Characterization of urease from the phototrophic bacteriumRhodobacter capsulatus E1F1

Rhodobacter capsulatus E1F1 showed high cytosolic urease activity when growing on urea, purines, and purine metabolites as nitrogen source. Molecular mass ofR. capsulatus enzyme is similar to that of other bacteria and greatly differs from that of jack bean. Kinetic parameters of partially purifiedR. capsulatus enzyme resemble those described in other bacterial ureases. The activity was inhibited by metal-chelating agents and by mercurials. Urease fromR. capsulatus E1F1 was negligible in nitrogen-starved cells or in cells cultured with nitrate, ammonium, or amino acids. Moreover, ammonium inhibited both the urea uptake and the urease activity expression inR. capsulatus cells.     

Kinetic and metabolic effects of nitrogen, magnesium and sulphur restriction in Xanthomonas campestris batch cultures

By reducing the concentration of nitrogen (from 5.0 to 2.5 mmol 1^-1), batch cultures of Xanthomonas campestris induced the enzyme UDP-glucose dehydrogenase and stimulated the Entner-Doudoroff pathway enzyme glucose-6-P dehydrogenase. The surplus energy generation was directed to xanthan biosynthesis resulting in a 10% polysaccharide increase. The nitrogen restriction led to a higher consumption of nitrogen (93%) whereas glucose consumption did not surpass 75% utilization. Low concentrations of both magnesium and sulphur exerted a negative effect on xanthan formation. Both restrictions reduced the phosphomannose isomerase enzyme activity by 10-fold turning the mannose transference presumably into the rate-limiting step for xanthan biosynthesis. Conversely, the rate of synthesis of glucuronic acid residues did not affect the rate of xanthan biosynthesis. Polysaccharide synthesis in magnesium and sulphur cultures was negatively affected in comparison with cell formation as the cell volumetric production rate increased from 0.037 to 0.091 g 1^-1 h^-1 and the xanthan volumetric production rate dropped from 0.133 g 1^-1 h^-1 to the minimum obtained at 0.083 g 1^-1 h^-1. The efficiency of the carbon substrate conversion was also greatly changed.     

Expression of the α-thionin gene from barley in tobacco confers enhanced resistance to bacterial pathogens

Thionins are cysteine-rich, 5 kDa polypeptides which are toxic to plant pathogens in vitro. Expression of the gene encoding α-thionin from barley endosperm, under the 35S promoter from cauliflower mosaic virus, conferred to transgenic tobacco enhanced resistance to the bacterial plant pathogens Pseudomonas syringae pv. tabaci 153 and P. syringae pv. syringae. The barley α-thionin gene, which has two introns, was correctly spliced in tobacco. The α-thionin in transgenic plants had the expected mobility in the gradient, when separated by high-performance liquid chromatography, reacted with monospecific antibodies and showed the expected antibiotic properties in vitro.     

PHYLOGENETIC INTERRELATIONSHIPS AND REDUCTIVE EVOLUTION IN NEOTROPICAL CHARACIDIIN FISHES (CHARACIFORMES, OSTARIOPHYSI)

Abstract— Miniaturization, which results in the presence of numerous apparently paedomorphic characters associated with reduced size, is a common phenomenon among neotropical fishes, with over 85 miniature species distributed among the five major ordinal groups. Eleven species are recognized as miniatures within the Characidiinae, a monophyletic subunit of Characiformes. A reconstruction of characidiin phylogeny is used to analyze the history of miniaturization events. Former hypotheses of origin of miniaturization among characidiins are rejected, underscoring the need for phylogenetic frameworks in the study of ontogenetic changes associated with the phenomenon of miniaturization. The 11 instances of miniature species can be most parsimoniously attributed to three independent miniaturization events within the Characidiinae.
Reductive characters comprise a large proportion of phylogenetically informative characters within the Characidiinae. In the largest group of miniatures, reductive characters represent more than half of the character state transformations affecting supraspecific relationships among Elachocharax, Klausewitzia, Odontocharacidium and Microcharacidium . An analysis of patterns of character state distributions fails to reject the null hypothesis of character independence. A distinction is made between the concepts of character independence, defined as the origination of character states from different (non-simultaneous) evolutionary events, and character correlation, defined as the association of character states in terminal taxa. Character correlation is not a sufficient criterion to reject Hennig's auxiliary principle, according to which the "presence of apomorphous characters in different species is always reason for suspecting kinship, and their origin by convergence should not be assumed a priori". High values of character correlation are the expected result of congruent patterns of character distribution.     

