Life at the energetic edge: kinetics of circumneutral iron oxidation by lithotrophic iron-oxidizing bacteria isolated from the wetland-plant rhizosphere

Batch cultures of a lithotrophic Fe(II)-oxidizing bacterium, strain BrT, isolated from the rhizosphere of a wetland plant, were grown in bioreactors and used to determine the significance of microbial Fe(II) oxidation at circumneutral pH and to identify abiotic variables that affect the partitioning between microbial oxidation and chemical oxidation. Strain BrT grew only in the presence of an Fe(II) source, with an average doubling time of 25 h. In one set of experiments, Fe(II) oxidation rates were measured before and after the cells were poisoned with sodium azide. These experiments indicated that strain BrT accounted for 18 to 53% of the total iron oxidation, and the average cellular growth yield was 0.70 g of CH2O per mol of Fe(II) oxidized. In a second set of experiments, Fe(II) was constantly added to bioreactors inoculated with live cells, killed cells, or no cells. A statistical model fitted to the experimental data demonstrated that metabolic Fe(II) oxidation accounted for up to 62% of the total oxidation. The total Fe(II) oxidation rates in these experiments were strongly limited by the rate of Fe(II) delivery to the system and were also influenced by O2 and total iron concentrations. Additionally, the model suggested that the microbes inhibited rates of abiotic Fe(II) oxidation, perhaps by binding Fe(II) to bacterial exopolymers. The net effect of strain BrT was to accelerate total oxidation rates by up to 18% compared to rates obtained with cell-free treatments. The results suggest that neutrophilic Fe(II)-oxidizing bacteria may compete for limited O2 in the rhizosphere and therefore influence other wetland biogeochemical cycles.     

Specificity of gene regulation

The physiologically coordinated expression of our genome requires exquisite regulation of gene specificity. Recent advances demonstrate that this formidable task is accomplished by diverse mechanisms and networks that operate at distinct levels within the nucleus.     

Effects of cytotoxic T lymphocytes (CTL) directed against a single simian immunodeficiency virus (SIV) Gag CTL epitope on the course of SIVmac239 infection

Vaccine-induced cytotoxic T lymphocytes (CTL) have been implicated in the control of virus replication in simian immunodeficiency virus (SIV)-challenged and simian-human immunodeficiency virus-challenged macaques. Therefore, we wanted to test the impact that vaccine-induced CTL responses against an immunodominant Gag epitope might have in the absence of other immune responses. By themselves, these strong CTL responses failed to control SIVmac239 replication.     

Oxygen and nitrate-dependent regulation of <Emphasis Type="Italic">dmsABC</Emphasis> operon expression in <Emphasis Type="Italic">Escherichia coli</Emphasis>: sites for Fnr and NarL protein interactions

Background  

Escherichia coli can respire anaerobically using dimethyl sulfoxide (DMSO) or trimethylamine-N-oxide (TMAO) as the terminal electron acceptor for anaerobic energy generation. Expression of the dmsABC genes that encode the membrane-associated DMSO/TMAO reductase is positively regulated during anaerobic conditions by the Fnr protein and negatively regulated by the NarL protein when nitrate is present.     

Reducing malaria by mosquito-proofing houses

Sometimes, valuable lessons from history are forgotten, remain unknown, or worse, are ignored. This article reminds us of the pioneering work of Angelo Celli at the end of the 19th century, who demonstrated that people could be protected from malaria by screening their homes against mosquitoes. Since then, public health scientists have continued to show that simple changes in house design have the potential for protecting people against this life-threatening disease. Yet today, this type of intervention remains virtually ignored. The literature reviewed here demonstrates the enormous potential of these methods to reduce malaria, in the hope that it will stimulate scientific debate and further research.     

Host-ectoparasite specificity in a small mammal community in an area of Atlantic Rain Forest (Ilha Grande, State of Rio de Janeiro), Southeastern Brazil

The analyses of the ectoparasite species associated with a small mammal community on Ilha Grande, a coastal island in southern of the state of Rio de Janeiro, Brazil, evaluated the level of host-ectoparasite specificity. Was used the Jaccard index for qualitative data to analyse the similarity. The lowest value of similarity occurred between Proechimys iheringi and Marmosops incanus and between Sciurus aestuans and Nectomys squamipes (Cj=0.08) and the highest between P. iheringi and Oxymycterus sp. (Cj=0.33). This index showed a low value of similarity across the ectoparasite community. The only exception from this pattern of high host specificity occurred with P. iheringi and Oxymycterus sp., which shared five species of ectoparasites. The similarity values, for most of the cases, is smaller than 0.2.     

