Kinetic and phylogenetic characterization of an anaerobic dechlorinating microbial community

The reductive dechlorination (RD) of tetrachloroethene (PCE) to vinyl chloride (VC) and, to a lesser extent, to ethene (ETH) by an anaerobic microbial community has been investigated by studying the processes and kinetics of the main physiological components of the consortium. Molecular hydrogen, produced by methanol-utilizing acetogens, was the electron donor for the PCE RD to VC and ETH without forming any appreciable amount of other chlorinated intermediates and in the near absence of methanogenic activity. The microbial community structure of the consortium was investigated by preparing a 1 6S rDNA clone library and by fluorescence in situ hybridization (FISH). The PCR primers used in the clone library allowed the harvest of 16SrDNA from both bacterial and archaeal members in the community. A total of 616 clones were screened by RFLP analysis of the clone inserts followed by the sequencing of RFLP group representatives and phylogenetic analysis. The clone library contained sequences mostly from hitherto undescribed bacteria. No sequences similar to those of the known RD bacteria like 'Dehalococcoides ethenogenes' or Dehalobacter restrictus were found in the clone library, and none of these bacteria was present in the RD consortium according to FISH. Almost all clones fell into six previously described phyla of the bacterial domain, with the majority (56(.)6%) being deep-branching members of the Spirochaetes phylum. Other clones were in the Firmicutes phylum (18(.)5%), the Chloroflexi phylum (16(.)4%), the Bacteroidetes phylum (6(.)3%), the Synergistes genus (11(.)1%) and a lineage that could not be affiliated with existing phyla (11(.)1%). No archaeal clones were found in the clone library. Owing to the phylogenetic novelty of the microbial community with regard to previously cultured microorganisms, no specific microbial component(s) could be hypothetically affiliated with the RD phenotype. The predominance of Spirochaetes in the microbial consortium, the main group revealed by clone library analysis, was confirmed by FISH using a purposely developed probe.

Microscale structure and function of anaerobic-aerobic granules containing glycogen accumulating organisms

The spatial arrangement and metabolic activity of 'Candidatus Competibacter phosphatis' was investigated in granular sludge from an anaerobic-aerobic sequencing batch reactor enriched for glycogen-accumulating organisms. In this process, the electron donor (acetate) and the electron acceptor (oxygen) were supplied sequentially in each phase. The organism, identified by fluorescence in situ hybridisation, was present throughout the granules; however, metabolic activity was limited to a 100-mum-thick layer immediately below the surface of the granules. To investigate the cause of this, oxygen microsensors and a novel microscale biosensor for volatile fatty acids were used in conjunction with chemical staining for intracellular storage polymers. It was found that the limited distribution of activity was caused by mass transport limitation of oxygen into the granules during the aerobic phase. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.

A dynamic mathematical model for sequential leach bed anaerobic digestion of organic fraction of municipal solid waste

A mathematical model that describes the operation of a sequential leach bed process for anaerobic digestion of organic fraction of municipal solid waste (MSW) is developed and validated. This model assumes that ultimate mineralisation of the organic component of the waste occurs in three steps, namely solubilisation of particulate matter, fermentation to volatile organic acids (modelled as acetic acid) along with liberation of carbon dioxide and hydrogen, and methanogenesis from acetate and hydrogen. The model incorporates the ionic equilibrium equations arising due to dissolution of carbon dioxide, generation of alkalinity from breakdown of solids and dissociation of acetic acid. Rather than a charge balance, a mass balance on the hydronium and hydroxide ions is used to calculate pH. The flow of liquid through the bed is modelled as occurring through two zones-a permeable zone with high flushing rates and the other more stagnant. Some of the kinetic parameters for the biological processes were obtained from batch MSW digestion experiments. The parameters for flow model were obtained from residence time distribution studies conducted using tritium as a tracer. The model was validated using data from leach bed digestion experiments in which a leachate volume equal to 10% of the fresh waste bed volume was sequenced. The model was then tested, without altering any kinetic or flow parameters, by varying volume of leachate that is sequenced between the beds. Simulations for sequencing/recirculating 5 and 30% of the bed volume are presented and compared with experimental results. (C) 2002 Elsevier Science B.V. All rights reserved.

