MetR-Regulated Vibrio cholerae Metabolism Is Required for Virulence

LysR-type transcriptional regulators (LTTRs) are the largest, most diverse family of prokaryotic transcription factors, with regulatory roles spanning metabolism, cell growth and division, and pathogenesis. Using a sequence-defined transposon mutant library, we screened a panel of V. cholerae El Tor mutants to identify LTTRs required for host intestinal colonization. Surprisingly, out of 38 LTTRs, only one severely affected intestinal colonization in the suckling mouse model of cholera: the methionine metabolism regulator, MetR. Genetic analysis of genes influenced by MetR revealed that glyA1 and metJ were also required for intestinal colonization. Chromatin immunoprecipitation of MetR and quantitative reverse transcription-PCR (qRT-PCR) confirmed interaction with and regulation of glyA1, indicating that misregulation of glyA1 is likely responsible for the colonization defect observed in the metR mutant. The glyA1 mutant was auxotrophic for glycine but exhibited wild-type trimethoprim sensitivity, making folate deficiency an unlikely cause of its colonization defect. MetJ regulatory mutants are not auxotrophic but are likely altered in the regulation of amino acid-biosynthetic pathways, including those for methionine, glycine, and serine, and this misregulation likely explains its colonization defect. However, mutants defective in methionine, serine, and cysteine biosynthesis exhibited wild-type virulence, suggesting that these amino acids can be scavenged in vivo. Taken together, our results suggest that glycine biosynthesis may be required to alleviate an in vivo nutritional restriction in the mouse intestine; however, additional roles for glycine may exist. Irrespective of the precise nature of this requirement, this study illustrates the importance of pathogen metabolism, and the regulation thereof, as a virulence factor

INFLUENCE OF SCREW ACCESS CHANNEL ON THE COMPRESSIVE STRENGTH OF LITHIUM DISILICATE AND ZIRCONIA IMPLANT SUPPORTED CROWNS

Objetivo: Avaliar a influência de um canal de acesso do parafuso (CAP) sobre a resistência à compressão de coroas implantossuportadas fabricadas com abutments parafusados ou cimentados usando zircônia estabilizada com ítria (YSZ) ou estruturas de dissilicato de lítio infraestruturas (LS2). Materiais e Método: Quarenta espécimes compostos por análogos de implantes de conexão hexagonal externa e uma plataforma de 4,1 mm, pilares pré-fabricados de titânio para próteses cimentadas e infraestruturas para coroas totais foram confeccionados. Os corpos-de-prova foram divididos em quatro grupos (n = 10) com base no sistema cerâmico e presença de CAP da seguinte forma: G1 = YSZ coroa sem CAP (controle); G2 = YSZ com CAP; G3 = coroa LS2 sem CAP (controle); G4 = coroa LS2 com CAP. Todas as coroas foram cimentadas, e os orifícios de acesso dos parafusos nas coroas dos grupos experimentais foram restaurados com um compósito fotopolimerizável. Os corpos-de-prova foram submetidos a testes de compressão em máquina universal de teste de carga (EMIC DL 2000) a uma velocidade de 0,5 mm / min. A análise estatística foi realizada usando ANOVA de uma via, seguida do teste de Tukey (α = 0,05). Resultados: Diferenças significativas foram observadas entre os grupos (p <0,001); O grupo controle YSZ (G1 = 3372 ± 571 N) exibiu maior resistência à compressão do que o grupo experimental correspondente (G2 = 1675 ± 293 N), grupo controle LS2 (G3 = 1931 ± 430 N) e grupo experimental LS2 (G4 = 1447 ± 449 N). Entretanto, não houve diferenças entre as resistências à compressão de G2, G3 e G4 (p≥ 0,10). Conclusão: A fabricação de restaurações de implantes cimentadas e com CAP não compromete clinicamente a falha por fadiga das coroas LS2. Além disso, entre os tipos de coroas testadas, as coroas YSZ sem CAP exibiram falha por fadiga significativamente maior. Abstract Purpose: The purpose of this study was to evaluate the influence of a screw access channel (SAC) on the compressive strength of implant-supported crowns manufactured with screw-retained or cement-retained abutments using either yttria-stabilized zirconia (YSZ) or lithium disilicate (LS2) infrastructures. Materials and method: Forty specimens composed of external hexagonal implant analogs with a 4.1mm platform, prefabricated titanium abutments for cement-retained prostheses, and infrastructures for full crowns were fabricated. The specimens were divided into four groups (n = 10) based on the ceramic system and presence of SAC as follows: G1= YSZ crown without SAC (control); G2 = YSZ with SAC; G3 = LS2 crown without SAC (control); G4 = LS2 crown with SAC. All crowns were cemented, and the screw access holes in the crowns of the experimental groups were restored using a composite. The specimens were subjected to compression tests using a universal load-testing machine (EMIC DL 2000) at a speed of 0.5 mm/min. Statistical analysis was performed using one-way ANOVA, followed by Tukey’s test (α= 0.05). Results: Significant differences were observed between the groups (p<0.001); The YSZ control group (G1= 3372 ± 571 N) exhibited higher compressive strength than the corresponding experimental group (G2= 1675 ± 293 N), LS2 control group (G3=1931 ± 430 N), and LS2 experimental group (G4= 1447 ± 449 N). However, there were no differences between the compressive strengths of G2, G3, and G4 (p≥ 0.10). Conclusion: The fabrication of cement-retained implant restorations with SAC does not clinically compromise the fatigue failure of LS2 crowns. In addition, among the types of crowns tested, the YSZ crowns without SAC exhibited significantly higher fatigue failure.

