Nitrate-Removal Activity of a Biofilm Attached to a Perlite Carrier under Continuous Aeration Conditions

The nitrate-removal activity of a biofilm attached to a perlite carrier from an aerobic bioreactor used for treating dairy farm wastewater was examined by batch experiments under continuous aeration conditions. Despite aeration, the biofilm removed nitrate at a rate of 114.4 mg-N/kg-perlite/h from wastewater containing cow milk and manure. In a clone library analysis of the biofilm, bacteria showing high similarity to the denitrifying bacteria Thauera spp. were detected.     

一株吡啶降解菌Pseudomonas sp.ZX08的生物膜形成特性及影响因素

【背景】煤化工企业排放的废水中含有大量难降解、高毒性的有机污染物,采用以高效降解菌为基础的生物强化技术对其进行处理,是一种经济可行的策略;而促进高效降解菌在载体材料表面的生物膜形成,有助于提升生物膜法废水处理系统的效能。【目的】探究一株吡啶高效降解菌Pseudomonas sp. ZX08的生物膜形成过程和特性,识别不同的环境因子如温度、pH、Na⁺、K⁺、Ca²⁺、Mg²⁺等对其生物膜形成的影响规律,为实现人工调控其在实际废水处理系统中的成膜过程提供理论依据。【方法】采用改良的微孔板生物膜培养与定量方法,以单因子影响实验测定不同条件下菌株在12孔板内的生物膜形成量和浮游态细菌量;采用激光共聚焦显微镜(confocallaserscanning microscope,CLSM)观察和分析生物膜的结构特征。【结果】Pseudomonas sp. ZX08菌株具有良好的吡啶降解性能,且生物膜形成能力较强,CLSM观察到其在载体表面形成的生物膜可达40-50mm;生物膜外层的活细胞比例更高,分泌的胞外蛋白...     

A critical stage in the formation of acid mine drainage: Colonization of pyrite by Acidithiobacillus ferrooxidans under pH-neutral conditions

A dominant Acidithiobacillus ferrooxidans ssp. was isolated from the supergene copper deposit in Morenci, Arizona, USA. Washed bacterial suspensions (10⁸ MPN per treatment), in pH‐neutral buffer, were inoculated onto pyrite cubes for 24 h. Heterogeneous bacterial absorption onto the pyrite removed approximately 90% of the viable bacteria from the inoculum. At T = 0, the bacteria were observed primarily in regions enriched in phosphorus. Over 30 days, the bacterial population on the pyrite cubes increased from 1.3 × 10⁷ to 2.9 × 10⁸ bacteria cm^?2. During this growth stage, low levels of thiobacilli (228 ± 167 MPN mL^?1) were also recovered from the fluid phase; however, this population decreased to zero within 30 days. Growth on pyrite occurred as micrometre‐scale planar microcolonies, a biofilm, coating the mineral surfaces. These microcolonies possessed viable thiobacilli, even after 4 months at ‘circumneutral pH’. Imaging the pyrite cubes using SEM‐EDS and scanning force microscopy demonstrated that the thiobacilli grew as iron oxy‐hydroxide‐cemented cells, leading to the formation of mineralized microcolonies. Removing the iron oxy‐hydroxides with oxalic acid did not dislodge the bacteria, demonstrating that the secondary minerals were not responsible for ‘gluing’ the bacteria to the pyrite surface. Removing organic material, i.e. the cells, by an oxygen plasma treatment revealed the presence of corrosion pits the size and shape of bacteria. Because of the inherent geochemical constraints on pyrite oxidation at neutral pH, the colonization of pyrite under circumneutral pH conditions must be facilitated by the development of an acidic nanoenvironment between the bacteria and the pyrite mineral surface.     

Dyestuff wastewater treatment using chemical oxidation,physical adsorption and fixed bed biofilm process

