The effect of surface charge, negative and bipolar ionization on the deposition of airborne bacteria

Aims:  A series of experiments were conducted to evaluate the effect of surface charge and air ionization on the deposition of airborne bacteria.
Methods and Results:  The interaction between surface electrostatic potential and the deposition of airborne bacteria in an indoor environment was investigated using settle plates charged with electric potentials of 0, ±2·5kV and ±5kV. Results showed that bacterial deposition on the plates increased proportionally with increased potential to over twice the gravitational sedimentation rate at +5kV. Experiments were repeated under similar conditions in the presence of either negative or bipolar air ionization. Bipolar air ionization resulted in reduction of bacterial deposition onto the charged surfaces to levels nearly equal to gravitational sedimentation. In contrast, diffusion charging appears to have occurred during negative air ionization, resulting in an even greater deposition onto the oppositely charged surface than observed without ionization.
Conclusions:  Static charges on fomitic surfaces may attract bacteria resulting in deposition in excess of that expected by gravitational sedimentation or simple diffusion. Implementation of bipolar ionization may result in reduction of bacterial deposition.
Significance and Impact of Study:  Fomitic surfaces are important vehicles for the transmission of infectious organisms. This study has demonstrated a simple strategy for minimizing charge related deposition of bacteria on surfaces.     

Effect of bacterial heterogeneity on adhesion to uniform collectors by monoclonal populations

Abstract Transport of bacteria over significant distances through aquifer sediments occurs primarily among bacteria with low affinity for sediment materials. Bacterial affinity for a uniform collector surface has been represented quantitatively by a collision efficiency (α), defined as the fraction of colliding cells that adhere to the collector surface. Using a new method for estimating α during advective transport of monoclonal bacterial populations through a uniform bed of 40-μm borosilicate glass spheres, we found that α decreased 10-fold over a bed depth of only 1 cm. Depth-dependent differences in α were not related to variation in bacterial size or intra-strain genetic variation. Intra-population heterogeneity in biocolloid-collector affinity may be important determinant of subsurface bacterial transport characteristics, with critical implications for pathogen transport and dispersal of bacteria for the remediation of hazardous waste.     

Diffusion-limited binding explains binary dose response for local arterial and tumour drug delivery

Background:  Local drug delivery has transformed medicine, yet it remains unclear how drug efficacy depends on physicochemical properties and delivery kinetics. Most therapies seek to prolong release, yet recent studies demonstrate sustained clinical benefit following local bolus endovascular delivery.
Objectives:  The purpose of the current study was to examine interplay between drug dose, diffusion and binding in determining tissue penetration and effect.
Methods:  We introduce a quantitative framework that balances dose, saturable binding and diffusion, and measured the specific binding parameters of drugs to target tissues.
Results:  Model reduction techniques augmented by numerical simulations revealed that impact of saturable binding on drug transport and retention is determined by the magnitude of a binding potential, B_p , ratio of binding capacity to product of equilibrium dissociation constant and accessible tissue volume fraction. At low B_p (< 1), drugs are predominantly free and transport scales linearly with concentration. At high B_p (> 40), drug transport exhibits threshold dependence on applied surface concentration.
Conclusions:  In this paradigm, drugs and antibodies with large B_p penetrate faster and deeper into tissues when presented at high concentrations. Threshold dependence of tissue transport on applied surface concentration of paclitaxel and rapamycin may explain threshold dose dependence of in vivo biological efficacy of these drugs.     

Alterations in Adhesion, Transport, and Membrane Characteristics in an Adhesion-Deficient Pseudomonad

A stable adhesion-deficient mutant of Burkholderia cepacia G4, a soil pseudomonad, was selected in a sand column assay. This mutant (ENV435) was compared to the wild-type strain by examining the adhesion of the organisms to silica sand and their transport through two aquifer sediments that differed in their sand, silt, and clay contents. We compared the longitudinal transport of the wild type and the adhesion mutant to the transport of a conservative chloride tracer in 25-cm-long glass columns. The transport of the wild-type strain was severely retarded compared to the transport of the conservative tracer in a variety of aquifer sediments, while the adhesion mutant and the conservative tracer traveled at similar rates. An intact sediment core study produced similar results; ENV435 was transported at a faster rate and in much greater numbers than G4. The results of hydrophobic interaction chromatography revealed that G4 was significantly more hydrophobic than ENV435, and polyacrylamide gel electrophoresis revealed significant differences in the lipopolysaccharide O-antigens of the adhesion mutant and the wild type. Differences in this cell surface polymer may explain the decreased adhesion of strain ENV435.     

