Experimental Approach to the Role of Different Ecological Types of Protozoa in the Activated-sludge System

Relationship between bacteria and ciliates was investigated in continuous cultures with and without the recycling of flocculated biomass. Monocultures of ciliates of various ecological types were used together with mixed cultures of bacteria or bacteria and flagellates. The effect of ciliates on the distribution of flocculated and dispersed, biomass was tested with respect to characterizing an optimum mixed culture for activated-sludge treatment. Monoprotozoal populations were not successful in stabilizing the morphology of a bacterial community in a system with recycling of flocculated biomass. Stabilization was observed (with particular ecological types of ciliates) in the system with a high residence time without recycling and/or in the system with the recycling inoculated by both flagellates and ciliates.     

A continuous-flow culture system for organ culture of large explants of adult tissue: Effect of oxygen tension on mouse molar periodontium

Summary A modified continuous-flow culture system (CFCS) was developed to maintain large explants of periodontium from adult mouse in organ culture. The culture medium was stored in a reservoir outside of the incubator, pumped via polyvinyl tubing into small glass culture chambers that were placed in the oxygenator and then collected in a waste flask. Medium was analyzed for pO₂, pCO₂ and pH during the culture period. Three-molar and singlemolar explants of periodontium were maintained for 48 hr in the CFCS at two different pO₂ ranges: 100 to 120 mm Hg and 400 to 420 mm Hg. [³H]Proline was added 24 hr prior to sacrifice. Light-microscope morphological and radioautographic observations suggested that cell viability and incorporation of [³H]proline, probably into newly synthesized protein, increased with an increase in pO₂ and was related to a pO₂ gradient extending from the periphery to the center of the explants.     

A continuous flow-chamber to study prey preferences of Golden Perch (Macquaria ambigua Richardson) larvae

This paper describes the use of a continuous-flow chamber for maintaining small and fragile fish larvae and their prey in a healthy state and under suitable conditions over a 24 h period for studies on prey preferences. Survival of golden perch (Macquaria ambigua Richardson) larvae and prey was high and ten replicates on food preferences were carried out simultaneously. The larvae preferred small Daphnia carinata King (780–860 m) over larger ones (2000–3120 and 3680–5440 m) and preferred cladocerans (Daphnia carinata King and Moina micrura Kurz) over calanoids (Boeckella de Guerne & Richard). The chamber is also suitable for studies on feeding behaviour and diet requirements of fish larvae.     

Strange kinetic phase in the extremely early folding process of beta-lactoglobulin

A continuous-wave probed laser-induced temperature jump system was constructed and applied to monitor the changes in tryptophan fluorescence of the beta-lactoglobulin during its folding; the kinetic phases were traced from 300 ns to 10 ms after a temperature jump. Notably, an early phase with typical squeezed-exponential characteristics, [exp[-(kt)(beta)], beta>1.0], was observed around several tens of microseconds after the temperature jump, which is actually the earliest phase ever observed for beta-lactoglobulin. This process can be explained by conformational shift occurring within the unfolded ensemble (U-->U'), which is followed by the non-native intermediate (I) formation of this protein.     

生态毒理试验中的连续流系统设计及控制

长期连续流试验中,毒物浓度波动主要归因于毒物稀释系统的故障。为了提高毒性数据质量,毒物浓度水平监控是必不可少的.本文对现有连续流试验系统中的毒物稀释器作了改进,采用计量泵输送毒物和稀释水,提高毒物稀释系统的精确度。同时,在连续流试验系统中配置了实时监控系统(RTMS).RTMS由泵、样品室、分析仪器、记录仪等组成.在56d试验中,RTMS随时提供毒物稀释器运行的最新情况,各级毒物浓度变异系数在2.16%-6.13%之间。系统的运行成功为规范中、长期毒性试验提供了技术保证.       