Revealing the polar lipidome,pigment profiles,and antioxidant activity of the giant unicellular green alga,Acetabularia acetabulum

Marine algae are one of the most important sources of high-value compounds such as polar lipids, omega-3 fatty acids, photosynthetic pigments, or secondary metabolites with interesting features for different niche markets. Acetabularia acetabulum is a macroscopic green single-celled alga, with a single nucleus hosted in the rhizoid. This alga is one of the most studied dasycladalean species and represents an important model system in cell biology studies. However, its lipidome and pigment profile have been overlooked. Total lipid extracts were analyzed using hydrophilic interaction liquid chromatography-high resolution mass spectrometry (HILIC-HRMS), tandem mass spectrometry (MS/MS), and high-performance liquid chromatography (HPLC). The antioxidant capacity of lipid extracts was tested using DPPH and ABTS assays. Lipidomics identified 16 polar lipid classes, corresponding to glycolipids, betaine lipids, phospholipids, and sphingolipids, with a total of 191 lipid species, some of them recognized by their bioactivities. The most abundant polar lipids were glycolipids. Lipid classes less studied in algae were identified, such as diacylglyceryl-carboxyhydroxymethylcholine (DGCC) or hexosylceramide (HexCer). The pigment profile of A. acetabulum comprised carotenoids (17.19%), namely cis-neoxanthin, violaxanthin, lutein and β,β-carotene, and chlorophylls a and b (82.81%). A. acetabulum lipid extracts showed high antioxidant activity promoting a 50% inhibition (IC₅₀) with concentrations of 57.91 ± 1.20 μg · mL⁻¹ (438.18 ± 8.95 μmol Trolox · g⁻¹ lipid) in DPPH and 20.55 ± 0.60 μg · mL⁻¹ in ABTS assays (918.56 ± 27.55 μmol Trolox · g⁻¹ lipid). This study demonstrates the potential of A. acetabulum as a source of natural bioactive molecules and antioxidant compounds.     

Same species,different population dynamics: Spatio-temporal differences of Undaria pinnatifida (Ochrophyta,Phaeophyceae) in the intertidal of North Patagonia,Argentina

Population dynamics can be influenced by physical and biological factors, particularly in stressful environments. Introduced species usually have great physiological plasticity, resulting in populations with different traits. Undaria pinnatifida, a macroalga originally described from northeast Asia, was introduced in Northern Patagonia, Argentina (San Matías Gulf) around 2010. To describe the spatio-temporal variability in population structure and morphometry of U. pinnatifida, we conducted monthly field samplings for 2 years at the intertidal area of two contrasting sites in the San Matías Gulf. Individuals of U. pinnatifida were classified by developmental stage, and their morpho-gravimetric variables were measured. In both intertidal sites juveniles were found in higher proportion during austral autumn and grew and matured during the autumn-winter months (from May onwards), and individuals senesced during early austral summer (December and January). Conversely, density and biomass were largely different between sites, and individuals showed slight morphological variability between sites. Environmental (e.g., nutrient concentration, available substrate) and biological factors (e.g., facilitation, competition) may explain the observed differences. Since there is not a macroalga with U. pinnatifida morphometrical characteristics in the intertidal environments of San Matías Gulf, studying this recent introduction gives us a better understanding of its potential ecological effects.     

Do reproductive characteristics of the species explain differences in the investment in weapon size present in males?

Sexually selected traits, such as male weapons, are highly variable in shape and size across species. However, little is known about the mechanisms that may govern this variation. Because males with greater investment in weapon size tend to win more fights, but also pay higher costs related to weapon development and maintenance, larger weapons should be expected only in species in which victory in male–male fights generate reproductive benefits that outweigh investment costs. Here, we hypothesized that the reproductive characteristics that increase the chances of winners to access females or to fertilize eggs will favor the evolution of larger weapons. To evaluate this hypothesis, we conducted a meta-analysis using arthropods as model organisms. To measure investment in weapon size, we gathered both Pearson correlation coefficient and the standardized (but non centralized) slope values for the relationship between weapon size and body size. We found that none of the reproductive characteristics we investigated was related to male weapon size. Thus, it seems that greater certainty of accessing a female or fertilizing female eggs with a victory does not modulate the investment in male weapon size. Perhaps the cost–benefit ratio between weapon size investment and reproductive success is not the main factor driving the variation in weapon size.     

Influence of seasonal variation to the population growth and ecophysiology of Typha domingensis (Typhaceae)

Journal of Plant Research - Precipitation is an important climatic element that defines the hydrological regime, and its seasonal variation produces annual dry and wet periods in some areas. This...     

ON THE ORIGIN OF INCIPIENT REPRODUCTIVE ISOLATION: THE CASE OF DROSOPHILA ALBOMICANS AND D. NASUTA

The nasuta subgroup of Drosophila consists of 12 known species classified within the immigrans group. D. nasuta and D. albomicans are two sibling species widely distributed throughout the Indo-Pacific tropics, which, although morphologically indistinguishable, have different meta-phase-chromosome configurations: chromosomes X and 3 are attached in D. albomicans, so that about 60% of its genes are sex-linked. Our experiments show that, at least in the laboratory, there is no sexual, mechanical, or gametic isolation between the two species. There is, however, hybrid “breakdown” expressed in three ways: 1) reduction in the number of F₂ hybrids produced per culture; 2) reduction in the fertility of F₂ (males) and F₃ (males and females) hybrid progenies; and 3) abnormal sex ratios in the progenies of crosses between strains of certain localities. In experimental populations, the karyotypes of both species are still present in substantial frequencies after 20 generations, although the frequencies of the two karyotypes vary depending on the geographic origin of the strains. Our results support the hypothesis that, in allopatry, the evolution of postzygotic isolation precedes that of prezygotic isolation. The mtDNA is polymorphic in both D. nasuta and D. albomicans and fairly similar between them. Assuming typical rates of mtDNA evolution, the two species would have diverged from each other about 500,000 years ago, whereas the African and Indian populations of D. nasuta (considered to be different subspecies by some authors) might have diverged some 350,000 years ago.