Ecological interactions among microbial functional guilds in the plant-soil system and implications for ecosystem function

Plant and Soil - Soils harbour a remarkable diversity of interacting fungi, bacteria, and other microbes: together these perform a wide variety of ecological roles from nutrient cycling...     

A 20-Gene Set Predictive of Progression to Severe Dengue

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Direct determination of the effects of genotype and extreme temperature on the transposition of <Emphasis Type="Italic">roo</Emphasis> in long-term mutation accumulation lines of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Transposable elements (TEs) are mobile repetitive DNA sequences that constitute a structurally dynamic component of genomes. In order to understand the dynamics of TEs it is necessary to have information about the control of transposition and its dependence of environmental factors. After a great deal of previous work on transposition conducted on long-term mutation accumulation (MA) lines of Drosophila melanogaster started in 1987, only roo out of 16 families was found active in this genotype. Here we test the effect of the modification of the genetic background by introducing a Cy chromosome, and the effect of extreme temperature (28°C) on the transposition rate of roo. Thermal stress did not affect the transposition rate, whereas the presence of a Cy chromosome in heterozygosis lowered it. There was an excess of insertions in the X chromosome, with respect to autosomes, and in the proximal and distal regions of chromosome arms that can be interpreted as target site preference. One of the control lines became highly unstable with mean insertion and excision rates of 3.0 × 10⁻³ and 8.5 × 10⁻⁴, respectively. Instability arose spontaneously during generations of mutation accumulation, and can be attributed to “de novo” mutation. Transposition in the unstable line could be directly studied on the progeny of individual males and females, from where we deduced that transposition occurs mainly, if not exclusively, in males, with a rate of 1.125 insertions per gamete. In situ hybridization with an LTR probe showed that most excisions (12 out of 14) were precise. Our data show the prominent role of genotype in transposition control and can explain rapid turnovers in the genome without increasing the number of copies.     

Nucleation-driven regeneration promotes post-fire recovery in a Chilean temperate forest

Nucleation is a successional process in which extant vegetation facilitates seed dispersal and recruitment of other individuals and species around focal points in the landscape, leading to ecosystem recovery. This is an important process in disturbed sites where regeneration is limited by abiotic conditions or restrictive seed dispersal. We investigated forest recovery in a large burned area of evergreen temperate rainforest in southern Chile subjected to seasonal soil waterlogging, and assessed the relevance of nucleation processes in overcoming biotic and physical barriers for tree species regeneration. We measured richness and abundance of woody species in relation to patch size, as well as abiotic factors such as light and soil moisture within and outside patches. We found higher tree regeneration in existing patches than in open areas. We recorded an increase of patch size over time, associated with the increase in number of individuals and tree species. Soils in open areas were waterlogged, especially in winter, while patches were not. Trees in patches also acted as perches, enhancing bird-mediated seed rain. Seeds of fleshy-fruited tree species arrived first at patches and seedlings were more frequent in smaller, younger patches, while the number of seedlings of trees with wind-dispersed seeds increased in larger, older patches. Our study shows that woody species seem incapable of recruiting in open and waterlogged soils and depend strongly on extant vegetation patches to establish. In this fire-disturbed evergreen temperate forest regeneration occurs via nucleation, where new individuals contribute to a centrifugal kind of patch growth.     

Cytochrome b pseudogene originated from a highly divergent mitochondrial lineage in genus Rupicapra

We have identified a nuclear pseudogene (numt) of cytochrome b (cytb) in chamois. The comparison of a fragment of 402 nucleotides of cytb and the pseudogene between the 2 species Rupicapra rupicapra and Rupicapra pyrenaica allowed direct measurement of relative rates and patterns of evolution. Mitochondrial genes evolved 7 to 12 times faster than their nuclear counterparts. Substitutions in the nucleus include a frameshift and a stop codon. Phylogenetic analysis of nuclear and mitochondrial lineages on Rupicapra and related species showed that the nuclear branch evolved as a functional mitochondrial gene until the split of the 2 species of chamois and as a typical pseudogene later on. We propose that the pseudogene originated from a highly divergent mitochondrial lineage that did not persist in the mitochondrion and transposed to the nucleus in a time close to speciation. The concurrence of highly differentiated lineages at speciation points to hybridization between highly divergent populations.     

Serotypes of Candida albicans isolated from HIV positive patients.

Twenty-one HIV-positive patients in different stages of the disease were studied to evaluate candidosis in the oral cavity. All patients in clinical category C were infected with Candida. The most frequently observed clinical forms were pseudomembranous and hypertrophic, in contrast to reports by other authors. Candida albicans was the species isolated in these HIV-positive patients. Alterations of cell-mediated immunity were reflected in the negativity of intradermal test. The predominant serotype of C. albicans in these patients was A, in agreement with what has been found in non-immunosuppressed patients in Venezuela. There was no correlation between the serotype of C. albicans and the clinical forms of candidosis. Based in our results and those of other authors, no conclusions can be drawn concerning a particular serotype as an indicator of immunosuppression.     

Integrating phylogeographic patterns of microsatellite and mtDNA divergence to infer the evolutionary history of chamois (genus <Emphasis Type=Italic>Rupicapra</Emphasis>)

Background  

The chamois, distributed over most of the medium to high altitude mountain ranges of southern Eurasia, provides an excellent model for exploring the effects of historical and evolutionary events on diversification. Populations have been grouped into two species, Rupicapra pyrenaica from southwestern Europe and R. rupicapra from eastern Europe. However, a previous study of cytochrome b revealed that the two proposed species were non-monophyletic. The reconstruction of phylogenetic relationships between animal species often depends on the markers studied. To further elucidate the evolutionary history of chamois, we extended earlier studies by analysing DNA sequences of four mitochondrial regions (ND1, 12S, tRNApro and Control Region) and microsatellites (20 loci) to include all subspecies and cover its entire distribution range.     

Estimation of microsatellite mutation rates in Drosophila melanogaster

Microsatellite mutations were studied in a set of 175 mutation accumulation lines, all of them independently derived from a completely homozygous population of Drosophila melanogaster and maintained under strong inbreeding during 80 generations. We assayed 28 microsatellites and detected two mutations. One mutation consisted of a single addition of a dinucleotide repeat and the other was a deletion of five trinucleotide repeats. The average mutation rate was 5.1 x 10(-6), in full agreement with previous estimates from two different sets of mutation accumulation lines.     

Alkaline phosphatase at the cell wall of the yeast phase ofParacoccidioides brasiliensis

The activity of alkaline phosphatase demonstrated by histochemical techniques was shown at the cell wall of the yeast form ofParacoccidioides brasiliensis at 3, 6, and 9 days of culture. The results showed a very active deposition at the cell wall as early as 9 days of culture of the fungus which made us think an inactive salt precipitate was also present.