Fenton’s oxidation and activated carbon adsorption were examined as pretreatment processes for dyestuff wastewater having high salinity, colour, and non-biodegradable organic concentrations. In this work, each wastewater stream produced by individual production processes was classified as streams R1, R2, and R3. The stream having a value of BOD₅/COD lower than 0.4 was pretreated by Fenton’s oxidation or activated carbon adsorption to increase the ratio of BOD₅/COD which indicates biodegradability. For Fenton’s oxidation with one stream having a value of BOD₅/COD lower than 0.4, the optimal reaction pH was 3.0 and the minimum dosing concentration (mg l⁻¹) of H₂O₂:FeSO₄·7H₂O was 700:3500. Stream R3, which consisted mainly of methanol was efficiently treated by activated carbon adsorption. The ratio of BOD₅/COD was also increased to 0.432 and 0.31 from 0.06 in Fenton’s oxidation and activated carbon adsorption, respectively. A biological treatment system using a fixed bed reactor was also investigated to enhance biological treatment efficiency at various hydraulic retention times, pretreatment conditions by Fenton’s reagent and salt concentrations by dyestuff wastewater. In addition, the efficiency of Fenton’s oxidation as a post-treatment system was also investigated to present a total treatment process of dyestuff wastewater. As the influent COD and salinity were increased, the effluent SS and COD were consequently increased. However, as the microorganisms became adapted to the changed influent condition, the treatment efficiency of the fixed bed reactor quickly recovered under the high COD and salinity since the microorganisms were well adapted to toxic influent conditions. A wastewater treatment process consisting of chemical oxidation, activated carbon adsorption, fixed bed biofilm process and Fenton’s oxidation as a post-treatment system can be useful to treat dyestuff wastewater having high salinity, colour, and non-biodegradable organic concentration.     

New concept of contaminant removal from swine wastewater by a biological treatment process

Pollution from concentrated animal feeding operations (CAFOs) are the most serious pollution source in China now, and swine wastewater contains high concentrations of nutrients such as chemical oxygen demand (COD), biochemical oxygen demand 5 (BOD₅), ammonium, and emergent contaminants related to public health. Biological processes are the most popular treatment methods for COD and ammonium removal. Considering the low operation cost, easy maintenance and high removal rate of contaminants in recent years, nitrogen removal via nitrite and real-time control processes using oxidation-reduction potential (ORP) and/or pH as parameters to control the aerobic and anaerobic cycles of a system has received much attention for animal wastewater treatment. During the biological treatment process, the emergent contaminants such as estrogen, antibiotics, and disinfection reagents have been the focus of research recently, and degradation bacteria and resistance bacteria have also been extracted from activated sludge. The microbial analysis technique is also advancement in the field of biodegradation bacteria and resistance bacteria. All of these advancements in research serve to improve wastewater treatment and decrease environmental hazards, especially for using manure as a fertilizer source for crop production.     

Silica-immobilized Methylobacterium sp. NP3 and Acinetobacter sp. PK1 degrade high concentrations of phenol

Aims: To immobilize Methylobacterium sp. NP3 and Acinetobacter sp. PK1 to silica and determine the ability of the immobilized bacteria to degrade high concentrations of phenol. Methods and Results: The phenol degradation activity of suspended and immobilized Methylobacterium sp. NP3 and Acinetobacter sp. PK1 bacteria was investigated in batch experiments with various concentrations of phenol. The bacterial cells were immobilized by attachment to or encapsulation in silica. The encapsulated bacteria had the highest phenol degradation rate, especially at initial phenol concentrations between 7500 and 10 000 mg l^?1. Additionally, the immobilized cells could continuously degrade phenol for up to 55 days. Conclusions: The encapsulation of a mixed culture of Methylobacterium sp. NP3 and Acinetobacter sp. PK1 is an effective and easy technique that can be used to improve bacterial stability and phenol degradation. Significance and Impact of the Study: Wastewater from various industries contains high concentrations of phenol, which can cause wastewater treatment failure. Silica‐immobilized bacteria could be applied in bioreactors to initially remove the phenol, thereby preventing phenol shock loads to the wastewater treatment system.     

Alicycliphilus: current knowledge and potential for bioremediation of xenobiotics

Alicycliphilus is a promising candidate for participating in the development of novel xenobiotics bioremediation processes. Members of the Alicycliphilus genus are environmental bacteria mostly found in polluted sites such as landfills and contaminated watercourses, and in sewage sludges from wastewater treatment plants. They exhibit a versatile metabolism and the ability to use oxygen, nitrate and chlorate as terminal electron acceptors, which allow them to biodegrade xenobiotics under oxic or anoxic conditions. Pure cultures of Alicycliphilus strains are able to biodegrade some pollutants such as industrial solvents (acetone, cyclohexanol and N-methylpyrrolidone), aromatic hydrocarbons (benzene, toluene and anthracene), as well as polyurethane varnishes and foams, and they can even transform Cr(VI) to Cr(III). In addition, Alicycliphilus has also been identified in bacterial communities involved in wastewater treatment plants for denitrification, and the degradation of emerging pollutants such as triclosan, nonylphenol, N-heterocyclic aromatic compounds (indole and quinoline), and antibiotics (tetracycline and oxytetracycline). This work summarizes the current knowledge on the Alicycliphilus genus, describing its different metabolic characteristics, focusing on its xenobiotic biodegradation abilities and examining the distinct pathways and molecular bases that sustain them. We also discuss the progress made in genetic manipulation and ‘omics’ analyses, as well as Alicycliphilus participation in novel bioremediation strategies.     

