Showing papers by "National Autonomous University of Mexico published in 2001"

The causes of land-use and land-cover change: moving beyond the myths

Abstract: Common understanding of the causes of land-use and land-cover change is dominated by simplifications which, in turn, underlie many environment-development policies. This article tracks some of the major myths on driving forces of land-cover change and proposes alternative pathways of change that are better supported by case study evidence. Cases reviewed support the conclusion that neither population nor poverty alone constitute the sole and major underlying causes of land-cover change worldwide. Rather, peoples’ responses to economic opportunities, as mediated by institutional factors, drive land-cover changes. Opportunities and

Carbon dioxide emissions from the global cement industry

Abstract: ▪ Abstract The cement industry contributes about 5% to global anthropogenic CO2 emissions, making the cement industry an important sector for CO2-emission mitigation strategies. CO2 is emitted from the calcination process of limestone, from combustion of fuels in the kiln, as well as from power generation. In this paper, we review the total CO2 emissions from cement making, including process and energy-related emissions. Currently, most available data only includes the process emissions. We also discuss CO2 emission mitigation options for the cement industry. Estimated total carbon emissions from cement production in 1994 were 307 million metric tons of carbon (MtC), 160 MtC from process carbon emissions, and 147 MtC from energy use. Overall, the top 10 cement-producing countries in 1994 accounted for 63% of global carbon emissions from cement production. The average intensity of carbon dioxide emissions from total global cement production is 222 kg of C/t of cement. Emission mitigation options include en...

Interactions of chromium with microorganisms and plants

Abstract: Chromium is a highly toxic non-essential metal for microorganisms and plants. Due to its widespread industrial use, chromium (Cr) has become a serious pollutant in diverse environmental settings. The hexavalent form of the metal, Cr(VI), is considered a more toxic species than the relatively innocuous and less mobile Cr(III) form. The presence of Cr in the environment has selected microbial and plant variants able to tolerate high levels of Cr compounds. The diverse Cr-resistance mechanisms displayed by microorganisms, and probably by plants, include biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux. Some of these systems have been proposed as potential biotechnological tools for the bioremediation of Cr pollution. In this review we summarize the interactions of bacteria, algae, fungi and plants with Cr and its compounds.

Epidemiology and molecular pathology of gallbladder cancer.

Abstract: Gallbladder cancer is usually associated with gallstone disease, late diagnosis, unsatisfactory treatment, and poor prognosis. We report here the worldwide geographical distribution of gallbladder cancer, review the main etiologic hypotheses, and provide some comments on perspectives for prevention. The highest incidence rate of gallbladder cancer is found among populations of the Andean area, North American Indians, and Mexican Americans. Gallbladder cancer is up to three times higher among women than men in all populations. The highest incidence rates in Europe are found in Poland, the Czech Republic, and Slovakia. Incidence rates in other regions of the world are relatively low. The highest mortality rates are also reported from South America, 3.5-15.5 per 100,000 among Chilean Mapuche Indians, Bolivians, and Chilean Hispanics. Intermediate rates, 3.7 to 9.1 per 100,000, are reported from Peru, Ecuador, Colombia, and Brazil. Mortality rates are low in North America, with the exception of high rates among American Indians in New Mexico (11.3 per 100,000) and among Mexican Americans. The main associated risk factors identified so far include cholelithiasis (especially untreated chronic symptomatic gallstones), obesity, reproductive factors, chronic infections of the gallbladder, and environmental exposure to specific chemicals. These suspected factors likely represent promoters of carcinogenesis. The main limitations of epidemiologic studies on gallbladder cancer are the small sample sizes and specific problems in quantifying exposure to putative risk factors. The natural history of gallbladder disease should be characterized to support the allocation of more resources for early treatment of symptomatic gallbladder disease in high-risk populations. Secondary prevention of gallbladder cancer could be effective if supported by cost-effective studies of prophylactic cholecystectomy among asymptomatic gallstone patients in high-risk areas.

