The effect of decreasing alkalinity on microbial community dynamics in a sulfate-reducing bioreactor as analyzed by PCR-SSCP

PCR-single-strand conformation polymorphism (SSCP) and Southern blotting techniques were adopted to investigate microbial community dynamics in a sulfate-reducing bioreactor caused by decreasing influent alkalinity. Experimental results indicated that the sulfate-removal rate approached 87% in 25 d under the conditions of influent alkalinity of 4000 mg/L (as CaCO₃) and sulfate-loading rate of 4.8 g/(L·d), which indicated that the bioreactor started up successfully. The analysis of microbial community structure in this stage showed that Lactococcus sp., Anaerofilum sp. and Kluyvera sp. were dominant populations. It was found that when influent alkalinity reduced to 1000 mg/L, sulfate-removal rate decreased rapidly to 35% in 3 d. Then influent alkalinity was increased to 3000 mg/L, the sulfate-removal rate rose to 55%. Under these conditions, the populations of Dysgonomonas sp., Sporobacte sp., Obesumbacterium sp. and Clostridium sp. got to rich, which predominated in the community together with Lactococcus sp., Anaerofilum sp. and Kluyvera sp. However, when the alkalinity was decreased to 1500 mg/L, the sulfate-removal rate rose to and kept stable at 70% and populations of Dysgonomonas sp., Sporobacter sp. and Obesumbacterium sp. died out, while some strains of Desulfovibrio sp. and Clostridium sp. increased in concentration. In order to determine the minimum alkalinity value that the system could tolerate, the influent alkalinity was decreased from 1500 to 400 mg/L secondly. This resulted in the sulfate-removal rate, pH value and effluent alkalinity dropping quickly. The amount of Petrotoga sp., Prevotella sp., Kluyvera sp. and Neisseria sp. reduced obviously. The result data from Southern blotting indicated that the amount of sulfate-reducing bacteria (SRBs) decreased with influent alkalinity dropping. Analysis of the microbial community structure and diversity showed that the SRBs populations were very abundant in the inoculated activated sludge and the alkalinity decrease caused the reduction of the populations noted. Most of resident populations in the bioreactor were fermentative acidogenic bacteria (FABs), among which the phylum Firmicute was in the majority, but SRBs were very few. This community structure demonstrates the cooperation between SRBs and FABs, which sustains the system’s high sulfate-removal and operation stability.     

DG-DGGE分析产氢发酵系统微生物群落动态及种群多样性

应用双梯度-变性梯度凝胶电泳(DG-DGGE)对生物制氢反应器微生物种群的动态变化及多样性进行监测。间隔7d从反应器取厌氧活性污泥,以细菌16SrDNA通用引物进行V2～V3区域PCR扩增,长约450bp的PCR产物经DGGE分离后,获得污泥微生物群落的16SrDNA指纹图谱。污泥接种到反应器后微生物群落中既有原始种群的消亡和增长,也有次级种群的强化和演变。反应器在运行初期群落演替迅速,15d时微生物群落结构变化最大。群落结构的相似性随着演替时间的增加而逐渐升高,种群动态变化后形成稳定的群落结构。29d时微生物多样性基本保持不变,微生物优势种属达到19个OTU。在细菌竞争和协同作用制约下,种群多样性降低后趋于稳定,形成顶级群落。有些种群在群落结构中一直存在,是群落建成的原始种群,原始种群与次级种群在代谢过程中具有协同作用,表现出群落的综合生态特征。     

Effects of UV pretreatment on microbial community structure and metabolic characteristics in a subsequent biofilter treating gaseous chlorobenzene

To provide insight into effects of UV pretreatment on microorganisms in subsequent biofilters, the changes of microbial community structure and metabolic characteristics of biofilters with (UV–BF) and without (BF) UV pretreatment were studied. The respiratory quinone and BIOLOG methods were used to analyze microbial community structure and metabolic characteristics, respectively. The results indicated the quinone profiles, the species of dominant quinone and its molar fraction of the biofilm in both biofilters showed different behaviors. Ubiquinones-8 and menaquinone-9(H₂) was the dominant quinones in BF and UV–BF processes, respectively. The dissimilarity index of two biofilters markedly increased to nearly 60 after turning on the UV lamp. The microbial samples from UV–BF process showed higher metabolic activities of 0.040 cm⁻¹ h⁻¹ than 0.028 cm⁻¹ h⁻¹ in BF process. Moreover, the microorganisms in both biofilters demonstrated distinct metabolic characteristics. Further, the performance of biofilters showed good correlation with microbial community structure and metabolic characteristics.     

