Fed-batch cultivation of Saccharomyces cerevisiae in a hyperbaric bioreactor

Fed-batch is the dominating mode of operation in high-cell-density cultures of Saccharomyces cerevisae in processes such as the production of baker's yeast and recombinant proteins, where the high oxygen demand of these cultures makes its supply an important and difficult task. The aim of this work was to study the use of hyperbaric air for oxygen mass transfer improvement on S. cerevisiae fed-batch cultivation. The effects of increased air pressure up to 1.5 MPa on cell behavior were investigated. The effects of oxygen and carbon dioxide were dissociated from the effects of total pressure by the use of pure oxygen and gas mixtures enriched with CO(2). Fed-batch experiments were performed in a stirred tank reactor with a 600 mL stainless steel vessel. An exponential feeding profile at dilution rates up to 0.1 h(-)(1) was used in order to ensure a subcritical flux of substrate and, consequently, to prevent ethanol formation due to glucose excess. The ethanol production observed at atmospheric pressure was reduced by the bioreactor pressurization up to 1.0 MPa. The maximum biomass yield, 0.5 g g(-)(1) (cell mass produced per mass of glucose consumed) was attained whenever pressure was increased gradually through time. This demonstrates the adaptive behavior of the cells to the hyperbaric conditions. This work proved that hyperbaric air up to 1.0 MPa (0.2 MPa of oxygen partial pressure) could be applied to S. cerevisiae cultivation under low glucose flux. Above that critical oxygen partial pressure value, i.e., for oxygen pressures of 0.32 and 0.5 MPa, a drastic cell growth inhibition and viability loss were observed. The increase of carbon dioxide partial pressure in the gas mixture up to 48 kPa slightly decreased the overall cell mass yield but had negligible effects on cell viability.     

Effects of the Flooding Gradient on Tree Community Diversity in Várzea Forests of the Purus River,Central Amazon,Brazil

Amazonian floodplain forests have remarkable variation in tree diversity and structure related to flood duration. We assessed how floodplain forests respond to the continuum flooding gradient and found that Fisher's α values vary up to seven times across the landscape.     

Housekeeping proteins: How useful are they in skeletal muscle diabetes studies and muscle hypertrophy models?

The use of Western blot analysis is of great importance in research, and the measurement of housekeeping proteins is commonly used for loading controls. However, Ponceau S staining has been shown to be an alternative to analysis of housekeeping protein levels as loading controls in some conditions. In the current study, housekeeping protein levels were measured in skeletal muscle hypertrophy and streptozotocin-induced diabetes experimental models. The following housekeeping proteins were investigated: glyceraldehyde-3-phosphate dehydrogenase (GAPDH), β-actin, α-tubulin, γ-tubulin, and α-actinin. Evidence is presented that Ponceau S is more reliable than housekeeping protein levels for specific protein quantifications in Western blot analysis.     

Fine‐scale Beta‐diversity Patterns Across Multiple Arthropod Taxa Over a Neotropical Latitudinal Gradient

Documenting how diversity patterns vary at fine‐ and broad scales may help answer many questions in theoretical and applied ecology. However, studies tend to compare diversity patterns at the same scale and within the same taxonomic group, which limits the applicability and generality of the results. Here, we have investigated whether vegetation‐dwelling arthropods from different trophic ranks and with distinct life histories (i.e., ants, caterpillars, cockroaches, and spiders) have different beta‐diversity patterns at multiple scales. Specifically, we compared their beta diversity across architecturally distinct plant species (fine‐scale process) and a latitudinal gradient of sites (broad‐scale process) along 2040 km of coastal restinga vegetation in the Neotropics. Over 50 percent of the compositional changes (β‐diversity) in ants, caterpillars, and spiders and 41 percent of those in cockroaches were explained by plant identity within each site. Even groups that do not feed on plant tissues, such as omnivores and predators, were strongly affected by plant identity. Fine‐scale variation was more important than large‐scale processes for all studied groups. Performing a cross‐scale comparison of diversity patterns of groups with distinct life histories helps elucidate how processes that act at regional scales, such as dispersal, interact with local processes to assemble arthropod communities.     

Insufficient uracil supply in fully aerobic chemostat cultures of Saccharomyces cerevisiae leads to respiro-fermentative metabolism and double nutrient-limitation

A combination of chemostat cultivation and a defined medium was used to demonstrate that uracil limitation leads to a drastic alteration in the physiology of auxotrophic cells of Saccharomyces cerevisiae. Under this condition, the carbon source is dissimilated mainly to ethanol and acetate, even in fully aerobic cultures grown at 0.1 h^?1, which is far below the critical dilution rate. Differently from nitrogen-, sulphur-, or phosphate-limited cultures, uracil limitation leads to residual sugar (either glucose or sucrose) concentrations below 2 mM, which characterizes a situation of double-limitation: by the carbon source and by uracil. Furthermore, the specific rates of CO₂ production and O₂ consumption are increased when compared to the corresponding prototrophic strain. We conclude that when auxotrophic strains are to be used for quantitative physiological studies, special attention must be paid to the cultivation conditions, mainly regarding medium formulation, in order to avoid limitation of growth by the auxotrophic nutrient.     

