The effect of density-dependent treatment and behavior change on the dynamics of HIV transmission

In this work, we propose a model for heterosexual transmission of HIV/AIDS in a population of varying size with an intervention program in which treatment and/or behavior change of the infecteds occur as an increasing function of the density of the infected class in the population. This assumption has socio-economic implications which is important for public health considerations since density-dependent treatment/behavior change may be more cost-saving than a program where treatment/behavior change occurs linearly with respect to the number of infecteds. We will make use of the conservation law of total sexual contacts which enables us to reduce the two-sex model to a simpler one-sex formulation. Analytical results will be given. Unlike a similar model with linear treatment/behavior change in Hsieh (1996) where conditions were obtained for the eradication of disease, we will show that density-dependent treatment/behavior change cannot eradicate the disease if the disease is able to persist without any treatment/behavior change. This work demonstrates the need to further understand how treatment/behavior change occurs in a society with varying population.     

Helicobacter pylori in familial clusters based on antibody profile

Studies have shown a high prevalence of Helicobacter pylori infection in close communities and that intrafamilial spread during early childhood may be a route of transmission. A total of 72 household members from 21 families were enrolled in this study. Sera from individuals showed 50/72 (69.4%) seropositive for IgG against H. pylori by ELISA. Western blots showed diversity in the protein profiles with molecular masses ranging from approximately 8 to 130 kDa. Cohen's kappa statistical analysis of the blot patterns showed that nine families demonstrated similar profiles (100%), while 4 other families showed varying similarities (17-50%). The results support the hypothesis of intrafamilial transmission of H. pylori. Furthermore, serological studies can be used as an effective approach to determine the familial status in relation to H. pylori infection.     

Intercellular power transmission along trichomes of cyanobacteria

An attempt at demonstrating lateral power transmission over millimeter distances along a coupling membrane has been undertaken. Trichomes of the multicellular filamentous cyanobacteria Phormidium uncinatum were illuminated with a very narrow light beam forming a light spot that covered only 4–5% of a 1–2 mm long cyanobacterial trichome. Such illumination was found to support motility (gliding along agar surface) of the trichome under conditions when the light was the only energy source. It was also shown that illumination with the light spot caused rotation of rings of slime (accompanying the operation of the ‘motors’ responsible for the motility of cyanobacteria) not only in the illuminated, but also in the distal, nonilluminated part of the trichome. Electric potential transmission along trichomes was revealed by means of the extracellular electrode technique. The light spot was found to induce generation of an electric potential difference between two electrodes in the dark region of the trichomes, which were placed at different distances from the illuminated end. Cutting the trichomes between the light spot and the closest ‘dark’ electrode abolished this effect. Valinomycin + K⁺ and carbonyl cyanide p-trifluoromethoxyphenylhydrazone affected the potential difference formation between two ‘dark’ electrodes much stronger than that between a light and a dark electrode. All the light spot-induced effects develop in the seconds time scale. Both the amplitudes and the kinetics of the potential difference measured with four electrodes placed along the trichome prove to be in good agreement with the theoretical curves computed on the basis of the electric cable equation. It is concluded that transcellular power transmission in the form of Δψ takes place along trichomes of cyanobacteria. This confirms the hypothesis about the biological function of Δψ as a transportable form of energy.     

利用反向遗传技术研究H9N2亚型AIV传播途径的分子机制

利用反向遗传技术,通过基因重排方法,产生两个表面基因来自A/Chicken/Guangdong/SS/94(H9N2)禽流感病毒(avian influenza virus,AIV)株和其余基因来自A/Chicken/Shanghai/F/98(H9N2)AIV株的3株H9N2亚型重排AIV,动物传播性试验发现A/Chicken/Shanghai/F/98(H9N2)株、A/Chicken/Guangdong/SS/94(H9N2)AIV株和3株H9N2亚型重排AIV都可以经直接接触途径传播;在粪便接触途径下,3株重排AIV都不经粪便接触传播;只有A/Chicken/Shanghai/F/98(H9N2)株和重排AIV RF7/SSHA能经过气溶胶途径传播。HI试验结果进一步证明了以上的结果。实验结果表明H9N2亚型AIV的NA基因与H9N2亚型AIV气溶胶传播途径有重要的关系,即1998年中国大陆H9N2亚型AIV大流行可能是因为病毒获得气溶胶传播途径的特性,推测病毒的NA基因发挥了重要作用。     

蛋白质：生物界中又一类信息的储存者和传递者 ——对 prion 生物学相关知识的重新解读

蛋白质在相当一段时间内一直被认为只是 DNA 或 RNA 等遗传物质的表达形式,其单独不具有储存和传递生物信息的功能,而储存和传递生物信息却是遗传物质的两个基本属性 . 随着近年来 prion 生物学的出现和研究的逐步深入,人们已经认识到蛋白质单独就具有储存和传递生物信息的功能,从这个意义上讲,蛋白质也是一类遗传物质 . 所以很有必要站在这个角度对 prion 生物学的相关知识进行重新的梳理和再认识,通过对哺乳动物 prion 生物学和真菌 prion 生物学各自发展历程的简要回顾和最新研究成果的介绍,以及它们之间相同点和不同点的比较,总结出蛋白质储存和传递生物信息的一般规律并指出其表现形式的多样性 .     