The influence of cholesterol on interactions and dynamics of ibuprofen in a lipid bilayer

In this work, molecular dynamics (MD) simulations with atomistic details were performed to examine the influence of the cholesterol on the interactions and the partitioning of the hydrophobic drug ibuprofen in a fully hydrated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayer. Analysis of MD simulations indicated that ibuprofen molecules prefer to be located in the hydrophobic acyl chain region of DMPC/cholesterol bilayers. This distribution decreases the lateral motion of lipid molecules. The presence of ibuprofen molecules in the bilayers with 0 and 25 mol% cholesterol increases the ordering of hydrocarbon tails of lipids whereas for the bilayers with 50 mol% cholesterol, ibuprofen molecules perturb the flexible chains of DMPC lipids which leads to the reduction of the acyl chain order parameter. The potential of the mean force (PMF) method was used to calculate the free energy profile for the transferring of an ibuprofen molecule from the bulk water into the DMPC/cholesterol membranes. The PMF studies indicated that the presence of 50 mol% cholesterol in the bilayers increases the free energy barrier and slows down the permeation of the ibuprofen drug across the DMPC bilayer. This can be due to the condensing and ordering effects of the cholesterol on the bilayer.     

Effects of the internal recycling rate on biological nutrient removal and microbial community structure in a sequential anoxic/anaerobic membrane bioreactor

This study investigated the effects of the internal recycling rate on nutrients removal in a sequential anoxic/anaerobic membrane bioreactor (SAM). Microbial community structure in sludge from the SAM was studied using quinone profile method. Above 98% COD, 68% nitrogen, and 55% phosphorus removal efficiencies were achieved when the internal recycling rate was 2.5 times influent flow. At that rate, the optimum specific nitrate loading rate and COD/NO(3)-N ratio were found to be 2.24 mgNO(3)-N g(-1) MLSS h(-1) and 9.13, respectively. Batch tests demonstrated that anoxic condition suppressed phosphorus release, and that denitrification was also influenced by initial substrate concentration. Denitrification appeared to have some priority over phosphorus release for substrate uptake. Microbial community analysis revealed a predominance of the subclass beta-Proteobacteria. Furthermore, it was found that Rhodocyclus-related bacteria were efficient at phosphorus removal than Actinobacteria.     

施氮肥对华北平原土壤氨氧化细菌和古菌数量及群落结构的影响

利用荧光定量PCR、末端限制性片段长度多样性(T-RFLP)和基因克隆文库技术,比较了4种施氮水平(不施氮肥,0 kg N/hm~2,CK;施低水平氮肥,75 kg N/hm~2,N1;施中水平氮肥,150 kg N/hm~2,N2;施高水平氮肥,225 kg N/hm~2,N3)下华北平原地区小麦季表层(0—20 cm)土壤总细菌、氨氧化细菌(AOB)和氨氧化古菌(AOA)的丰度和群落结构。结果表明,土壤总细菌、AOB和AOA数量分别在每克干土5.74×10~9—7.50×10~9、8.89×10~6—2.66×10~7和3.83×10~8—7.78×10~8之间。不同施氮量土壤AOA数量均高于AOB数量,AOA/AOB值在81.72—14.38之间。增施氮肥显著显著提高AOB数量(P0.05),对总细菌和AOA数量的影响不显著(P0.05)。与CK相比,处理N1、N2和N3中AOB数量分别提高了0.64、1.50和1.99倍。增施氮肥显著改变了AOB和AOA的群落结构,且不同施氮量处理中AOB群落结构差异更大。系统进化分析显示,施氮肥小麦土壤AOB主要为Nitrosospira属类群,分布在Cluster 3的两个分支中;AOA分布在Cluster S的4个分支中。相关性分析显示,AOB数量与全氮和铵态氮含量呈显著正相关关系,与土壤pH和碳氮比呈显著负相关关系(P0.05);AOA数量与硝态氮含量和土壤pH呈显著正相关关系,与铵态氮含量呈显著负相关关系(P0.05)。研究结果表明:增施氮肥可显著改变华北平原地区碱性土壤AOB数量与群落结构,该地区小麦土壤中AOB比AOA对氮肥响应更敏感。     

