Radionuclide partitioning across great lakes natural interfaces

Several water and surface microlayer samples from Lake St. Clair, the Niagara River, and the North Shore of Lake Ontario collected during 1983–1986 have been assayed for a variety of radionuclides. In addition, the foam accumulating in the pool just below Niagara Falls was also analyzed and found to be the most efficient aqueous phase collector of¹³⁷Cs,²¹⁰Pb, and²²⁶Ra.The order of radioisotope specific activities from highest to lowest is: Lake Ontario sediment, Niagara River suspended solids, Niagara River foam, surface microlayer water, and subsurface water. Radiological dose rates to the sediments from¹³⁷Cs,²²⁶Ra, and²²⁸Th total about 5 mGy/y.     

Isolation and characterization of some polycyclic aromatic hydrocarbon degrading bacteria from Nsukka soils in Nigeria

Twenty-four bacteria capable of utilizing naphthalene, as their sole source of carbon and energy for growth were isolated from three different sites in Nsukka, Nigeria. By standard bacteriological methods, these bacteria were characterized taxonomically as belonging to the genus Pseudomonas, Burkholderia or Actinomycetes. Two of the isolates, which showed the highest growth during screening as demonstrated by an increase in their optical densities (OD₆₀₀) and identified as Pseudomonas aeruginosa and Burkholderia cepacia respectively, were also able to grow in anthracene and carbazole, but not very much so in 2,4-dichlorophenol and D-camphor. The isolates showed a concentration-dependent growth in all the compounds they grew in. There were visible changes in the colour of the growth medium of the isolates during their incubation, suggesting the production of different metabolites. There were also changes in their medium pH during growth. These studies demonstrate the possession by the bacterial species of novel degradative systems.     

The role of prokaryotes in subsurface weathering of hydrothermal sediments: A combined geochemical and microbiological investigation

A detailed geochemical and microbiological study of a ∼2 m sediment core from the inactive Alvin mounds within the TAG hydrothermal field was conducted to examine, for the first time, the role of prokaryotes in subsurface weathering of hydrothermal sediments. Results show that there has been substantial post-depositional remobilisation of metal species and diagenetic overprinting of the original high-temperature hydrothermal minerals, and aspects have involved prokaryotic processes. Prokaryotic enumeration demonstrates the presence of a population smaller than the average for deep sea sediments, probably due to the low organic carbon content, but not inhibited by (and hence adapted to) the metal rich environment. There was a small but significant increase in population size associated with the active redox boundary in an upper metal sulphide layer (50-70 cm) around which active metal remobilisation was concentrated (Cu, Au, Cd, Ag, U, Zn and Zn). Hence, subsurface prokaryotes were potentially obtaining energy from metal metabolism in this near surface zone. Close association of numbers of culturable Mn and Fe reducing prokaryotes with subsurface Fe²⁺ and Mn²⁺ pore water profiles suggested active prokaryotic metal reduction at depth in core CD102/43 (to ∼175 cm). In addition, a prokaryotic mechanism, which is associated with bacterial sulphate reduction, is invoked to explain the U enrichment on pyrite surfaces and Zn and Pb remobilisation in the upper sediment. Although prokaryotic populations are present throughout this metalliferous sediment, thermodynamic calculations indicated that the inferred low pH of pore waters and the suboxic/anoxic conditions limits the potential energy available from Fe(II) oxidation, which may restrict prokaryotic chemolithotrophic biomass. This suggests that intense prokaryotic Fe oxidation and weathering of seafloor massive sulphide deposits may be restricted to the upper portion of the deposit that is influenced by near neutral pH and oxic seawater unless there is significant subsurface fluid flow.     