Seasonal and spatial distribution of dissolved and particulate organic carbon and bacteria in the bank of an impounding reservoir on the Enns River, Austria

1. Interstitial bacterial abundance, production and ectoenzyme activity were investigated over an annual cycle in an Austrian river when infiltration of oligotrophic river water into a river-bank was artificially enhanced. These microbial parameters were related to porewater chemistry and the concentration of particulate (POC) and dissolved organic carbon (DOC).
2. Porewater chemistry reflected the hydrodynamic mixing of infiltrating river water with riparian groundwater. Seasonal fluctuations in the microbial parameters resulted mainly from changes in temperature and organic matter supply. Seasonal change in porewater chemistry in the river-bank was detectable laterally only within the first metre of the sediment and decreased rapidly with increasing distance from the sediment–water interface.
3. The DOC concentration decreased only slightly during lateral transport through the aquifer, while total organic carbon (TOC) concentration as well as abundance and activity of interstitial bacteria were reduced by up to one order of magnitude within the top metre of the sediment. Retention of incoming particulate matter structured the lateral distribution pattern of TOC concentration. The POC and not the DOC pool was the main source of carbon for interstitial bacteria and, therefore, the quality of POC determines the distribution of microbial metabolism within the riparian zone.     

Inactivation of Mycobacterium avium ssp. paratuberculosis in milk by UV treatment

Aims:  To determine the effect of UV radiation on the viability of two strains of Mycobacterium avium ssp. paratuberculosis (Map) inoculated into milk.
Methods and Results:  Mycobacterium avium ssp. paratuberculosis in a ultra heat treated milk matrix was subjected to increasing doses of UV-C radiation from 0 to 1836 mJ ml⁻¹ using a pilot-scale UV reactor (20 l capacity). Survival of Map was monitored by culture on Herrold's egg yolk medium, Middlebrook 7H10 medium and the FASTPlaque TB™ phage assay. Differences in sensitivity to UV treatment were observed between strains, however, at 1000 mJ ml⁻¹ a Map kill rate of 0·1–0·6 log₁₀ was achieved regardless of strain used or method employed to enumerate Map. Although the inactivation trend was similar on the culture and phage assay, the former gave a consistently higher viable count.
Conclusions:  The use of UV radiation alone does not represent an alternative to current pasteurization regimes for a large reduction in viable Map in milk.
Significance and Impact of the Study:  To the authors' knowledge the work here represents the first pilot-scale UV treatment process used to assess UV efficacy to inactivate Map in milk. The results are similar to those obtained with a laboratory-scale process indicating the difficulties associated with UV treatment of an opaque liquid and the recalcitrance of Map towards inimical treatments.     

Temporal variation in the drift of plant litter and propagules in a small boreal river

SUMMARY 1. Rivers are linear ecosystems across landscapes with an effective transport of organisms, sediment and organic matter. Dispersal is studied mostly during single events and for single species, and there is little knowledge on how the drift of plant litter and propagules varies within and between years for entire communities.
2. We used floating traps for collecting waterborne plant litter and propagules in a small boreal river over 2 years. We installed the traps at four different locations along the river, and emptied them at least once a week during the ice-free season. We analysed propagule content by sorting and identifying species and through germination tests on bare soil.
3. In total, we recorded at least 54 taxa in the samples, and the highest density recorded in one sample was 5000 propagules per 100 g litter (dry weight). Large temporal variations in litter and propagule transport were revealed, both within and between years.
4. The longitudinal pattern was consistent between years, with an increasing mass of litter and number of propagule taxa downstream. The results highlight the importance of the temporal and longitudinal dimensions in river management.     

