A. L . Mills - Academia.edu (original) (raw)
Papers by A. L . Mills
World Environmental and Water Resources Congress 2008, 2008
Excess nitrate, mainly due to agricultural fertilizers, is a common problem in the surface water ... more Excess nitrate, mainly due to agricultural fertilizers, is a common problem in the surface water and groundwater of the Coastal Plain of the eastern United States. Baseflow conditions have been studied in an effort to understand nutrient loading to coastal waters, but there are many unanswered questions pertaining to nitrate flux during storm events. An automated stream sampler was deployed to collect water from a stream on the Eastern Shore of Virginia, USA, whenever stream stage rose following a rainfall event. Baseflow nitrate concentrations were typically 2.0-2.2 mg NO 3-N L-1 , and concentrations decreased rapidly with the onset of precipitation. Slightly in advance of peak discharge, the typical streamwater concentration was reduced to approximately 0.2-0.4 mg NO 3-N L-1. Streamwater nitrate concentrations slowly returned to pre-storm levels after the discharge level returned to baseflow. Even though the nitrate concentration of surface water decreased during storms, the average storm nitrate flux was approximately a factor of 3 times greater than the average base flow nitrate. Large quantities of nitrate were quickly transferred during storms due to the large volume of water with low nitrate concentrations flowing in the stream. Insights to nutrient management, particularly considering rates of biological uptake of nitrate, are supported by this more complete understanding of the dynamic flux of streamwater nitrate to coastal waters.
Environmental Science & Technology, 1995
Parameters used to describe the transport of colloids (including bacteria) through porous media e... more Parameters used to describe the transport of colloids (including bacteria) through porous media either implicitly or explicitly account for colloidal particle size but assume that the particles are spheres of uniform size. Bacteria found in soils and in aquifers exhibit a variety of shapes as well as sizes. We sought to determine if there exists a systematic effect of cell shape on the transport of bacteria in columns packed with clean quartz sand. A pulse of resting cells (14 strains of bacteria isolated from aquifers) suspended in an artificial groundwater was passed through a short column. Properties of the bacteria in the influent pulse were compared with those in the eluent from the columns. Cell shape, as quantified by the ratio of cell width to cell length, affects the transport of bacterial cells through porous media. In addition, the distributions of size and shape of cells in the effluent differed from those in the influent suspension with cells in the effluent being smaller and rounder. Short rods with low water contact angles (a measure of cell-surface hydrophobicity) showed the greatest decrease in cell length during passage through short columns.
Bulletin of Environmental Contamination and Toxicology, 1977
Metal ions enter Chesapeake Bay in varying amounts and from a variety of sources. Sources traced ... more Metal ions enter Chesapeake Bay in varying amounts and from a variety of sources. Sources traced to human activities provide at least one half of the Cr, Cu, Cd, and Pb entering the estuary, while at the present time the human contribution to the input of Mn, Fe, Co, Ni, and Zn is somewhat less (HELZ, 1976). Furthermore, it has been established that the impact of such inputs could be felt not only on a local scale but on a regional one as well. In order to ascertain the potential effect of high concentrations of metal ions on the microflora of Chesapeake Bay, an investigation was undertaken to measure the effects of metals on microbial photosynthesis, nitrification, and glucose oxidation in Chesapeake Bay water and sediment. Aerobic, heterotrophic bacterial populations showing resistance to metal ions in water and sediment samples collected from Colgate Creek, (Baltimore Harbor), an area of high metal stress (VILLA and JOHNSON, 1974), and a station in the middle of the ship channel near Chesapeake Beach, an area near the center of the Bay containing much lower metal concentrations than Baltimore Harbor (HELZ, 1976) were enumerated.
Applied and Environmental Microbiology, 1978
Factors associated with accuracy and precision in the enumeration of aquatic aerobic heterotrophs... more Factors associated with accuracy and precision in the enumeration of aquatic aerobic heterotrophs by the spread plate method were evaluated by using a nested analysis of variance experimental design. Variances associated with individual components of the spread plate procedure were isolated, and optimal replications of each step were allocated. A practical scheme for optimal allocation of resources is proposed, consisting of four subsamples and two plates per subsample and yielding a total variance decrease of 70% from a single-subsample, 10-plate series. Data transformation was, in general, unnecessary for intraexperiment or intrasample statistical analysis, whereas interexperiment or intersample comparisons may require transformation of data. Rapid changes in the numbers of organisms in stored water samples were observed that were not reproducible and did not follow detectable trends, with increases or decreases in counts occurring in samples regardless of whether they were stored...