Microbial lipids from a nearshore sediment from Bowling Green Bay,North Queensland: The fatty acid composition of intact lipid fractions

Samples from a sediment core collected in Bowling Green Bay, North Queensland have been analysed for hexane/isopropanol extractable lipids and fatty acids. These data revealed a subsurface lipid abundance maximum at 3–4 cm depth and consistent low total fatty acid abundances (ca 2 μg/g) in the deeper samples ( > 10 cm depth). Lipid phosphate was below the level of detection in all the samples. Bacterial community structure was found to vary markedly in the upper 10 cm of the core, with the 18:1Δ11 bacterial chemotype predominant in the surface sediment and trans-acid chemotypes dominating in the 3–4 cm depth sediment. Based on the fatty acid composition, the bacterial biomass was estimated to vary from 199 μg/g at 3–4 cm depth toca 8 μg/g at 11–13 cm depth, although the fatty acid distributions indicated possible interference from protozoan detritus. In order to test this possibility, a surface sediment sample from a nearby site was extracted and analysed for fatty acids in lipid fractions separated by silica column chromatography. The fatty acid distributions in lipid fractions containing wax/steryl esters, triacylglycerols, glycolipids and phospholipids were markedly different. These analyses were interpreted in terms of fatty acid contributions to the extractable lipids from bacteria, cyanobacteria, protozoan detritus and highly degraded organic matter.     

Contribution of bacteria to redox potential (E h) measurements in sediments

Increasing evidence suggests that bacteria are capable of creating specific redox conditions which are visible as species-specific continuous redox potential (E _h) measurements. It has been demonstrated that continuous measurements of E _h are valuable for tracking bacterial metabolic activities of bacterial species in liquid cultures. However, it remains uncertain whether this phenomenon is widespread among bacterial species and whether E _h measurements reflect similar mechanisms in more complex systems such as soils and sediments. The purpose of this study is therefore to evaluate whether bacteria that naturally occur in sediments have the capacity to control E _h and assess the relative partitioning of biological processes involved in E _h in natural sediments. To this end, continuous E _h measurements are linked to growth of bacteria in liquid cultures and bacterial metabolic activity in aquatic sediment microcosms containing the bioturbator Tubifex spp., in which we evaluate bacterial partitioning in microcosms treated with the bacteriocide formalin. The tested bacterial species (Micrococcus luteus, Paracoccus pantotrophus and Aminobacter aminovarans) appeared to have specific stable E _h signals during linear-exponential growth phase, suggesting that these species are capable of exerting an extracellular control on E _h measurements, thereby supporting the notion that species-specific E _h signals may be widespread among bacterial species. Formalin treatment reduced temporal variability of E _h in sediment microcosms. This outcome suggests that bacterial metabolism and inherent relative contributions of members of bacterial community principally determine development of E _h in sediment systems and that quantitation of sediment electrochemical properties may offer a potential indicator that characterizes bacterial processes.     

Use of annular flumes to determine the influence of current velocity and bivalves on material flux at the sediment-water interface

A benthic annular flume for both laboratory and in situ deployment on intertidal mudflats is described. The flume provides a means of quantifying material flux (i.e., biodeposition of suspended particulates, sediment resuspension, nutrients, oxygen, and contaminants) across the sediment-water interface in relation to changes in current velocity and benthic community structure and/or population density of key macrofauna species. Flume experiments have investigated the impact of the infaunal bivalveMacoma balthica and the epifaunal bivalveMytilus edulis on seston and sediment flux at the sediment-water interface. The bioturbatorMacoma was found to increase the sediment resuspension and/or erodability by 4-fold, at densities similar to those recorded at the Skeffling mudflat (Humber estuary) (i.e., >1000 individuals m^?2). There was a significant correlation between sediment resuspension andMacoma density (r=0.99; p<0.001), which supported previous in situ field observations indicating bioturbation byMacoma enhanced sediment erodability. Biodeposition rates (g m^?2 h¹) ofMytilus edulis andCerastoderma edule were quantified and related to changes in population density in a mussel bed (Cleethorpes, Humber estuary). Biodeposition rates were up to 40-times the natural sedimentation rates. At the highest mussel bed densities (i.e., 50–100% cover or >1400 mussels m^?2) the physical presence of this epifaunal bivalve on the sediment surface reduced erosion by 10-fold. The shift from net biodeposition to net erosion occurred at current velocities of 20–25 cm s^?1. These results demonstrate that infaunal and epifaunal bivalves can have a significant impact on seston flux or sediment deposition and on sediment resuspension or erodability in estuaries where there are extensive mudflats.     

