as 48 % of the daily phytoplankton production in the marginal ice zone.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Analysis of Plankton Dynamics in a Southwestern U.S.A. Reservoir Using ATP Assays

Plankton biomass in size segregated (i.e. 0.45–10 μm, 10–64 μm, 64–165 μm, and > 165 μm) samples was measured using ATP assays for two years in H. H. Moss Reservoir. The presence of variable numbers of microcrustacean zooplankton in the > 165 μ size class introduced significant, and perhaps inaccurate, variance into temporal dynamics of total ATP concentrations. As many as six physiochemical parameters, measured during 1975–76, were required to produce a significant multiple regression against ATP concentrations; a significant correlation between total ATP measured in the photic zone and surface temperature was observed. A large standing crop of nannoplankton (i.e. 0.45–10 μm) existed in the anaerobic and aphotic hypolimnion during summer stratification both years. This suggested that microbial heterotrophy was an especially important primary trophic event in the reservoir. Particulate (POC) and dissolved (DOC) organic carbon were measured in 1976–77. Organic carbon (POC + DOC) regressed significantly against ATP concentration in the 0.45–10 μm size class and microbial biomass (i.e. 0.45–165 μm) averaged 32 per cent of POC. When biomass was monitored over 24-hour periods in the photic zone, significant changes were documented in various size classes, especially nannoplankton; but total microbial biomass remained relatively constant.     

Use of an ATP assay to determine viable microbial biomass in Fennoscandian Shield groundwater from depths of 3-1000 m

Bioluminescent biomass in pure cultures and in 94 samples of shallow and deep Fennoscandian Shield groundwater was analysed using a commercial ATP assay, and the results were compared with microscopic counts and counts based on cultivation methods. The assay appeared robust and reliable and had a detection range that covered all samples analysed. The detection limit in groundwater was determined to 2x10(3) cells ml(-1). ATP concentrations were found to correlate with the microscopic counts and with the volume and metabolic status of the investigated pure culture and groundwater cells. The results suggested that bacterial populations in deep groundwater vary significantly in size, and that metabolic activity is a function of prevailing environmental conditions. In cases in which analysis of the total and viable number of cells produced very low numbers, suggesting that the detected cells were of low viability, ATP analysis of the ratio of ATP to the total number of cells was able to verify such an interpretation of the obtained data.     

A Vigorous Specialized Microbial Food Web in the Suboxic Waters of a Shallow Subtropical Coastal Lagoon

To examine the extent of the microbial food web in suboxic waters of a shallow subtropical coastal lagoon, the density and biomass of bacteria and protozooplankton were quantified under different dissolved oxygen (DO) levels. In addition, bottom waters of a stratified site were compared with bottom waters of a homogeneous site under periods of high and low biological oxygen production/consumption in the lagoon. At the stratified site, microbial biomass decreased with oxygen decline, from oxia to suboxia, with a recovery of the initial total biomass after a 20-day period of persistent suboxia. A peak in density and biomass of purple sulfur bacteria (PSB) (90 μg C L(-1)) occurred in the suboxic waters 20 days prior to the peak in biomass of ciliates >50 μm (Loxophyllum sp. of 150 μm) (160 μg C L(-1)), demonstrating a top down biomass control. Ciliates >50 μm were positively correlated with PSB and bacteriochlorophyll a (photosynthetic pigment of PSB). Total protozoan biomass reached 430 μg C L(-1) in the suboxic waters of the stratified site, with ciliates >50 μm accounting for 90% of the total ciliate biomass and of 55 % of biomass of protozoa. At the homogeneous site, total protozoan biomass was only 66 μg C L(-1), where flagellates and ciliates <25 μm were the dominant microorganisms. Therefore, as light is available for primary producers in the bottom waters of shallow stratified coastal lagoons or estuaries, one can expect that high primary production of PSB may favor a specialized microbial food web composed by larger microorganisms, accessible to zooplankton that tolerate low DO levels.     

