Assessment of biostimulation and bioaugmentation for removing chlorinated volatile organic compounds from groundwater at a former manufacture plant

Site in a former chemical manufacture plant in China was found contaminated with high level of chlorinated volatile organic compounds (CVOCs). The major contaminants chloroform (CF), 1,2-dichloroethane (1,2-DCA) and vinyl chloride (VC) in groundwater were up to 4.49 × 10⁴, 2.76 × 10⁶ and 4.35 × 10⁴ μg/L, respectively. Ethene and methane were at concentrations up to 2219.80 and 165.85 μg/L, respectively. To test the hypothesis that the CVOCs in groundwater at this site could be removed via biodegradation, biomarker analyses and microcosm studies were conducted. Dehalococcoides 16S rRNA gene and VC-reductase gene vcrA at densities up to 1.5 × 10⁴ and 3.2 × 10⁴ copies/L were detected in some of the groundwater samples, providing strong evidence that dechlorinating bacteria were present in the aquifer. Results from the microcosm studies showed that at moderate concentrations (CF about 4000 μg/L and 1,2-DCA about 100 μg/L), CF was recalcitrant under natural condition but was degraded under biostimulation and bioaugmentation, while 1,2-DCA was degraded under all the three conditions. At high concentration (CF about 1,000,000 μg/L and 1,2-DCA about 20,000 μg/L), CF was recalcitrant under all the three treatments and 1,2-DCA was only degraded under bioaugmentation, indicating that high concentrations of contaminants were inhibitory to the bacteria. Electron donors had influence on the degradation of contaminants. Of the four fatty acids (pyruvate, acetate, propionate and lactate) examined, all could stimulate the degradation of 1,2-DCA at both moderate and high concentrations, whereas only pyruvate and acetate could stimulate the degradation of CF at moderate concentration. In the microcosms, the observed first-order degradation rates of CF and 1,2-DCA were up to 0.12 and 0.11/day, respectively. Results from the present study provided scientific basis for remediating CVOCs contaminated groundwater at the site.     

Infrared Plasmonic Transmission Resonances of Gold Film with Hexagonally Ordered Hole Arrays on ZnSe Substrate

The high fractional open area of metal thin film coatings, with two dimensional, hexagonally ordered, close packed arrays of holes, makes them of interest for the incorporation of plasmonic effects into a variety of optical devices. Gold films with hexagonal patterns of circular holes have been created on ZnSe infrared windows. The films have 2.50 μm diameter holes and a hexagonal lattice parameter of 3.06 μm which places the primary transmission resonances of the ZnSe/gold interface at ~1,400 cm^?1 (7.14 μm) and that of the air/gold interface at ~3,800 cm^?1 (2.63 μm). This geometry produces useful transmission across the whole traditional mid-infrared range. The dispersion of these resonances has been measured by changing the angle of incident light. The data is modeled with explicit momentum matching equations in two different, high symmetry geometries, allowing the effective index of refraction to vary with wavelength. The response of these resonances to the addition of an acetaldehyde coating is described.     

Association of Bacteria with Marine Invertebrates: Implications for Ballast Water Management

Bacteria associated with plankton are of importance in marine bioinvasions and the implementation of ship’s ballast water treatment technologies. In this study, epibiotic and endobiotic bacteria associated with zooplankton, including barnacle nauplii, veliger larvae, and adults of the copepod Oithona sp., were characterized and quantified. Barnacle nauplius and veliger larva harbored ~4.4 × 10⁵ cells ind^?1 whereas Oithona sp. had 8.8 × 10⁵ cells ind^?1. Computation of bacterial contribution based on biovolume indicated that despite being the smallest zooplankton tested, veliger larvae harbored the highest number of bacteria, while barnacle nauplii, the largest of the zooplankton, tested in terms of volume contributed the least. Pulverization of zooplankton led to an increase in bacterial numbers; for example, Vibrio cholerae, which was initially 3.5 × 10³, increased to 5.4 × 10⁵ CFU g^?1; Escherichia coli increased from 5.0 × 10² to 1.3 × 10⁴ CFU g^?1; and Streptococcus faecalis increased from 2.1 × 10² to 2.5 × 10⁵ CFU g^?1, respectively. Pulverized zooplankton was aged in the dark to assess the contribution of bacteria from decaying debris. Aging of pulverized zooplankton led to emergence of Chromobacterium violaceum, which is an opportunistic pathogen in animals and humans.     

