Slow motion extinction: inbreeding,introgression, and loss in the critically endangered mangrove finch (<Emphasis Type="Italic">Camarhynchus heliobates</Emphasis>)

The critically endangered mangrove finch is now limited to one small population on the west coast of Isabela Island in the Galápagos, but 100 years ago multiple populations were found on the islands of Isabela and Fernandina. By accessing genetic datasets through museum sampling, we are able to put current levels of genetic diversity and hybridization with congenerics into a historical context for enhanced conservation. In this study, we compared neutral genetic diversity of the now extinct Fernandina population to historical and current diversity of the Isabela population using 14 microsatellite markers. We found that current genetic diversity of the last remnant population (~80–100 individuals) is far below levels 100 years ago, with only about half of the allelic diversity retained. Current genetic diversity is close to levels in the Fernandina population that went extinct by the 1970s. Bottleneck analysis did not show a strong signature of recent decline, and instead implies that this species may have consistently had low population sizes with wide fluctuations. Hybridization with congeneric woodpecker finches was found in the modern Isabela population, implying that some individuals within the few remaining breeding pairs are finding mates with woodpecker finches. Within the context of historical low population sizes and wide fluctuations, current conservation efforts may help the mangrove finch face current extinction threats and avoid the fate of the Fernandina population. However, this historically small lineage will likely continue to face challenges associated with small specialist species surrounded by a widely-distributed sister lineage producing viable hybrids.     

Modeling of eicosapentaenoic acid (EPA) production from Phaeodactylum tricornutum cultures in tubular photobioreactors. Effects of dilution rate, tube diameter, and solar irradiance

A model for the prediction of eicosapentaenoic acid (EPA) productivity from Phaeodactylum tricornutum cultures that takes into account the existence of photolimitation and photoinhibition of growth under outdoor conditions is presented. The effects of the external irradiance on the culture surface, the average irradiance inside the culture, and the light regime at which the cells are exposed on pigments and EPA content are studied. The chlorophyll content decreases exponentially with the average irradiance, whereas the carotenoids content increases linearly with the external irradiance due to a higher extension of photoinhibition. A decrease in the fatty acid content of the biomass with irradiance on reactor surface is observed when photoinhibition becomes relevant. The average irradiance within the culture mainly influenced the fatty acid profile of the biomass. As the average irradiance becomes higher, percentages of saturated and monounsaturated fatty acids decrease, increasing the portion of EPA. By taking into account the different relationships among pigment and EPA content with the irradiance, the variation in EPA productivity over the year can be simulated as a function of average and external irradiance. For the two photobioreactors employed the maximum EPA productivity is attained in spring and fall (30 mg L(-1) day(-1) for tube diameter 0. 06 m and 50 mg L(-1) day(-1) for tube diameter 0.03 m). In winter, the biomass productivity is limited by low light availability although the EPA content is maximum. In summer, the biomass productivity is higher although the EPA content diminished by photoinhibition; the higher the dilution rate, the lower the minimum. Thus, the conditions that increase the biomass productivity and the polyunsaturated fatty acids content are in opposition, the optimum being reached by operating under photolimitation with high growth rates in order to produce a high proportion of polyunsaturated fatty acids.     

Modeling brewers' yeast flocculation

Flocculation of yeast cells occurs during the fermentation of beer. Partway through the fermentation the cells become flocculent and start to form flocs. If the environmental conditions, such as medium composition and fluid velocities in the tank, are optimal, the flocs will grow in size large enough to settle. After settling of the main part of the yeast the green beer is left, containing only a small amount of yeast necessary for rest conversions during the next process step, the lagering. The physical process of flocculation is a dynamic equilibrium of floc formation and floc breakup resulting in a bimodal size distribution containing single cells and flocs. The floc size distribution and the single cell amount were measured under the different conditions that occur during full scale fermentation. Influences on flocculation such as floc strength, specific power input, and total number of yeast cells in suspension were studied. A flocculation model was developed, and the measured data used for validation. Yeast floc formation can be described with the collision theory assuming a constant collision efficiency. The breakup of flocs appears to occur mainly via two mechanisms, the splitting of flocs and the erosion of yeast cells from the floc surface. The splitting rate determines the average floc size and the erosion rate determines the number of single cells. Regarding the size of the flocs with respect to the scale of turbulence, only the viscous subrange needs to be considered. With the model, the floc size distribution and the number of single cells can be predicted at a certain point during the fermentation. For this, the bond strength between the cells, the fractal dimension of the yeast, the specific power input in the tank and the number of yeast cells that are in suspension in the tank have to be known. Copyright 1998 John Wiley & Sons, Inc.     