Water Resources Research, 1999
Miscible displacement experiments were performed on intact sand columns ranging from 15 to 60 cm ... more Miscible displacement experiments were performed on intact sand columns ranging from 15 to 60 cm in length to determine whether bacterial deposition varies at the centimeter scale within aquifer sediments. A 1‐pore‐volume pulse of radiolabeled cell suspension was introduced into the columns followed by a 2‐pore‐volume flush of artificial groundwater. The columns were then drained and dissected along the axis of flow. At ∼1‐cm intervals, nine samples were removed for the enumeration of sediment‐associated bacteria. Concentrations of sediment‐associated (deposited) bacteria varied by up to 2 orders of magnitude in the direction perpendicular to flow demonstrating that bacterial deposition cannot be described mechanistically by a single rate coefficient. Incorporation of a distribution of sediment size and porosity values into Monte Carlo simulations indicates that physical heterogeneities are only partially responsible for the observed variability in deposited bacteria. A simple first‐order model (classic filtration theory) adequately described the average spatial distribution of bacteria with depth within the 15‐cm column. For the longer columns, however, the average concentration of deposited bacteria did not decrease exponentially with depth. A second‐order model, modified to include an influent suspension of bacteria consisting of two subpopulations with separate sticking efficiencies (dual‐alpha population), was required to describe the observed decreases of deposited bacteria with depth. A sensitivity analysis was performed with a first‐order dual‐alpha model to understand the effects of an influent suspension with two subpopulations of bacteria on the decrease of deposited bacteria with flow path length. Numerical simulations show that even for small fractions (0.01) of nonsticky bacteria, the decrease in deposited bacteria may deviate substantially from the exponential decrease expected from colloid‐filtration theory. Results from experimental as well as numerical studies demonstrate the importance of column dissections for understanding bacterial deposition in saturated porous media.
Talanta, 1984
Interpreting the redox chemistry of sulphur in aqueous systems requires the analysis of mixtures ... more Interpreting the redox chemistry of sulphur in aqueous systems requires the analysis of mixtures of various sulphoxy anions. Previous methods have been too involved to permit high sample throughout if good quality control is to be maintained. Methods based on ion chromatography have been
Journal of Contaminant Hydrology, 2001
The injection of bacteria in the subsurface has been identified as a potential method for in situ... more The injection of bacteria in the subsurface has been identified as a potential method for in situ cleanup of contaminated aquifers. For high bacterial loadings, the presence of previously deposited bacteria can result in decreased deposition rates-a phenomenon known as blocking. Ž. Miscible displacement experiments were performed on short sand columns ; 5 cm to determine how bacterial deposition on positively charged metal-oxyhydroxide-coated sands is affected by the presence of previously deposited bacteria. Approximately 8 pore volumes of a radiolabeled bacterial suspension at a concentration of ; 1 = 10 9 cells ml y1 were introduced into the columns followed by a 2-pore-volume flush of cell-free buffer. It was found that the presence of Al-and Fe-coated sand increased both deposition rates and maximum fractional surface coverage of bacteria on the sediment surfaces. The effect of grain size on maximum bacterial retention capacity, however, was not significant. Decreasing ionic strength from 10 y1 to 10 y2 M KCl Ž. Ž. resulted in noticeable decreases in sticking efficiency a and maximum surface coverage u max for clean silica sand-results consistent with DLVO theory. In columns containing positively charged Al-and Fe-coated sands, however, changes in a and u due to decreasing ionic max strength were minimal. These findings demonstrate the importance of geochemical controls on the maximum bacterial retention capacity of sands.
Applied and Environmental Microbiology, 1987
Several anaerobic bacteria isolated from the sediments of Contrary Creek, an iron-rich environmen... more Several anaerobic bacteria isolated from the sediments of Contrary Creek, an iron-rich environment, produced magnetite when cultured in combinations but not when cultured alone in synthetic iron oxyhydroxide medium. When glucose was added as a carbon source, the pH of the medium decreased (to 5.5) and no magnetite was formed. When the same growth medium without glucose was used, the pH increased (to 8.5) and magnetite was formed. In both cases, Fe 2+ was released into the growth medium. Geochemical equilibrium equations with E h and pH as master variables were solved for the concentrations of iron and inorganic carbon that were observed in the system. Magnetite was predicted to be the dominant iron oxide formed at high pHs, while free Fe 2+ or siderite were the dominant forms of iron expected at low pHs. Thus, magnetite formation occurs because of microbial alteration of the local E h and pH conditions, along with concurrent reduction of ferric iron (direct biological reduction or a...