Variability of the microbial community in the western Antarctic Peninsula from late fall to spring during a low ice cover year

Although winter conditions play a major role in determining the productivity of the western Antarctic Peninsula (WAP) waters for the following spring and summer, a few studies have dealt with the seasonal variability of microorganisms in the WAP in winter. Moreover, because of regional warming, sea-ice retreat is happening earlier in spring, at the onset of the production season. In this context, this study describes the dynamics of the marine microbial community in the Melchior Archipelago (WAP) from fall to spring 2006. Samples were collected monthly to biweekly at four depths from the surface to the aphotic layer. The abundance and carbon content of bacteria, phytoplankton and microzooplankton were analyzed using flow cytometry and inverted microscopy, and bacterial richness was examined by PCR–DGGE. As expected, due to the extreme environmental conditions, the microbial community abundance and biomass were low in fall and winter. Bacterial abundance ranged from 1.2 to 2.8 × 10⁵ cells ml^?1 showing a slight increase in spring. Phytoplankton biomass was low and dominated by small cells (<2 μm) in fall and winter (average chlorophyll a concentration, Chl-a, of, respectively, 0.3 and 0.13 μg l^?1). Phytoplankton biomass increased in spring (Chl-a up to 1.13 μg l^?1), and, despite potentially adequate growth conditions, this rise was small and phytoplankton was still dominated by small cells (2–20 μm). In addition, the early disappearing of sea-ice in spring 2006 let the surface water exposed to ultraviolet B radiations (UVBR, 280–320 nm), which seemed to have a negative impact on the microbial community in surface waters.     

Abundance and diversity of ammonia-oxidizing archaea in a biological aerated filter process

Ammonia-oxidizing archaea (AOA) represent an important group of ammonia-oxidizing microorganisms that are able to convert ammonia to nitrite, a function which is crucial for the removal of nitrogen from wastewater. In this study, we investigated the abundance and diversity of AOA in a full-scale wastewater treatment plant (WWTP) which used a biological aerated filter (BAF) as the main processing mode. According to the quantitative PCR results, AOA clearly outnumbered ammonia-oxidizing bacteria (AOB) during the whole process. The abundance of AOA amoA genes in the filter layer of BAF was highest with the value varied from 6.32 × 10³ to 3.8 × 10⁴ copies/ng DNA. The highest abundance of AOB amoA genes was 1.32 × 10² copies/ng DNA, recorded in the effluent of the ACTIFLO® settling tank. The ratios of AOA/AOB in the WWTP were maintained at two or three orders of magnitude. Most AOA obtained from the WWTP fell within the Nitrosopumilus cluster. The abundance of AOA and AOB was significantly correlated with ammonium nitrogen concentrations and pH value. The community structure of AOA was significantly influenced by dissolved oxygen concentrations, pH value and chemical oxygen demand.     

Spatiotemporal Variation of Bacterial Assemblages in a Shallow Subtropical Coastal Lagoon in Southern Brazil

A study on the bacterioplankton of Conceição Lagoon (27°34′ S–48°27′ W), Southern Brazil, was carried out in July 2005 (austral winter) and January 2006 (austral summer) to characterize the bacterial spatiotemporal distribution and to determine the heterotrophic and photoautotrophic bacterial dominance in hypoxic/oxic stratified waters. Bacterial abundance increased significantly (p?5 (winter) to 3.21?×?10⁶ cells mL^?1 (summer), heterotrophic coccus/rod-shaped (HCR) cells from 7.00?×?10⁴ to 3.60?×?10⁶ cells mL^?1, and heterotrophic filamentous (HF) bacteria from 2.90?×?10³ to 2.74?×?10⁵ cells mL^?1. Bacterial biovolumes also increased in summer with mean biovolumes of CCY ranging from 0.38 to 1.37 μm³, HCR cells from 0.31 to 1.12 μm³, and HF from 3.32 to 11.34 μm³. Principal component analysis showed that salinity, temperature, and light were the abiotic factors that better explained the temporal variability of bacterial assemblages. Bacterial heterotrophy dominated in the lagoon, excepted by the southern and part of central sector in January 2006, when autotrophic-dominated microbial community occurred. Spatially, bacterial assemblages were influenced by nutrient gradient, oxygen, and salinity with a positive relationship between biovolumes and nutrients and a negative relationship between abundance of coccus cyanobacteria and nutrients. area revealed a singular temporal pattern with hypoxic bottom waters in winter and oxygen-rich waters appearing in summer related with the availability of light and predominant microbes. Thus, oxygen consumption/production is likely to be regulated by the amount of light reaching the bottom, stimulating the production of oxygen by oxygenic phototrophs.     

