The friendship paradox in scale-free networks

Our friends have more friends than we do. That is the basis of the friendship paradox. In mathematical terms, the mean number of friends of friends is higher than the mean number of friends. In the present study, we analyzed the relationship between the mean degree of vertices (individuals), , and the mean number of friends of friends, , in scale-free networks with degrees ranging from a minimum degree (k_min) to a maximum degree (k_max). We deduced an expression for - for scale-free networks following a power-law distribution with a given scaling parameter (alpha). Based on this expression, we can quantify how the degree distribution of a scale-free network affects the mean number of friends of friends.Comment: 9 pages, 2 figure

A glucuronoxylan-specific xylanase from a new Paenibacillus favisporus strain isolated from tropical soil of Brazil

A new xylanolytic strain, Paenibacillus favisporus CC02-N2, was isolated from sugarcane plantation fi elds in Brazil. The strain had a xylan-degrading system with multiple enzymes, one of which, xylanase Xyn30A, was identifi ed and characterized. The enzyme is a single-domain xylanase belonging to family 30 of the glycosyl hydrolases (GH30). Xyn30A shows high activity on glucuronoxylans, with a Vmax of 267.2 U mg–1, a Km of 4.0 mg/ml, and a kcat of 13,333 min–1 on beechwood xylan, but it does not hydrolyze arabinoxylans. The three- dimensional structure of Xyn30A consists of a common (β/α)8 barrel linked to a side-chain-associated β-structure, similar to previously characterized GH30 xylanases. The hydrolysis products from glucuronoxylan were methylglucuronic-acid-substituted xylooligomers (acidic xylooligosaccharides). The enzyme bound to insoluble xylan but not to crystalline cellulose. Our results suggest a specifi c role for Xyn30A in xylan biodegradation in natural habitats. The enzyme is a good candidate for the production of tailored xylooligosaccharides for use in the food industry and in the biotechnological transformation of biomass. [Int Microbiol 2014; 17(3):175-184]Keywords: Paenibacillus favisporus · xylanase · glycosyl hydrolases GH3

Morfoanatomia foliar em mudas de Schinus terebinthifolius sob diferentes níveis de saturação hídrica.

As características morfológicas e anatômicas foliares de espécies vegetais são importantes indicadores de sua ecologia e de seus hábitats. Objetivou-se caracterizar a plasticidade fenotípica de Schinus terebinthifolius Raddi em diferentes condições de saturação hídrica. As mudas foram produzidas em tubetes plásticos, permanecendo em estufa por quatro meses, sendo irrigadas normalmente. Em seguida foram submetidas aos tratamentos: T1- testemunha, T2- alagamento parcial e T3- alagamento total. Após três semanas sob alagamento, foram realizadas descrições anatômicas foliares comparativas e avaliadas as características morfológicas área foliar, área específica foliar, espessura foliar, teor de água e densidade estomática. Durante 10 semanas foram observadas as modificações fenotípicas adaptativas. Foi observado aumento da espessura da base do caule, clorose e abscisão foliar, surgimento de lenticelas e raízes adventícias. Após três semanas de alagamento, não foram verificadas grandes modificações na morfologia das folhas, principalmente para a AF e AEF. Em T3, o teor de água foi maior e a espessura foliar menor. Não houve diferença entre os tratamentos para DE. Quanto aos aspectos anatômicos, observou-se uma redução na espessura do mesofilo e das nervuras, assim como a produção de compostos fenólicos por alguns tipos celulares. Os espaços intercelulares são progressivamente mais amplos nas plantas submetidas ao alagament

A glucuronoxylan-specific xylanase from a new Paenibacillus favisporus strain isolated from tropical soil of Brazil