Applied and Environmental Microbiology, 1985
One arm of Lake Anna, Va., receives acid mine drainage (AMD) from Contrary Creek (SO 4 2− concent... more One arm of Lake Anna, Va., receives acid mine drainage (AMD) from Contrary Creek (SO 4 2− concentration = 2 to 20 mM, pH = 2.5 to 3.5). Acid-volatile sulfide concentrations, SO 4 2− reduction rates, and interstitial SO 4 2− concentrations were measured at various depths in the sediment at four stations in four seasons to assess the effects of the AMD-added SO 4 2− on bacterial SO 4 2− reduction. Acid-volatile sulfide concentrations were always an order of magnitude higher at the stations receiving AMD than at a control station in another arm of the lake that received no AMD. Summer SO 4 2− reduction rates were also an order of magnitude higher at stations that received AMD than at the control station (226 versus 13.5 mmol m −2 day −1 ), but winter values were inconclusive, probably due to low sediment temperature (6°C). Profiles of interstitial SO 4 2− concentrations at the AMD stations showed a rapid decrease with depth (from 1,270 to 6 μM in the top 6 cm) due to rapid SO 4 2− redu...
Applied and Environmental Microbiology, 1987
The critical assumptions of the dilution method for estimating grazing rates of microzooplankton ... more The critical assumptions of the dilution method for estimating grazing rates of microzooplankton were tested by using a community from the sediment-water interface of Lake Anna, Va. Determination of the appropriate computational model was achieved by regression analysis; the exponential model was appropriate for bacterial growth at Lake Anna. The assumption that the change in grazing pressure is linearly proportional to the dilution factor was tested by analysis of variance with a lack-of-fit test. There was a significant ( P < 0.0001) linear ( P > 0.05) relationship between the dilution factor and time-dependent change in ln bacterial abundance. The assumption that bacterial growth is not altered by possible substrate enrichment in the dilution treatment was tested by amending diluted water with various amounts of dissolved organic carbon (either yeast extract or extracted carbon from lake sediments). Additions of carbon did not significantly alter bacterial growth rates duri...
Applied and Environmental Microbiology, 1994
Understanding the interaction between bacterial cells and solid surfaces is essential to our atte... more Understanding the interaction between bacterial cells and solid surfaces is essential to our attempts to quantify and predict the transport of microbes in groundwater aquifers, whether from the point of view of contamination or from that of bioremediation. The sorption of bacterial cells suspended in groundwater to porous medium grains was examined in batch studies. Bacterial sorption to clean quartz sand yielded equilibrium, linear, adsorption isotherms that varied with the bacterial strain used and the ionic strength of the aqueous solution. Values of K d (the slope of the linear sorption isotherm) ranged from 0.55 to 6.11 ml g -1 , with the greatest sorption observed for the highest groundwater ionic strength. These findings are consistent with the interpretation that an increasingly compressed electrical double layer results in stronger adsorption between the like-charged mineral surface and the bacterial cells. When iron-oxyhydroxide-coated sand was used, however, all of the ad...
Applied and Environmental Microbiology, 1991
Resting-cell suspensions of bacteria isolated from groundwater were added as a pulse to the tops ... more Resting-cell suspensions of bacteria isolated from groundwater were added as a pulse to the tops of columns of clean quartz sand. An artificial groundwater solution (AGW) was pumped through the columns, and bacterial breakthrough curves were established and compared to test the effects of ionic strength of the AGW, cell size (by using strains of similar cell surface hydrophobicity but different size), mineral grain size, and presence of heterogeneities within the porous media on transport of the bacteria. The proportion of cells recovered in the effluent ranged from nearly 90% for AGW of a higher ionic strength (I = 0.0089 versus 0.00089 m), small cells (0.75-micron-diameter spheres versus 0.75 by 1.8-micron rods), and coarse-grained sand (1.0 versus 0.33 mm) to less than 1% for AGW of lower ionic strength, large cells, and fine-grained sand. Differences in the widths of peaks (an indicator of dispersion) were significant only for the cell size treatment. For treatments containing h...
Applied and Environmental Microbiology, 1976
Of 38 pure cultures of microorganisms tested, only one, Pseudomonas stutzeri, was capable of form... more Of 38 pure cultures of microorganisms tested, only one, Pseudomonas stutzeri, was capable of forming dimethylnitrosamine from dimethylamine and nitrite during growth. Resting cells of P. stutzeri, Cryptococcus terreus, Escherichia coli, and Xanthomonas campestris formed dimethylnitrosamine, although no nitrosamine was found in growing cultures of the latter three organisms. No nitrosamine was produced by either growing cultures or resting-cell suspensions of Pseudomonas fragi or Proteus mirabilis. Boiled cells of P. stutzeri, but not those of C. terreus, E. coli, and X. campestris, formed dimethylnitrosamine, and this nitrosamine was also produced by extracts of E. coli cells at pH 5.0.