Genome sequence, structural proteins, and capsid organization of the cyanophage Syn5: a "horned" bacteriophage of marine synechococcus

Marine Synechococcus spp and marine Prochlorococcus spp are numerically dominant photoautotrophs in the open oceans and contributors to the global carbon cycle. Syn5 is a short-tailed cyanophage isolated from the Sargasso Sea on Synechococcus strain WH8109. Syn5 has been grown in WH8109 to high titer in the laboratory and purified and concentrated retaining infectivity. Genome sequencing and annotation of Syn5 revealed that the linear genome is 46,214 bp with a 237 bp terminal direct repeat. Sixty-one open reading frames (ORFs) were identified. Based on genomic organization and sequence similarity to known protein sequences within GenBank, Syn5 shares features with T7-like phages. The presence of a putative integrase suggests access to a temperate life cycle. Assignment of 11 ORFs to structural proteins found within the phage virion was confirmed by mass-spectrometry and N-terminal sequencing. Eight of these identified structural proteins exhibited amino acid sequence similarity to enteric phage proteins. The remaining three virion proteins did not resemble any known phage sequences in GenBank as of August 2006. Cryo-electron micrographs of purified Syn5 virions revealed that the capsid has a single “horn”, a novel fibrous structure protruding from the opposing end of the capsid from the tail of the virion. The tail appendage displayed an apparent 3-fold rather than 6-fold symmetry. An 18 Å resolution icosahedral reconstruction of the capsid revealed a T = 7 lattice, but with an unusual pattern of surface knobs. This phage/host system should allow detailed investigation of the physiology and biochemistry of phage propagation in marine photosynthetic bacteria.     

Occurrence,Molecular Characterization and Vector Transmission of a Phytoplasma Associated with Rapeseed Phyllody in Iran

Symptoms of rapeseed phyllody were observed in rapeseed fields of Fars, Ghazvin, Isfahan, Kerman and Yazd provinces in Iran. Circulifer haematoceps leafhoppers testing positive for phytoplasma in polymerase chain reaction (PCR) successfully transmitted a rapeseed phyllody phytoplasma isolate from Zarghan (Fars province) to healthy rapeseed plants directly after collection in the field or after acquisition feeding on infected rapeseed in the greenhouse. The disease agent was transmitted by the same leafhopper from rape to periwinkle, sesame, stock, mustard, radish and rocket plants causing phytoplasma‐type symptoms in these plants. PCR assays using phytoplasma‐specific primer pair P1/P7 or nested PCR using primers P1/P7 followed by R16F2n/R2, amplified products of expected size (1.8 and 1.2 kbp, respectively) from symptomatic rapeseed plants and C. haematoceps specimens. Restriction fragment length polymorphism analysis of amplification products of nested PCR and putative restriction site analysis of 16S rRNA gene indicated the presence of aster yellows‐related phytoplasmas (16SrI‐B) in naturally and experimentally infected rapeseed plants and in samples of C. haematoceps collected in affected rapeseed fields. Sequence homology and phylogenetic analysis of 16S rRNA gene confirmed that the associated phytoplasma detected in Zarghan rapeseed plant is closer to the members of the subgroup 16SrI‐B than to other members of the AY group. This is the first report of natural occurrence and characterization of rapeseed phyllody phytoplasma, including its vector identification, in Iran.     

Variability in the transmission efficiency of potyviruses by different clones ofAphis gossypii

A sample of seventy-twoAphis gossypii Glover (Homoptera: Aphididae) clones was collected in south-eastern France. The efficiency of these clones to transmit a potyvirus (papaya ringspot virus T-strain) was assessed in controlled conditions. In a first screening, the virus was transmitted by all clones and a 3.5-fold difference between the most and least efficient clones was obtained. During subsequent trials, which were carried out to confirm the differences in the transmission efficiency of these clones, only one clone proved to be more efficient than the others. This difference appeared consistent over a 1-year period, and was also confirmed with 4 other related potyviruses.

---

Résumé Un échantillon de 72 clones deA. gossypii a été collecté dans le Sud-Est de la France. L'efficacité de transmission d'un potyvirus (PRSV-T) a été mesurée en conditions contr?lées pour chacun de ces clones. Un premier screening a permis de montrer que tous les clones transmettaient ce virus, et qu'un rapport de 3,5 existait entre l'efficacité de transmission du clone le plus efficace et celle du clone le moins efficace. Au cours des essais ultérieurs destinés à confirmer ces différences, un seul clone s'est montré significativement plus efficace que les autres. Cette différence s'est maintenue pendant la période d'essais (1 an). Elle s'est reproduite avec 4 autre potyvirus apparentés.

     

Convergence to stationary distributions in two-species stochastic competition models

Two sets of sufficient conditions are given for convergence to stationary distributions, for some general models of two species competing in a randomly varying environment. The models are nonlinear stochastic difference equations which define Markov chains. One set of sufficient conditions involves strong continuity and -irreducibility of the transition probability for the chain. The second set has a much weaker irreducibility condition, but is only applicable to monotonic models. The results are applied to a stochastic two-species Ricker model, and to Chesson's lottery model with vacant space, to illustrate how the assumptions can be checked in specific models.