Isolation of a conjugative F-like plasmid from a multidrug-resistant Escherichia coli strain CM6 using tandem shock wave-mediated transformation.

Genetic characterization of plasmids from bacterial strains provides insight about multidrug resistance. Ten wild type Escherichia coli (E. coli) strains isolated from cow fecal samples were characterized by their antibiotic resistance profile, plasmid patterns and three different identification methods. From one of the strains, a fertility factor-like plasmid was replicated using tandem shock wave-mediated transformation. Underwater shock waves with a positive pressure peak of up to approximately 40 MPa, followed by a pressure trough of approximately -19 MPa were generated using an experimental piezoelectric shock wave source. Three different shock wave energies and a fixed delay of 750 µs were used to study the relationship between energy and transformation efficiency (TE), as well as the influence of shock wave energy on the integrity of the plasmid. Our results showed that the mean shock wave-mediated TE and the integrity of the large plasmid (~70 kb) were reduced significantly at the energy levels tested. The sequencing analysis of the plasmid revealed a high identity to the pHK17a plasmid, including the replication system, which was similar to the plasmid incompatibility group FII. It also showed that it carried an extended spectrum beta-lactamase gene, ctx-m-14. Furthermore, diverse genes for the conjugative mechanism were identified. Our results may be helpful in improving methodologies for conjugative plasmid transfer and directly selecting the most interesting plasmids from environmental samples.

Physico-chemical changes in cladodes (nopalitos) from cultivated and wild cacti (Opuntia spp.).

Physico-chemical and nutritional composition from four different nopalitos (young cladodes from cacti): Blanco sin Espinas, Blanco con Espinas, Verde Valtierrilla (cultivated materials) and a wild material from the central region of México were studied at different sizes of harvesting. The first three are commercial crops. None of the tested materials exhibited superior characteristics in all of the evaluated parameters in relation to each one of them. In various cases properties of the wild crop were comparable, if not superior, to commercial ones. Some important changes were observed in total soluble solids, water content, texture, acidity and pH as affected by size of cladode and specific crop. Most cladode samples appear to be a good source of beta-carotene and lutein. The presence of these compounds is important for human nutraceutical purposes.

Agrobacterium tumefaciens- mediated transformation of embryogenic avocado cultures and regeneration of somatic embryos.

Embryogenic avocado cultures were genetically transformed with the uidA (GUS) and nptII genes, and transformed somatic embryos were recovered from these cultures. Embryogenic avocado cultures derived from zygotic embryos of `Thomas' and consisting of proembryonic masses were gently separated and co-cultivated with disarmed, acetosyringone-activated Agrobacterium tumefaciens strain A208, which contained the cointegrative vector pTiT37-ASE::pMON9749 (9749 ASE). Kanamycin-resistant embryogenic suspension cultures were selected in two steps: (1) initial selection in maintenance medium, consisting of MS basal medium, supplemented with 0.1 mg l-1 picloram and 50 mg l-1 kanamycin sulfate for 2-4 months and (2) subsequent selection in maintenance medium with 100 mg/ml kanamycin sulfate for 2 months in order to eliminate chimeras. Somatic embryo maturation was initiated by subculture onto semisolid maturation medium (without picloram) followed by transfer to maturation medium with 100 mg l-1 kanamycin sulfate. Genetic transformation of embryogenic cultures and somatic embryos was confirmed by the X-gluc reaction, and integration of nptII and uidA into the avocado genome was confirmed by PCR and Southern hybridization, respectively.

Alternative oxidase from mango (Mangifera indica, L.) is differentially regulated during fruit ripening.