Vertical Distribution of Ammonia-Oxidizing Archaea and Bacteria in Sediments of a Eutrophic Lake

In order to characterize the vertical variation of abundance and community composition of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in sediments of a eutrophic lake, Lake Taihu, molecular techniques including real-time PCR, clone library, and sequencing were carried out in this study. Abundances of archaeal amoA gene (ranged from 2.34 × 10⁶ to 4.43 × 10⁷ copies [g dry sediment]^?1) were higher than those of bacterial amoA gene (ranged from 5.02 × 10⁴ to 6.91 × 10⁶ copies [g dry sediment]^?1) for all samples and both of them exhibited negative correlations with the increased depths. Diversities of archaeal and bacterial amoA gene increased with the elevated depths. There were no significant variations of AOB community structures derived from different sediment depths, whereas obvious differences were observed for the AOA community compositions. The information acquired in this study would be useful to elucidate the roles of AOA and AOB in the nitrogen cycling of freshwater ecosystems.     

Adhesion study of silicone coatings: the interaction of thickness,modulus and shear rate on adhesion force

Abstract

Interactions between coating thickness, modulus and shear rate on pseudobarnacle adhesion to a platinum-cured silicone coating were studied using a statistical experimental design. A combined design method was used for two mixture components and two process variables. The two mixture components, vinyl end-terminated polydimethylsiloxanes (V21: MW = 6 kg mole^?1 and V35: MW = 4 9.5 kg mole^?1, Gelest Inc.) were mixed at five different levels to vary the modulus. The dry coating thickness was varied from 160 – 740 μm and shear tests were performed at four different shear rates (2, 7, 12, and 22 μm s^?1). The results of the statistical analysis showed that the mixture components were significant factors on shear stress, showing an interaction with the process variable. For the soft silicone coating based on the high molecular weight polydimethylsiloxane (E = 0.08 MPa), shear stress significantly increased as coating thickness decreased, while shear rate slightly impacted shear force especially at 160 μm coating thickness. As the modulus was increased (E = 1.3 MPa), more force was required to detach the pseudobarnacle from the coatings, but thickness and rate dependence on shear stress became less important.     

Effect of Seawater–Sewage Cross-Transplants on Bacterial Metabolism and Diversity

Bioassays experiments were conducted to determine the metabolic and community composition response of bacteria to transplants between relatively pristine coastal seawater and sewage-impacted seawater. There were four treatments: (1) pristine seawater bacteria?+?pristine seawater (Pb?+?Pw), (2) sewage-impacted bacteria?+?sewage-impacted water (Sb?+?Sw), (3) pristine seawater bacteria?+?sewage-impacted water (Pb?+?Sw), and (4) sewage-impacted bacteria?+?pristine seawater (Sb?+?Pw). Sewage-derived DOC was more labile and readily utilized by bacteria, which favored the growth of high nucleic acid (HNA) bacteria, resulting in high bacterial production (BP, 113?±?4.92 to 130?±?15.8 μg C l^?1?day^?1) and low respiration rate (BR, <67?±?11.3 μg C l^?1?day^?1), as well as high bacterial growth efficiency (BGE, 0.68?±?0.09 to 0.71?±?0.05). In contrast, at the relatively pristine site, bacteria utilized natural marine-derived dissolved organic matter (DOM) at the expense of lowering their growth efficiency (BGE, <0.32?±?0.02) with low BP (<62?±?6.3 μg C l^?1?day^?1) and high BR 133?±?14.2 μg C l^?1?day^?1). Sewage DOM input appeared to alter the partitioning of carbon between respiration and production of bacteria, resulting in a shift toward higher BGE, which would not enhance oxygen consumption. Taxonomic classification based on 454 pyrosequencing reads of the 16S rRNA gene amplicons revealed that changes in bacterial community structure occurred when seawater bacteria were transferred to the eutrophic sewage-impacted water. Sewage DOM fueled the growth of Gammma-proteobacteria and Epsilson-proteobacteria and reduced the bacterial richness, but the changes in the community were not apparent when sewage-impacted bacteria were transferred to pristine seawater.     