An anorexic lipid mediator regulated by feeding

Abstract: Oleylethanolamide (OEA) is a natural analogue of the endogenous cannabinoid anandamide. Like anandamide, OEA is produced in cells in a stimulus-dependent manner and is rapidly eliminated by enzymatic hydrolysis, suggesting a function in cellular signalling. However, OEA does not activate cannabinoid receptors and its biological functions are still unknown. Here we show that, in rats, food deprivation markedly reduces OEA biosynthesis in the small intestine. Administration of OEA causes a potent and persistent decrease in food intake and gain in body mass. This anorexic effect is behaviourally selective and is associated with the discrete activation of brain regions (the paraventricular hypothalamic nucleus and the nucleus of the solitary tract) involved in the control of satiety. OEA does not affect food intake when injected into the brain ventricles, and its anorexic actions are prevented when peripheral sensory fibres are removed by treatment with capsaicin. These results indicate that OEA is a lipid mediator involved in the peripheral regulation of feeding.

Accretion disks around young objects. iii. grain growth

Abstract: We present detailed models of irradiated T Tauri disks including dust grain growth with power-law size distributions. The models assume complete mixing between dust and gas and solve for the vertical disk structure self-consistently including the heating effects of stellar irradiation as well as local viscous heating. For a given total dust mass, grain growth is found to decrease the vertical height of the surface where the optical depth to the stellar radiation becomes unity and thus the local irradiation heating, while increasing the disk emission at mm and submillimeter wavelengths. The resulting disk models are less geometrically thick than our previous models assuming interstellar medium dust, and agree better with observed spectral energy distributions and images of edge-on disks, like HK Tau/c and HH 30. The implications of models with grain growth for determining disk masses from long-wavelength emission are considered.

Rapid Formation of Molecular Clouds and Stars in the Solar Neighborhood

Abstract: We show how molecular clouds in the solar neighborhood might be formed and produce stars rapidly enough to explain stellar population ages, building on results from numerical simulations of the turbulent interstellar medium and general considerations of molecular gas formation. Observations of both star-forming regions and young, gas-free stellar associations indicate that most nearby molecular clouds form stars only over a short time span before dispersal; large-scale —ows in the diUuse interstellar medium have the potential for forming clouds sufficiently rapidly and for producing stellar populations with ages much less than the lateral crossing times of their host molecular clouds. We identify four important factors for understanding rapid star formation and short cloud lifetimes. First, much of the accumulation and dispersal of clouds near the solar circle might occur in the atomic phase; only the

Burkholderia, a Genus Rich in Plant-Associated Nitrogen Fixers with Wide Environmental and Geographic Distribution

Abstract: The genus Burkholderia comprises 19 species, including Burkholderia vietnamiensis which is the only known N2-fixing species of this bacterial genus. The first isolates of B. vietnamiensis were recovered from the rhizosphere of rice plants grown in a phytotron, but its existence in natural environments and its geographic distribution were not reported. In the present study, most N2-fixing isolates recovered from the environment of field-grown maize and coffee plants cultivated in widely separated regions of Mexico were phenotypically identified as B. cepacia using the API 20NE system. Nevertheless, a number of these isolates recovered from inside of maize roots, as well as from the rhizosphere and rhizoplane of maize and coffee plants, showed similar or identical features to those of B. vietnamiensis TVV75T. These features include nitrogenase activity with 10 different carbon sources, identical or very similar nifHDK hybridization patterns, very similar protein electrophoregrams, identical amplified 16S rDNA restriction (ARDRA) profiles, and levels of DNA-DNA reassociation higher than 70% with total DNA from strain TVV75T. Although the ability to fix N2 is not reported to be a common feature among the known species of the genus Burkholderia, the results obtained show that many diazotrophic Burkholderia isolates analyzed showed phenotypic and genotypic features different from those of the known N2-fixing species B. vietnamiensis as well as from those of B. kururiensis, a bacterium identified in the present study as a diazotrophic species. DNA-DNA reassociation assays confirmed the existence of N2-fixing Burkholderia species different from B. vietnamiensis. In addition, this study shows the wide geographic distribution and substantial capability of N2-fixing Burkholderia spp. for colonizing diverse host plants in distantly separated environments.