Ash content modulation of torsionally derived effective material properties in cortical mouse bone

The purpose of this study was to evaluate the effects of isolated alterations in mineral content on mouse bone torsional properties. The femora and tibiae from 25 eight-week-old male A/J strain mice were divided into five groups and selectively decalcified from 5% to 20%. The right femora were then tested to failure in torsion while the tibiae were ashed to determine final mineral content of the decalcified bones. Contralateral femora were serially cross-sectioned to determine geometric properties, and effective material properties were then calculated from the geometric and structural properties of each femoral pair. We found that the relationship between ash content and effective shear modulus or maximum effective shear stress could best be characterized through a power law, with an exponential factor of 6.79 (R2 = 0.85) and 4.04 (R2 = 0.67), respectively. This indicates that in a murine model, as with other species, small changes in ash content significantly influence effective material properties. Furthermore, it appears that (in adolescent A/J strain mice) effective shear modulus is more heavily affected by changes in mineralization than is maximum effective shear stress when these properties are derived from whole bone torsional tests to failure.     

Changes in ectonucleotidase activities in rat Sertoli cells during sexual maturation

Sertoli cell maturation is a complex process involving both morphological and biochemical changes. These cells have previously been shown to be targets for extracellular purine structures such as ATP and adenosine. These compounds evoke responses in rat Sertoli cells through the purinoceptor families, P₂X and P₂Y and PA₁. The signals to purinoceptors are usually terminated by the action of ectonucleotidases. In a previous work, we demonstrated that rat Sertoli cells have ecto-ATPdiphosphohydrolase (EC 3.6.1.5), ecto-5-nucleotidase (EC 3.1.3.5) and ecto-adenosine deaminase (ecto-ADA) (EC 3.5.4.4) activities. Here we investigated whether some changes occur during rat Sertoli cell maturation in these activities. Rat Sertoli cells obtained from rats of different ages representing the pre pubertal, mid pubertal and young adult (10-, 18- and 35-day-old, respectively) were cultured and used for different assays. The nucleotide hydrolysis was estimated by measuring the Pi released using a colorimetric method and by HPLC analysis. ATP and ADP hydrolysis was increased 3-fold during sexual maturation. AMP hydrolysis increased 4-fold in 10- to 35-day-old Sertoli cells. Similar results were obtained when we used other substrates to measure the extracellular hydrolysis of nucleotides (GTP, GDP, GMP and IMP). The ecto-ADA activity showed a 2-fold increase in the specific activity (18- to 35-day-old Sertoli cells). The termination of the purine cascade by adenosine degradation was faster in the 35- than in 18-day-old Sertoli cells. Follicle Stimulating Hormone (FSH) influences on the ectonucleotidase activities were investigated in 10- and 18-day-old Sertoli cells and a significant increase in the ATP and ADP hydrolysis was observed. Our results show an increase in the extracellular purine cascade during the Sertoli cell development, indicating a rise in the purine communication inside the seminiferous tubules with rat sexual maturation.     

Cell-to-cell movement of potexviruses: evidence for a ribonucleoprotein complex involving the coat protein and first triple gene block protein

The triple gene block proteins (TGBp1-3) and coat protein (CP) of potexviruses are required for cell-to-cell movement. Separate models have been proposed for intercellular movement of two of these viruses, transport of intact virions, or a ribonucleoprotein complex (RNP) comprising genomic RNA, TGBp1, and the CP. At issue therefore, is the form(s) in which RNA transport occurs and the roles of TGBp1-3 and the CP in movement. Evidence is presented that, based on microprojectile bombardment studies, TGBp1 and the CP, but not TGBp2 or TGBp3, are co-translocated between cells with viral RNA. In addition, cell-to-cell movement and encapsidation functions of the CP were shown to be separable, and the rate-limiting factor of potexvirus movement was shown not to be virion accumulation, but rather, the presence of TGBp1-3 and the CP in the infected cell. These findings are consistent with a common mode of transport for potexviruses, involving a non-virion RNP, and show that TGBp1 is the movement protein, whereas TGBp2 and TGBp3 are either involved in intracellular transport or interact with the cellular machinery/docking sites at the plasmodesmata.     

The joys of HexNAc. The synthesis and function of N-andO-glycan branches

This review covers discoveries made over the past 30–35 years that were important to our understanding of the synthetic pathway required for initiation of the antennae or branches on complex N-glycans and O-glycans. The review deals primarily with the author's contributions but the relevant work of other laboratories is also discussed. The focus of the review is almost entirely on the glycosyltransferases involved in the process. The following topics are discussed. (1) The localization of the synthesis of complex N-glycan antennae to the Golgi apparatus. (2) The evolutionary boundary at the stage in N-glycan processing where there is a change from oligomannose to complex N-glycans; this switch correlates with the appearance of multicellular organisms. (3) The discovery of the three enzymes which play a key role in this switch, N-acetylglucosaminyltransferases I and II and mannosidase II. (4) The yellow brick road which leads from oligomannose to highly branched complex N-glycans with emphasis on the enzymes involved in the process and the factors which control the routes of synthesis. (5) A short discussion of the characteristics of the enzymes involved and of the genes that encode them. (6) The role of complex N-glycans in mammalian and Caenorhabditis elegans development. (7) The crystal structure of N-acetylglucosaminyltransferase I. (8) The discovery of the enzymes which synthesize O-glycan cores 1, 2, 3 and 4 and their elongation.