Enhancing Transport of Hydrogenophagaflava ENV735 for Bioaugmentation of Aquifers Contaminated with Methyl tert-Butyl Ether

The gasoline oxygenate methyl tert-butyl ether (MTBE) has become a widespread contaminant in groundwater throughout the United States. Bioaugmentation of aquifers with MTBE-degrading cultures may be necessary to enhance degradation of the oxygenate in some locations. However, poor cell transport has sometimes limited bioaugmentation efforts in the past. The objective of this study was to evaluate the transport characteristics of Hydrogenophaga flava ENV735, a pure culture capable of growth on MTBE, and to improve movement of the strain through aquifer solids. The wild-type culture moved only a few centimeters in columns of aquifer sediment. An adhesion-deficient variant (H. flava ENV735:24) of the wild-type strain that moved more readily through sediments was obtained by sequential passage of cells through columns of sterile sediment. Hydrophobic and electrostatic interaction chromatography revealed that the wild-type strain is much more hydrophobic than the adhesion-deficient variant. Electrophoretic mobility assays and transmission electron microscopy showed that the wild-type bacterium contains two distinct subpopulations, whereas the adhesion-deficient strain has only a single, homogeneous population. Both the wild-type strain and adhesion-deficient variant degraded MTBE, and both were identified by 16S rRNA analysis as pure cultures of H. flava. The effectiveness of surfactants for enhancing transport of the wild-type strain was also evaluated. Many of the surfactants tested were toxic to ENV735; however, one nonionic surfactant, Tween 20, enhanced cell transport in sand columns. Improving microbial transport may lead to a more effective bioaugmentation strategy for MTBE-contaminated sites where indigenous oxygenate degraders are absent.     

Faecal indicator bacteria enumeration in beach sand: a comparison study of extraction methods in medium to coarse sands

Aims:  The absence of standardized methods for quantifying faecal indicator bacteria (FIB) in sand hinders comparison of results across studies. The purpose of the study was to compare methods for extraction of faecal bacteria from sands and recommend a standardized extraction technique.
Methods and Results:  Twenty-two methods of extracting enterococci and Escherichia coli from sand were evaluated, including multiple permutations of hand shaking, mechanical shaking, blending, sonication, number of rinses, settling time, eluant-to-sand ratio, eluant composition, prefiltration and type of decantation. Tests were performed on sands from California, Florida and Lake Michigan. Most extraction parameters did not significantly affect bacterial enumeration. anova revealed significant effects of eluant composition and blending; with both sodium metaphosphate buffer and blending producing reduced counts.
Conclusions:  The simplest extraction method that produced the highest FIB recoveries consisted of 2 min of hand shaking in phosphate-buffered saline or deionized water, a 30-s settling time, one-rinse step and a 10 : 1 eluant volume to sand weight ratio. This result was consistent across the sand compositions tested in this study but could vary for other sand types.
Significance and Impact of the Study:  Method standardization will improve the understanding of how sands affect surface water quality.     

Enhancing transport of hydrogenophaga flava ENV735 for bioaugmentation of aquifers contaminated with methyl tert-butyl ether

The gasoline oxygenate methyl tert-butyl ether (MTBE) has become a widespread contaminant in groundwater throughout the United States. Bioaugmentation of aquifers with MTBE-degrading cultures may be necessary to enhance degradation of the oxygenate in some locations. However, poor cell transport has sometimes limited bioaugmentation efforts in the past. The objective of this study was to evaluate the transport characteristics of Hydrogenophaga flava ENV735, a pure culture capable of growth on MTBE, and to improve movement of the strain through aquifer solids. The wild-type culture moved only a few centimeters in columns of aquifer sediment. An adhesion-deficient variant (H. flava ENV735:24) of the wild-type strain that moved more readily through sediments was obtained by sequential passage of cells through columns of sterile sediment. Hydrophobic and electrostatic interaction chromatography revealed that the wild-type strain is much more hydrophobic than the adhesion-deficient variant. Electrophoretic mobility assays and transmission electron microscopy showed that the wild-type bacterium contains two distinct subpopulations, whereas the adhesion-deficient strain has only a single, homogeneous population. Both the wild-type strain and adhesion-deficient variant degraded MTBE, and both were identified by 16S rRNA analysis as pure cultures of H. flava. The effectiveness of surfactants for enhancing transport of the wild-type strain was also evaluated. Many of the surfactants tested were toxic to ENV735; however, one nonionic surfactant, Tween 20, enhanced cell transport in sand columns. Improving microbial transport may lead to a more effective bioaugmentation strategy for MTBE-contaminated sites where indigenous oxygenate degraders are absent.     