Structure shape and stability of nanometric sized particles

Abstract: Nanoparticles are a state of matter that has properties different from either molecules or bulk solids. In the present work, we review the shape and structure of nanometer-sized particles; several shapes are discussed, such as the octahedron and truncated octahedron, the icosahedron, the Marks decahedron, the truncated “star-like” decahedron, the rounded decahedron and the regular decahedron. Experimental high-resolution transmission electron microscopy (TEM) images of each type of particle are presented together with the Fast Fourier Transform and a model of the particle. We consider only gold particles grown by vapor deposition or by colloidal methods. High-resolution TEM images of the particles in different orientations are shown. We discuss two basic types of particles uncapped and capped. Data for other metals and semiconductors are reviewed. We have also performed very extensive simulations obtaining the total energy and pair correlation functions for each cluster under study. Furthermore, distributions of single atom energy for every cluster are displayed in order to reveal the effect of surface on the stability of different types and sizes of clusters. We discuss the structure of the particles from ∼1 to ∼100 nm. The mechanisms for stress release as the particles grow larger are reviewed and a mechanism is suggested. Finally, we discuss the parameters that define the shape of a nanoparticle and the possible implications in technological applications.Nanoparticles are a state of matter that has properties different from either molecules or bulk solids. In the present work, we review the shape and structure of nanometer-sized particles; several shapes are discussed, such as the octahedron and truncated octahedron, the icosahedron, the Marks decahedron, the truncated “star-like” decahedron, the rounded decahedron and the regular decahedron. Experimental high-resolution transmission electron microscopy (TEM) images of each type of particle are presented together with the Fast Fourier Transform and a model of the particle. We consider only gold particles grown by vapor deposition or by colloidal methods. High-resolution TEM images of the particles in different orientations are shown. We discuss two basic types of particles uncapped and capped. Data for other metals and semiconductors are reviewed. We have also performed very extensive simulations obtaining the total energy and pair correlation functions for each cluster under study. Furthermore, distribut...

Transitions in histone acetylation reveal boundaries of three separately regulated neighboring loci

Abstract: We have studied developmentally regulated patterns of histone acetylation at high resolution across ∼54 kb of DNA containing three independently regulated but neighboring genetic loci These include a folate receptor gene, a 16 kb condensed chromatin region, the chicken β-globin domain and an adjacent olfactory receptor gene Within these regions the relative levels of acetylation appear to fall into three classes The condensed chromatin region maintains the lowest acetylation at every developmental stage Genes that are inactive show similarly low levels, but activation results in a dramatic increase in acetylation The highest levels of acetylation are seen at regulatory sites upstream of the genes These patterns imply the action of more than one class of acetylation Notably, there is a very strong constitutive focus of hyperacetylation at the 5′ insulator element separating the globin locus from the folate receptor region, which suggests that this insulator element may harbor a high concentration of histone acetylases

Epidemiology of HPV infection among Mexican women with normal cervical cytology.

Abstract: Cervical cancer is caused by human papillomavirus (HPV) and is the most common cancer among Mexican women, but no population-based studies have reported the prevalence and determinants of HPV infection in Mexico. A population-based study was carried out between 1996 and 1999, based on an age-stratified random sample of 1,340 women with normal cytologic diagnoses from 33 municipalities of Morelos State, Mexico. The prevalence of cervical HPV DNA was determined by reverse line blot strip assay to detect 17 cancer-associated and 10 non-cancer-associated HPV types. Two peaks of HPV DNA prevalence were observed. A first peak of 16.7% was observed in the age group under 25 years. HPV DNA prevalence declined to 3.7% in the age group 35-44 years, then increased progressively to 23% among women 65 years and older. Cancer-associated HPV types were the most common in all age groups; non-cancer-associated HPV types were rare in the young and became more common linearly with age. Twenty-four types of HPV were detected; HPV 16, HPV 53, HPV 31 and HPV 18 were the most common, but none was present in more than 1.7% of subjects. The main determinant of infection with both cancer-associated and non-cancer-associated HPV types was the number of sexual partners in all age groups. Less-educated women were at an increased risk of infection with cancer-associated but not with non-cancer-associated HPV types; low socioeconomic status was associated with detection of non-cancer-associated HPV types. Among young women an increasing number of pregnancies was associated with lower HPV detection and among older women low socioeconomic status was related to increased HPV detection, particularly for the age group 35-54 years. Among women with cancer-associated HPV types, there was a higher intensity of polymerase chain reaction signal in younger than in older age groups (p < 0.001). We present additional evidence for the sexually transmitted nature of HPV infection, regardless of age group and HPV type. We confirm previous findings of a second peak of high-risk HPV infections in postmenopausal women, in this case with a clear predominance of cancer-associated HPV types. In populations with this pattern, which can be related to reactivation of latent HPV infections or high previous exposure in older women, screening with HPV testing can have a reduced specificity among older women if proper cut-off points for HPV positivity are not used. Longitudinal studies of immune responses to HPV infection in different age groups are warranted.