Abundance and relationship of bacteria with transparent exopolymer particles during the 1996 summer monsoon in the Arabian Sea

Bacterial abundance and production, numbers, sizes and concentrations of transparent exopolymer particles (TEP) and total organic carbon (TOC) were measured during the 1996 summer monsoon to understand the relationship between TEP, the most labile particulate organic carbon, and bacteria. While high regional variability in the vertical distribution of TOC was discernible, TEP concentrations were high in surface waters at 18–20°N along 64°E with concentrations well over 25 mg alginic acid equivalents I⁻¹ due to upwelling induced productivity. Their concentrations decreased with depth and were lower between 200 and 500 m. Bacterial concentrations were up to 1.99 × 10⁸ I^–1 in the surface waters and decreased by an order of magnitude or more at depths below 500 m. A better relationship has been found between bacterial abundance and concentrations of TEP than between bacteria and TOC, indicating that bacterial metabolism is fueled by availability of TEP in the Arabian Sea. Assuming a carbon assimilation of 33%, bacterial carbon demand (BCD) is estimated to be 1.017 to 4.035 g C m^–2 d^–1 in the surface waters. The observed TEP concentrations appear to be sufficient in meeting the surface and subsurface BCD in the northern Arabian Sea.     

Microbial mercury transformations in marine,estuarine and freshwater sediment downstream of the Idrija Mercury Mine,Slovenia

The Idrija Mine, the second largest Hg mine in the world, ceased operation in 1995, but still delivers large quantities of Hg downstream including into the northern Adriatic Sea, 100 km away. Transformation of Hg species in sediment in sites over 60 km from the mine, including marine sites in the Adriatic Sea, was measured to determine the ability of the system to transform and mobilize Hg and to produce methylmercury (MeHg). Cores from a freshwater impoundment, a brackish estuarine site, and three marine sites in the Gulf of Trieste were sectioned anaerobically, and Hg methylation and MeHg demethylation activities determined using radio-techniques (²⁰³Hg for methylation and ¹⁴C-MeHg for demethylation). Total and dissolved Hg and MeHg were determined as were other geochemical parameters. In addition, rates of SO₄ reduction were determined in marine sediment using a ³⁵S technique. Mercury was readily methylated and demethylated at all sites. Marine sediment was investigated in winter and summer with rates of Hg transformation and SO₄ reduction corresponding only in winter. Methylation of Hg in summer displayed subsurface peaks that may have been influenced by bioturbation. Total Hg and MeHg were most abundant in the freshwater, estuarine, and near-shore marine sites, but dissolved pore water Hg and MeHg were highest in the estuarine region where S cycling appeared ideal for the mobilization of Hg. The impoundment sediment also seemed to be a ‘hotspot’ of Hg transformations. MeHg demethylation occurred via the oxidative demethylation pathway (CO₂ produced from MeHg), except in surficial sediment offshore in the Gulf during winter, where sediment was more oxidizing and significant amounts of CH₄ were liberated during MeHg degradation via reductive demethylation. The CH₄ formation was likely due to an increased influence from the expression of MeHg degradative enzymes encoded by the mer detoxification bacterial genetic system. The freshwater site also liberated CH₄ from MeHg, but it appeared to be due to oxidative demethylation by methanogenic bacteria.     

Wave effects on the vertical migration of two benthic microalgae: Hantzschia virgata var. intermedia and Euglena proxima