Depth trends of soil organic matter C:N and 15N natural abundance controlled by association with minerals

Anaerobic ammonium oxidation (anammox) is believed to be an important sink for fixed inorganic nitrogen in terrestrial and aquatic ecosystems, and many studies have reported that macroscale oxic–anoxic interfaces, such as riparian zones, were hotspots of anammox reaction. However, no research has linked microscale interfaces with the anammox process in natural environments. This study provides evidence for the presence of anammox bacteria and potential anammox activity on the suspended sediment (SPS) in the oxic water of the Yellow River. The anammox bacteria in the overlying water were mainly attached to SPS. The abundance of anammox bacteria in the overlying water was positively correlated with SPS concentration (R ² = 0.97, P < 0.01), with abundance ranging from 9.5 × 10² to 1.5 × 10⁴ hydrazine synthase gene copies per g of SPS. Phylogenic analysis of anammox bacteria revealed that the SPS phase was dominated by Candidatus Brocadia. Candidatus Scalindua genera was detected in this study with a conductivity of 1100 μS cm^?1. Moreover, \(^{15} {\text{NH}}_{4}^{ + }\)-amended anaerobic incubation of the overlying water showed that the average potential anammox activity was 0.076 nmol-N L^?1 day^?1. The ¹⁵N labeling simulation experiments demonstrated the occurrence of anammox in the oxic water of the Yellow River. This study suggests that the anammox process at the SPS–water interface might be a non-negligible pathway for the loss of fixed nitrogen in natural freshwaters, but this remains to be determined in further studies.     

Dietary Supplementation of Usnic Acid,an Antimicrobial Compound in Lichens,Does Not Affect Rumen Bacterial Diversity or Density in Reindeer

Reindeer (Rangifer tarandus tarandus) may include large proportions of lichens in their winter diet. These dietary lichens are rich in phenolic secondary compounds, the most well-known being the antimicrobial usnic acid. Previous studies have shown that reindeer host rumen bacteria resistant to usnic acid and that usnic acid is quickly detoxified in their rumen. In the present study, reindeer (n = 3) were sampled before, during, and after usnic acid supplementation to determine the effect on their rumen microbial ecology. Ad libitum intake of usnic acid averaged up to 278 mg/kg body mass. Population densities of rumen bacteria and methanogenic archaea determined by real-time PCR, ranged from 1.36 × 10⁹ to 11.8 × 10⁹ and 9.0 × 10⁵ to 1.35 × 10⁸ cells/g wet weight, respectively, and the two populations did not change significantly during usnic acid supplementation (repeated measures ANOVA) or vary significantly between the rumen liquid and particle fraction (paired t test). Rumen bacterial community structure determined by denaturing gradient gel electrophoresis did not change in response to intake of usnic acid. Firmicutes (38.7 %) and Bacteriodetes (27.4 %) were prevalent among the 16S rRNA gene sequences (n = 62) from the DGGE gels, but representatives of the phyla Verrucomicrobia (14.5 %) and Proteobacteria (1.6 %) were also detected. Rapid detoxification of the usnic acid or resistance to usnic acid may explain why the diversity of the dominant bacterial populations and the bacterial density in the reindeer rumen does not change during usnic acid supplementation.     

The ecological roles of bacterial populations in the surface sediments of coastal lagoon environments in Japan as revealed by quantification and qualification of 16S rDNA

Based on quantification and qualification of bacterial 16S rDNA, we verified the bacterial ecological characteristics of surface sediments of Lakes Shinji and Nakaumi, which are representative of coastal lagoons in Japan. Quantification and qualification of the 16S rDNA sequences was carried out using real time polymerase chain reaction and polymerase chain reaction denaturing gradient gel electrophoresis and non-metric multidimensional scaling, respectively. The results revealed that the copy number per gram of sediment ranged from 8.33 × 10⁸ (Lake Nakaumi) to 1.69 × 10¹¹ (Honjo area), suggesting that bacterial carbon contributed only 0.05–9.64 % of the total carbon content in the samples. Compared with other aquatic environments, these results indicate that sedimentary bacteria are not likely to be important transporters of nutrients to higher trophic levels, or to act as carbon sinks in the lagoons. The bacterial compositions of Lake Shinji and Lake Nakaumi and the Honjo area were primarily influenced by sediment grain sizes and salinity, respectively. Statistical comparisons of the environmental properties suggested that the areas that were oxygen-abundant (Lake Shinji) and at a higher temperature (Honjo area) presented efficient organic matter degradation. The 16S rDNA copy number per gram of carbon and nitrogen showed the same tendency. Consequently, the primary roles of bacteria were degradation and preservation of organic materials, and this was affected by oxygen and temperature. These roles were supported by the bacterial diversity rather than the differences in the community compositions of the sedimentary bacteria in these coastal lagoons.     