The effect of internal capacitance on power quality and energy efficiency in a tubular microbial fuel cell

The pseudo-capacitive behaviour of a high surface area carbon veil electrode in a tubular microbial fuel cell (MFC) was investigated as a mechanism to enhance power quality and energy efficiency. Accumulated charge and energy from the anodic biofilm after prolonged open circuit times (1–120 min) were compared against equivalent periods of steady state loading (R = 100–3000 Ω). A significant difference in the amount of accumulated charge with different loads was observed, resulting in 1.051 C (R = 100 Ω) compared to 0.006 C (R = 3 kΩ). The automated application of short open and closed circuit (0.5–10 s) cycles resulted in an increase of power/current production (closed circuit alone), but presented lower efficiency considering entire open and closed period. The cumulative charge on the carbon veil electrode with biofilm was 39,807 C m⁻² at 100 Ω. Electrochemical Impedance Spectroscopy (EIS) showed that the Helmholtz layer presented a double layer capacitance of more than ten times the biofilm on electrode. The results indicate that the capacitive behaviour could be utilized to increase the power quality, i.e. its availability/applicability with respect to the operation of low power consuming devices.     

The protective effect of astaxanthin on the ganglion cell complex in glutamate/aspartate transporter deficient mice,a model of normal tension glaucoma,analyzed by spectral domain-optical coherence tomography

Astaxanthin (AST), a natural marine carotenoid, possess a wide variety of biological functions. In particular, as a strong antioxidant, AST effectively scavenges oxygen free radicals and reduces oxidative stress. In addition, recent in vitro studies have suggested that AST attenuates glutamate-induced apoptosis and cytotoxicity. The glutamate/aspartate transporter (GLAST) deficient (GLAST^-/-) mouse is a mouse model of normal tension glaucoma (NTG) caused by both the glutamate neurotoxicity and oxidative stress in the retina. In the present study, we investigated the effects of AST on the ganglion cell complex, indicator of glaucomatous structural damage, using spectral domain-optical coherence tomography. As a result, AST significantly attenuated the thinning of ganglion cell complex in GLAST^-/- mice in comparison to an AST-free control group. Our results suggest the possibility that AST has protective effects against glutamate neurotoxicity and oxidative stress in the retina. At present, the only treatment for NTG that is available in the clinical setting is to reduce the IOP as much as possible. Thus, our results suggest that AST supplementation may be effective for some types of NTG in which glutamate neurotoxicity and oxidative stress are involved.     

The effect of benzo[a]pyrene on sponges as model organisms in marine pollution

The majority of the investigations were performed with the marine sponge Tethya lyncurium at concentrations of 2 X 10(-8) to 1 X 10(-11) g/ml of benzo[a]pyrene (BaP). Sea-pollution was characterized as BaP equivalent activity in the Ames test. Increased activity of ornithine decarboxylase (ODC) was observed when sponges were artificially exposed at polluted marine areas for 3 weeks. In contrast to the situation in higher animals no ODC induction of the fast type was observed. Mixed function oxygenases (MFO) were not detected in sponges nor could they be induced as in vertebrates. BaP was absorbed by Tethya and concentrated 30--60-fold. In live, but not dead, artificially perfused sponges [3H]- and [14C]BaP-radiolabeled became firmly associated with DNA, RNA and protein of the sponges. The association persisted in isolated fractions, in nucleotides, in nucleosides and in protein hydrolysates. The BaP binding ratio to DNA was found to be strongly correlated to the concentration of BaP. Light modifies BaP and thus enables binding. In the dark only very low association, if any, is observed. The possible consequences of these findings are discussed.     