Two benthic microalgal species, Euglena proxima (Dangeard) and the diatom Hantzschia virgata var. intermedia (Grun) Round, congregated at the sediment surface of intertidal sand flats surrounding the Duke University Marine Laboratory in Beaufort, North Carolina, during low tide and migrated below the surface prior to tidal flooding. E. proxima was found down to a depth of 12 cm below the surface during high tide while H. virgata was not found below 8 cm. One potential advantage of vertical migration for benthic microalgae is avoidance of the sediment surface during high tide when the winnowing action of waves can remove cells from the intertidal habitat. This hypothesis was tested by comparing the mean depths of E. proxima and H. virgata exposed to calm water conditions with their mean depths under wave-exposed conditions in shallow outdoor tidal tanks equipped with wave generators. Two sediment treatments were tested in each tank to evaluate the effect of a subsurface layer of black sediment (subsurface sediments, presumably reduced) on vertical migration: a uniform column of light brown sand (surface sediments; presumably oxygenated), and a layered column with light brown sand overlying a layer of black sediment. One-way and two-way ANOVAs indicated that wave action increased the mean depth of both species under certain conditions related to the presence, absence, and depth of a subsurface layer of black sediment. In an experiment with a shallow black layer (5 mm), wave action did not result in a significant increase in the mean depth of H. virgata as it did in a previous experiment with a deeper black layer (3 cm). Unlike H. virgata, E. proxima exhibited a wave effect only in the absence of a subsurface black layer. A subsurface black layer seemed to reinforce downward migration in E. proxima under both calm water and wave conditions. The absence of a wave effect in the presence of a subsurface black layer suggests that the mean depth of E. proxima during high tide was more tightly controlled by the depth of the black layer than wave energy. *** DIRECT SUPPORT *** A01BY085 00009     

The Influence of Oyster Farming on Sediment Bacterial Communities

Aquaculture currently provides half of all fish for human consumption, and this proportion is expected to increase to meet the growing global demand for protein. As aquaculture, including oyster farming, expands, it is increasingly important to understand effects on coastal ecosystems. The broad-scale ecological effects of oyster aquaculture are well documented; however, less is known regarding the influence of oyster aquaculture on sediment bacterial communities. To better understand this relationship, we compared three different oyster farming practices that varied in oyster biomass and proximity of oysters to the sediment. We used high-throughput sequencing and quantitative polymerase chain reaction to examine the effect of oyster farming on sediment bacterial communities. We examined the entire bacterial community and looked specifically at bacteria that support essential estuarine ecosystem services (denitrifiers), as well as bacteria that can be detrimental to human health (members of the Vibrio genus). We found that oyster biomass increased Vibrio richness and sediment carbon content, which influenced bacterial community composition. When compared to reference sites, the overall abundance of bacteria was increased by the bottom planting method, but the associated increases in denitrifiers and Vibrio were not significant. We were unable to detect V. parahaemolyticus, V. vulnificus, or V. cholera, the three most common Vibrio pathogens, in any sample, suggesting that oyster farming did not enhance these potential human pathogens in sediments at the time of sampling. These results highlight how differences in oyster farming practice can affect sediment bacterial communities, and the ecosystem services they provide.     

Rate of tube building and sediment particle size selection during tube construction by the tanaid crustacean,Leptochelia dubia

In estuaries, organic coatings play an important role in the aggregation of mineral particles. Particles acquire adhesive surfaces through the activities of bacteria and microalgae in the sediment and water column. Eventually, they may become incorporated into larger aggregates and structures, such as tubes, constructed by infaunal benthic animals. Where these structures are large enough, and the adhesive bonds between particles strong enough, individual particles may remain in place at bed shear stresses otherwise strong enough to cause sediment transport. This study examined the aggregation of particles during tube building by the ubiquitous tanaid crustaceanLeptochelia dubia. Particle size selection and rates of tube building were determined as functions of animal size, temperature, and the presence or absence of bacteria and microalgae. These data were used to model seasonal patterns of sediment binding by a population ofL. dubia in Yaquina Bay, Oregon, taking into account seasonal changes in sizes and abundance of animals. Rates of tube building (mass of sediment per day) increased with animal size, but temperature had no effect. The model indicated that the field population ofL. dubia bound sediment into tubes at a gross rate of 350 g m^?2 d^?1, averaged over a 2-yr period. Seasonally, gross rates of tube building were predicted to range from 70 g m^?2 d^?1 (during late winter-early spring) to 600 g m^?2 d^?1 (during autumn). When constructing tubes from sterile sediments, small animals selected silt-sized particles while large animals discriminated against these particles. The presence of microbes in sediments tended to reduce particle selectivity.     