Particle-wall collisions in a viscous fluid

Abstract: This paper presents experimental measurements of the approach and rebound of a particle colliding with a wall in a viscous fluid. The particle's trajectory was controlled by setting the initial inclination angle of a pendulum immersed in a fluid. The resulting collisions were monitored using a high-speed video camera. The diameters of the particles ranged from 3 to 12 mm, and the ratio of the particle density to fluid density varied from 1.2 to 7.8. The experiments were performed using a thick glass or Lucite wall with different mixtures of glycerol and water. With these parameters, the Reynolds number defined using the velocity just prior to impact ranged from 10 to approximately 3000. A coefficient of restitution was defined from the ratio of the velocity just prior to and after impact. The experiments clearly demonstrate that the rebound velocity depends on the impact Stokes number (defined from the Reynolds number and the density ratio) and weakly on the elastic properties of the material. Below a Stokes number of approximately 10, no rebound of the particle occurred. For impact Stokes number above 500 the coefficient of restitution appears to asymptote to the values for dry collisions. The coefficients of restitution were also compared with previous experimental studies. In addition, the approach of the particle to the wall indicated that the particle slowed prior to impacting the surface. The distance at which the particle's trajectory varied due to the presence of the wall was dependent on the impact Stokes number. The particle surface roughness was found to affect the repeatability of some measurements, especially for low impact velocities.

Detoxification of dilute acid hydrolysates of lignocellulose with lime

Abstract: The hydrolysis of hemicellulose to monomeric sugars by dilute acid hydrolysis is accompanied by the production of inhibitors that retard microbial fermentation. Treatment of hot hydrolysate with Ca(OH)(2) (overliming) is an effective method for detoxification. Using ethanologenic Escherichia coli LY01 as the biocatalyst, our results indicate that the optimal lime addition for detoxification varies and depends on the concentration of mineral acids and organic acids in each hydrolysate. This optimum was shown to be readily predicted on the basis of the titration of hydrolysate with 2 N NaOH at ambient temperature to either pH 7.0 or pH 11.0. The average composition of 15 hydrolysates prior to treatment was as follows (per L): 95.24 +/- 7.29 g sugar, 5.3 +/- 2.99 g acetic acid, 1.305 +/- 0.288 g total furans (furfural and hydroxymethylfurfural), and 2.86 +/- 0.34 g phenolic compounds. Optimal overliming resulted in a 51 +/- 9% reduction of total furans, a 41 +/- 6% reduction in phenolic compounds, and a 8.7 +/- 4.5% decline in sugar. Acetic acid levels were unchanged. Considering the similarity of microorganisms, it is possible that the titration method described here may also prove useful for detoxification and fermentation processes using other microbial biocatalysts.

Idiopathic pulmonary fibrosis: an epithelial/fibroblastic cross-talk disorder

Abstract: Idiopathic pulmonary fibrosis is a chronic and usually progressive lung disorder of unknown etiology. A growing body of evidence suggests that, in contrast to other interstitial lung diseases, IPF is a distinct entity in which inflammation is a secondary and non-relevant pathogenic partner. Evidence includes the presence of similar mild/moderate inflammation either in early or late disease, and the lack of response to potent anti-inflammatory therapy. Additionally, it is clear from experimental models and some human diseases that it is possible to have fibrosis without inflammation. An evolving hypothesis proposes that IPF may result from epithelial micro-injuries and abnormal wound healing.

The detection of large HNO3-containing particles in the winter Arctic stratosphere.

Abstract: Large particles containing nitric acid (HNO3) were observed in the 1999/2000 Arctic winter stratosphere. These in situ observations were made over a large altitude range (16 to 21 kilometers) and horizontal extent (1800 kilometers) on several airborne sampling flights during a period of several weeks. With diameters of 10 to 20 micrometers, these sedimenting particles have significant potential to denitrify the lower stratosphere. A microphysical model of nitric acid trihydrate particles is able to simulate the growth and sedimentation of these large sizes in the lower stratosphere, but the nucleation process is not yet known. Accurate modeling of the formation of these large particles is essential for understanding Arctic denitrification and predicting future Arctic ozone abundances.