Determination of Matrix Pore Size Distribution in Fractured Clayey Till and Assessment of Matrix Migration of Dechlorinating Bacteria

The pore structure and pore size distribution (PSD) in the clayey till matrix from three Danish field sites were investigated by image analysis to assess the matrix migration of dechlorinating bacteria in clayey till. Clayey till samples had a wide range of pore sizes, with diameters of 0.1–100 μm, and two typical peaks of pore sizes were observed in all clayey till samples. A large area fraction of the individual pores centered around 2 μm in diameter, and another fraction centered around 20 μm. In general, the typical macropore sizes (1 μm < D < 30 μm) in clayey tills determined by image analysis account for approximately 30–60% of the total porosity (20–26%), which is within the range of those reported for clayey soils and other clayey deposits in the literature. The pore size, PSD, and interconnectivity of pores in clayey till matrix may play an important role in evaluation of the migration of dechlorinating bacteria between fractures and clayey till matrix. Dechlorinating bacteria are small (0.3–1 μm) and may have the ability to morphologically adapt to space constraints. The results in this paper in combination with recent field data indicate that the migration of dechlorinating bacteria in fractures and into the clayey till matrix is likely, which is of significance for natural and stimulated degradation of chlorinated solvents by reductive dechlorination in clayey tills.     

Choleoeimeria ghaffari n. sp. (Apicomplexa: Eimeriidae) from the gallbladder of Eryx jayakari Boulenger (Serpentes: Boidae) in Saudi Arabia

Choleoeimeria ghaffari n. sp. is described from the gallbladder of Eryx jayakari Boulenger in Saudi Arabia. Oöcysts are tetrasporocystic, cylindroidal, 23 × 14 μm, with a smooth bi-layered wall and length/width ratio of 1.5, without micropyle, oöcyst residuum and polar granule. Sporocysts are subspheroidal to ellipsoidal, 8 × 6 μm, with length/width ratio of 1.4, without Stieda, sub-Stieda and para-Stieda bodies but with sporocyst residuum. Sporozoites are banana-shaped measuring 10 × 1.5 μm. The endogenous development was found to occur in the gallbladder epithelium and the extrahepatic bile ducts. Mature meronts are spheroidal, c.10 μm wide, and suspected to produce 12–16 merozoites. Microgamonts are irregular in shape, 13 × 10 μm, whereas macrogamonts are mostly subspheroidal, c.12 μm wide, with a prominent centrally-located nucleus. Based on oöcyst morphology and the site of endogenous development (epithelium of the gallbladder and bile ducts) the new eimeriid coccidian was placed in the genus Choleoeimeria Paperna & Landsberg, 1989.     

Nitrogen removal through different pathways in an aged refuse bioreactor treating mature landfill leachate

In this study, an aged refuse bioreactor was constructed to remove nitrogen in a mature landfill leachate. The nitrogen removal efficiency and the microbial community composition in the bioreactor were investigated. The results showed that the aged refuse bioreactor removed more than 90 % of total nitrogen in the leachate under the nitrogen loading rate (NLR) of 0.74 g/kg (vs) day, and the total nitrogen removal rate decreased to 62.2 % when NLR increased up to 2.03 g/kg (vs) day. Quantitative polymerase chain reaction results showed that the average cell number of ammonia-oxidizing bacteria in the bioreactor was 1.58?×?10⁸ cells/g, which accounted for 0.41 % of total bacteria. The number of anammox bacteria in the reactor was 1.09?×?10⁸ cells/g, which accounted for 0.27 % of total bacteria. Isotopic ¹⁵N tracing experiments showed that nearly 10 % of nitrogen was removed by anammox. High-throughout 454 pyrosequencing revealed that the predominant bacteria in the bioreactor were Proteobacteria, Chloroflexi, Actinobacteria, Bacteroidetes, and Gemmatimonadetes, including various nitrifiers and denitrifiers with diverse heterotrophic and autotrophic metabolic pathways, supporting that nitrogen was removed through different pathways in this aged refuse bioreactor.     