Manganese-reducing Pseudomonas fluorescens-group bacteria control arsenic mobility in gold mining-contaminated groundwater

Previous studies show the importance of iron- and arsenate-reducing bacteria in mobilizing arsenic in groundwater. Here the authors present experimental evidence of arsenic mobilization in connection with bacterially mediated manganese reduction in groundwater affected by mining activities. Manganese-reducing Pseudomonas species were enriched, isolated and identified by 16S rRNA gene phylogeny from groundwater containing high co-dissolved arsenic (as As^III) and manganese. Enrichment cultures dissolved synthetic birnessite and hausmannite efficiently, but Mn reduction by isolates was reduced at the upper range of environmental levels of dissolved As^III. Results suggest either a self-limiting release of arsenic coupled to bacterial manganese reduction, in the absence of other electron donors like sulfide, or increased arsenic resistance conferred to Mn-reducing bacteria in consortia.     

Archaea mediate anaerobic oxidation of methane in deep euxinic waters of the Black Sea

We evaluate anaerobic oxidation of methane (AOM) in the Black Sea water column by determining distributions of archaea-specific glyceryl dialkyl glyceryl tetraethers (GDGTs) and ¹³C isotopic compositions of their constituent biphytanes in suspended particulate matter (SPM), sinking particulate matter collected in sediment traps, and surface sediments. We also determined isotopic compositions of fatty acids specific to sulfate-reducing bacteria to test for biomarker and isotopic evidence of a syntrophic relationship between archaea and sulfate-reducing bacteria in carrying out AOM. Bicyclic and tricyclic GDGTs and their constituent ¹³C-depleted monocyclic and bicyclic biphytanes (down to −67‰) indicative of archaea involved in AOM were present in SPM in the anoxic zone below 700 m depth. In contrast, GDGT-0 and crenarchaeol derived from planktonic crenarchaeota dominated the GDGT distributions in the oxic surface and shallow anoxic waters. Fatty acids indicative of sulfate-reducing bacteria (i.e., iso- and anteiso-C₁₅) were not strongly isotopically depleted (e.g., −32 to −25‰), although anteiso-C₁₅ was 5‰ more depleted in ¹³C than iso-C₁₅. Our results suggest that either AOM is carried out by archaea independent of sulfate-reducing bacteria or those sulfate-reducing bacteria involved in a syntrophy with methane-oxidizing archaea constitute a small enough fraction of the total sulfate-reducing bacterial community that an isotope depletion in their fatty acids is not readily detected. Sinking particulate material collected in sediment traps and the underlying sediments in the anoxic zone contained the biomarker and isotope signature of upper-water column archaea. AOM-specific GDGTs and ¹³C-depleted biphytanes characteristic of the SPM in the deep anoxic zone are not incorporated into sinking particles and are not efficiently transported to the sediments. This observation suggests that sediments may not always record AOM in overlying euxinic water columns and helps explain the absence of AOM-derived biomarkers in sediments deposited during past periods of elevated levels of methane in the ocean.     

The onset of anthropogenic activity recorded in lake sediments in the vicinity of the Horne smelter in Quebec,Canada: Sulfur isotope evidence

Contents and δ³⁴S values of several S compounds, enumerations of S-reducing bacteria (SRB) and Fe-reducing bacteria (IRB), and Fe, Pb and In concentrations were determined for ²¹⁰Pb-dated sediment cores from two lakes in Quebec, Canada. Both lakes are located approximately 70 km downwind of the Horne smelter and refinery in Rouyn-Noranda. Increases in Fe, Pb and In concentrations and a decrease in the δ³⁴S values of total S in both lake sediment cores coincide with the start-up of the smelter in 1927. The shift towards more negative δ³⁴S values was primarily caused by an increase in the extent of S isotope fractionation during bacterial (dissimilatory) SO₄ reduction due to SO₄ loading of the lakes after smelting began. Consequently, an enhanced accumulation of ³²S-enriched reduced inorganic S compounds is evident in the sediments. δ³⁴S values of organic S in the sediments decreased only slightly due to the smelter emissions between 1930 and 1980. Hence, due to the sulfide depositing mechanisms, S isotope ratios constitute a useful tracer recording the onset of S pollution in sediments of the two previously SO₄-limited lakes investigated. In contrast, total S concentrations alone are not reliable indicators for anthropogenic S loading in lake sediment records.     

