National Autonomous University of Mexico

About: National Autonomous University of Mexico is a education organization based out in Mexico City, Distrito Federal, Mexico. It is known for research contribution in the topics: Population & Galaxy. The organization has 72868 authors who have published 127797 publications receiving 2285543 citations. The organization is also known as: UNAM & Universidad Nacional Autónoma de México.

Improvement of Escherichia coli production strains by modification of the phosphoenolpyruvate:sugar phosphotransferase system

Abstract: The application of metabolic engineering in Escherichia coli has resulted in the generation of strains with the capacity to produce metabolites of commercial interest. Biotechnological processes with these engineered strains frequently employ culture media containing glucose as the carbon and energy source. In E. coli, the phosphoenolpyruvate:sugar phosphotransferase system (PTS) transports glucose when this sugar is present at concentrations like those used in production fermentations. This protein system is involved in phosphoenolpyruvate-dependent sugar transport, therefore, its activity has an important impact on carbon flux distribution in the phosphoenolpyruvate and pyruvate nodes. Furthermore, PTS has a very important role in carbon catabolite repression. The properties of PTS impose metabolic and regulatory constraints that can hinder strain productivity. For this reason, PTS has been a target for modification with the purpose of strain improvement. In this review, PTS characteristics most relevant to strain performance and the different strategies of PTS modification for strain improvement are discussed. Functional replacement of PTS by alternative phosphoenolpyruvate-independent uptake and phosphorylation activities has resulted in significant improvements in product yield from glucose and productivity for several classes of metabolites. In addition, inactivation of PTS components has been applied successfully as a strategy to abolish carbon catabolite repression, resulting in E. coli strains that use more efficiently sugar mixtures, such as those obtained from lignocellulosic hydrolysates.

Major Earthquakes of Chile: A Historical Survey, 1535-1960

Abstract: This paper is an update of a 1970 publication, “Major Earthquakes and Tsunamis in Chile” (Lomnitz, 1970), which appeared in the Geologische Rundschau , now International Journal of Earth Sciences. The reference has always been hard to find and in recent years has become almost impossible to locate. Additionally, the database was overdue for revision in light of more recent results. The earlier conclusion of the paper, that “Chile emerges as perhaps the most highly seismic region in the world, with the possible exception of Japan”, still stands. One might add that Chilean earthquakes have provided data for important historical advances in the Earth sciences. For example, the 1835 earthquake in southern Chile was described by Darwin (1845) and has provided the earliest reliable observations of geodetic uplift along a subduction zone. The 1960 Chile earthquake ( Mw 9.5), possibly the largest earthquake in world history, continues to provide invaluable data and challenges for research. Tectonic changes in the coastal morphology of Chile may well be unique (Lomnitz, 1969). As part of a 5,000-km subduction system and with a subduction rate of more than 7 cm/year, Chile is located atop one of the most highly active subduction zones in the world. Available information on the history of earthquakes in Chile is limited. This is partly due to the nature of the terrain. The northern part of Chile is a desert, where rain falls about once every 25 years. The southern part is extremely rainy and is covered with a dense rain forest. Farther south along the coast one finds glaciers. The country is also wedged between the Pacific Ocean and the Andes Mountains. With the exception of a few scattered ports, most of the population lives in a narrow longitudinal valley between latitudes 32° and 45° south. I have experienced …

Phylogenetic analysis of enteroaggregative and diffusely adherent Escherichia coli.

Abstract: The phylogenetics of the various pathotypes of diarrheagenic Escherichia coli are not completely understood. In this study, we identified several plasmid and chromosomal genes in the pathogenic enteroaggregative E. coli (EAEC) prototype strain 042 and determined the prevalence of these loci among EAEC and diffusely adherent E. coli strains. The distribution of these genes is analyzed within an evolutionary framework provided by the characterization of allelic variation in housekeeping genes via multilocus enzyme electrophoresis. Our data reveal that EAEC strains are heterogeneous with respect to chromosomal and plasmid-borne genes but that the majority harbor a member of a conserved family of virulence plasmids. Comparison of plasmid and chromosomal relatedness of strains suggests clonality of chromosomal markers and a limited transfer model of plasmid distribution.

Production of pions, kaons and protons in pp collisions at root s=900 GeV with ALICE at the LHC

Abstract: The production of π+, π−, K+, K−, p, and \(\overline{\mathrm{p}}\) at mid-rapidity has been measured in proton-proton collisions at \(\sqrt{s} = 900~\mathrm{GeV}\) with the ALICE detector. Particle identification is performed using the specific energy loss in the inner tracking silicon detector and the time projection chamber. In addition, time-of-flight information is used to identify hadrons at higher momenta. Finally, the distinctive kink topology of the weak decay of charged kaons is used for an alternative measurement of the kaon transverse momentum (pt) spectra. Since these various particle identification tools give the best separation capabilities over different momentum ranges, the results are combined to extract spectra from pt=100 MeV/c to 2.5 GeV/c. The measured spectra are further compared with QCD-inspired models which yield a poor description. The total yields and the mean pt are compared with previous measurements, and the trends as a function of collision energy are discussed.