Quantitative and qualitative study of the bacterial flora of farmed freshwater prawn (Macrobrachium rosenbergii) larvae

Quantitative and qualitative studies of the bacterial flora of farmed freshwater prawn (Macrobrachium rosenbergii) larvae in Saudi Arabia were performed, and isolates identified where possible. Physico‐chemical characteristics, bacterial counts, and the nature of the bacterial flora of larvae rearing tank water, sediment, tank wall surfaces, larval surface, supplied water, and feed were investigated. Bacterial counts ranged from 2.1 ± 1.3 × 10⁵ to 2.2 ± 0.8 × 10⁷ colony forming units (CFU) ml^?1 in tank water; 4.4 ± 0.9 × 10⁷ to 8.3 ± 1.7 ×10⁹ CFU g^?1 in tank sediment; 8.6 ± 1.0 × 10² to 9.8 ±0.7 × 10⁴ CFU cm^?2 on the tank wall surface; 1.3 ± 1.1 × 10⁴ to 7.7 ± 1.6 × 10⁶ CFU per larva surface, 7.9 ± 1.2 × 10⁵ to 5.0 ± 1.5 × 10⁷ CFU g^?1 in washed larval tissue slurries, 9.1 ± 0.7 × 10³ CFU ml^?1 in supplied water, and 2.4 ± 1.9 ×10¹⁰ CFU g^?1 in mixed feed. Fourteen bacterial genera were identified, including Chryseomonas sp., Vibrio spp., Cellulomonas sp., Aeromonas hydrophila, and Pasteurella sp. The tank water and sediment had similar bacteria to those on the prawn larvae. Chryseomonas sp., Cellulomonas sp. and Vibrio sp. were the most dominant species (prevalence >10%) in tank water; Chryseomonas sp., Pseudomonas alcaligenes and Shewanella putrefaciens in the sediment; Ps. alcaligenes and Cellulomonas sp. on the tank wall surface; Chryseomonas sp., and Cellulomonas sp. on the larval surface; and Chryseomonas sp., Vibrio vulnificus, Sh. putrefaciens and V. alginolyticus in the washed larval tissue slurries (prevalence 10%). Pseudomonas alcaligenes, Moraxella sp., Serratia liquefaciens, Gordona sp. and Burkholderia glumae were absent in larvae but identified in the culture water, tank sediment, and tank wall surface. Pseudomonas sp., Chryseomonas sp., Pasteurella sp. and V. alginolyticus were the prevalent bacteria (>12%) in supplied water. The feed contained V. alginolyticus, A. hydrophila and Cellulomonas sp. as the dominant bacteria (>13%). In the culture water and larvae samples, 83% of the feed and supplied water bacteria were identified.     

Active Bacterial Populations and Grazing Impact Revealed by an In Situ Experiment in a Shallow Aquifer

To elucidate bacterial population dynamics in an aquifer, we attempted to reveal the impact of protozoan grazing on bacterial productivity and community structure by an in situ incubation experiment using a diffusion chamber. The abundance and vertical distribution of bacteria and protozoa in the aquifer were revealed using wells that were drilled in a sedimentary rock system in Itako, Ibaraki, Japan. The water column in the wells possessed aerobic and anaerobic layers. Active bacterial populations under the grazing pressure of protozoa were revealed through in situ incubation with grazer eliminating experiment by the filtration. On August 19, 2003, the total number of bacteria (TDC) decreased from 1.5 × 10⁶ cells ml^{? 1} at 2.2 m depth to 3.0 × 10⁵ cells ml^{? 1} at 10 m depth. The relative contribution of the domain Bacteria to TDC ranged between 63% and 84%. Protozoa existed at a density of 4.2 × 10⁴ to 1.9 × 10⁵ cells ml^{? 1} in both aerobic and microaerobic conditions. A grazing elimination experiment in situ for 6 days brought about clearly different bacterial community profiles between the 2.2 m and 10 m samples. The bacterial composition of the initial community was predominantly β- and γ -proteobacteria at 2.2 m, while at 10 m β-, α - and γ -proteobacteria represented 56%, 26% and 13% of the community, respectively. The distribution of bacterial abundance, community composition and growth rates in the subsurface were influenced by grazing as well as by geochemical factors (dissolved oxygen and concentrations of organic carbon, methane and sulfate). Results of the in situ incubation experiment suggested that protozoan grazing contributes significantly to bacterial population dynamics.     