Diode laser treatment of pre-threshold and threshold retinopathy of prematurity

Purpose: Retinopathy of prematurity (ROP) is a sight-threatening condition of premature infants. This study aimed to investigate the efficacy of diode laser photocoagulation in the treatment of pre-threshold and threshold ROP. Methods: A retrospective review was conducted of patients who underwent diode laser treatment for ROP by one author (GAG) from 1992 to 2000. During this time, 2137 babies

The influence of substrate kinetics on the microbial community structure in granular anaerobic biomass

The development of a strong, active granular sludge bed is necessary for optimal operation of upflow anaerobic sludge blanket reactors. The microbial and mechanical structure of the granules may have a strong influence on desirable properties such as growth rate, settling velocity and shear strength. Theories have been proposed for granule microbial structure based on the relative kinetics of substrate degradation, but contradict some observations from both modelling and microscopic studies. In this paper, the structures of four granule types were examined from full-scale UASB reactors, treating wastewater from a cannery, a slaughterhouse, and two breweries. Microbial structure was determined using fluorescence in situ hybridisation probing with 16S rRNA-directed oligonucleotide probes, and superficial structure and microbial density (volume occupied by cells and microbial debris) assessed using scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The granules were also modelled using a distributed parameter biofilm model, with a previously published biochemical model structure, biofilm modelling approach, and model parameters. The model results reflected the trophic structures observed, indicating that the structures were possibly determined by kinetics. Of particular interest were results from simulations of the protein grown granules, which were predicted to have slow growth rates, low microbial density, and no trophic layers, the last two of which were reflected by microscopic observations. The primary cause of this structure, as assessed by modelling, was the particulate nature of the wastewater, and the slow rate of particulate hydrolysis, rather than the presence of proteins in the wastewater. Because solids hydrolysis was rate limiting, soluble substrate concentrations were very low (below Monod half saturation concentration), which caused low growth rates. (C) 2003 Elsevier Ltd. All rights reserved.

Issues in boys' education: A question of teacher threshold knowledges?

This paper explores the effects of specific teacher threshold knowledges about boys and gender on the implementation of a so-called 'boy friendly' curriculum at one junior secondary high school in Australia. Through semi-structured inter-views with selected staff at the school, it examines the normalizing assumptions and 'truth claims' about boys, as gendered subjects, which drive the pedagogical impetus for such a curriculum initiative. This research raises crucial questions about the need for the formulation of both school and governmental policy grounded in sound research-based knowledge about the social construction of gender and its impact on the lives of both boys and girls and their experiences of schooling. This is crucial, we argue, in light of the recent parliamentary report on boys' education in Australia which rejects gender theorizing and given the failure of key staff in the research school to interrogate the binary ways in which masculinity and femininity are socially constructed and institutionalized in schools through a particular 'gender regime'. While some good things are happening in the research school, the failure to acknowledge the social construction of gender means that ultimately the school's programs cannot be successful.

The relationship of adult attachment to emotion, catastrophizing, control, threshold and tolerance, in experimentally-induced pain