Geobiology, 2003
17 β-estradiol (E2), one of the natural estrogen compounds, is an endocrine disruptor, and low le... more 17 β-estradiol (E2), one of the natural estrogen compounds, is an endocrine disruptor, and low levels in natural waters can impair the reproductive health of aquatic organisms. Its presence has been reported in animal faecal wastes and some aquatic habitats, including surface waters impacted by intense animal agriculture or sewage contamination. Little is known about its transport in hydrological systems or its persistence in water supplies. We routinely sampled stream and soil water over the growing season in an instrumented 1.2-km 2 agricultural watershed in central Virginia. E2 concentrations in stream water ranged from 0.01 to 0.12 ng mL − 1 ; soilwater values ranged from 0.03 to 0.18 ng mL − 1. The highest concentrations were observed early in the growing season shortly after application of composted poultry litter to the cropped fields, and values decreased both with hydrological transport distance from the cropped field and over the course of the summer. Given the known application rate, E2 must be lost from the soil solution, and we explored biodegradation as a mechanism for this loss. A bacterial consortium cultured from the poultry compost biodegraded E2 in laboratory flasks amended with solutions of 1 : 1 acetate : glucose at concentrations ranging from 0.1 to 10 g L − 1 dissolved organic carbon (DOC), spiked with 1.8 ng mL − 1 E2, and incubated at different temperatures. A loss of 97-98% of the initial E2 occurred within 180 h in experiments at 22 ° C and 28 ° C with 1.0 or 0.1 g L − 1 DOC amendments. Higher DOC concentrations and lower temperatures slowed the rates of reaction, suggesting that more readily available carbon inhibits use of the E2 by degrading microorganisms. The rapid rates of biodegradation in the laboratory incubations are inconsistent with the persistence of E2 in the watershed. This suggests that either the rates of biodegradation are reduced compared with the laboratory experiments or that E2 probably interacts with the components of the natural environment through complexation, sorption or abiotic transformation in the ageing process that leads to diminished bioavailability.
Canadian Journal of Microbiology, 1977
A total of 230 strains of metal-tolerant bacteria from water and sediment samples collected in Ch... more A total of 230 strains of metal-tolerant bacteria from water and sediment samples collected in Chesapeake Bay were isolated on a medium containing cobalt, lead, mercury, or molybdenum. In addition, a set of 71 cultures were simultaneously isolated on glucose tryptone yeast extract agar medium without metals. Twenty-three reference strains were also included in the numerical taxonomy study of these bacteria, bringing the grand total of strains examined to 324. All strains were examined for 112 biochemical, cultural, morphological, and physiological characters. The taxonomic data obtained were analyzed by computer and the simple matching (SSM) and Jaccard (SJ) coefficients were calculated. Clustering achieved by unweighted average linkage is presented and. from sorted similarity matrices and dendrograms, 294 strains, i.e., 97% of the total, were recovered in 12 phenetic groups defined at the 75 to 80% similarity level. Among the strains there were nine phena presumptively identified a...
Soil Biology and Biochemistry, 2001
The relative effectiveness of average-well-color-development-normalized single-point absorbance r... more The relative effectiveness of average-well-color-development-normalized single-point absorbance readings (AWCD) vs the kinetic parameters m m , l, A, and integral (AREA) of the modi®ed Gompertz equation ®t to the color development curve resulting from reduction of a redox sensitive dye from microbial respiration of 95 separate sole carbon sources in microplate wells was compared for a dilution series of rhizosphere samples from hydroponically grown wheat and potato ranging in inoculum densities of 1 £ 10 4 2 4 £ 10 6 cells ml 21. Patterns generated with each parameter were analyzed using principal component analysis (PCA) and discriminant function analysis (DFA) to test relative resolving power. Samples of equivalent cell density (undiluted samples) were correctly classi®ed by rhizosphere type for all parameters based on DFA analysis of the ®rst ®ve PC scores. Analysis of undiluted and 1:4 diluted samples resulted in misclassi®cation of at least two of the wheat samples for all parameters except the AWCD normalized (0.50 abs. units) data, and analysis of undiluted, 1:4, and 1:16 diluted samples resulted in misclassi®cation for all parameter types. Ordination of samples along the ®rst principal component (PC) was correlated to inoculum density in analyses performed on all of the kinetic parameters, but no such in¯uence was seen for AWCD-derived results. The carbon sources responsible for classi®cation differed among the variable types with the exception of AREA and A, which were strongly correlated. These results indicate that the use of kinetic parameters for pattern analysis in CLPP may provide some additional information, but only if the in¯uence of inoculum density is carefully considered.