A new xylanolytic strain, Paenibacillus favisporus CC02-N2, was isolated from sugarcane plantation fi elds in Brazil. The strain had a xylan-degrading system with multiple enzymes, one of which, xylanase Xyn30A, was identifi ed and characterized. The enzyme is a single-domain xylanase belonging to family 30 of the glycosyl hydrolases (GH30). Xyn30A shows high activity on glucuronoxylans, with a Vmax of 267.2 U mg1, a Km of 4.0 mg/ml, and a kcat of 13,333 min1 on beechwood xylan, but it does not hydrolyze arabinoxylans. The three- dimensional structure of Xyn30A consists of a common (β/α)8 barrel linked to a side-chain-associated β-structure, similar to previously characterized GH30 xylanases. The hydrolysis products from glucuronoxylan were methylglucuronic-acid-substituted xylooligomers (acidic xylooligosaccharides). The enzyme bound to insoluble xylan but not to crystalline cellulose. Our results suggest a specifi c role for Xyn30A in xylan biodegradation in natural habitats. The enzyme is a good candidate for the production of tailored xylooligosaccharides for use in the food industry and in the biotechnological transformation of biomass. [Int Microbiol 2014; 17(3):175-184

Stomatal behavior and components of the antioxidative system in coffee plants under water stress

Coffee (Coffea arabica) plants show a positive relationship between stomatal closure and formation and accumulation of H2O2. However, for coffee plants under water restriction such relationship has never been studied. The objective of the present study was evaluate the stomatal movement and the antioxidant capacity of coffee seedlings under different water regimes. Eight months old coffee seedlings of cv. Catuaí IAC 99 were submitted to field capacity, gradual and total suspension of irrigation during a period of 21 days. Evaluations of leaf water potential (Ψw) were performed in the beginning of the morning, and stomatal resistance, transpiration rate and vapor pressure deficit were determined at 10 am and 5 pm. All biochemical and enzymatic determinations were performed in leaves collected at 5 pm. Evaluations and samplings were performed at three days intervals. There was no variation in Ψw during the evaluated period for plants in field capacity. However, an expressive decrease of Ψw following day 12, reaching values near -2.5 MPa at the end of the experiment was observed for plants submitted to gradual suspension of irrigation. For plants submitted to total suspension of irrigation, Ψw decreases after the sixth day, reaching -2.5 MPa at day 15. The decay of Ψw in plants submitted to gradual and total suspension of irrigation reflected in increased stomatal resistance and in a decreased transpiration rate leading to an increase in hydrogen peroxide formation and, on final stages, increase in lipid peroxidation. As a conclusion, an increase in the activity of antioxidant enzymes as well as in the levels of ascorbate and dehydroascorbate was observed, which act in the detoxification of free radicals formed as result of the water stress.Para o cafeeiro (Coffea arabica) existe uma comprovada relação positiva entre fechamento estomático e formação e acúmulo de H2O2. Entretanto, tal relação para a cultura sob restrição hídrica ainda não foi estudada. Avaliou-se o movimento estomático e a capacidade antioxidante em mudas de cafeeiro sob diferentes regimes hídricos. Mudas de cafeeiro cv. Catuaí IAC 99, com oito meses de idade, foram submetidas à capacidade de campo, suspensão gradativa e suspensão total da irrigação por um período de 21 dias. Foram realizadas avaliações do potencial hídrico (Ψw) foliar na antemanhã e resistência estomática, taxa transpiratória e déficit de pressão de vapor foram avaliados as 10h00 e 17h00. As determinações bioquímicas e enzimáticas foram realizadas em folhas coletadas às 17h00. Todas as avaliações e coletas foram realizadas em intervalos de três dias. Nas plantas em capacidade de campo não houve variação no Ψw durante o período de avaliação. Para a suspensão gradativa da irrigação, houve queda expressiva a partir dos 12 dias, chegando próximo a -2,5 Mpa, ao final do experimento. Já nas plantas em suspensão total da irrigação observou-se queda no Ψw a partir do sexto dia, chegando a -2,5 MPa aos 15 dias. A queda no Ψw para as plantas em suspensão gradual e total da irrigação refletiu em aumentos na resistência estomática e diminuição da taxa transpiratória, ocasionando aumento na formação de peróxido de hidrogênio e nos períodos finais, aumentos na peroxidação de lipídios. Em conseqüência obervaram-se aumentos na atividade das enzimas antioxidantes, bem como nos teores de ascorbato e dehidroascorbato, atuando na detoxificação dos radicais livres formados em função do estresse