Abundance,Condition and Size of a Foundation Species Vary with Altered Soil Conditions,Remnant Type and Potential Competitors

Ecosystems - Native biodiversity often depends on remnant vegetation for survival in agricultural landscapes. However, the size and shape of remnant patches can affect their conservation values...     

Modulation at a Distance of Proton Conductance through the Saccharomyces cerevisiae Mitochondrial F1F0-ATP Synthase by Variants of the Oligomycin Sensitivity-Conferring Protein Containing Substitutions near the C-Terminus

We have sought to elucidate how the oligomycin sensitivity-conferring protein (OSCP) of the mitochondrial F₁F₀-ATP synthase (mtATPase) can influence proton channel function. Variants of OSCP, from the yeast Saccharomyces cerevisiae, having amino acid substitutions at a strictly conserved residue (Gly166) were expressed in place of normal OSCP. Cells expressing the OSCP variants were able to grow on nonfermentable substrates, albeit with some increase in generation time. Moreover, these strains exhibited increased sensitivity to oligomycin, suggestive of modification in functional interactions between the F₁ and F₀ sectors mediated by OSCP. Bioenergetic analysis of mitochondria from cells expressing OSCP variants indicated an increased respiratory rate under conditions of no net ATP synthesis. Using specific inhibitors of mtATPase, in conjunction with measurement of changes in mitochondrial transmembrane potential, it was revealed that this increased respiratory rate was a result of increased proton flux through the F₀ sector. This proton conductance, which is not coupled to phosphorylation, is exquisitely sensitive to inhibition by oligomycin. Nevertheless, the oxidative phosphorylation capacity of these mitochondria from cells expressing OSCP variants was no different to that of the control. These results suggest that the incorporation of OSCP variants into functional ATP synthase complexes can display effects in the control of proton flux through the F₀ sector, most likely mediated through altered protein—protein contacts within the enzyme complex. This conclusion is supported by data indicating impaired stability of solubilized mtATPase complexes that is not, however, reflected in the assembly of functional enzyme complexes in vivo. Given a location for OSCP atop the F₁-₃₃ hexamer that is distant from the proton channel, then the modulation of proton flux by OSCP must occur at a distance. We consider how subtle conformational changes in OSCP may be transmitted to F₀.     

Selective inhibition of fibroblast growth factor (FGF)-stimulated mitogenesis by a FGF receptor-1-derived phosphopeptide.

The activated fibroblast growth factor receptor (FGFR)-1 is phosphorylated on five tyrosine residues outside the catalytic site. Although one such residue, Tyr730, is flanked by potential binding sites for phosphotyrosine-interacting molecules, a physiological role for this region is still controversial. We report that a cell-permeant phosphopeptide mimic of this site, FGFR730(p)Y, inhibits FGF-mediated mitogenesis in cells with no effect on responses stimulated by other growth factors. A similar phosphopeptide corresponding to the phospholipase Cgamma binding site on the receptor had no effect on the mitogenic response. The FGFR730(p)Y peptide did not inhibit phosphorylation of p90/FRS2 or Erk, suggesting that it does not act by inhibiting the Erk-kinase cascade. However, the FGFR730(p)Y peptide bound Shc in a manner requiring both phosphorylated tyrosine and a putative PTB domain binding determinant. These data suggest that the peptide might inhibit mitogenesis by competing with the corresponding site on the FGFR for the ability to bind SHC.     

Reproductive history and nest environment are correlated with circulating androgen and glucocorticoid concentrations in a parental care-providing teleost fish

Using a long-term study population of wild smallmouth bass Micropterus dolomieu in a connected river-lake system, we investigated whether circulating glucocorticoid (cortisol) and androgen (testosterone) concentrations are influenced by reproductive investment and nesting environment in fish providing nest-guarding paternal care. For all individuals, we collected measures of reproductive history and the value of current parental care. We assessed nest environment and monitored individuals to quantify seasonal reproductive success. Finally, we measured circulating cortisol concentrations following a standardized stressor and circulating testosterone concentrations. Using general linear models, we found that poststress circulating cortisol concentrations were positively related to water temperature and were higher in fish nesting in the river than in the lake. Circulating testosterone concentrations were negatively related to water temperature and were higher in reproductively experienced fish. When considering the factors that influence reproductive success, we found that only parental size was positively related to current nest success. In summary, the results demonstrate that nesting environment is correlated with parental stress responses during parental care, while reproductive history and nesting environment are correlated with circulating androgen concentrations. Collectively, these results offer insight into the roles of both glucocorticoid and androgen steroid hormones during parental care in teleost fish.     