World Environmental and Water Resources Congress 2008, 2008
Excess nitrate, mainly due to agricultural fertilizers, is a common problem in the surface water ... more Excess nitrate, mainly due to agricultural fertilizers, is a common problem in the surface water and groundwater of the Coastal Plain of the eastern United States. Baseflow conditions have been studied in an effort to understand nutrient loading to coastal waters, but there are many unanswered questions pertaining to nitrate flux during storm events. An automated stream sampler was deployed to collect water from a stream on the Eastern Shore of Virginia, USA, whenever stream stage rose following a rainfall event. Baseflow nitrate concentrations were typically 2.0-2.2 mg NO 3-N L-1 , and concentrations decreased rapidly with the onset of precipitation. Slightly in advance of peak discharge, the typical streamwater concentration was reduced to approximately 0.2-0.4 mg NO 3-N L-1. Streamwater nitrate concentrations slowly returned to pre-storm levels after the discharge level returned to baseflow. Even though the nitrate concentration of surface water decreased during storms, the average storm nitrate flux was approximately a factor of 3 times greater than the average base flow nitrate. Large quantities of nitrate were quickly transferred during storms due to the large volume of water with low nitrate concentrations flowing in the stream. Insights to nutrient management, particularly considering rates of biological uptake of nitrate, are supported by this more complete understanding of the dynamic flux of streamwater nitrate to coastal waters.
Environmental Science & Technology, 1995
Parameters used to describe the transport of colloids (including bacteria) through porous media e... more Parameters used to describe the transport of colloids (including bacteria) through porous media either implicitly or explicitly account for colloidal particle size but assume that the particles are spheres of uniform size. Bacteria found in soils and in aquifers exhibit a variety of shapes as well as sizes. We sought to determine if there exists a systematic effect of cell shape on the transport of bacteria in columns packed with clean quartz sand. A pulse of resting cells (14 strains of bacteria isolated from aquifers) suspended in an artificial groundwater was passed through a short column. Properties of the bacteria in the influent pulse were compared with those in the eluent from the columns. Cell shape, as quantified by the ratio of cell width to cell length, affects the transport of bacterial cells through porous media. In addition, the distributions of size and shape of cells in the effluent differed from those in the influent suspension with cells in the effluent being smaller and rounder. Short rods with low water contact angles (a measure of cell-surface hydrophobicity) showed the greatest decrease in cell length during passage through short columns.
Bulletin of Environmental Contamination and Toxicology, 1977
Metal ions enter Chesapeake Bay in varying amounts and from a variety of sources. Sources traced ... more Metal ions enter Chesapeake Bay in varying amounts and from a variety of sources. Sources traced to human activities provide at least one half of the Cr, Cu, Cd, and Pb entering the estuary, while at the present time the human contribution to the input of Mn, Fe, Co, Ni, and Zn is somewhat less (HELZ, 1976). Furthermore, it has been established that the impact of such inputs could be felt not only on a local scale but on a regional one as well. In order to ascertain the potential effect of high concentrations of metal ions on the microflora of Chesapeake Bay, an investigation was undertaken to measure the effects of metals on microbial photosynthesis, nitrification, and glucose oxidation in Chesapeake Bay water and sediment. Aerobic, heterotrophic bacterial populations showing resistance to metal ions in water and sediment samples collected from Colgate Creek, (Baltimore Harbor), an area of high metal stress (VILLA and JOHNSON, 1974), and a station in the middle of the ship channel near Chesapeake Beach, an area near the center of the Bay containing much lower metal concentrations than Baltimore Harbor (HELZ, 1976) were enumerated.
Applied and Environmental Microbiology, 1978
Factors associated with accuracy and precision in the enumeration of aquatic aerobic heterotrophs... more Factors associated with accuracy and precision in the enumeration of aquatic aerobic heterotrophs by the spread plate method were evaluated by using a nested analysis of variance experimental design. Variances associated with individual components of the spread plate procedure were isolated, and optimal replications of each step were allocated. A practical scheme for optimal allocation of resources is proposed, consisting of four subsamples and two plates per subsample and yielding a total variance decrease of 70% from a single-subsample, 10-plate series. Data transformation was, in general, unnecessary for intraexperiment or intrasample statistical analysis, whereas interexperiment or intersample comparisons may require transformation of data. Rapid changes in the numbers of organisms in stored water samples were observed that were not reproducible and did not follow detectable trends, with increases or decreases in counts occurring in samples regardless of whether they were stored...