Asian-American Variants of Human Papillomavirus 16 and Risk for Cervical Cancer: a Case–Control Study

Abstract: BACKGROUND Human papillomavirus 16 (HPV16) has a number of variants, each with a different geographic distribution and some that are associated more often with invasive neoplasias We investigated whether the high incidence of cervical cancer in Mexico (50 cases per 100 000 women) may be associated with a high prevalence of oncogenic HPV16 variants METHODS Cervical samples were collected from 181 case patients with cervical cancer and from 181 age-matched control subjects, all from Mexico City HPV16 was detected with an E6/E7 gene-specific polymerase chain reaction, and variant HPV classes and subclasses were identified by sequencing regions of the E6 and L1/MY genes Clinical data and data on tumor characteristics were also collected All statistical tests were two-sided RESULTS HPV16 was detected in cervical scrapes from 508% (92 of 181) of case patients and from 11% (20 of 181) of control subjects All HPV16-positive samples, except one, contained European (E) or Asian-American (AA) variants AA and E variants were found statistically significantly more often in case patients (AA = 232% [42 of 181]; E = 271% [49 of 181]) than in control subjects (AA = 11% [two of 181]; E = 10% [18 of 181]) (P<001 for case versus control subjects for either E or AA variants, chi2 test) However, the frequency of AA variants was 21 times higher in cancer patients than in control subjects, whereas that ratio for E variants was only 27 (P =006, chi2 test) The odds ratio (OR) for cervical cancer associated with AA variants (OR = 270; 95% confidence interval [CI] = 64 to 1137) was higher than that associated with E variants (OR = 34; 95% CI = 19 to 60) AA-positive case patients (462 +/- 125 years [mean +/- standard deviation]) were 77 years younger than E-positive case patients (539 +/- 122 years) (P =004, Student's t test) AA variants were associated with squamous cell carcinomas and adenocarcinomas, but E variants were associated with only squamous cell carcinomas (P =014, Fisher's exact test) CONCLUSIONS The high frequency of HPV16 AA variants, which appear to be more oncogenic than E variants, might contribute to the high incidence of cervical cancer in Mexico

RegulonDB (version 3.2): transcriptional regulation and operon organization in Escherichia coli K-12

Abstract: RegulonDB is a database on mechanisms of transcription regulation and operon organization in Escherichia coli K-12. The current version has considerably increased numbers of regulatory elements such as promoters, binding sites and terminators. The complete repertoire of known and predicted DNA-binding transcriptional regulators can be considered to be included in this version. The database now distinguishes different allosteric conformations of regulatory proteins indicating the one active in binding and regulating the different promoters. A new set of operon predictions has been incorporated. The relational design has been modified accordingly. Furthermore, a major improvement is a graphic display enabling browsing of the database with a Java-based graphic user interface with three zoom-levels connected to properties of each chromo­somal element. The purpose of these modifications is to make RegulonDB a useful tool and control set for tran­scriptome experiments. RegulonDB can be accessed on the web at the URL: http://www.cifn.unam.mx/Computational_Biology/regulondb/