Diel rhythmicity in amino acid uptake by Prochlorococcus

The marine cyanobacterium Prochlorococcus , the most abundant phototrophic organism on Earth, numerically dominates the phytoplankton in nitrogen (N)-depleted oceanic gyres. Alongside inorganic N sources such as nitrite and ammonium, natural populations of this genus also acquire organic N, specifically amino acids. Here, we investigated using isotopic tracer and flow cytometric cell sorting techniques whether amino acid uptake by Prochlorococcus is subject to a diel rhythmicity, and if so, whether this was linked to a specific cell cycle stage. We observed, in contrast to diurnally similar methionine uptake rates by Synechococcus cells, obvious diurnal rhythms in methionine uptake by Prochlorococcus cells in the tropical Atlantic. These rhythms were confirmed using reproducible cyclostat experiments with a light-synchronized axenic Prochlorococcus (PCC9511 strain) culture and ³⁵S-methionine and ³H-leucine tracers. Cells acquired the tracers at lower rates around dawn and higher rates around dusk despite >10⁴ times higher concentration of ammonium in the medium, presumably because amino acids can be directly incorporated into protein. Leucine uptake rates by cells in the S+G₂ cell cycle stage were consistently 2.2 times higher than those of cells at the G₁ stage. Furthermore, S+G₂ cells upregulated amino acid uptake 3.5 times from dawn to dusk to boost protein synthesis prior to cell division. Because Prochlorococcus populations can account from 13% at midday to 42% at dusk of total microbial uptake of methionine and probably of other amino acids in N-depleted oceanic waters, this genus exerts diurnally variable, strong competitive pressure on other bacterioplankton populations.     

The cysteine protease α-clostripain is not essential for the pathogenesis of Clostridium perfringens-mediated myonecrosis

Clostridium perfringens is the causative agent of clostridial myonecrosis or gas gangrene and produces many different extracellular toxins and enzymes, including the cysteine protease α-clostripain. Mutation of the α-clostripain structural gene, ccp, alters the turnover of secreted extracellular proteins in C. perfringens, but the role of α-clostripain in disease pathogenesis is not known. We insertionally inactivated the ccp gene C. perfringens strain 13 using TargeTron technology, constructing a strain that was no longer proteolytic on skim milk agar. Quantitative protease assays confirmed the absence of extracellular protease activity, which was restored by complementation with the wild-type ccp gene. The role of α-clostripain in virulence was assessed by analysing the isogenic wild-type, mutant and complemented strains in a mouse myonecrosis model. The results showed that although α-clostripain was the major extracellular protease, mutation of the ccp gene did not alter either the progression or the development of disease. These results do not rule out the possibility that this extracellular enzyme may still have a role in the early stages of the disease process.     

Iron incorporation and post-malaria anaemia

Background

Iron supplementation is employed to treat post-malarial anaemia in environments where iron deficiency is common. Malaria induces an intense inflammatory reaction that stalls reticulo-endothelial macrophagal iron recycling from haemolysed red blood cells and inhibits oral iron absorption, but the magnitude and duration of these effects are unclear.

Methodology/Principal Findings

We examined the red blood cell incorporation of oral administered stable isotopes of iron and compared incorporation between age matched 18 to 36 months old children with either anaemia post-malaria (n = 37) or presumed iron deficiency anaemia alone (n = 36). All children were supplemented for 30 days with 2 mg/kg elemental iron as liquid iron sulphate and administered ⁵⁷Fe and ⁵⁸Fe on days 1 and 15 of supplementation respectively. ⁵⁷Fe and⁵⁸Fe incorporation were significantly reduced (8% vs. 28%: p<0.001 and 14% vs. 26%: p = 0.045) in the malaria vs. non-malaria groups. There was a significantly greater haemoglobin response in the malaria group at both day 15 (p = 0.001) and 30 (p<0.000) with a regression analysis estimated greater change in haemoglobin of 7.2 g/l (s.e. 2.0) and 10.1 g/l (s.e. 2.5) respectively.

Conclusion/Significance

Post-malaria anaemia is associated with a better haemoglobin recovery despite a significant depressant effect on oral iron incorporation which may indicate that early erythropoetic iron need is met by iron recycling rather than oral iron. Supplemental iron administration is of questionable utility within 2 weeks of clinical malaria in children with mild or moderate anaemia.