Interaction effects of fish, nutrients, mixing and sediments on autotrophic picoplankton and algal composition

1. We examined the effects of nutrients, turbulent mixing, mosquitofish, Gambusia affinis Baird and Girard and sediments on algal composition, algal biomass and autotrophic picoplankton (APP) abundance in a 6-week experiment of factorial design in twenty-four 5-m³ outdoor mesocosms during late autumn 1995.
2. Turbulent mixing decreased surface temperature and increased turbidity, which also was increased by the addition of sediments. Total algal biomass was significantly enhanced by nutrients and mixing, and decreased by the sediment treatment. In the mixing × nutrient treatment, algal biomass increased more than expected from the individual effects, while the fish × mixing and mixing × sediment treatments increased algal biomass less than expected.
3.  Cryptomonas (cryptomonad) blooms were observed in the unmixed, high nutrient treatment; Synedra (diatom) blooms were observed in the high nutrient, high sediment treatment; Ulothrix (green algae) blooms were observed in the mixed, high nutrient, low sediment treatment.
4. Eukaryotic APP abundances were increased by sediment addition and by turbulent mixing, and increased synergistically by mixing × sediment and mixing × nutrient interactions. Prokaryotic APP abundances were decreased by nutrient enhancement and by a mixing × nutrient interaction. There were no main effects of fish on APP abundance, but fish were involved in some of the two–way interactions.
5. The large number of significant interaction effects indicates that APP and other phytoplankton are regulated by a complex set of interdependent factors which should be considered simultaneously in studies of phytoplankton population dynamics and community composition.     

Estimation of the in-situ settling velocity of particles in lakes using a time series sediment trap

SUMMARY 1. We outline a simple method for estimating the in-situ settling velocity of particles in wind disturbed lakes. The total sedimentation rate (primary and secondary sedimentation) was measured during storm events in two lakes using a time series sediment trap.
2. The sediment trap had 12 sample bottles which were programmed to open for periods of 3–4 h, giving total deployment times ranging from 36 to 48 h.
3. Wave mixed layer theory was used to infer if and when sediment resuspension occurred and the first order rate equation was used to estimate the settling velocity of resuspended particles.
4. The settling velocity during three resuspension events in Lough Neagh and one in Lough Macnean were 34.3, 29.5, 24.1 and 77.3 m day⁻¹, respectively. These are similar to values obtained using recent in-situ video imaging in marine environments, but much larger than previous lake sediment trap studies.     

Inbreeding depression and its effect on intrinsic population dynamics in engraver beetles

Abstract.  1. Phloem-feeding bark beetles (Coleoptera: Curculionidae, Scolytinae) generally disperse before mating, leading to expectations of outbreeding. New York and British Columbia populations of engraver beetles ( Ips pini ) were tested for inbreeding depression using different methods. Among several traits measured, only the number of offspring surviving to adulthood was strongly reduced by inbreeding.
2. There was no evidence of avoidance of inbreeding depression in two possible mechanisms considered: differential male and female emergence times within full sib broods, and early termination of brood construction in forced sib mating.
3. Sib-mated females lay more eggs and have longer galleries than those in outbred crosses, despite a low rate of survival to adulthood for such eggs. This difference may be due to the ability of engraver beetles to assess crowding in broods as larvae begin to feed, and allows partial compensation for the effects of inbreed depression.
4. Population models assuming density-dependent generational effects were modified to account for inbreeding depression. Inbreeding depression makes populations less prone to cyclical behaviour, particularly at lower carrying capacities.
5. Inbreeding depression has not been previously measured in scolytids, nor has inbreeding-related behaviour been explicitly considered outside of exclusively inbreeding tribes.     