Although insecure attachment has been associated with a range of variables linked with problematic adjustment to chronic pain, the causal direction of these relationships remains unclear. Adult attachment style is, theoretically, developmentally antecedent to cognitions, emotions and behaviours (and might therefore be expected to contribute to maladjustment). It can also be argued, however, that the experience of chronic pain increases attachment insecurity. This project examined this issue by determining associations between adult attachment characteristics, collected prior to an acute (coldpressor) pain experience, and a range of emotional, cognitive, pain tolerance, intensity and threshold variables collected during and after the coldpressor task. A convenience sample of 58 participants with no history of chronic pain was recruited. Results demonstrated that attachment anxiety was associated with lower pain thresholds; more stress, depression, and catastrophizing; diminished perceptions of control over pain; and diminished ability to decrease pain. Conversely, secure attachment was linked with lower levels of depression and catastrophizing, and more control over pain. Of particular interest were findings that attachment style moderated the effects of pain intensity on the tendency to catastrophize, such that insecurely attached individuals were more likely to catastrophize when reporting high pain intensity. This is the first study to link attachment with perceptions of pain in a pain-free sample. These findings cast anxious attachment as a vulnerability factor for chronic pain following acute episodes of pain, while secure attachment may provide more resilience. (c) 2006 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.

Antibiotic susceptibilities of Pseudomonas aeruginosa isolates derived from patients with cystic fibrosis under aerobic, anaerobic, and biofilm conditions

Recent studies have determined that Pseudomonas aeruginosa can live in a biofilm mode within hypoxic mucus in the airways of patients with cystic fibrosis (CF). P. aeruginosa grown under anaerobic and biofilm conditions may better approximate in vivo growth conditions in the CF airways, and combination antibiotic susceptibility testing of anaerobically and biofilm-grown isolates may be more relevant than traditional susceptibility testing under planktonic aerobic conditions. We tested 16 multidrug-resistant isolates of P. aeruginosa derived from CF patients using multiple combination bactericidal testing to compare the efficacies of double and triple antibiotic combinations against the isolates grown under traditional aerobic planktonic conditions, in planktonic anaerobic conditions, and in biofilm mode. Both anaerobically grown and biofilm-grown bacteria were significantly less susceptible (P < 0.01) to single and combination antibiotics than corresponding aerobic planktonically grown isolates. Furthermore, the antibiotic combinations that were bactericidal under anaerobic conditions were often different from those that were bactericidal against the same organisms grown as biofilms. The most effective combinations under all conditions were colistin (tested at concentrations suitable for nebulization) either alone or in combination with tobramycin (10 mu g ml(-1)), followed by meropenem combined with tobramycin or ciprofloxacin. The findings of this study illustrate that antibiotic sensitivities are dependent on culture conditions and highlight the complexities of choosing appropriate combination therapy for multidrug-resistant P. aeruginosa in the CF lung.

Concurrent microscopic observations and activity measurements of cellulose hydrolyzing and methanogenic populations during the batch anaerobic digestion of crystalline cellulose

This study compares process data with microscopic observations from an anaerobic digestion of organic particles. As the first part of the study, this article presents detailed observations of microbial biofilm architecture and structure in a 1.25-L batch digester where all particles are of an equal age. Microcrystalline cellulose was used as the sole carbon and energy source. The digestions were inoculated with either leachate from a 220-Lanaerobic municipal solid waste digester or strained rumen contents from a fistulated cow. The hydrolysis rate, when normalized by the amount of cellulose remaining in the reactor, was found to reach a constant value 1 day after inoculation with rumen fluid, and 3 days after inoculating with digester leachate. A constant value of a mass specific hydrolysis rate is argued to represent full colonization of the cellulose surface and first-order kinetics only apply after this point. Additionally, the first-order hydrolysis rate constant, once surfaces were saturated with biofilm, was found to be two times higher with a rumen inoculum, compared to a digester leachate inoculum. Images generated by fluorescence in situ hybridization (FISH) probing and confocal laser scanning microscopy show that the microbial communities involved in the anaerobic biodegradation process exist entirely within the biofilm. For the reactor conditions used in these experiments, the predominant methanogens exist in ball-shaped colonies within the biofilm. (C) 2005 Wiley Periodicals, Inc.

