The polypeptides COX2A and COX2B are essential components of the mitochondrial cytochrome c oxidase of Toxoplasma gondii

Two genes encoding cytochrome c oxidase subunits, Cox2a and Cox2b, are present in the nuclear genomes of apicomplexan parasites and show sequence similarity to corresponding genes in chlorophycean algae. We explored the presence of COX2A and COX2B subunits in the cytochrome c oxidase of Toxoplasma gondii. Antibodies were raised against a synthetic peptide containing a 14-residue fragment of the COX2A polypeptide and against a hexa-histidine-tagged recombinant COX2B protein. Two distinct immunochemical stainings localized the COX2A and COX2B proteins in the parasite's mitochondria. A mitochondria-enriched fraction exhibited cyanide-sensitive oxygen uptake in the presence of succinate. T. gondii mitochondria were solubilized and subjected to Blue Native Electrophoresis followed by second dimension electrophoresis. Selected protein spots from the 2D gels were subjected to mass spectrometry analysis and polypeptides of mitochondrial complexes III, IV and V were identified. Subunits COX2A and COX2B were detected immunochemically and found to co-migrate with complex IV; therefore, they are subunits of the parasite's cytochrome c oxidase. The apparent molecular mass of the T. gondii mature COX2A subunit differs from that of the chlorophycean alga Polytomella sp. The data suggest that during its biogenesis, the mitochondrial targeting sequence of the apicomplexan COX2A precursor protein may be processed differently than the one from its algal counterpart.     

Regulation of testosterone degradation in Comamonas testosteroni

Recently, we have identified a gene encoding a LuxR-type factor, TeiR (Testosterone-inducible Regulator), which positively regulates steroid degradation in Comamonas testosteroni. Herein, we demonstrate that TeiR interacts in vivo with steroid catabolic gene promoters. The presence of testosterone induces a significant TeiR protein increase at the early logarithmic phase of growth. Interestingly, it is not until the early stationary phase where the activation of a steroid-inducible gene promoter is observed, indicating that testosterone might not be the true inductor of the steroid degradation pathway. In addition, beta-galactosidase expression driven by a testosterone-inducible promoter is prematurely activated in cells cultured in medium supplemented with ethyl acetate extracts obtained from the early stationary phase cell-free supernatants of C. testosteroni grown in presence of testosterone. Complementation experiments of C. testosteroni wild type performed with teiR deletion constructs indicate that extra-copies of deleted-TeiR exert a dominant negative effect on the wild-type TeiR protein. While, when C. testosteroni teiR mutants were used to carry out complementation assays only the full length gene can overcome the teiR mutant phenotype. Altogether these findings indicate that TeiR regulates steroid catabolic genes interacting with their promoters and suggest that this interaction requires the presence of a testosterone-derived metabolite to induce the system.     

Trophic status based on nutrient concentration scales and primary producers community of tropical coastal lagoons influenced by groundwater discharges

Changes in the rate of primary production as an indication of trophic status of aquatic ecosystems have been one of the major indicators of their health. Despite different approaches been devised for evaluating this process, few are useful for comparison and generalization of their results. The coastal zone ecosystems of Yucatan (SE Mexico) exhibit hydrological variability closely associated with the groundwater discharges, which are the only freshwater sources in the coastal ecosystems. In order to learn about the trophic status of karstic tropical coastal lagoons, three of them (Celestun, Chelem and Dzilam) located in Yucatan (SE, Mexico) were monitored for inorganic nutrients, Chl-a, phytoplankton and macrophyte productivity. The nitrate concentrations suggest that the trophic status was influenced by fresh water springs, being meso-eutrophic in Celestun, oligotrophic in Chelem, and mesotrophic in Dzilam. In the case of ammonium ions, the three lagoons were mesotrophic, indicating that processes such as remineralization play an important role in the trophic dynamic of these shallow ecosystems. According to phosphate concentrations, Celestun and Dzilam were mesotrophic, and Chelem was oligotrophic. External inputs of phosphate and bioturbation by waterfowl may be responsible of these differences. Primary productivity at Celestun was greater than at Chelem and Dzilam lagoons and the contribution by seagrasses was significant in all three. It is found that indices based on nutrient concentration and phytoplankton biomass are useful as an indication of trophic status in groundwater influenced coastal lagoons. Moreover, estimations on the total system productivity, and the relative contribution of each primary producer, is a holistic approach useful for understanding trophic dynamic in shallow tropical coastal ecosystems.     

Trachypogon plumosus (Poaceae,Andropogoneae): ancient thatch and more from the ceren site,El Salvador

Paleoethnobotanical studies in the Zapotitdn Valley of north-central El Salvador revealed that a species of grass,Trachypogon plumosus, was in common use as a thatch material at the Ceren site, a small mesoamerican farming community inundated by volcanic ash circaa.d. 590. Although the grass must have been common in Precolumbian times, repeated attempts to collect fresh specimens from the modern valley were unsuccessful. A survey of the major herbaria with collections from El Salvador likewise demonstrated a lack of modern specimens from the Zapotitdn Valley. The elimination of theT. plumosus from this area and its characteristic savanna habitat probably occurred as a result of the introduction of competing Old World grasses and excessive herbivory. This finding demonstrates why conservationists working in the tropics should be concerned not only with the extinction of rain forest habitats, but with the elimination of other habitats as well.     

