Migración contemporánea mexicana: redes sociales transnacionales y políticas migratorias : la experiencia migratoria de la comunidad de Tunkás, Yucatán en el sur de California

This research explores the impacts of the most recent U.S. economic crisis on the Mexican immigrant labour market, specifically from the town of Tunkás, Yucatan. Based on Bourdieu.’s theory of Capital production, and the transnational theoretical perspective, this study aims to build a conceptual frame for the migrant’s social capital in modern societies. A key element of this analysis is that a pioneer migrant-woman has initiated the tunkaseño social network in Los Angeles and Orange County, California; and has set the route to migrate to North. Finally this analysis presents how U.S. worksite enforcement policy affects the labour market that tunkaseños encounter in Southern California in the midst of a financial crisis. Tunkás, our Mayan community, native from the Southern Mexican state of Yucatan has experienced a constant migration process to California ever since the Bracero Program started. Mayan migrants have acquired new responsibilities, and a hybrid identity as transnational citizens. Yucatecan migration is defined as a contemporary Mexican migration, mostly undocumented, exacerbated during the nineties, in the midst of the Mexican financial crisis from 1994 to 1997. The present work is part of a broader research that discusses the transformation of Mexican migration patterns of different states of Mexico. This project is based on fieldwork in the communities of origin and destination. As well, on the survey results and life stories obtained during 2005-2006, and 2008-2009 by MMFRP1, where I took part in both editions as a researcher...

Fitness cost and interference of Arm/Rmt aminoglycoside resistance with the RsmF housekeeping methyltransferases

Arm/Rmt methyltransferases have emerged recently in pathogenic bacteria as enzymes that confer high-level resistance to 4,6-disubstituted aminoglycosides through methylation of the G1405 residue in the 16S rRNA (like ArmA and RmtA to -E). In prokaryotes, nucleotide methylations are the most common type of rRNA modification, and they are introduced posttranscriptionally by a variety of site-specific housekeeping enzymes to optimize ribosomal function. Here we show that while the aminoglycoside resistance methyltransferase RmtC methylates G1405, it impedes methylation of the housekeeping methyltransferase RsmF at position C1407, a nucleotide that, like G1405, forms part of the aminoglycoside binding pocket of the 16S rRNA. To understand the origin and consequences of this phenomenon, we constructed a series of in-frame knockout and knock-in mutants of Escherichia coli, corresponding to the genotypes rsmF(+), ΔrsmF, rsmF(+) rmtC(+), and ΔrsmF rmtC(+). When analyzed for the antimicrobial resistance pattern, the ΔrsmF bacteria had a decreased susceptibility to aminoglycosides, including 4,6- and 4,5-deoxystreptamine aminoglycosides, showing that the housekeeping methylation at C1407 is involved in intrinsic aminoglycoside susceptibility in E. coli. Competition experiments between the isogenic E. coli strains showed that, contrary to expectation, acquisition of rmtC does not entail a fitness cost for the bacterium. Finally, matrix-assisted laser desorption ionization (MALDI) mass spectrometry allowed us to determine that RmtC methylates the G1405 residue not only in presence but also in the absence of aminoglycoside antibiotics. Thus, the coupling between housekeeping and acquired methyltransferases subverts the methylation architecture of the 16S rRNA but elicits Arm/Rmt methyltransferases to be selected and retained, posing an important threat to the usefulness of aminoglycosides worldwide.