Specific bonds between an iron oxide surface and outer membrane cytochromes MtrC and OmcA from Shewanella oneidensis MR-1

Shewanella oneidensis MR-1 is purported to express outer membrane cytochromes (e.g., MtrC and OmcA) that transfer electrons directly to Fe(III) in a mineral during anaerobic respiration. A prerequisite for this type of reaction would be the formation of a stable bond between a cytochrome and an iron oxide surface. Atomic force microscopy (AFM) was used to detect whether a specific bond forms between a hematite (Fe(2)O(3)) thin film, created with oxygen plasma-assisted molecular beam epitaxy, and recombinant MtrC or OmcA molecules coupled to gold substrates. Force spectra displayed a unique force signature indicative of a specific bond between each cytochrome and the hematite surface. The strength of the OmcA-hematite bond was approximately twice that of the MtrC-hematite bond, but direct binding to hematite was twice as favorable for MtrC. Reversible folding/unfolding reactions were observed for mechanically denatured MtrC molecules bound to hematite. The force measurements for the hematite-cytochrome pairs were compared to spectra collected for an iron oxide and S. oneidensis under anaerobic conditions. There is a strong correlation between the whole-cell and pure-protein force spectra, suggesting that the unique binding attributes of each cytochrome complement one another and allow both MtrC and OmcA to play a prominent role in the transfer of electrons to Fe(III) in minerals. Finally, by comparing the magnitudes of binding force for the whole-cell versus pure-protein data, we were able to estimate that a single bacterium of S. oneidensis (2 by 0.5 microm) expresses approximately 10(4) cytochromes on its outer surface.     

The movement protein of cucumber mosaic virus traffics into sieve elements in minor veins of nicotiana clevelandii

The location of the 3a movement protein (MP) of cucumber mosaic virus (CMV) was studied by quantitative immunogold labeling of the wild-type 3a MP in leaves of Nicotiana clevelandii infected by CMV as well as by using a 3a-green fluorescent protein (GFP) fusion expressed from a potato virus X (PVX) vector. Whether expressed from CMV or PVX, the 3a MP targeted plasmodesmata and accumulated in the central cavity of the pore. Within minor veins, the most extensively labeled plasmodesmata were those connecting sieve elements and companion cells. In addition to targeting plasmodesmata, the 3a MP accumulated in the parietal layer of mature sieve elements. Confocal imaging of cells expressing the 3a-GFP fusion protein showed that the 3a MP assembled into elaborate fibrillar formations in the sieve element parietal layer. The ability of 3a-GFP, expressed from PVX rather than CMV, to enter sieve elements demonstrates that neither the CMV RNA nor the CMV coat protein is required for trafficking of the 3a MP into sieve elements. CMV virions were not detected in plasmodesmata from CMV-infected tissue, although large CMV aggregates were often found in the parietal layer of sieve elements and were usually surrounded by 3a MP. These data suggest that CMV traffics into minor vein sieve elements as a ribonucleoprotein complex that contains the viral RNA, coat protein, and 3a MP, with subsequent viral assembly occurring in the sieve element parietal layer.     

Cell-to-cell and phloem-mediated transport of potato virus X. The role of virions

Movement-deficient potato virus X (PVX) mutants tagged with the green fluorescent protein were used to investigate the role of the coat protein (CP) and triple gene block (TGB) proteins in virus movement. Mutants lacking either a functional CP or TGB were restricted to single epidermal cells. Microinjection of dextran probes into cells infected with the mutants showed that an increase in the plasmodesmal size exclusion limit was dependent on one or more of the TGB proteins and was independent of CP. Fluorescently labeled CP that was injected into epidermal cells was confined to the injected cells, showing that the CP lacks an intrinsic transport function. In additional experiments, transgenic plants expressing the PVX CP were used as rootstocks and grafted with nontransformed scions. Inoculation of the PVX CP mutants to the transgenic rootstocks resulted in cell-to-cell and systemic movement within the transgenic tissue. Translocation of the CP mutants into sink leaves of the nontransgenic scions was also observed, but infection was restricted to cells close to major veins. These results indicate that the PVX CP is transported through the phloem, unloads into the vascular tissue, and subsequently is transported between cells during the course of infection. Evidence is presented that PVX uses a novel strategy for cell-to-cell movement involving the transport of filamentous virions through plasmodesmata.     

Cloning and expression analysis of two distinct HIF-alpha isoforms – gcHIF-1alpha and gcHIF-4alpha – from the hypoxia-tolerant grass carp,Ctenopharyngodon idellus

Background  

Hypoxia-inducible factors (HIFs) are involved in adaptive and survival responses to hypoxic stress in mammals. In fish, very little is known about the functions of HIFs.     

Effects of size asymmetry on aggression and food acquisition in Arctic charr

The feeding rate of a group (DS) of two small, two medium and two large 1+ Arctic charr Salvelinus alpinus was higher than in a group of six fish of the same size (SS), suggesting that size distribution had an effect on feeding behaviour, with a correlation between the size of the fish and the amount of food eaten–the largest fish eating the most. Against predictions, rate of aggression was not higher in the SS groups; rather there was a modest tendency of higher aggression among individuals in the DS groups.     

The effect of prenatal procarbazine treatment on brain development in the rat

Groups of pregnant Sprague-Dawley rats were treated orally with procarbazine, an antineoplastic drug, at dose levels of 0, 1.0, 2.5, 5.0, 7.5, and 10.0 mg/kg/day from days 12 through 15 of gestation. Following normal delivery, offspring were raised until day 21 and sacrificed, and their brains removed and weighed. A dose-dependent micrencephaly, characterized by hypoplasia of the cerebral hemispheres, was seen starting at 2.5 mg/kg/day. In a second study, groups of pregnant female rats were given a single dose of 10 mg/kg procarbazine on gestation day 12, 13, 14, or 15. Micrencephaly occurred in 21-day-old offspring from all groups, with the greatest effect induced on days 13, 14 and 15. Analysis of brain region weights revealed a maximum reduction in neocortex weight in offspring from groups treated on days 13 and 14. The hippocampus, cerebellum, and diencephalon-midbrain were also reduced in size, depending on the day of treatment, while the corpus striatum and pons-medulla were spared. In a final study, embryos from females treated on gestation days 12 through 15 were removed, fixed, and sectioned at 24-hour intervals starting on gestation days 13. Necrosis and cellular degeneration were observed with decreasing severity in the telencephalon, diencephalon, mesencephalon, and medulla. The neocortex of 20-day treated fetuses was characterized by a thickening of the ventricular zone and reduced cellularity of the cortical plate.     

Envelope diversity, characteristics of V3 region and predicted co-receptor usage of human immunodeficiency viruses infecting north indians

Subtypes of human immunodeficiency virus type 1 circulating in 21 north Indian patients were characterized based on the partial sequence of the gp120 envelope protein. A majority of viruses (85.7%, 18/21) were subtype C, while 14.3% (3/21) were subtype A. Sequence analysis revealed that the V3 region was highly conserved compared with V4 and V5. The predicted use of co-receptors indicated exclusive usage of R5, except for two subtype A viruses (AIIMS279 and AIIMS281). Our results demonstrate conservation within the V3 loop of subtype C viruses, and suggest the emergence of non-clade C viruses in the north Indian population.