Distribution and Composition of Microbial Populations in a Landfill Leachate Contaminated Aquifer (Grindsted, Denmark)

Abstract To investigate whether landfill leachates affected the microbial biomass and/or community composition of the extant microbiota, 37 samples were collected along a 305-m transect of a shallow landfill-leachate polluted aquifer. The samples were analyzed for total numbers of bacteria by use of the acridine orange direct count method (AODC). Numbers of dominant, specific groups of bacteria and total numbers of protozoa were measured by use of the most probable number method (MPN). Viable biomass estimates were obtained from measures of ATP and ester-linked phospholipid fatty acid (PLFA) concentrations. The estimated numbers of total bacteria by direct counts were relatively constant throughout the aquifer, ranging from a low of 4.8 × 10⁶ cells/g dry weight (dw) to a high of 5.3 × 10⁷ cells/g dw. Viable biomass estimates based on PLFA concentrations were one to three orders of magnitude lower with the greatest concentrations (up to 4 × 10⁵ cells/g dw) occurring at the border of the landfill and in samples collected from thin lenses of clay and silt with sand streaks. Cell number estimates based on ATP concentrations were also found to be lower than the direct count measurements (<2.2 × 10⁶ cells/g dw), and with the greatest concentrations close to the landfill. Methanogens (Archaea) and reducers of sulfate, iron, manganese, and nitrate were all observed in the aquifer. Methanogens were found to be restricted to the most polluted and reduced part of the aquifer at a maximum cell number of 5.4 × 10⁴ cells/g dw. Populations of sulfate reducers decreased with an increase in horizontal distance from the landfill ranging from a high of 9.0 × 10³ cells/g dw to a low of 6 cells/g dw. Iron, manganese, and nitrate reducers were detected throughout the leachate plume all at maximum cell numbers of 10⁶ cells/g dw. Changes in PLFA profiles indicated that a shift in microbial community composition occurred with increasing horizontal distance from the landfill. The types and patterns of lipid biomarkers suggested that increased proportions of sulfate- and iron-reducing bacteria as well as certain microeukaryotes existed at the border of the landfill. The presence of these lipid biomarkers correlated with the MPN results. There was, however, no significant correlation between the abundances of the specific PLFA biomarkers and quantitative measurements of redox processes. The application of AODC, MPN, PLFA, and ATP analyses in the characterization of the extant microbiota within the Grindsted aquifer revealed that as distance increased from the leachate source, viable biomass decreased and community composition shifted. These results led to the conclusion that the landfill leachate induced an increase in microbial cell numbers by altering the subsurface aquifer so that it was conducive to the growth of methanogens and of iron-and sulfate-reducing bacteria and fungi. Received: 11 June 1998; Accepted: 10 December 1998     

Relation of rumen ATP concentration to bacterial and protozoal numbers.

Cultures of Streptococcus bovis and mixed populations of rumen bacteria were used to investigate the concentration of ATP and rumen bacterial numbers at various stages of growth. ATP, extracted with Tris buffer, was analyzed using the firefly luciferin-luciferase bioluminescent reaction. ATP concentrations of S. bovis and mixed cultures of rumen bacteria significantly correlated with live cell counts during the log phase of growth but not during the stationary phase. The average cellular ATP concentration of rumen bacteria was calculated to be 0.3 fg of ATP per cell. Studies done with in vivo artificial rumen apparatus revealed that the protozoal contribution to rumen fluid ATP pool size was much more substantial than was the bacterial contribution. The rumen fluid ATP concentration was greater in cattle with protozoa than in those that were defaunated. Differences in ATP concentration due to size differences of ciliate protozoa were observed. Due to the unbalanced distribution of ATP in rumen microbes, ATP appears to be an unsuitable indicator of rumen microbial biomass.     