Periphyton responds differentially to nutrients recycled in dissolved or faecal pellet form by the snail grazer Theodoxus fluviatilis

1. We aimed to separate the effects of grazers on periphyton via grazing from that of nutrient recycling from their faecal pellets. 2. We set up three different experimental treatments (snails/no snails/faecal pellets) and sampled over 16 days. The ‘snail’ treatment contained a low density (snail biomass c. 14 g^?2) of the gastropod grazer Theodoxus fluviatilis and the ‘faecal pellet’ treatment received the same amount of faecal pellets as were produced in the ‘snail’ treatment. Whereas the ‘faecal pellet’ treatment provided extra nutrients to periphyton from the faeces, the ‘snail’ treatment provided nutrients in the form of both faeces and in excreta. There was also direct grazing on periphyton in the ‘snail’ treatment. The ‘no snail’ was not grazed and received no nutrients in faeces or excreta. 3. We measured periphyton C, N and P content, chlorophyll‐a (chl‐a), primary production, bacterial biomass, bacterial production and bacterial respiratory activity. In the water column we measured dissolved inorganic N and soluble reactive P. 4. Snails increased the amount of dissolved inorganic N in the water. On day 16, the periphyton N : P ratio in the ‘faecal pellet’ treatment was lower, and periphyton P content was higher, than in the other two treatments. N : P ratios decreased over time in the ‘faecal pellet’ treatment. Primary and bacterial production were positively correlated in all treatments. 5. Algal chl‐a and primary production of periphyton per unit area and periphyton chl‐a : C ratios increased over the 16 day in the ‘snail’ treatment, and thus excretion of dissolved N by snails had a stronger positive effect on the periphyton community than N and P in faecal pellets. 6. Our data show that excretion and egestion can have different effects on periphyton, probably because of the higher proportion of dissolved N in excreta and the higher proportion of P recycled in faecal pellets. The relative effect of nutrients recycled in egesta or in excretions, probably depends on the form of nutrient limitation of the periphyton. Further, the different components of the periphyton matrix could react differently to the different forms of nutrient recycling. 7. We conclude that direct grazing effects are less important than nutrient effects when nutrients are limiting and grazing pressure is low. Further, the spatial separation of different grazing effects can lead to differences in periphyton production and nutrient stoichiometry. This might be an explanation for the patchiness of periphyton in nature.     

Potential of a new biotreatment:<Emphasis Type="Italic"> Sphingomonas cloacae</Emphasis> S-3<Superscript>T</Superscript> degrades nonylphenol in industrial wastewater

Sphingomonas cloacae S-3^T, a nonylphenol (NP)-degrading bacterium, was evaluated for its utility in the remediation of NP-contaminated wastewater. In flask-scale experiments, S-3^T cells immobilized on porous polypropylene carriers (beads) efficiently degraded NP to concentrations routinely measured in aquatic environments [a few parts per billion (ppb), or micrograms per liter). Therefore, we constructed and evaluated a laboratory-scale wastewater treatment system with a 3-l carrier-filled column. The system worked properly and consistently removed several hundred ppb of NP to ecologically safe concentrations of less than 10 ppb in industrial wastewater without the addition of nutrients. The effect of wastewater pH on the system performance was also evaluated; and wastewater samples with pH values of 6 or 8 were treated efficiently without pH adjustment. These results suggest that a biotreatment system using NP-degrading bacteria can efficiently remediate industrial wastewater and contribute to the preservation of aquatic environments.     