Regulation of embryonic and induced pluripotency by aurora kinase-p53 signaling

Many signals must be integrated to maintain self-renewal and pluripotency in embryonic stem cells (ESCs) and to enable induced pluripotent stem cell (iPSC) reprogramming. However, the exact molecular regulatory mechanisms remain elusive. To unravel the essential internal and external signals required for sustaining the ESC state, we conducted a short hairpin (sh) RNA screen of 104 ESC-associated phosphoregulators. Depletion of one such molecule, aurora kinase A?(Aurka), resulted in compromised self-renewal and consequent differentiation. By integrating global gene expression and computational analyses, we discovered that loss of Aurka leads to upregulated p53 activity?that triggers ESC differentiation. Specifically, Aurka regulates pluripotency through phosphorylation-mediated inhibition of p53-directed ectodermal and mesodermal gene expression. Phosphorylation of p53 not only impairs p53-induced ESC differentiation but also p53-mediated suppression of iPSC reprogramming. Our studies demonstrate an essential role for Aurka-p53 signaling in the regulation of self-renewal, differentiation, and somatic cell reprogramming.     

Utilization of <Emphasis Type="Italic">Anabaena</Emphasis> sp. in CO<Subscript>2</Subscript> removal processes

This paper focuses on modelling the growth rate and exopolysaccharides production of Anabaena sp. ATCC 33047, to be used in carbon dioxide removal and biofuels production. For this, the influence of dilution rate, irradiance and aeration rate on the biomass and exopolysaccharides productivity, as well as on the CO₂ fixation rate, have been studied. The productivity of the cultures was maximum at the highest irradiance and dilution rate assayed, resulting to 0.5 g_bio l⁻¹ day⁻¹ and 0.2 g_eps l⁻¹ day⁻¹, and the CO₂ fixation rate measured was 1.0 gCO₂ l⁻¹ day⁻¹. The results showed that although Anabaena sp. was partially photo-inhibited at irradiances higher than 1,300 μE m⁻² s⁻¹, its growth rate increases hyperbolically with the average irradiance inside the culture, and so does the specific exopolysaccharides production rate. The latter, on the other hand, decreases under high external irradiances, indicating that the exopolysaccharides metabolism hindered by photo-damage. Mathematical models that consider these phenomena have been proposed. Regarding aeration, the yield of the cultures decreased at rates over 0.5 v/v/min or when shear rates were higher than 60 s⁻¹, demonstrating the existence of thus existence of stress damage by aeration. The behaviour of the cultures has been verified outdoors in a pilot-scale airlift tubular photobioreactor. From this study it is concluded that Anabaena sp. is highly recommended to transform CO₂ into valuable products as has been proved capable of metabolizing carbon dioxide at rates of 1.2 gCO₂ l⁻¹ day⁻¹ outdoors. The adequacy of the proposed equations is demonstrated, resulting to a useful tool in the design and operation of photobioreactors using this strain.     

Characterization of an iron-containing superoxide dismutase from a higher plant, Citrus limonum

An iron-containing superoxide dismutase (SOD, EC 1.15.1.1) was fully characterized from leaves of the higher plant Citrus limonum R. cv. Verna. This enzyme is the first iron-containing SOD to be characterized in the plant family Rutaceae . The purified Fe-SOD has a molecular mass of about 47 kDa and is composed of two non-covalently joined equal subunits. The amino acid composition determined for the enzyme was compared with that of a wide range of SODs and had highest degree of homology with the Fe-SODs from Brassica campestris and Nuphar luteum . The enzyme was more labile at high temperatures than some eucaryotic and procaryotic Fe-SODs. It showed a maximum stability at pH 7.8. The sensitivity of the enzyme to cyanide, hydrogen peroxide and o -phenanthroline was similar to those reported for other Fe-SODs. but the lemon enzyme was comparatively resistant to H₂O₂. By kinetic competition experiments, the rate constant for the disproportionation of superoxide radicals by lemon Fe-SOD was found to be 1.9 × 10⁹ M ⁻¹ s⁻¹ at pH 7.8 and 25°C. A comparative study between the molecular properties of this higher plant Fe-SOD and SODs from different origins is presented.     

Variation of fatty acid profile with solar cycle in outdoor chemostat culture ofIsochrysis galbana ALII-4

Outdoor chemostat cultures of the marine microalgaIsochrysis galbana at constant dilution rate (0.034 h^–1 ) have been carried out under different weather conditions. Steady-state biomass concentrations were 1.61±0.03 kg m^–3 in May and 0.95±0.04 kg m^–3 in July, resulting in biomass output rates of 0.54 kg m^–3 d^–1 and 0.32 kg m^–3 d^–1 in May and July, respectively. Two patterns of daily variation with the solar cycle were observed in the fatty acid content. Saturated and mono-unsaturated fatty acids (16:0 and 16:1n7) show significant variation with the solar cycle, associated with short-term changes in environmental factors. Palmitic and palmitoleic acids are generated during daylight and consumed during the dark period. However, polyunsaturated fatty acids do not show a significant response to the solar cycle and their changes are associated with long-term variation in environmental factors. The maximum EPA productivity was obtained in May, 14.1 g m^–3 d^–1, which is close to that found in the literature for indoor continuous cultures. Nonetheless, the outdoor EPA content (up to 2.61 % d.wt) was lower than the indoor EPA content from a previous study (5% d.wt).