The impact of crop plant cultivation and peat amendment on soil microbial activity and structure

A rapid means for restoring soil fertility could be addition of peat to the plough layer. The impact of cultivation of eight different crops (the joint impact of plant and the management tailored for each plant), with and without soil amendment by peat treatment on soil microbiological, physical and chemical properties was assessed for two consecutive growing seasons. As a measure of the functional diversity of soil microbial community we estimated the activity of several different extracellular soil enzymes using the ZymProfiler® test kit. ATP content was measured to yield information on the amount of the active microbial biomass, and phospholipid fatty acid (PLFA) profiles were analysed to reveal the microbial community structure. The enzyme activity patterns of the soil samples indicated several differences due to the different crops and years but ATP content and PLFA profiles were rather stable. However, microbial biomass as total amount of PLFAs depended on the plant and peat treatment and ATP content varied between the years. The effects of the peat treatments were less clearly indicated by the biological parameters one or two years after the amendment, as only arylsulphatase and β-xylosidase activities were affected in both the years. Soil moisture, affecting enzyme activities, depended on the year and crop plant and peat addition increased it. Abbreviations: AMC – 7-amino-4-methylcoumarin; AP – aminopeptidase; ATP – adenosine triphosphate; C_mic– microbial biomass carbon; DNA – deoxyribonucleic acid; EC – electrical conductivity; FAME – fatty acid methyl ester; fw – fresh weight; MUF – 4-methylumbelliferyl; na – not added; N_mic– microbial biomass nitrogen; PDE – phosphodiesterase; PLFA – phospholipid fatty acid; PME – phosphomonoesterase; SOM – soil organic matter     

Correlation of Direct Viable Counts with Heterotrophic Activity for Marine Bacteria

Viable-bacteria counts, heterotrophic activity, and substrate responsiveness of viable bacteria have been used to measure microbial activity. However, the relationship between these parameters is not clear. Thus, the direct viable count (DVC) method was used to analyze seawater samples collected from several different geographical locations. Samples collected from offshore waters of the South China Sea and western Pacific Ocean yielded DVC that indicated the presence of surface and subsurface peaks of viable, substrate-responsive bacteria which could be correlated with turnover rates of amino acids obtained by using uniformly ¹⁴C-labeled amino acids. DVC were always less than total viable counts (acridine orange direct counts), and the DVC subsurface peak occurred close to and within the chlorophyll a zone, suggesting algal-bacterial interactions within the layer. For comparison with the open-ocean samples, selected substrates were used to determine the response of viable bacteria present in seawater samples collected near an ocean outfall of the Barceloneta Regional Waste Treatment Plant, Barceloneta, Puerto Rico. The number of specific substrate-responsive bacteria at the outfall stations varied depending on the substrate used and the sampling location. Changes in the population size or physiological condition of the bacteria were detected and found to be associated with the presence of pharmaceutical waste.     

Microbial characteristics of soils on a latitudinal transect in Siberia

Soil microbial properties were studied from localities on a transect along the Yenisei River, Central Siberia. The 1000 km‐long transect, from 56°N to 68°N, passed through tundra, taiga and pine forest characteristic of Northern Russia. Soil microbial properties were characterized by dehydrogenase activity, microbial biomass, composition of microbial community (PLFAs), respiration rates, denitrification and N mineralization rates. Relationships between vegetation, latitude, soil quality (pH, texture), soil organic carbon (SOC) and the microbial properties were examined using multivariate analysis. In addition, the temperature responses of microbial growth (net growth rate) and activity (soil respiration rate) were tested by laboratory experiments. The major conclusions of the study are as follows: 1. Multivariate analysis of the data revealed significant differences in microbial activity. SOC clay content was positively related to clay content. Soil texture and SOC exhibited the dominant effect on soil microbial parameters, while the vegetation and climatic effects (expressed as a function of latitude) were weaker but still significant. The effect of vegetation cover is linked to SOC quality, which can control soil microbial activity. 2. When compared to fine‐textured soils, coarse‐textured soils have (i) proportionally more SOC bound in microbial biomass, which might result in higher susceptibility of SOC transformation to fluctuation of environmental factors, and (ii) low mineralization potential, but with a substantial part of the consumed C being transformed to microbial products. 3. The soil microbial community from the northernmost study region located within the permafrost zone appears to be adapted to cold conditions. As a result, microbial net growth rate became negative when temperature rose above 5 °C and C mineralization then exceeded C accumulation.     