Characterization and performance of constructed nitrifying biofilms during nitrogen bioremediation of a wastewater effluent

Constructed ammonium oxidizing biofilms (CAOB) and constructed nitrite oxidizing biofilms (CNOB) were characterized during the bioremediation of a wastewater effluent. The maximum ammonium removal rate and removal efficiency in CAOB was 322 mg N-NH₄⁺ m⁻³ d⁻¹ and 96%, respectively, while in CNOB a maximum removal rate of 255 mg N-NH₄⁺ m⁻³ d⁻¹ and a removal efficiency of 76% was achieved. Both constructed biofilms on low-density polyester Dacron support achieved removal efficiencies higher than that of the concentrations normally present in reactors without constructed biofilms (P < 0.05). Nitrifying bacteria from the constructed biofilms cultures were typed by sequencing 16S rRNA genes that had been amplified by PCR from genomic DNA. Analysis of enrichment biofilms has therefore provided evidence of high removal of ammonium and the presence of Nitrosomonas eutropha, N. halophila and N. europaea in CAOB, while in CNOB Nitrobacter hamburgensis, N. winogradskyi and N. alkalicus were identified according to 16S rRNA gene sequences comparison. The biofilm reactors were nitrifying over the whole experimental period (15 days), showing a definite advantage of constructed biofilms for enhancing a high biomass concentration as evidenced by environmental electron microscopic analysis (ESEM). Our research demonstrates that low-density polyester Dacron can be effectively used for the construction of nitrifying biofilms obtaining high removal efficiencies of nitrogen in a relatively short time from municipal effluents from wastewater treatment plants. CAOB and CNOB are potentially promissory for the treatment of industrial wastewaters that otherwise requires very large and expensive reactors for efficient bioremediation of effluents.     

Biofilm Dynamics and Kinetics during High-Rate Sulfate Reduction under Anaerobic Conditions

The sulfate kinetics in an anaerobic, sulfate-reducing biofilm were investigated with an annular biofilm reactor. Biofilm growth, sulfide production, and kinetic constants (K_m and V_max) for the bacterial sulfate uptake within the biofilm were determined. These parameters were used to model the biofilm kinetics, and the experimental results were in good agreement with the model predictions. Typical zero-order volume rate constants for sulfate reduction in a biofilm without substrate limitation ranged from 56 to 93 μmol of SO²₄-cm⁻³ h⁻¹ at 20°C. The temperature dependence (Q₁₀) of sulfate reduction was equivalent to 3.4 at between 9 and 20°C. The measured rates of sulfate reduction could explain the relatively high sulfide levels found in sewers and wastewater treatment systems. Furthermore, it has been shown that sulfate reduction in biofilms just a few hundred micrometers thick is limited by sulfate diffusion into biofilm at concentrations below 0.5 mM. This observation might, in some cases, be an explanation for the relatively poor capacity of the sulfate-reducing bacteria to compete with the methanogenic bacteria in anaerobic wastewater treatment in submerged filters.     

Removal of Mercury from Chloralkali Electrolysis Wastewater by a Mercury-Resistant Pseudomonas putida Strain

A mercury-resistant bacterial strain which is able to reduce ionic mercury to metallic mercury was used to remediate in laboratory columns mercury-containing wastewater produced during electrolytic production of chlorine. Factory effluents from several chloralkali plants in Europe were analyzed, and these effluents contained total mercury concentrations between 1.6 and 7.6 mg/liter and high chloride concentrations (up to 25 g/liter) and had pH values which were either acidic (pH 2.4) or alkaline (pH 13.0). A mercury-resistant bacterial strain, Pseudomonas putida Spi3, was isolated from polluted river sediments. Biofilms of P. putida Spi3 were grown on porous carrier material in laboratory column bioreactors. The bioreactors were continuously fed with sterile synthetic model wastewater or nonsterile, neutralized, aerated chloralkali wastewater. We found that sodium chloride concentrations up to 24 g/liter did not inhibit microbial mercury retention and that mercury concentrations up to 7 mg/liter could be treated with the bacterial biofilm with no loss of activity. When wastewater samples from three different chloralkali plants in Europe were used, levels of mercury retention efficiency between 90 and 98% were obtained. Thus, microbial mercury removal is a potential biological treatment for chloralkali electrolysis wastewater.     

A glimpse under the rim – the composition of microbial biofilm communities in domestic toilets