Modelling of two-stage anaerobic digestion using the IWA Anaerobic Digestion Model No. 1 (ADM1)

The aim of the study presented was to implement a process model to simulate the dynamic behaviour of a pilot-scale process for anaerobic two-stage digestion of sewage sludge. The model implemented was initiated to support experimental investigations of the anaerobic two-stage digestion process. The model concept implemented in the simulation software package MATLAB(TM)/Simulink(R) is a derivative of the IWA Anaerobic Digestion Model No.1 (ADM1) that has been developed by the IWA task group for mathematical modelling of anaerobic processes. In the present study the original model concept has been adapted and applied to replicate a two-stage digestion process. Testing procedures, including balance checks and 'benchmarking' tests were carried out to verify the accuracy of the implementation. These combined measures ensured a faultless model implementation without numerical inconsistencies. Parameters for both, the thermophilic and the mesophilic process stage, have been estimated successfully using data from lab-scale experiments described in literature. Due to the high number of parameters in the structured model, it was necessary to develop a customised procedure that limited the range of parameters to be estimated. The accuracy of the optimised parameter sets has been assessed against experimental data from pilot-scale experiments. Under these conditions, the model predicted reasonably well the dynamic behaviour of a two-stage digestion process in pilot scale. (C) 2004 Elsevier Ltd. All rights reserved.

Anaerobic metabolism of propionate by polyphosphate-accumulating organisms in enhanced biological phosphorus removal systems

Propionate, a carbon substrate abundant in many prefermenters, has been shown in several previous studies to be a more favorable substrate than acetate for enhanced biological phosphorus removal (EBPR). The anaerobic metabolism of propionate by polyphosphate accumulating organisms (PAOs) is studied in this paper. A metabolic model is proposed to characterize the anaerobic biochemical transformations of propionate uptake by PAOs. The model is demonstrated to predict very well the experimental data from a PAO culture enriched in a laboratory-scale reactor with propionate as the sole carbon source. Quantitative fluorescence in-situ hybridization (FISH) analysis shows that Candidatus Accumulibacter phosphatis, the only identified PAO to date, constitute 63% of the bacterial population in this culture. Unlike the anaerobic metabolism of acetate by PAOs, which induces mainly poly-beta-hydroxybutyrate (PHB) production, the major fractions of poly-beta-hydroxyalkanoate (PHA) produced with propionate as the carbon source are poly-beta-hydroxyvalerate (PHV) and poly-beta-hydroxy-2-methylvalerate (PH2MV). PHA formation correlates very well with a selective (or nonrandom) condensation of acetyl-CoA and propionyl-CoA molecules. The maximum specific propionate uptake rate by PAOs found in this study is 0.18 C-mol/C-mol-biomass h, which is very similar to the maximum specific acetate uptake rate reported in literature. The energy required for transporting 1 carbon-mole of propionate across the PAO cell membrane is also determined to be similar to the transportation of 1 carbon-mole of acetate. Furthermore, the experimental results suggest that PAOs possess a similar preference toward acetate and propionate uptake on a carbon-mole basis. (c) 2005 Wiley Periodicals, Inc.

Serum antibodies to oral anaerobic bacteria in patients with rheumatoid arthritis

BACKGROUND: This study was conducted to determine the component that causes the disease in rheumatoid arthritis (RA), which shows great resemblance to periodontitis in a pathologic context. MATERIALS AND METHODS: Within this study, the pathogen-specific IgG levels formed against Porphyromonas gingivalis FDC 381, Prevotella melaninogenica ATCC 25845, Actinobacillus actinomycetemcomitans Y4, Bacteroides forsythus ATCC 43047, and Prevotella intermedia 25611 oral bacteria were researched from the blood serum samples of 30 RA patients and 20 healthy controls with the enzyme-linked immunosorbent assay (ELISA) method. RESULTS: The IgG levels of P gingivalis, P intermedia, P melaninogenica, and B forsythus were found to be significantly higher in RA patients when compared with those of the controls. Of the other bacteria antibodies, A actinomycetemcomitans was not found at greater levels in RA serum samples in comparison with the healthy samples. CONCLUSION: The antibodies formed against P gingivalis, P intermedia, P melaninogenica, and B forsythus could be important to the etiopathogenesis of RA.