Water Resources Research, 1999
Miscible displacement experiments were performed on intact sand columns ranging from 15 to 60 cm ... more Miscible displacement experiments were performed on intact sand columns ranging from 15 to 60 cm in length to determine whether bacterial deposition varies at the centimeter scale within aquifer sediments. A 1‐pore‐volume pulse of radiolabeled cell suspension was introduced into the columns followed by a 2‐pore‐volume flush of artificial groundwater. The columns were then drained and dissected along the axis of flow. At ∼1‐cm intervals, nine samples were removed for the enumeration of sediment‐associated bacteria. Concentrations of sediment‐associated (deposited) bacteria varied by up to 2 orders of magnitude in the direction perpendicular to flow demonstrating that bacterial deposition cannot be described mechanistically by a single rate coefficient. Incorporation of a distribution of sediment size and porosity values into Monte Carlo simulations indicates that physical heterogeneities are only partially responsible for the observed variability in deposited bacteria. A simple first‐order model (classic filtration theory) adequately described the average spatial distribution of bacteria with depth within the 15‐cm column. For the longer columns, however, the average concentration of deposited bacteria did not decrease exponentially with depth. A second‐order model, modified to include an influent suspension of bacteria consisting of two subpopulations with separate sticking efficiencies (dual‐alpha population), was required to describe the observed decreases of deposited bacteria with depth. A sensitivity analysis was performed with a first‐order dual‐alpha model to understand the effects of an influent suspension with two subpopulations of bacteria on the decrease of deposited bacteria with flow path length. Numerical simulations show that even for small fractions (0.01) of nonsticky bacteria, the decrease in deposited bacteria may deviate substantially from the exponential decrease expected from colloid‐filtration theory. Results from experimental as well as numerical studies demonstrate the importance of column dissections for understanding bacterial deposition in saturated porous media.
Talanta, 1984
Interpreting the redox chemistry of sulphur in aqueous systems requires the analysis of mixtures ... more Interpreting the redox chemistry of sulphur in aqueous systems requires the analysis of mixtures of various sulphoxy anions. Previous methods have been too involved to permit high sample throughout if good quality control is to be maintained. Methods based on ion chromatography have been
Journal of Contaminant Hydrology, 2001
The injection of bacteria in the subsurface has been identified as a potential method for in situ... more The injection of bacteria in the subsurface has been identified as a potential method for in situ cleanup of contaminated aquifers. For high bacterial loadings, the presence of previously deposited bacteria can result in decreased deposition rates-a phenomenon known as blocking. Ž. Miscible displacement experiments were performed on short sand columns ; 5 cm to determine how bacterial deposition on positively charged metal-oxyhydroxide-coated sands is affected by the presence of previously deposited bacteria. Approximately 8 pore volumes of a radiolabeled bacterial suspension at a concentration of ; 1 = 10 9 cells ml y1 were introduced into the columns followed by a 2-pore-volume flush of cell-free buffer. It was found that the presence of Al-and Fe-coated sand increased both deposition rates and maximum fractional surface coverage of bacteria on the sediment surfaces. The effect of grain size on maximum bacterial retention capacity, however, was not significant. Decreasing ionic strength from 10 y1 to 10 y2 M KCl Ž. Ž. resulted in noticeable decreases in sticking efficiency a and maximum surface coverage u max for clean silica sand-results consistent with DLVO theory. In columns containing positively charged Al-and Fe-coated sands, however, changes in a and u due to decreasing ionic max strength were minimal. These findings demonstrate the importance of geochemical controls on the maximum bacterial retention capacity of sands.
Applied and Environmental Microbiology, 1987
Several anaerobic bacteria isolated from the sediments of Contrary Creek, an iron-rich environmen... more Several anaerobic bacteria isolated from the sediments of Contrary Creek, an iron-rich environment, produced magnetite when cultured in combinations but not when cultured alone in synthetic iron oxyhydroxide medium. When glucose was added as a carbon source, the pH of the medium decreased (to 5.5) and no magnetite was formed. When the same growth medium without glucose was used, the pH increased (to 8.5) and magnetite was formed. In both cases, Fe 2+ was released into the growth medium. Geochemical equilibrium equations with E h and pH as master variables were solved for the concentrations of iron and inorganic carbon that were observed in the system. Magnetite was predicted to be the dominant iron oxide formed at high pHs, while free Fe 2+ or siderite were the dominant forms of iron expected at low pHs. Thus, magnetite formation occurs because of microbial alteration of the local E h and pH conditions, along with concurrent reduction of ferric iron (direct biological reduction or a...