Aim: To determine the microbial composition of biofilms in domestic toilets by molecular means. Methods and Results: Genomic DNA was extracted from six biofilm samples originating from households around Düsseldorf, Germany. While no archaeal 16S rRNA or fungal ITS genes were detected by PCR, fingerprinting of bacterial 16S rRNA genes revealed a diverse community in all samples. These communities also differed considerably between the six biofilms. Using the Ribosomal Database Project (RDP) classifier tool, 275 cloned 16S rRNA gene sequences were assigned to 11 bacterial phyla and 104 bacterial genera. Only 15 genera (representing 121 sequences affiliated with Acidobacteria, Actinobacteria, Bacteroidetes, Planctomycetes and Proteobacteria) occurred in at least half of the samples or contributed at least 10% of the sequences in a single biofilm. These sequences were defined as ‘typical’ for toilet biofilms, and they were examined in more detail. On a 97% sequence similarity level, these sequences represented 56 species. Twelve of these were closely related to well‐described bacterial species, and only two of them were categorized as belonging to risk group 2. No 16S rRNA genes of typical faecal bacteria were detected in any sample. Virtually all ‘typical’ clones were found to be closely related to bacteria or to sequences obtained from environmental sources, implicating that the flushing water is the main source of recruitment. Conclusion: In view of the great diversity of mostly yet‐uncultured bacteria and the considerable differences between individual toilets, very general strategies appear to be most suited for the removal and prevention of toilet biofilms. Significance and Impact of the Study: For the first time, a molecular fingerprinting and cloning approach was used to monitor the species composition in biofilm samples taken from domestic toilets. Knowledge about the microbial composition of biofilms in domestic toilets is a prerequisite for developing and evaluating strategies for their removal and prevention.     

Escherichia coli biofilm: development and therapeutic strategies

Escherichia coli biofilm consists of a bacterial colony embedded in a matrix of extracellular polymeric substances (EPS) which protects the microbes from adverse environmental conditions and results in infection. Besides being the major causative agent for recurrent urinary tract infections, E. coli biofilm is also responsible for indwelling medical device‐related infectivity. The cell‐to‐cell communication within the biofilm occurs due to quorum sensors that can modulate the key biochemical players enabling the bacteria to proliferate and intensify the resultant infections. The diversity in structural components of biofilm gets compounded due to the development of antibiotic resistance, hampering its eradication. Conventionally used antimicrobial agents have a restricted range of cellular targets and limited efficacy on biofilms. This emphasizes the need to explore the alternate therapeuticals like anti‐adhesion compounds, phytochemicals, nanomaterials for effective drug delivery to restrict the growth of biofilm. The current review focuses on various aspects of E. coli biofilm development and the possible therapeutic approaches for prevention and treatment of biofilm‐related infections.     

A deep maximum of green sulphur bacteria ('Chlorochromatium aggregatum') in a strongly stratified reservoir

1. Fine‐scale physical and chemical gradients and deep photosynthetic microbial populations were assessed to provide an initial characterisation of a small, thermally stratified reservoir (Cross Reservoir, Kansas, U.S.A.) and its deep chlorophyll maxima (DCM). Factors were identified that may affect vertical positioning of subepilimnetic photosynthetic sulphur bacteria (PSB) in lakes. 2. Results indicate that Cross Reservoir is a mesotrophic, dimictic lake with large subepilimnetic chlorophyll maxima containing dense layers of PSB. Characteristics of the deep PSB community of Cross Reservoir strongly correlate with both light and nutrient gradients. 3. The deep bacterial community mostly contained single‐celled and aggregating green sulphur bacteria, specifically free‐living Chlorobium limicola and the conspicuous motile ectosymbiotic consortium known as ‘Chlorochromatium aggregatum’. The bacteria were within the anaerobic hypolimnion, beneath a metalimnetic plate of Cryptomonas spp. and within very low sulphide and light conditions [mean of 67 μgS L^?1 and 0.05% photosynthetically active radiation (PAR)]. Pigment concentrations and fluorescence trends indicate that the bacteria made up a larger proportion of the DCM biomass than did phytoplankton in 1996. 4. Cross Reservoir shares characteristics with natural lakes world‐wide that also include a deep PSB community containing dense layers of ‘C. aggregatum’. Correlation analyses indicate that PSB community positioning and density are related to light, sulphide supply, redox potentials and pH. A 2‐factor principal components analysis (PCA) and other data trends supported these interpretations and indicated that PSB are sensitive to the thermal stability of the water column, are nitrogen limited and regulated more by sulphide or sulphide to light ratios than local levels of light. The sensitivity of these deep photosynthetic bacteria to environmental gradients, and their significance to some aquatic systems, demonstrate their potential as indicators of environmental disturbance.     