Effects of ammonium and nitrite on communities and populations of ammonia-oxidizing bacteria in laboratory-scale continuous-flow reactors

This study investigated the effects of ammonium and nitrite on ammonia-oxidizing bacteria (AOB) from an activated sludge process in laboratory-scale continuous-flow reactors. AOB communities were analyzed using specific PCR followed by denaturing gel gradient electrophoresis, cloning and sequencing of the 16S rRNA gene, and AOB populations were quantified using real-time PCR. To study the effect of ammonium, activated sludge from a sewage treatment system was enriched in four reactors receiving inorganic medium containing four different ammonium concentrations (2, 5, 10 and 30 mM NH(4) (+)-N). One of several sequence types of the Nitrosomonas oligotropha cluster predominated in the reactors with lower ammonium loads (2, 5 and 10 mM NH(4) (+)-N), whereas Nitrosomonas europaea was the dominant AOB in the reactor with the highest ammonium load (30 mM NH(4) (+)-N). The effect of nitrite was studied by enriching the enriched culture possessing both N. oligotropha and N. europaea in four reactors receiving 10-mM-ammonium inorganic medium containing four different nitrite concentrations (0, 2, 12 and 22 mM NO(2) (-)-N). Nitrosomonas oligotropha comprised the majority of AOB populations in the reactors without nitrite accumulation (0 and 2 mM NO(2) (-)-N), whereas N. europaea was in the majority in the 12- and 22-mM NO(2) (-)-N reactors, in which nitrite concentrations were 2.1-5.7 mM (30-80 mg N L(-1)).     

A high-sampling-rate automated continuous-flow fluorometric technique for the analysis of nanogram levels of histamine in biological samples

An automated continuous-flow technique of the modified fluorometric method of Shore was devised to obtain a high sampling rate (60/h) and a sensitive measurement of the histamine content of biological samples. The volumes of samples range from 50 to 500 microliter. A linear relationship is obtained from 0 to 5 micrograms/ml (histamine base) with a good specificity. The limit of detection is 25 pg (actual amount). The coefficient of variation is less than or equal to +/- 5% for concentrations of less than 2 ng/ml and from +/- 0.2 to +/- 2% for higher concentrations. With this technique more sensitive, more specific, and twice as fast as similar ones, histamine content in 350-400 unknowns can be measured routinely in a working day. It has been used for more than 4 years and has proven to be a reliable and useful tool for the numerous research studies in which histamine is involved: immunology, allergy, pharmacology, dermatology, cancer, nutrition.     

Three decades of nucleic acid aptamer technologies: Lessons learned,progress and opportunities on aptamer development

Aptamers are short single-stranded nucleic acid sequences capable of binding to target molecules in a way similar to antibodies. Due to various advantages such as prolonged shelf life, low batch to batch variation, low/no immunogenicity, freedom to incorporate chemical modification for enhanced stability and targeting capacity, aptamers quickly found their potential in diverse applications ranging from therapy, drug delivery, diagnosis, and functional genomics to bio-sensing. Aptamers are generated by a process called SELEX. However, the current overall success rate of SELEX is far from being satisfactory, and still presents a major obstacle for aptamer-based research and application. The need for an efficient selection strategy consisting of defined procedures to deal with a wide variety of targets is significantly important. In this work, by analyzing key aspects of SELEX including initial library design, target preparation, PCR optimization, and single strand DNA separation, we provide a comprehensive analysis of individual steps to facilitate researchers intending to develop personalized protocols to address many of the obstacles in SELEX. In addition, this review provides suggestions and opinions for future aptamer development procedures to address the concerns on key SELEX steps, and post-SELEX modifications.     

Plasmid dynamics in a model soil column

Continuous-flow column reactors were used to study the dynamics of plasmid exchange in a structured, thermodynamically open system containing either Enterobacter cloacae or Pseudomonas cepacia , both carrying the transmissible recombinant plasmid R388::Tn1721. Plasmid transfer rates were higher in vermiculite and sterile soil columns supplied with nutrient solution than those in sterile and non-sterile soil columns without input of nutrient solution. For both species, donor and recipient strains took about 5 days to reach their maximum densities in effluents from the columns supplied with nutrient solution. After about 8 day s the donor and transconjugant populations of P. cepacia in the effluent solution decreased exponentially, whereas E. cloacae donor, recipient and transconjugant strains maintained steady-state concentrations. The difference between plasmid stability in the two species may have significant consequences in terms of releasing plasmid-bearing genetically modified microorganisms into the natural environment. The plasmid is persistent in E. cloacae in non-sterile soil even though its transfer to the marked recipient in non-sterile soil was minimal.