Microbial Diversity in Uranium Mine Waste Heaps

Two different uranium mine waste heaps near Ronneburg, Thuringia, Germany, which contain the remains of the activity of the former uranium-mining Soviet-East German company Wismut AG, were analyzed for the occurrence of lithotrophic and chemoorganotropic leach bacteria. A total of 162 ore samples were taken up to a depth of 5 m. Cell counts of ferrous iron-, sulfur-, sulfur compound-, ammonia-, and nitrite-oxidizing bacteria were determined quantitatively by the most-probable-number technique. Sulfate-, nitrate-, ferric iron-, and manganese-reducing bacteria were also detected. In addition, the metabolic activity of sulfur- and iron-oxidizing bacteria was measured by microcalorimetry. Generally, all microorganisms mentioned above were detectable in the heaps. Aerobic and anaerobic microorganisms thrived up to a depth of 1.5 to 2 m. Up to 99% of Thiobacillus ferrooxidans cells, the dominant leaching bacteria, occurred to this depth. Their numbers correlated with the microbial activity measurements. Samples below 1.5 to 2 m exhibited reduced oxygen concentrations and reduced cell counts for all microorganisms.     

Factors influencing the abundance and metabolic capacities of microorganisms in Eastern Coastal Plain sediments

The abundance and metabolic capacities of microorganisms residing in 49 sediment samples from 4 boreholes in Atlantic Coastal Plain sediments were examined. Radiolabeled time-course experiments assessing in situ mirobial capacities were initiated within 30 min of core recovery. Acetate (1-¹⁴C- and³H-) incorporation into lipids, microbial colony forming units, and nutrient limitations were examined in aliquots of subsurface sediments. Water-saturated sands exhibited activity and numbers of viable microorganisms that were orders of magnitude greater than those of the low permeability dense clays. Increased radioisotope utilization rates were observed after 6–24-h incubation times when sediments were amended with additional water and/or nutrients. Supplements of water, phosphate, nitrate, sulfate, glucose, or minerals resulted in the stimulation of microbial activities, as evidenced by the rate of acetate incorporation into microbial lipids. Additions of water or phosphate resulted in the greatest stimulation of microbial activities. Regardless of depth, sediments that contained >20% clay particles exhibited lower activities and biomass densities, and greater stimulation with abundant water supplementation than did sediments containing >66% sands and hydraulic conductivities > 200 μm sec.^?1.     

Biodegradation of organic compounds in vadose zone and aquifer sediments.

The microbial processes that occur in the subsurface under a typical Midwest agricultural soil were studied. A 26-m bore was installed in November of 1988 at a site of the Purdue University Agronomy Research Center. Aseptic collections of soil materials were made at 17 different depths. Physical analysis indicated that the site contained up to 14 different strata. The site materials were primarily glacial tills with a high carbonate content. The N, P, and organic C contents of sediments tended to decrease with depth. Ambient water content was generally less than the water content, which corresponds to a -0.3-bar equivalent. No pesticides were detected in the samples, and degradation of added 14C-labeled pesticides (atrazine and metolachlor) was not detected in slurry incubations of up to 128 days. The sorption of atrazine and metolachlor was correlated with the clay content of the sediments. Microbial biomass (determined by direct microscopic count, viable count, and phospholipid assay) in the tills was lower than in either the surface materials or the aquifer located at 25 m. The biodegradation of glucose and phenol occurred rapidly and without a lag in samples from the aquifer capillary fringe, saturated zone, and surface soils. In contrast, lag periods and smaller biodegradation rates were found in the till samples. Subsurface sediments are rich in microbial numbers and activity. The most active strata appear to be transmissive layers in the saturated zone. This implies that the availability of water may limit activity in the profile.