Determining the effectiveness of resistance to subterranean clover mottle sobemovirus in different genotypes of subterranean clover in the field using the grazing animal as virus vector

The effectiveness of resistance to subterranean clover mottle sobemovirus (SCMoV) previously identified in different genotypes of subterranean clover (Trifolium subterraneum) inoculated with infective sap in the glasshouse, was tested in two field experiments which used the grazing animal as virus vector. Replicated plots each consisting of paired test rows of 20 different genotypes were used. Clover plants infected with SCMoV were transplanted in between the paired test rows and these acted as sources of the virus for spread by grazing sheep. Although used in different years at different sites with different virus isolates, the field exposure methodology employed produced consistent results. The genotypes each behaved similarly in both experiments as regards the relative extents of SCMoV infection that developed, levels ranging from 0–98%. The previously identified resistance in six ‘highly resistant’ and three ‘partially resistant’ cultivars was effective under field conditions. However, the ‘partial resistance’ in three others was overcome, cvs Green Range and Mt Barker developing levels of infection approaching those in ‘susceptible’ cultivars, while an intermediate infection level developed in cv. Karridale. The three cultivars in which partial resistance was not effective all belonged to ssp. subterraneum. In subterranean clover breeding programmes, field screening using the grazing animal as a vector is advisable to determine whether SCMoV resistance found by sap inoculation is still effective under field conditions.     

Nutrients determine the spatial architecture of Paracoccus sp. biofilm

Bacterial biofilms adapt and shape their structure in response to varied environmental conditions. A statistical methodology was adopted in this study to empirically investigate the influence of nutrients on biofilm structural parameters deduced from confocal scanning laser microscope images of Paracoccus sp.W1b, a denitrifying bacterium. High concentrations of succinate, Mg⁺⁺, Ca⁺⁺, and Mn⁺⁺ were shown to enhance biofilm formation whereas higher concentration of iron decreased biofilm formation. Biofilm formed at high succinate was uneven with high surface to biovolume ratio. Higher Mg⁺⁺ or Ca⁺⁺ concentrations induced cohesion of biofilm cells, but contrasting biofilm architectures were detected. Biofilm with subpopulation of pillar-like protruding cells was distributed on a mosaic form of monolayer cells in medium with 10 mM Mg⁺⁺. 10 mM Ca⁺⁺ induced a dense confluent biofilm. Denitrification activity was significantly increased in the Mg⁺⁺- and Ca⁺⁺-induced biofilms. Chelator treatment of various biofilm ages indicated that divalent cations are important in the initial stages of biofilm formation.     

Parasitic ‘Candidatus Aquarickettsia rohweri’ is a marker of disease susceptibility in Acropora cervicornis but is lost during thermal stress

Holobiont phenotype results from a combination of host and symbiont genotypes as well as from prevailing environmental conditions that alter the relationships among symbiotic members. Corals exemplify this concept, where shifts in the algal symbiont community can lead to some corals becoming more or less thermally tolerant. Despite linkage between coral bleaching and disease, the roles of symbiotic bacteria in holobiont resistance and susceptibility to disease remains less well understood. This study thus characterizes the microbiome of disease-resistant and -susceptible Acropora cervicornis coral genotypes (hereafter referred to simply as ‘genotypes’) before and after high temperature-mediated bleaching. We found that the intracellular bacterial parasite ‘Ca. Aquarickettsia rohweri’ was strikingly abundant in disease-susceptible genotypes. Disease-resistant genotypes, however, had notably more diverse and even communities, with correspondingly low abundances of ‘Ca. Aquarickettsia’. Bleaching caused a dramatic reduction of ‘Ca. Aquarickettsia’ within disease-susceptible corals and led to an increase in bacterial community dispersion, as well as the proliferation of opportunists. Our data support the hypothesis that ‘Ca. Aquarickettsia’ species increase coral disease risk through two mechanisms: (i) the creation of host nutritional deficiencies leading to a compromised host-symbiont state and (ii) the opening of niche space for potential pathogens during thermal stress.     

Impact of different developmental stages of <Emphasis Type="Italic">Daphnia</Emphasis> <Emphasis Type="Italic">magna</Emphasis> (Straus) on the plankton community under different trophic conditions

In situ 24-h incubation experiments were performed to analyse the grazing effects of Daphnia magna on a planktonic microbial community. Three field grazing experiments under different nutrient concentrations were carried out on treated effluents of a wastewater treatment plant. The grazing effects of three different D. magna size classes (small (0.6–1.6 mm), medium (1.7–2.5 mm) and large individuals (2.6–3.7 mm)) were compared. The different sizes classes had similar effects on the plankton community. However, our results showed big differences in effects among experiments. Our findings suggest that in spite of D. magna’s non-selective feeding behaviour and the fact that different developmental stages (i.e. its size) had similar effects on the microbial planktonic community, these effects can differ according to the initial structure and composition of the community and the resulting cascading trophic interactions. Moreover, D. magna effects can be direct through grazing (as is the case with ciliates), or indirect through trophic cascade interactions (as is the case with bacteria).