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.     

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.     

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.     

ISOZYME VARIABILITY IN TRYPANOSOMA CRUZI,THE AGENT OF CHAGAS' DISEASE: GENETICAL,TAXONOMICAL, AND EPIDEMIOLOGICAL SIGNIFICANCE

A genetic interpretation of the zymograms of 524 Trypanosoma cruzi stocks from various hosts and representing a broad geographical range (United States to Southern Brazil) reveals high genetic variability (only one monomorphic locus out of 15) and suggests that this parasite has a diploid structure. The data do not give any indication of Mendelian sexuality, although many opportunities are present for genetic exchange between extremely different genotypes. The population structure of T. cruzi appears to be multiclonal and complex. The natural clones evidenced by isozyme analysis are numerous (43 different ones are recorded among 121 stocks assayed at 15 gene loci) and exhibit a large range of genotypes, in a nonhierarchical structure; it is not possible to cluster them into a few strictly delimited groups which could represent natural taxa. The available data suggest that the genetic variability of T. cruzi reflects the long separate evolution of multiple clones. It is suggested that long clonal evolution may explain the present biological and medical variability of the causative agent of Chagas' disease.     

Chromatographic methods for amylases

This review surveys recent developments in chromatographic methods for the separation of amylases from complex extracts, including the separation of isozymes. It contains two tables with the properties and molecular characteristics of α- and β-amylases from different sources as well as an updated review of methods for the determination of amylase activity. The main subject of this review is a detailed evaluation of the application of newly developed chromatographic methods for the purification of amylases.     

Manipulating photosynthesis

The levels of individual photosynthetic proteins can be independently decreased by theAgrobacterium-mediated transformation of plants with antisens RNA constructs. Protocols for the introduction of such constructs intoAgrobacterium, theAgrobacterium-mediated transformation of tobacco leaf disks, and the screening and analysis of the transgenic plants produced are described.     

Spatial patterns in a two-tiered semi-arid shrubland in southeastern Spain

Abstract. Single species and bivariate distribution patterns in a semi-arid shrubland in southeastern Spain, dominated by the tall leguminous shrub Retama sphaerocarpa, were investigated by second-order spatial analysis based on Ripley's K-function. Shrubs were significantly clumped because of a strong association of dwarf shrubs, mostly Artemisia barrelieri, under the canopy of Retama. Retama shrubs were randomly distributed, but when different size-classes were analysed separately, the pattern changed from significantly clumped to random and then to regular with increasing canopy diameter, suggesting increasing intraspecific competition with shrub size. Artemisia was significantly clumped at all scales because of aggregation under the canopy of large Retama shrubs. The association between the species became stronger with increasing canopy diameter of Retama shrubs, suggesting that facilitation prevailed over interspecific competition because of niche separation in different tiers, both above and below ground. Retama shrub size thus determined both the type of pattern for its own size class and tier, and the scale and intensity of the association with its understorey shrubs.