The structure of the bacterial and archaeal community in a biogas digester as revealed by denaturing gradient gel electrophoresis and 16S rDNA sequencing analysis

Aims:  To identify the bacterial and archaeal composition in a mesophilic biogas digester treating pig manure and to compare the consistency of two 16S rDNA-based methods to investigate the microbial structure.
Methods and results:  Sixty-nine bacterial operational taxonomic units (OTU) and 25 archaeal OTU were identified by sequencing two 16S rDNA clone libraries. Most bacterial OTU were identified as phyla of Firmicutes (47·2% of total clones), Bacteroides (35·4%) and Spirochaetes (13·2%). Methanoculleus bourgensis (29·0%), Methanosarcina barkeri (27·4%) and Methanospirillum hungatei (10·8%) were the dominant methanogens. Only 9% of bacterial and 20% of archaeal OTU matched cultured isolates at a similarity index of ≥97%. About 78% of the dominant bacterial (with abundance >3%) and 83% of archaeal OTU were recovered from the denaturing gradient gel electrophoresis (DGGE) bands of V3 regions in 16S rDNAs.
Conclusions:  In the digester, most bacterial and archaeal species were uncultured; bacteria belonging to Firmicutes , Bacteroides and Spirochaetes seem to take charge of cellulolysis, proteolysis, acidogenesis, sulfur-reducing and homoacetogenesis; the most methanogens were typical hydrogenotrophic or hydrogenotrophic/aceticlastic; DGGE profiles reflected the dominant microbiota.
Significance and Impact of the Study:  This study gave a first insight of the overall microbial structure in a rural biogas digester and also indicated DGGE was useful in displaying its dominant microbiota.     

Light-induced cytosolic calcium transients in green plant cells. ll. The effect on a K+ channel as studied by a kinetic analysis in Chara corallina

The fluorescent dye chlorotetracycline was used to study the relationship between the light-induced decrease in cytosolic free calcium concentration, [Ca²⁺]_c, and its effect on ion transport at the plasma membrane in the giant cells of Chara corallina Klein ex Willd. A kinetic analysis of the simultaneously measured light-induced changes in membrane potential and in [Ca²⁺]_c led to the same time constant of about 40 s. The reversal potential of the light effect on membrane potential was in agreement with the dominant role of a K⁺ channel in the plasma membrane. Thus, the experiments reported here provide evidence for the following light-driven signal transduction chain from the chloroplasts to K⁺ transport of the plasma membrane: (i) light causes an uptake of Ca²⁺ into the chloroplasts, (ii) this causes a decrease in cytosolic [Ca²⁺]_c, (iii) this leads to a decrease in the activity of a K⁺ channel. The results also initiated a re-analysis of previously published data of the light effect on the velocity of cytosolic streaming and supported the hypothesis that Ca²⁺ fluxes coming out of the chloroplasts upon darkening cause a Ca²⁺-induced phosphorylation of myosin, which slows down cytoplasmic streaming. Received: 3 May 1997 / Accepted: 19 May 1998     

The effect of volatile fatty acids as a sole carbon source on lipid accumulation by Cryptococcus albidus for biodiesel production

The use of volatile fatty acids (VFAs) for microbial lipid accumulation was investigated in flask cultures of Cryptococcus albidus. The optimum culture temperature and pH were 25 °C and pH 6.0, respectively, and the highest lipid content (27.8%) was obtained with ammonia chloride as a nitrogen source. The lipid yield coefficient on VFAs was 0.167 g/g of C. albidus with a VFAs (acetic, propionic, butyric acids) ratio of 8:1:1, which was in good agreement with a theoretically predicted lipid yield coefficient of the VFAs as a carbon source. The major fatty acids of the lipids accumulated by C. albidus were similar to those of soybean oil and jatropha oil. A preliminary cost analysis shows that VFAs-based biodiesel production is competitive with current palm and soybean based biodiesels. Further process development for lower aeration cost and higher lipid yield will make this process more economical.