Applied and Environmental Microbiology, 1985
One arm of Lake Anna, Va., receives acid mine drainage (AMD) from Contrary Creek (SO 4 2− concent... more One arm of Lake Anna, Va., receives acid mine drainage (AMD) from Contrary Creek (SO 4 2− concentration = 2 to 20 mM, pH = 2.5 to 3.5). Acid-volatile sulfide concentrations, SO 4 2− reduction rates, and interstitial SO 4 2− concentrations were measured at various depths in the sediment at four stations in four seasons to assess the effects of the AMD-added SO 4 2− on bacterial SO 4 2− reduction. Acid-volatile sulfide concentrations were always an order of magnitude higher at the stations receiving AMD than at a control station in another arm of the lake that received no AMD. Summer SO 4 2− reduction rates were also an order of magnitude higher at stations that received AMD than at the control station (226 versus 13.5 mmol m −2 day −1 ), but winter values were inconclusive, probably due to low sediment temperature (6°C). Profiles of interstitial SO 4 2− concentrations at the AMD stations showed a rapid decrease with depth (from 1,270 to 6 μM in the top 6 cm) due to rapid SO 4 2− redu...
Applied and Environmental Microbiology, 1987
The critical assumptions of the dilution method for estimating grazing rates of microzooplankton ... more The critical assumptions of the dilution method for estimating grazing rates of microzooplankton were tested by using a community from the sediment-water interface of Lake Anna, Va. Determination of the appropriate computational model was achieved by regression analysis; the exponential model was appropriate for bacterial growth at Lake Anna. The assumption that the change in grazing pressure is linearly proportional to the dilution factor was tested by analysis of variance with a lack-of-fit test. There was a significant ( P < 0.0001) linear ( P > 0.05) relationship between the dilution factor and time-dependent change in ln bacterial abundance. The assumption that bacterial growth is not altered by possible substrate enrichment in the dilution treatment was tested by amending diluted water with various amounts of dissolved organic carbon (either yeast extract or extracted carbon from lake sediments). Additions of carbon did not significantly alter bacterial growth rates duri...
Applied and Environmental Microbiology, 1994
Understanding the interaction between bacterial cells and solid surfaces is essential to our atte... more Understanding the interaction between bacterial cells and solid surfaces is essential to our attempts to quantify and predict the transport of microbes in groundwater aquifers, whether from the point of view of contamination or from that of bioremediation. The sorption of bacterial cells suspended in groundwater to porous medium grains was examined in batch studies. Bacterial sorption to clean quartz sand yielded equilibrium, linear, adsorption isotherms that varied with the bacterial strain used and the ionic strength of the aqueous solution. Values of K d (the slope of the linear sorption isotherm) ranged from 0.55 to 6.11 ml g -1 , with the greatest sorption observed for the highest groundwater ionic strength. These findings are consistent with the interpretation that an increasingly compressed electrical double layer results in stronger adsorption between the like-charged mineral surface and the bacterial cells. When iron-oxyhydroxide-coated sand was used, however, all of the ad...
Applied and Environmental Microbiology, 1991
Resting-cell suspensions of bacteria isolated from groundwater were added as a pulse to the tops ... more Resting-cell suspensions of bacteria isolated from groundwater were added as a pulse to the tops of columns of clean quartz sand. An artificial groundwater solution (AGW) was pumped through the columns, and bacterial breakthrough curves were established and compared to test the effects of ionic strength of the AGW, cell size (by using strains of similar cell surface hydrophobicity but different size), mineral grain size, and presence of heterogeneities within the porous media on transport of the bacteria. The proportion of cells recovered in the effluent ranged from nearly 90% for AGW of a higher ionic strength (I = 0.0089 versus 0.00089 m), small cells (0.75-micron-diameter spheres versus 0.75 by 1.8-micron rods), and coarse-grained sand (1.0 versus 0.33 mm) to less than 1% for AGW of lower ionic strength, large cells, and fine-grained sand. Differences in the widths of peaks (an indicator of dispersion) were significant only for the cell size treatment. For treatments containing h...
Applied and Environmental Microbiology, 1976
Of 38 pure cultures of microorganisms tested, only one, Pseudomonas stutzeri, was capable of form... more Of 38 pure cultures of microorganisms tested, only one, Pseudomonas stutzeri, was capable of forming dimethylnitrosamine from dimethylamine and nitrite during growth. Resting cells of P. stutzeri, Cryptococcus terreus, Escherichia coli, and Xanthomonas campestris formed dimethylnitrosamine, although no nitrosamine was found in growing cultures of the latter three organisms. No nitrosamine was produced by either growing cultures or resting-cell suspensions of Pseudomonas fragi or Proteus mirabilis. Boiled cells of P. stutzeri, but not those of C. terreus, E. coli, and X. campestris, formed dimethylnitrosamine, and this nitrosamine was also produced by extracts of E. coli cells at pH 5.0.
