Reloj

martes, 30 de enero de 2018

El animal que no cumple la «ley natural» del envejecimiento

Una investigación publicada recientemente ha presentado resultados que indican que las ratas topo desnudas (Heterocephalus glaber), unos roedores lampiños y armados con dos exagerados dientes, no cumplen la fórmula de Gompertz. Después de alcanzar la edad adulta, a los seis meses, su probabilidad de morir permanece constante e incluso disminuye un poco con el tiempo. Por eso, quizás, estos animales alcanzan los 30 años de edad en cautividad, frente a los cuatro de otros roedores también criados en jaulas. Estos animales tienen una elevada actividad reparadora de ADN y, por otra, altos niveles de chaperonas, unas proteínas que ayudan a otras a plegarse para funcionar adecuadamente. 


En el mundo de los animales de laboratorio, dominado por ratas albinas y moscas, las ratas topo desnudas son súperestrellas. Muy raramente tienen cáncer, son inmunes a ciertos tipos de dolor (como el de las quemaduras), pueden sobrevivir 18 minutos sin oxígeno, cambiando su metabolismo, y son increíblemente longevas: les correspondería vivir seis años, pero pueden llegar a los 30, y conservando su fertilidad. Por todo esto, no llama la atención que los investigadores quieran estudiarlas en beneficio de la salud humana.



viernes, 26 de enero de 2018

Nuevos sistemas de defensa frente a fagos en bacterias

The arms race between bacteria and phages led to the development of sophisticated antiphage defense systems, including CRISPR-Cas and restriction-modification systems. Evidence suggests that unknown defense systems are located in “defense islands” in microbial genomes. 

We comprehensively characterized the bacterial defensive arsenal by examining gene families that are clustered next to known defense genes in prokaryotic genomes. Candidate defense systems were systematically engineered and validated in model bacteria for their antiphage activities. 

We report nine previously unknown antiphage systems and one antiplasmid system that are widespread in microbes and strongly protect against foreign invaders. These include systems that adopted components of the bacterial flagella and condensin complexes. Our data also suggest a common, ancient ancestry of innate immunity components shared between animals, plants, and bacteria.

Bacteria and archaea are frequently attacked by viruses (phages), and as a result have developed multiple, sophisticated lines of active defense (13) that can collectively be referred to as the prokaryotic “immune system.” Antiphage defense strategies include restriction-modification (R-M) systems that target specific sequences on the invading phage (4), CRISPR-Cas, which provides acquired immunity through memorization of past phage attacks (5), abortive infection systems (Abi) that lead to cell death or metabolic arrest upon infection (6), and additional systems whose mechanism of action is not yet clear such as BREX (7), prokaryotic Argonautes (pAgos) (8) and DISARM (9). Different bacteria encode different sets of defense systems: CRISPR-Cas systems are found in about 40% of all sequenced bacteria (1011), R-M systems are found in about 75% of prokaryote genomes (12) while pAgos and BREX appear in about 10% (713). It has been suggested that many currently unknown defense systems reside in genomes and plasmids of nonmodel bacteria and archaea and await discovery (214).
Antiphage defense systems were found to be frequently physically clustered in bacterial and archaeal genomes such that, for example, genes encoding restriction enzymes commonly reside in the vicinity of genes encoding abortive infection systems and other phage resistance systems (1415). The observation that defense systems are clustered in genomic “defense islands” has led to the suggestion that genes of unknown function residing within such defense islands may also participate in antiphage defense (1516). Indeed, recent studies that focused on individual genes enriched next to known defense genes resulted in the discovery of new systems that protect bacteria against phages (7917).



Enlace al trabajo

A global atlas of the dominant bacteria found in soil

The immense diversity of soil bacterial communities has stymied efforts to characterize individual taxa and document their global distributions. We analyzed soils from 237 locations across six continents and found that only 2% of bacterial phylotypes (~500 phylotypes) consistently accounted for almost half of the soil bacterial communities worldwide. Despite the overwhelming diversity of bacterial communities, relatively few bacterial taxa are abundant in soils globally. We clustered these dominant taxa into ecological groups to build the first global atlas of soil bacterial taxa. Our study narrows down the immense number of bacterial taxa to a “most wanted” list that will be fruitful targets for genomic and cultivation-based efforts aimed at improving our understanding of soil microbes and their contributions to ecosystem functioning.







sábado, 6 de enero de 2018

Abiotic synthesis of purine and pyrimidine ribonucleosides in aqueous microdroplets



Importancia del trabajo

Discovery of an improved prebiotic method for the synthesis of ribonucleosides provides support to theories that posit a central role for RNA in the origin of life. It has been assumed that ribonucleosides arose through an abiotic process in which ribose and nucleobases became conjoined, but the direct condensation of nucleobases with ribose to give ribonucleosides in bulk solution is thermodynamically uphill. We show a general synthetic path for ribonucleosides, both purine and pyrimidine bases, using an abiotic salvage pathway in a microdroplet environment with divalent magnesium ion (Mg2+) as a catalyst. Purine and pyrimidine ribonucleosides are formed simultaneously under the same conditions, which suggests a possible scenario for the spontaneous production of random ribonucleosides necessary to generate various types of primitive RNA.