Establishing a laboratory model of dental unit waterlines bacterial biofilms using a CDC biofilm reactor

In this study, a laboratory model to reproduce dental unit waterline (DUWL) biofilms was developed using a CDC biofilm reactor (CBR). Bacteria obtained from DUWLs were filtered and cultured in Reasoner’s 2A (R2A) for 10 days, and were subsequently stored at ?70°C. This stock was cultivated on R2A in batch mode. After culturing for five days, the bacteria were inoculated into the CBR. Biofilms were grown on polyurethane tubing for four days. Biofilm accumulation and thickness was 1.3 × 10⁵ CFU cm^?2 and 10–14 μm respectively, after four days. Bacteria in the biofilms included cocci and rods of short and medium lengths. In addition, 38 bacterial genera were detected in biofilms. In this study, the suitability and reproducibility of the CBR model for DUWL biofilm formation were demonstrated. The model provides a foundation for the development of bacterial control methods for DUWLs.     

Inherent errors of the fixed-frame counting method for corneal endothelial cell density in eye banks

The aim of this work was to analyze the magnitude of inherent errors associated with the fixed-frame counting method for corneal endothelial cell density (ECD) measurements. This technique is common among most eye banks worldwide. Three types of mosaics were used: regular and irregular tessellated mosaics (eight increasing densities ranging from 800 to 3,600 cells/mm² by steps of 400 cells/mm²) generated by a computer, and real mosaics (four specimens) obtained from human corneal endothelium flat mounted and stained with Alizarin red. On the three mosaics, the fixed-frame counting method was applied using a computer program. The ECD was calculated for 3,000 successive random positions from calibrated grids which area ranged from 50 × 50 to 300 × 300 μm² (incremental steps of 25 μm). For each grid, the ECD was expressed either as a single count, a mean of five or a mean of 10 measures. The fixed-frame count was constantly associated with an inherent variability but repeatability increased with larger grid size and ECD. The mean calculated out of 10 measures was the most reliable, but still, we noted ±5 % of residual variability from the real ECD. The 100 × 100 μm² grid manual counts, performed in many eye banks, should be abandoned and upgraded to at least 200 × 200 μm² grid counts. Digital image analysis with a variable frame counting method would be the best alternative.     

Effects of amlodipine and adenosine on coronary haemodynamics: in vivo study and numerical simulation

Amlodipine (AMLO) is a calcium channel blocker with vasodilating properties, in which the specific effects on the coronary circulation are not fully known. Coronary flow velocity–pressure (F/P) curves were obtained at rest and during administration of AMLO (10 mg to 20 mg iv) or adenosine (ADO, 1 mg ic) in 10 normal subjects (six women, age 48 ± 14 years). F/P curves were reproduced in a numerical simulator of systemic and coronary circulations (CARDIOSIM^©) by adjustment of coronary resistance ( > or < 100 μm diameter vessels) and extravascular resistance applied to smaller vessels at endocardial (ENDO), middle and epicardial (EPI) myocardial layers. Best matching of in silico to in vivo curves was achieved by trial and error approach. ADO induced 170% and 250% increase in coronary flow velocity CFV and F/P diastolic slope as compared to 80% and 25–30% increase induced by AMLO, respectively. In the cardiovascular model, AMLO effects were predicted by progressive reduction of>100 μm vessels resistance from EPI to ENDO. ADO effects were mimicked by reducing resistance of both>100 μm and < 100 μm vessels, progressively from EPI to ENDO in the latter. Additional reduction in extravascular resistance avoided to impose a transmural gradient of vasodilating effect for both drugs. Numerical simulation predicts vasodilating effects of AMLO mainly on larger arteries and of ADO on both>and < 100 μm vessels. In vivo F/P loops could be completely reproduced in silico by adding extravascular resistance reduction for both drugs. Numerical simulator is useful tool for exploring the coronary effects of cardioactive drugs.