Geobiology, 2003
17 β-estradiol (E2), one of the natural estrogen compounds, is an endocrine disruptor, and low le... more 17 β-estradiol (E2), one of the natural estrogen compounds, is an endocrine disruptor, and low levels in natural waters can impair the reproductive health of aquatic organisms. Its presence has been reported in animal faecal wastes and some aquatic habitats, including surface waters impacted by intense animal agriculture or sewage contamination. Little is known about its transport in hydrological systems or its persistence in water supplies. We routinely sampled stream and soil water over the growing season in an instrumented 1.2-km 2 agricultural watershed in central Virginia. E2 concentrations in stream water ranged from 0.01 to 0.12 ng mL − 1 ; soilwater values ranged from 0.03 to 0.18 ng mL − 1. The highest concentrations were observed early in the growing season shortly after application of composted poultry litter to the cropped fields, and values decreased both with hydrological transport distance from the cropped field and over the course of the summer. Given the known application rate, E2 must be lost from the soil solution, and we explored biodegradation as a mechanism for this loss. A bacterial consortium cultured from the poultry compost biodegraded E2 in laboratory flasks amended with solutions of 1 : 1 acetate : glucose at concentrations ranging from 0.1 to 10 g L − 1 dissolved organic carbon (DOC), spiked with 1.8 ng mL − 1 E2, and incubated at different temperatures. A loss of 97-98% of the initial E2 occurred within 180 h in experiments at 22 ° C and 28 ° C with 1.0 or 0.1 g L − 1 DOC amendments. Higher DOC concentrations and lower temperatures slowed the rates of reaction, suggesting that more readily available carbon inhibits use of the E2 by degrading microorganisms. The rapid rates of biodegradation in the laboratory incubations are inconsistent with the persistence of E2 in the watershed. This suggests that either the rates of biodegradation are reduced compared with the laboratory experiments or that E2 probably interacts with the components of the natural environment through complexation, sorption or abiotic transformation in the ageing process that leads to diminished bioavailability.
Canadian Journal of Microbiology, 1977
A total of 230 strains of metal-tolerant bacteria from water and sediment samples collected in Ch... more A total of 230 strains of metal-tolerant bacteria from water and sediment samples collected in Chesapeake Bay were isolated on a medium containing cobalt, lead, mercury, or molybdenum. In addition, a set of 71 cultures were simultaneously isolated on glucose tryptone yeast extract agar medium without metals. Twenty-three reference strains were also included in the numerical taxonomy study of these bacteria, bringing the grand total of strains examined to 324. All strains were examined for 112 biochemical, cultural, morphological, and physiological characters. The taxonomic data obtained were analyzed by computer and the simple matching (SSM) and Jaccard (SJ) coefficients were calculated. Clustering achieved by unweighted average linkage is presented and. from sorted similarity matrices and dendrograms, 294 strains, i.e., 97% of the total, were recovered in 12 phenetic groups defined at the 75 to 80% similarity level. Among the strains there were nine phena presumptively identified a...
Soil Biology and Biochemistry, 2001
The relative effectiveness of average-well-color-development-normalized single-point absorbance r... more The relative effectiveness of average-well-color-development-normalized single-point absorbance readings (AWCD) vs the kinetic parameters m m , l, A, and integral (AREA) of the modi®ed Gompertz equation ®t to the color development curve resulting from reduction of a redox sensitive dye from microbial respiration of 95 separate sole carbon sources in microplate wells was compared for a dilution series of rhizosphere samples from hydroponically grown wheat and potato ranging in inoculum densities of 1 £ 10 4 2 4 £ 10 6 cells ml 21. Patterns generated with each parameter were analyzed using principal component analysis (PCA) and discriminant function analysis (DFA) to test relative resolving power. Samples of equivalent cell density (undiluted samples) were correctly classi®ed by rhizosphere type for all parameters based on DFA analysis of the ®rst ®ve PC scores. Analysis of undiluted and 1:4 diluted samples resulted in misclassi®cation of at least two of the wheat samples for all parameters except the AWCD normalized (0.50 abs. units) data, and analysis of undiluted, 1:4, and 1:16 diluted samples resulted in misclassi®cation for all parameter types. Ordination of samples along the ®rst principal component (PC) was correlated to inoculum density in analyses performed on all of the kinetic parameters, but no such in¯uence was seen for AWCD-derived results. The carbon sources responsible for classi®cation differed among the variable types with the exception of AREA and A, which were strongly correlated. These results indicate that the use of kinetic parameters for pattern analysis in CLPP may provide some additional information, but only if the in¯uence of inoculum density is carefully considered.