Chimeric contribution of human extended pluripotent stem cells to monkey embryos ex vivo

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Reproductive ecology of <Emphasis Type="Italic">Agave colorata</Emphasis>: the importance of nectar-feeding bats and the germination consequences of self-pollination

Agave colorata is a paniculate agave distributed along the migratory route of the nectar-feeding bat Leptonycteris yerbabuenae. In this paper, we evaluate the importance of nectar-feeding bats in the reproduction of A. colorata in a population in Sonora, Mexico, and describe the germination consequences of self-pollination. We estimated abundance using five plots and set pollination treatments to evaluate the importance of bats. We recorded 14.8?±?6.8 plants/400 m², with a bimodal size distribution. Flowers are protandrous and visited mainly (>?20 visits/plant/30 min) by L. yerbabuenae. Pollination exclusion experiments showed that flowers excluded from diurnal visitors had maximum fruit set values (0.49?±?0.42), while the autonomous self-pollination treatment had the lowest value (0.03?±?0.06). Similarly, the greatest number of viable seeds per fruit was recorded in the diurnal exclusion treatment, while the greatest number of empty seeds was observed in the self-pollination treatment. Fruit set values among untreated plants varied from 32 to 54%, with a mean value of 41.8%. Seeds derived from self-pollination had a narrower window of opportunity for germination compared to seeds derived from nocturnal pollination. Self-pollinated seeds had lower germination, rate of germination or lag time in response to light, osmotic potential and heat shock treatments, compared to other pollination treatments, revealing an inbreeding cost. Overall, our results show that L. yerbabuenae is the likely major pollinator of the studied A. colorata population. However, under pollinator limitation A. colorata may produce seeds by autonomous self-pollination, at a cost expressed as lower germination.     

From mesophilic to thermophilic conditions: one-step temperature increase improves the methane production of a granular sludge treating agroindustrial effluents

Objectives

To assess the effect of one-step temperature increase, from 35 to 55 °C, on the methane production of a mesophilic granular sludge (MGS) treating wine vinasses and the effluent of a hydrogenogenic upflow anaerobic sludge blanket (UASB) reactor.

Results

One-step temperature increase from mesophilic to thermophilic conditions improved methane production regardless of the substrate tested. The biomethane potentials obtained under thermophilic conditions were 1.8–2.9 times higher than those obtained under mesophilic conditions. The MGS also performed better than an acclimated thermophilic digestate, producing 2.2–2.5 times more methane than the digestate under thermophilic conditions. Increasing the temperature from 35 to 55 °C also improved the methane production rate of the MGS (up to 9.4 times faster) and reduced the lag time (up to 1.9 times). Although the temperature increase mediated a decrease in the size of the sludge granules, no negative effects on the performance of the MGS was observed under thermophilic conditions.

Conclusions

More methane is obtained from real agroindustrial effluents at thermophilic conditions than under mesophilic conditions. One-step temperature increase (instead of progressive sequential increases) can be used to implement the thermophilic anaerobic digestion processes with MGS.

     

Anaerobic biotransformation of hexachlorocyclohexane isomers by <Emphasis Type="Italic">Dehalococcoides</Emphasis> species and an enrichment culture

The biotransformation of hexachlorocyclohexane isomers (HCH) by two Dehalococcoides mccartyi strains (195 and BTF08) and an enrichment culture was investigated and compared to conversion by the obligate anaerobic strain Clostridium pasteurianum strain DSMZ 525. The D. mccartyi strains preferentially transformed γ-HCH over α-HCH and δ-HCH isomers while β-HCH biotransformation was not significant. In case of the enrichment culture, γ-HCH was preferentially transformed over the δ-HCH, β-HCH and α-HCH isomers. Major observed metabolites in both cases were tetrachlorocyclohexene and as end products monochlorobenzene (MCB) and benzene. Dechlorination of the γ-HCH isomer was linked to an increase in cell numbers for strain 195. γ-HCH transformation was linked to considerable carbon stable isotope fractionation with the enrichment factor ε_c?=???5.5?±?0.8‰ for D. mccartyi strain 195, ε_c?=???3.1?±?0.4‰ for the enrichment culture and ε_c?=???4.1?±?0.6‰ for co-metabolic transformation by C. pasteurianum.     

Ganglioside GD3 and GD3-lactone mediated regulation of the intermolecular organization in mixed monolayers with dipalmitoylphosphatidylcholine

The interactions of dpPC with ganglioside GD3 and two lactones, GD3LacI or GD3LacII, in lipid monolayers occur with reduced, unaltered, or increased molecular area and surface potential/molecule, respectively. dpPC is fully miscible with GD3 and GD3LacI but films with GD3LacII show immiscibility above 75 mol% lactone. At low proportions of GD3 in mixtures with dpPC, GD3 undergoes condensation and depolarization; dpPC is depolarized and its molecular area is reduced above 50 mol% GD3. GD3LacI forms ideally mixed films with dpPC. Mixtures of dpPC with GD3LacII at mole fractions below 0.3 show increased mean molecular area and surface potential/molecule mostly due to lactone alterations. Between mole fractions of 0.3 and 0.75 the surface parameters of dpPC are altered, and above these proportions both lipids are immiscible. Defined variations of molecular properties induced by ganglioside lactonization are selectively transduced to changes of the intermolecular organization and surface electrostatics in mixed interfaces with dpPC. Thus, changes in the relative proportions of a ganglioside and its lactone forms may act as sensitive biotransducers for membrane-mediated cellular functions, without the need for metabolically altering the concentration of gangliosides.