1,721,030 research outputs found
EVOLUTION OF WOLBACHIA SYMBIOSIS IN ARTHOPODS AND NEMATODES: INSIGTHS FROM PHYLOGENETICS AND COMPARATIVE GENOMICS
Full text linkWolbachia is a bacterium observed in relationship with a wide array of arthropod and nematode species. This is an obligate intracellular symbiont, maternally transferred through the host oocytes. In arthropods Wolbachia is able to manipulate reproduction, using multiple strategies to increase the fitness of infected females. In nematodes the bacterium has a fundamental, and not completely understood, role in larvae development. Wolbachia infects ~50% of all the arthropod species worldwide, and in some of them it can be considered the most important sex determination factor. In contrast, Wolbachia presence is much more limited in nematodes, being present in a limited number of filarial species. The taxonomic status within the Wolbachia genus is highly debated, with the current classification dividing all strains in 14 'supergroups'.
During my Ph.D. I studied the evolution of the symbiotic relationship between Wolbachia and its arthropod and nematode hosts, using genomic approaches.
Indeed, during the evolution of the Wolbachia-host relationship, genetic signs have been left in the Wolbachia genomes. I worked to identify these genomic signs and to evaluate them within an evolutionary frame, in order to obtain a better understanding of how the Wolbachia-host symbiosis evolved.
The work here presented can be organized in three major sections: i) the sequencing and analysis of the genome of the filarial nematode Dirofilaria immitis and of its symbiotic Wolbachia strain, wDi; ii) the sequencing of the genome of Wolbachia endosymbiont of Litomosoides sigmodontis, and the phylogenomic reconstruction of the Wolbachia supergroups A-D; iii) a comparison of the genomes of 26 Wolbachia strains spanning the A to F supergroups.
Here a schematic summary of the results is reported:
1. Dirofilaria immitis and the Wolbachia symbiont wDi show metabolic complementarity for
fundamental pathways
2. The metabolic pathway for the synthesis of wDi membrane proteins is one evolving the fastest in the genome of the bacterium
3. Nematode Wolbachia belonging to supergroups C and D are monophyletic, indicating that a single transition to mutualism likely occurred during the evolution of Wolbachia
4. Wolbachia strains of the C supergroup show genomic features that are unique in the genus, such as a much higher level of synteny compared to the rest of Wolbachia supergroups, and a newly generated pattern of GC skew curves, typically observed in free-living bacteria genomes
5. Wolbachia supergroups show conserved genomic features, which suggest genomic
isolation among them
A customizable gene selection and clustering software for phylogenomics and duplication/recombination analyses
No full textA bioinformatic algorithm based on graph representation of data was developed and allowed to create a customizable gene selection and clustering software for phylogenomics and duplication/recombination analyses
Batteri della famiglia Midichloriaceae (ordine Rickettsiales): possibili patogeni emergenti per i vertebrati?
No full textLa famiglia Midichloriaceae è una famiglia batterica il cui nome deriva da Midichloria mitochondrii, simbionte intramitocondriale presente nell’ovario della zecca Ixodes ricinus (Montagna et al., 2013). Le Midichloriaceae sono comparabili, per numero di specie e per complessità, alle altre due famiglie dell’ordine Rickettsiales (Rickettsiaceae ed Anaplasmataceae), di cui fanno parte diversi batteri intracellulari patogeni per l’uomo ed altri vertebrati. In seguito alla scoperta di M. mitochondrii in I. ricinus e di batteri a esso correlati in altre specie di zecca dura, altri batteri della famiglia Midichloriaceae sono stati osservati in organismi molto diversi tra loro, spaziando da artropodi parassiti (ad esempio, pulci e cimici dei letti) e organismi dei phyla Porifera e Cnidaria, fino ad arrivare a organismi acquatici quali protisti appartenenti a specie di ciliati e ad amebe patogene del genere Acanthamoeba (Montagna et al., 2013). L’associazione di alcune midichloriaceae con organismi parassiti fa supporre un loro possibile coinvolgimento nel ruolo patogeno svolto dall’ospite parassita. Questa ipotesi è in primo luogo supportata da dati molecolari e sierologici riguardanti M. mitochondrii in I. ricinus: è infatti noto che questo batterio, presente anche nelle ghiandole salivari e nel rostro della zecca, viene trasmesso all’ospite vertebrato durante il pasto di sangue (Mariconti et al., 2012; Bazzocchi et al., 2013), anche se il suo destino, una volta inoculato nell’ospite, è tutt’ora ignoto. Altre linee di evidenza riguardanti l’infettività di batteri ascritti alla famiglia Midichloriaceae sono riscontrabili nell’ipotesi di un loro coinvolgimento nello sviluppo di patologie quali la red mark syndrome/strawberry disease nella trota iridea (Onchorynchus mykiss) (Cafiso et al., 2015) e di un possibile ruolo come coadiuvante nello sviluppo delle cheratiti oculari da Ancanthamoeba spp. Tuttavia al momento la potenziale patogenicità di alcuni membri della famiglia Midichloriaceae per l’uomo e altri vertebrati deve ancora essere dimostrata. Ad esempio, in soggetti parassitati da zecca che mostrano aspetti clinici attribuibili a rickettsiosi o ehrlichiosi, ma che mancano di titolo anticorpale contro microrganismi trasmessi tipicamente con il morso da zecca, le infezioni dovrebbero essere re-investigate sulla base di segni derivanti da infezioni correlate a Midichloriaceae. In conclusione, quindi, diversi aspetti suggeriscono il possibile ruolo di alcuni membri appartenenti alla famiglia Midichloriaceae come agenti infettivi/patogeni per i vertebrati
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Relationship between taste sensitivity and oral microbiota composition : exploring their role in obesity development
No full textObesity in childhood and adolescence is considered the most prevalent nutritional disorder, in which diet and related eating behaviors represent important factors of influence. Although many aspects contribute to eating behaviors, taste is considered the main predictor. It has been suggested that obese subjects might have a reduced or distorted taste sensitivity that could increase the willingness to ingest foods that involve greater stimulation of the taste and oral somatosensory system. Recently, it has been suggested that oral bacteria could have a direct role in obesity development and a relationship between taste sensitivity and oral bacteria was proposed. In this context, the aim of the present study was to investigate the relationship among aspects potentially affecting weight gain , especially sensory perception and oral microbiota composition, in obese (OB) and normal-weight (NW) children and adolescents.
In a cross-sectional study thirty-four OB (BMI ≥ 95th percentile; 45% F) and thirty-three NW subjects (56% F) aged between six and fourteen years old were recruited. Taste ability was assessed through gustatory function screening (using the ‘Taste Strips’ method) and Fungiform Papillae count. Unstimulated whole saliva samples were collected and the bacterial composition of saliva was determined by 16S rRNA gene profiling.
Results showed that OB subjects presented a significantly lower ability to identify the correct taste qualities and were characterized by a greater number of FP/cm2 compared to NW subjects. The structure of the bacterial consortia, at the phylum level as well as at finer taxonomic rankings, resulted very similar in the two groups. Nonetheless, the levels of Bacteroidetes were different in children and adolescents characterized by a greater ability in identifying the bitter taste, independently of their nutritional status. The potentiality of this multidisciplinary approach could help to better understand and deepen the sensory-driven and microbiological factors related to weight gain
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