Abundance and seasonality of meiofauna,including harpacticoid copepod species,associated with stems of the salt-marsh cord grass,Spartina alterniflora

Ten Spartina alterniflora plants were sampled monthly in a Louisiana estuary to determine the abundance and species composition of stem-dwelling meiofauna and small macrofauna. Most organisms were associated with epiphytic algae found relatively high on standing stems; one harpacticoid copepod, Leptocaris brevicornis, was associated with vascular tissue. Only 15% of the stem fauna was found within 6 cm of the sediment surface. Highest abundance of total meiofauna (>8,000 individuals per 100 cm² stem surface) occurred in July. The overall seasonal average was 1,563 individuals per 100 cm² (about 800 per stem). Nematodes (24% of the total) and harpacticoids (adults and copepodites 19%, and nauplii 15%), were abundant and omnipresent taxa. Rotifers (30%) were limited to the summer months, but were extremely abundant when present, 5,037 individuals per 100 cm² in July. Mites were common (10%) while several groups, for example, amphipods, isopods, polychaetes, and insect larvae, were rare. The stem harpacticoid assemblage was not diverse; four sediment-dwelling and three species reported only from stems were recorded. Overall, abundance was low from December to May, and high from June through November. Winter and spring minima may have resulted from several factors. Estuarine water levels in the Gulf of Mexico are lowered by as much as 25 cm in the winter, and stems likely were desiccated. Highest rhizomatic growth occurs in the spring, and the resulting reduced epiphyte populations may have influenced meiofauna. The density of stem meiofauna above the sediment surface averaged about 225 individuals per 10 cm² sediment surface, but frequently exceeded that in the surrounding sediments.     

High- and low-affinity binding sites for Cd on the bacterial cell walls of Bacillus subtilis and Shewanella oneidensis

Bulk Cd adsorption isotherm experiments, thermodynamic equilibrium modeling, and Cd K edge EXAFS were used to constrain the mechanisms of proton and Cd adsorption to bacterial cells of the commonly occurring Gram-positive and Gram-negative bacteria, Bacillus subtilis and Shewanella oneidensis, respectively. Potentiometric titrations were used to characterize the functional group reactivity of the S. oneidensis cells, and we model the titration data using the same type of non-electrostatic surface complexation approach as was applied to titrations of B. subtilis suspensions by Fein et al. (2005). Similar to the results for B. subtilis, the S. oneidensis cells exhibit buffering behavior from approximately pH 3-9 that requires the presence of four distinct sites, with pK_a values of 3.3 ± 0.2, 4.8 ± 0.2, 6.7 ± 0.4, and 9.4 ± 0.5, and site concentrations of 8.9(±2.6) × 10⁻⁵, 1.3(±0.2) × 10⁻⁴, 5.9(±3.3) × 10⁻⁵, and 1.1(±0.6) × 10⁻⁴ moles/g bacteria (wet mass), respectively. The bulk Cd isotherm adsorption data for both species, conducted at pH 5.9 as a function of Cd concentration at a fixed biomass concentration, were best modeled by reactions with a Cd:site stoichiometry of 1:1. EXAFS data were collected for both bacterial species as a function of Cd concentration at pH 5.9 and 10 g/L bacteria. The EXAFS results show that the same types of binding sites are responsible for Cd sorption to both bacterial species at all Cd loadings tested (1-200 ppm). Carboxyl sites are responsible for the binding at intermediate Cd loadings. Phosphoryl ligands are more important than carboxyl ligands for Cd binding at high Cd loadings. For the lowest Cd loadings studied here, a sulfhydryl site was found to dominate the bound Cd budgets for both species, in addition to the carboxyl and phosphoryl sites that dominate the higher loadings. The EXAFS results suggest that both Gram-positive and Gram-negative bacterial cell walls have a low concentration of very high-affinity sulfhydryl sites which become masked by the more abundant carboxyl and phosphoryl sites at higher metal:bacteria ratios. This study demonstrates that metal loading plays a vital role in determining the important metal-binding reactions that occur on bacterial cell walls, and that high affinity, low-density sites can be revealed by spectroscopy of biomass samples. Such sites may control the fate and transport of metals in realistic geologic settings, where metal concentrations are low.     