An evolutionary tolerance model explaining spatial patterns in species richness under environmental gradients and geometric constraints

In this study, we developed a simulation model based on the ecological and evolutionary dynamics of geographical ranges, to understand the role of species' environmental tolerances and the strength of the environmental gradient in determining spatial patterns in species richness. Using an one-dimensional space, we present the model and dissect its parameters. Also, we test the ability of the model to simulate richness in complex two-dimensional domains and to fit real patterns in species richness, using South American Tyrannidae as an example. We found that a mid-spatial peak in species richness arises spontaneously under conditions of high environmental tolerances and/or a weak environmental gradient, since this condition causes wide species' geographic ranges, which are constrained by domain's boundary and tend to overlap in the middle. Our model was also a good predictor of real patterns in species richness, especially under conditions of high environmental strength and small species' tolerance. We conclude that this kind of spatial simulation models based on species' physiological tolerance may be an important tool to understand the evolutionary dynamics of species' geographic ranges and in spatial patterns of species richness.     

Phylogeography and genetic differentiation along the distributional range of the orchid Epidendrum fulgens: a Neotropical coastal species not restricted to glacial refugia

Aim Phylogeographical studies in the Brazilian Atlantic Forest (BAF) have mostly included species associated with forest habitats, whereas taxa associated with grassland and sand‐dune plant communities have so far been largely overlooked. This study examines the phylogeography of the orchid Epidendrum fulgens, which occurs on coastal sand dunes and granitic outcrops, in order to identify major genetic divergences or disjunctions across the range of the species and to investigate the genetic signatures of past range contractions and expansions. Location Southern and south‐eastern seashore vegetation along the BAF biome, and granitic and arenitic outcrops that occur in the subtropical grassland plant communities located south of the BAF. Methods Nine nuclear and four plastid microsatellite loci were used to genotype 424 individuals from 16 populations across the distributional range of E. fulgens. For both sets of markers, we estimated genetic diversity and population differentiation, testing for a north–south gradient of genetic diversity. The plastid haplotype network and a Bayesian assignment analysis of nuclear markers were used to infer population structure. Past demographic changes were investigated using a coalescence approach. Results A deep disjunction was found between northern populations within the BAF and southern populations outside the BAF that occur on granitic and arenitic outcrops. Recent demographic reductions were detected in northern populations on coastal sands. Such demographic changes were not expected for those populations, as previous studies with forest species had found evidence of population expansion in the same areas. Higher genetic diversity was found in southern populations on granite, in contrast to patterns observed in previous studies of forest species. Main conclusions The results are consistent with the long‐term persistence of E. fulgens. Bottlenecks were detected in populations from areas where population expansion events have been detected in other plant (and animal) species, suggesting that forest expansion after the Last Glacial Maximum played a role in the population fragmentation and decrease in genetic diversity in E. fulgens. A substantial genetic division in E. fulgens corresponds to the ‘Portal de Torres’, a region that demarcates the northern limits of subtropical grassland plant communities and the southern limits of the BAF.     

Calcicole behaviour of Callisthene fasciculata Mart., an Al‐accumulating species from the Brazilian Cerrado

• Most aluminium (Al)‐accumulating species are found on soils with high Al saturation and low Ca availability (Ca poor). Callisthene fasciculata Mart. (Vochysiaceae), however, is an Al‐accumulating tree restricted to Ca‐rich soils with low Al saturation in the Brazilian Cerrado savanna. Here we tested its calcicole behaviour, and the possible role of organic acids in detoxification of Al during the early stages of plant development.
• We assessed growth, dry mass, nutrients, Al and organic acids in seedlings grown for 50 days on two contrasting Cerrado soils; one with high Ca concentrations and low Al saturation and the other with low Ca availability and high Al saturation.
• Relative to plants on Ca‐rich soil, plants on Ca‐poor soil had necrotic spots and bronzing of leaves. Roots and shoots contained reduced concentrations of P and Cu, but higher concentrations of Fe, Al and citrate. Despite lower concentrations in the soil, Ca and Mg increased in shoots. Shoot concentrations of oxalate were also higher.
• We confirmed C. fasciculata as an Al‐accumulating species with calcicole behaviour. The increased concentrations of organic acids in plants with higher Al accumulation suggest that high availability of soluble Al does not prevent occurrence of this species on soils with high Al saturation. Instead, the absence of C. fasciculata from Ca‐poor soils is probably due to imbalances in tissue Fe, Cu and Zn imposed by this soil type.