Mixed aerobic and anaerobic microbial communities in benzene-contaminated groundwater

Aims:  To investigate the factors affecting benzene biodegradation and microbial community composition in a contaminated aquifer.
Methods and Results:  We identified the microbial community in groundwater samples from a benzene-contaminated aquifer situated below a petrochemical plant. Eleven out of twelve groundwater samples with in situ dissolved oxygen concentrations between 0 and 2·57 mg l⁻¹ showed benzene degradation in aerobic microcosm experiments, whereas no degradation in anaerobic microcosms was observed. The lack of aerobic degradation in the remaining microcosm could be attributed to a pH of 12·1. Three groundwaters, examined by 16S rRNA gene clone libraries, with low in situ oxygen concentrations and high benzene levels, each had a different dominant aerobic (or denitrifying) population, either Pseudomonas , Polaromonas or Acidovorax species. These groundwaters also had syntrophic organisms, and aceticlastic methanogens were detected in two samples. The alkaline groundwater was dominated by organisms closely related to Hydrogenophaga .
Conclusions:  Results show that pH 12·1 is inimical to benzene biodegradation, and that oxygen concentrations below 0·03 mg l⁻¹ can support aerobic benzene-degrading communities.
Significance and Impact of the Study:  These findings will help to guide the treatment of contaminated groundwaters, and raise questions about the extent to which aerobes and anaerobes may interact to effect benzene degradation.     

Pilot- and bench-scale testing of faecal indicator bacteria survival in marine beach sand near point sources

Aim:  Factors affecting faecal indicator bacteria (FIB) and pathogen survival/persistence in sand remain largely unstudied. This work elucidates how biological and physical factors affect die-off in beach sand following sewage spills.
Methods and Results:  Solar disinfection with mechanical mixing was pilot-tested as a disinfection procedure after a large sewage spill in Los Angeles. Effects of solar exposure, mechanical mixing, predation and/or competition, season, and moisture were tested at bench scale. First-order decay constants for Escherichia coli ranged between −0·23 and −1·02 per day, and for enterococci between −0·5 and −1·0 per day. Desiccation was a dominant factor for E. coli but not enterococci inactivation. Effects of season were investigated through a comparison of experimental results from winter, spring, and fall.
Conclusions:  Moisture was the dominant factor controlling E. coli inactivation kinetics. Initial microbial community and sand temperature were also important factors. Mechanical mixing, common in beach grooming, did not consistently reduce bacterial levels.
Significance and Impact of the Study:  Inactivation rates are mainly dependent on moisture and high sand temperature. Chlorination was an effective disinfection treatment in sand microcosms inoculated with raw influent.     

When time is of the essence: choosing a currency for prey-handling costs

1.  Heartbeat rate was measured in shore crabs Carcinus maenas (L.) feeding on mussels Mytilus edulis L. in order to estimate the energetic cost of handling prey and to assess the relative importance of energy and time as costing currencies.
2.  Energetic handling costs represented approximately 2% of corresponding gains.
3.  The tendency of profitability (gain per unit handling time) to increase with prey size was weakened by including energetic handling costs.
4.  Time was judged to be a more appropriate currency than energy for costing prey-handling behaviour.
5.  The importance of time as a costing currency, either through the principle of lost opportunity or through exposure to mortality risk, may extend to other behavioural systems, including aggression.     

Application of microbial source tracking methods in a Gulf of Mexico field setting

Aims:  Microbial water quality and possible human sources of faecal pollution were assessed in a Florida estuary that serves shellfishing and recreational activities.
Methods and Results:  Indicator organisms (IO), including faecal coliforms, Escherichia coli and enterococci, were quantified from marine and river waters, sediments and oysters. Florida recreational water standards were infrequently exceeded (6–10% of samples); however, shellfishing standards were more frequently exceeded (28%). IO concentrations in oysters and overlaying waters were significantly correlated, but oyster and sediment IO concentrations were uncorrelated. The human-associated esp gene of Enterococcus faecium was detected in marine and fresh waters at sites with suspected human sewage contamination. Lagrangian drifters, used to determine the pathways of bacterial transport and deposition, suggested that sediment deposition from the Ochlockonee River contributes to frequent detection of esp at a Gulf of Mexico beach.
Conclusions:  These data indicate that human faecal pollution affects water quality in Wakulla County and that local topography and hydrology play a role in bacterial transport and deposition.
Significance and Impact of the Study:  A combination of IO enumeration, microbial source tracking methods and regional hydrological study can reliably inform regulatory agencies of IO sources, improving risk assessment and pollution mitigation in impaired waters.     