The effect of species diversity on metal adsorption onto bacteria

In this study, we measure proton, Pb, and Cd adsorption onto the bacteria Deinococcus radiodurans, Thermus thermophilus, Acidiphlium angustum, Flavobacterium aquatile, and Flavobacterium hibernum, and we calculate the thermodynamic stability constants for the important surface complexes. These bacterial species represent a wide genetic diversity of bacteria, and they occupy a wide range of habitats. All of the species, except for A. angustum, exhibit similar proton and metal uptake. The only species tested that exhibits significantly different protonation behavior is A. angustum, an acidophile that grows at significantly lower pH than the other species of this study. We demonstrate that a single, metal-specific, surface complexation model can be used to reasonably account for the acid/base and metal adsorption behaviors of each species. We use a four discrete site non-electrostatic model to describe the protonation of the bacterial functional groups, with averaged pK_a values of 3.1 ± 0.3, 4.8 ± 0.2, 6.7 ± 0.1, and 9.2 ± 0.3, and site concentrations of (1.0 ± 0.17) × 10⁻⁴, (9.0 ± 3.0) × 10⁻⁵, (4.6 ± 1.8) × 10⁻⁵, and (6.1 ± 2.3) × 10⁻⁵ mol of sites per gram wet mass of bacteria, respectively. Adsorption of Cd and Pb onto the bacteria can be accounted for by the formation of complexes with each of the bacterial surface sites. The average log stability constants for Cd complexes with Sites 1-4 are 2.4 ± 0.4, 3.2 ± 0.1, 4.4 ± 0.1, and 5.3 ± 0.1, respectively. The average log stability constants for Pb complexes with Sites 1-4 are 3.3 ± 0.2, 4.5 ± 0.3, 6.5 ± 0.1, and 7.9 ± 0.5, respectively. This study demonstrates that a wide range of bacteria exhibit similar proton and metal adsorption behaviors, and that a single set of averaged acidity constants, site concentrations, and stability constants for metal-bacterial surface complexes yields a reasonable model for the adsorption behavior of many of these species. The differences in adsorption behavior that we observed for A. angustum demonstrate that genetic differences do exist between the cell wall functional group chemistries of some bacterial species, and that significant exceptions to the typical bacterial adsorption behavior do exist.     

Distribution ofVibrio parahaemolyticus in Chesapeake Bay during the summer season

The distribution ofVibrio parahaemolyticus in Chesapeake Bay during the warmer weather of the summer months was examined. This species was found throughout the Chesapeake Bay and its tributaries, even in areas of very low salinity. Counts of this species ranged from 0.04 per 100 ml to 46 per 100 ml in the water column and 2.03 to ≥2.4×10³ per 100 cc of sediment. A variety of physical, chemical and bacteriological properties associated with the incidence and distribution ofV. parahaemolyticus were examined and salinity was found to be the major influence among the factors examined. Correlation and regression analysis showed that the population size of this species increased with increasing salinity in the estuary.     

Microbial diversity in contaminated soils along the T22 trench of the Chernobyl experimental platform

The diversity of bacterial communities exposed to radioactive contamination in Chernobyl soils was examined by a combination of molecular and culture-based approaches. A set of six radioactive soil samples, exhibiting high levels of ¹³⁷Cs contamination, were collected from the T22 trench. Three samples were also collected in nearby soils with low contamination. Complex bacterial community structures were observed in both highly and weakly contaminated samples, using a molecular approach targeting the 16S rRNA gene. However, the presence of specific populations within samples from highly contaminated soils could not be revealed by statistical analysis of the DGGE profiles. More than 200 culturable isolates, representative of dominant morphotypes, were grouped into 83 Operational Taxonomic Units (OTUs) and affiliated to Firmicutes, Actinobacteria, Alpha-, Beta-, Gamma-Proteobacteria and Bacteroïdetes. No specific pattern linked to contamination was observed for these culturable bacteria. The results show that both highly and weakly contaminated soils host a wide diversity of bacteria, suggesting that long term exposure to radionuclides does not lead to the extinction of bacterial diversity.