Alternative oxidase is a respiratory-chain component of higher plants and fungi that catalyzes cyanide-resistant oxygen consumption. The activity of a alternative oxidase has been detected during ripening in several climacteric fruit including mango (Mangifera indica L.). Synthetic oligonucleotides, corresponding to conserved regions of the Sauromatum guttatum and Arabidopsis thaliana nucleotide sequences, were used as primers for polymerase chain reaction to amplify genomic DNA extracted from mango leaves. The 623-bp fragment was found to encode an open reading frame of 207 amino acids showing high identity to the S. guttatum enzyme. Using this fragment to screen a ripe mango mesocarp cDNA library, one full-length cDNA clone, designated pAOMI.1, was obtained that contained an open reading frame encoding a polypeptide of 318 amino acids. The predicted amino-acid sequence exhibited 62, 64 and 68% identity to the S. guttatum, soybean, and A. thaliana enzymes respectively, indicating that this cDNA encodes a mango homologue of the alternative oxidase. Gel blot hybridization showed that pAOMI.1 is likely to be encoded by a single-copy gene. The 1.6 kb-transcript was induced during mango fruit ripening although the transcript was clearly detectable in unripe and developing fruit. Antibodies raised against the S. guttatum enzyme recognized three bands of approximately 27, approximately 33 and approximately 36 kDa from mitochondrial mango proteins. Two of the bands were detectable before ripening and increase in ripe fruit, the other band (27 kDa) was barely present in unripe fruit but accumulated during ripening. The clone pAOMI.1 was able to complement an Escherichia coli hemA mutant deficient in cytochrome-mediated aerobic respiration. This is the first report on the analysis of alternative oxidase at the molecular level during the ripening of a climacteric fruit.

Isolation and characterization of a gene involved in ethylene biosynthesis from Arabidopsis thaliana.

The ethylene forming enzyme (EFE) is a key factor in ethylene biosynthesis. To understand better the regulation of ethylene biosynthesis in vegetative tissues, we set out to isolate and characterize a complementary DNA (cDNA) encoding the EFE from Arabidopsis thaliana. An A. thaliana cDNA library was screened with pTOM 13, a tomato cDNA coding for the EFE. A cDNA clone (pEAT1) was isolated. The cDNA is 1200 nucleotides (nt) in length and predicts a protein of M(r) 36,663. The insert includes the complete open reading frame of 972 bp and shows strong homology with several reported sequences, both at the nt and amino acid level. In whole seedlings, expression of pEAT1 was enhanced by wounding, ethrel, Fe2+, and 1-amino-cyclopropane-carboxylic acid (ACC) treatments. In contrast, heat shock had no effect on the expression.

Comparison of segmental and global ejection fraction in ischaemic heart disease.

In order to evaluate whether segmental ejection fraction (SEF) is a better index of left ventricular (LV) performance than global ejection fraction (EF), 25 patients with significant coronary stenosis and normal EF were studied. SEF was estimated from the LV cineangiogram after dividing the LV into eight segments by means of a long axis and three equally spaced chords perpendicular to it. The area of a given segment was measured in the end-diastole and the end-systole and SEF was calculated by determining the percent decrease in area for each segment. 12 out of the 25 patients presented hypokinesis, akinesis or dyskinesis of at least two segments; the inferior apical and both diaphragmatic segments were the regions most frequently affected. In 7 patients, these abnormalities were compensated by hyperkinesis of two or three other segments, whereas in the remaining 5 patients contraction abnormalities were not accompanied by hyperkinesis in spite of a normal EF. It is concluded that SEF is a more sensitive index of regional LV function than EF in patients with ischaemic heart disease.

Conversores analogodigitales para la minicomputadora CID-201-B / Analog-to-digital and digital-to-analog converters for the minicomputer CID-201-B

Se plantea que en su acepción más amplia, un coversor es un dispositivo que transforma una información de un cierto tipo, en otra de diferente tipo que guarda una cierta relación de equivalencia con la primera. Específicamente un conversor digital analógico (DA) transforma una señal digital de entrada en una salida analógica, y un conversor analogodigital (AD) realiza el proceso de la inversa. Se señala que uno de los aspectos fundamentales que debe considerarse en la selección de un conversor DA o AD para una aplicación determinada, es el denominado "error de cuantización", que es inversamente proporcional a la cantidad de bits de la parte digital (entrada o salida) del conversor; otro de los aspectos esenciales que debe considerarse es la velocidad de conversión requerida en el caso concreto (AU)