Rates of ammonia release from sediments by chironomid larvae

SUMMARY. 1. Microcosms of Lake Balaton mud and sterilized sand and aerated water were used to evaluate ammonia increments in the overlying water as influenced by chironomid density and temperature. In the two approaches, the effects of sediment disturbance and metabolic excretion of chironomids were measured.
2. The activity of larvae increased the ammonia content of the overlying water at temperatures above 10°C. A rise of temperature to 20°C resulted in a 5–20-fold increase in ammonia release in both systems with chironomids.
3. At 10°C combined effects of sediment disturbance and of excretion produced lower release rates than did excretion rates alone (mud-water v. sand-water treatments). At higher temperatures (15 and 20°C) release rates of ammonia by sediment disturbance plus excretion were higher than excretion rates alone. Ammonia excretion contributed significantly to the total release at each temperature.
4. Metabolic mineralization of nitrogen compounds appears to be an important mechanism contributing to nitrogen regeneration from aerobic lake sediments. High N:P ratio (14:1) of chironomid excretion materials supports this interpretation.     

Effects of land cover on sediment regime and fish assemblage structure in four southern Appalachian streams

SUMMARY 1. We examined the relationship between catchment land cover, sediment regime and fish assemblage structure in four small streams in the upper Little Tennessee River basin of North Carolina. Study streams drained similar sized catchments (17–31 km²) with different fractions of non-forested land cover. Non-forested land cover was <3% in two 'reference' streams, whereas it was 13 and 22% in two 'disturbed' streams. Land cover data were compared with sediment transport data (suspended and bedload), benthic habitat data (embeddedness, substratum composition and coverage of fines) and fishes collected in autumn 1997.
2. Suspended sediment concentration was significantly higher in disturbed streams during both baseflow and stormflow. During baseflow disturbed streams nearly always exceeded 10 nephelometric turbidity units (NTU), whereas reference streams never exceeded this threshold. The difference in suspended sediment concentration between reference and disturbed streams was more consistent at baseflow than at stormflow. Therefore, baseflow turbidity may be a useful indicator of potential stream degradation.
3. Disturbed sites had five- to nine-fold more bedload transport than reference sites. Both embeddedness and streambed instability increased with increasing non-forested land cover.
4. Relative abundance of fishes requiring clean cobble/gravel substratum for spawning was lower in disturbed streams, whereas relative abundance of mound-building cyprinids, their nest associates and fishes that excavate nests in soft sediments (centrarchids) was higher. Relative abundance of fishes spawning in benthic crevices and gravel (BC + G) declined as the proportion of non-forested land cover increased. This study supports growing evidence that human-induced sedimentation alters stream fish assemblages.     

Geomorphic thresholds in riverine landscapes

1. Rivers are subject to thresholds of several types that define significant changes in processes and morphology and delimit distinctive riverine landscapes and habitats. Thresholds are set by the conditions that govern river channel process and form, amongst which the most important are the flow regime, the quantity and calibre of sediment delivered to the channel, and the topographic setting (which determines the gradient of the channel). These factors determine the sediment transport regime and the character of alluvial deposits along the channel.
2. Changes occur systematically along the drainage system as flow, gradient and sediment character change, so a characteristic sequence of morphological and habitat types – hence of riverine landscapes – can be described from uplands to distal channels. The sequence is closely associated with stream competence to move sediment and with bank stability.
3. The paper proposes a first order classification of river channel and landscape types based on these factors. The riverine landscape is affected seasonally by flow thresholds, and further seasonal thresholds in northern rivers are conditioned by the ice regime.
4. It is important to understand geomorphic thresholds in rivers not only for the way they determine morphology and habitat, but because human activity can precipitate threshold crossings which change these features significantly, through either planned or inadvertent actions. Hence, human actions frequently dictate the character of the riverine landscape.