Asteroids Were Born Big

How big were the first planetesimals? We attempt to answer this question by conducting coagulation simulations in which the planetesimals grow by mutual collisions and form larger bodies and planetary embryos. The size frequency distribution (SFD) of the initial planetesimals is considered a free parameter in these simulations, and we search for the one that produces at the end objects with a SFD that is consistent with asteroid belt constraints. We find that, if the initial planetesimals were small (e.g. km-sized), the final SFD fails to fulfill these constraints. In particular, reproducing the bump observed at diameter D~100km in the current SFD of the asteroids requires that the minimal size of the initial planetesimals was also ~100km. This supports the idea that planetesimals formed big, namely that the size of solids in the proto-planetary disk ``jumped'' from sub-meter scale to multi-kilometer scale, without passing through intermediate values. Moreover, we find evidence that the initial planetesimals had to have sizes ranging from 100 to several 100km, probably even 1,000km, and that their SFD had to have a slope over this interval that was similar to the one characterizing the current asteroids in the same size-range. This result sets a new constraint on planetesimal formation models and opens new perspectives for the investigation of the collisional evolution in the asteroid and Kuiper belts as well as of the accretion of the cores of the giant planets.Comment: Icarus (2009) in pres

Delivery of Dark Material to Vesta via Carbonaceous Chondritic Impacts

NASA's Dawn spacecraft observations of asteroid (4) Vesta reveal a surface with the highest albedo and color variation of any asteroid we have observed so far. Terrains rich in low albedo dark material (DM) have been identified using Dawn Framing Camera (FC) 0.75 {\mu}m filter images in several geologic settings: associated with impact craters (in the ejecta blanket material and/or on the crater walls and rims); as flow-like deposits or rays commonly associated with topographic highs; and as dark spots (likely secondary impacts) nearby impact craters. This DM could be a relic of ancient volcanic activity or exogenic in origin. We report that the majority of the spectra of DM are similar to carbonaceous chondrite meteorites mixed with materials indigenous to Vesta. Using high-resolution seven color images we compared DM color properties (albedo, band depth) with laboratory measurements of possible analog materials. Band depth and albedo of DM are identical to those of carbonaceous chondrite xenolith-rich howardite Mt. Pratt (PRA) 04401. Laboratory mixtures of Murchison CM2 carbonaceous chondrite and basaltic eucrite Millbillillie also show band depth and albedo affinity to DM. Modeling of carbonaceous chondrite abundance in DM (1-6 vol%) is consistent with howardite meteorites. We find no evidence for large-scale volcanism (exposed dikes/pyroclastic falls) as the source of DM. Our modeling efforts using impact crater scaling laws and numerical models of ejecta reaccretion suggest the delivery and emplacement of this DM on Vesta during the formation of the ~400 km Veneneia basin by a low-velocity (<2 km/sec) carbonaceous impactor. This discovery is important because it strengthens the long-held idea that primitive bodies are the source of carbon and probably volatiles in the early Solar System.Comment: Icarus (Accepted) Pages: 58 Figures: 15 Tables:

Seafood in Food Security: a call for bridging the terrestrial-aquatic divide

The contribution of seafood to global food security is being increasingly highlighted in policy. However, the extent to which such claims are supported in the current food security literature is unclear. This review assesses the extent to which seafood is represented in the recent food security literature, both individually and from a food systems perspective, in combination with terrestrially-based production systems. The results demonstrate that seafood remains under-researched compared to the role of terrestrial animal and plant production in food security. Furthermore, seafood and terrestrial production remain siloed, with very few papers addressing the combined contribution or relations between terrestrial and aquatic systems. We conclude that far more attention is needed to the specific and relative role of seafood in global food security and call for the integration of seafood in a wider interdisciplinary approach to global food system research

Seafood in Food Security: A Call for Bridging the Terrestrial-Aquatic Divide

The contribution of seafood to global food security is being increasingly highlighted in policy. However, the extent to which such claims are supported in the current food security literature is unclear. This review assesses the extent to which seafood is represented in the recent food security literature, both individually and from a food systems perspective, in combination with terrestrially-based production systems. The results demonstrate that seafood remains under-researched compared to the role of terrestrial animal and plant production in food security. Furthermore, seafood and terrestrial production remain siloed, with very few papers addressing the combined contribution or relations between terrestrial and aquatic systems. We conclude that far more attention is needed to the specific and relative role of seafood in global food security and call for the integration of seafood in a wider interdisciplinary approach to global food system research