Substructure and Halo Density Profiles in a Warm Dark Matter Cosmology

Abstract: We performed a series of high-resolution collisionless N-body simulations designed to study the substructure of Milky Way-size galactic halos (host halos) and the density profiles of halos in a warm dark matter (WDM) scenario with a nonvanishing cosmological constant. The virial masses of the host halos range from 3.5 × 1012 to 1.7 × 1012 h-1 M☉, and they have more than 105 particles each. A key feature of the WDM power spectrum is the free-streaming length Rf,WDM, which fixes an additional parameter for the model of structure formation. We analyze the substructure of host halos using three Rf,WDM values: 0.2, 0.1, and 0.05 Mpc, and compare results to the predictions of the cold dark matter (CDM) model. We find that guest halos (satellites) do form in the WDM scenario, but are more easily destroyed by dynamical friction and tidal disruption than their counterparts in a CDM model. The small number of guest halos that we find in the WDM models with respect to the CDM one is the result of a lower guest halo accretion and a higher satellite destruction rate. These two phenomena operate almost with the same intensity in delivering a reduced number of guest halos at z = 0. For the model with Rf,WDM = 0.1 Mpc, the number of accreted small halos is a factor of 2.5 below that of the CDM model, while the fraction of destroyed satellites is almost twice as large as that of the CDM model. The larger the Rf,WDM value, the greater the size of these two effects and the smaller the abundance of satellites. Under the assumption that each guest halo hosts a luminous galaxy, we find that the observed circular velocity function of satellites around the Milky Way and Andromeda is well described by the Rf,WDM = 0.1 Mpc WDM model. In the Rf,WDM = 0.1-0.2 Mpc models, the surviving guest halos at z = 0, whose masses are in the range Mh ≈ 109-1011 h-1 M☉, have an average concentration parameter c1/5 = r(Mh)/r(Mh/5), which is approximately twice as small as that of the corresponding CDM guest halos. This difference very likely produces the higher satellite destruction rate found in the WDM models. The density profile of host halos is well described by the Navarro, Frenk, & White (NFW) fit, whereas guest halos show a wide variety of density profiles. A tendency to form shallow cores is not evident; the profiles, however, are limited by a poor mass resolution in the innermost regions where shallow cores could be expected.

Late Miocene adakites and Nb-enriched basalts from Vizcaino Peninsula, Mexico: Indicators of East Pacific Rise subduction below southern Baja California?

Abstract: A typical slab melt association was emplaced from 11 to 8 Ma in the Santa Clara volcanic field, Vizcaino Peninsula, Baja California Sur. It includes adakitic domes and associated pyroclastic flow deposits, together with lava flows of niobium-enriched basalts. The trace element and isotopic (Sr-Nd-Pb) signatures of adakites are consistent with melting of altered mid-ocean ridge basalts, and the sources of the Nb-enriched basalts contain an enriched mantle wedge component. Such associations commonly form at depths of 70–80 km during low-dip subduction of very young oceanic crust. However, the Santa Clara field is relatively close (100 km) to the paleotrench, which suggests that the genesis of its adakites and Nb- enriched basalts occurred in a very high thermal regime linked to the subduction of the then-active Guadalupe spreading center of the East Pacific Rise. Our data suggest that the asthenospheric window documented below northern Baja California also developed beneath the south of the peninsula during the Neogene. This hypothesis is consistent with the spatial distribution and the ages of adakites and magnesian andesites from this region.

Cloning and functional characterization of the Pseudomonas aeruginosa rhlC gene that encodes rhamnosyltransferase 2, an enzyme responsible for di-rhamnolipid biosynthesis.

Abstract: Pseudomonas aeruginosa is an opportunistic pathogen capable of producing a wide variety of virulence factors, including extracellular rhamnolipids and lipopolysaccharide. Rhamnolipids are tenso-active glycolipids containing one (mono-rhamnolipid) or two (di-rhamnolipid) L-rhamnose molecules. Rhamnosyltransferase 1 (RhlAB) catalyses the synthesis of mono-rhamnolipid from dTDP-L-rhamnose and beta-hydroxydecanoyl-beta-hydroxydecanoate, whereas di-rhamnolipid is produced from mono-rhamnolipid and dTDP-L-rhamnose. We report here the molecular characterization of rhlC, a gene encoding the rhamnosyltransferase involved in di-rhamnolipid (L-rhamnose-L-rhamnose-beta-hydroxydecanoyl-beta-hydroxydecanoate) production in P. aeruginosa. RhlC is a protein consisting of 325 amino acids with a molecular mass of 35.9 kDa. It contains consensus motifs that are found in other glycosyltransferases involved in the transfer of L-rhamnose to nascent polymer chains. To verify the biological function of RhlC, a chromosomal mutant, RTII-2, was generated by insertional mutagenesis and allelic replacement. This mutant was unable to produce di-rhamnolipid, whereas mono-rhamnolipid was unaffected. In contrast, a null rhlA mutant (PAO1-rhlA) was incapable of producing both mono- and di-rhamnolipid. Complementation of mutant RTII-2 with plasmid pRTII-26 containing rhlC restored the level of di-rhamnolipid production in the recombinant to a level similar to that of the wild-type strain PAO1. The rhlC gene was located in an operon with an upstream gene (PA1131) of unknown function. A sigma54-type promoter for the PA1131-rhlC operon was identified, and a single transcriptional start site was mapped. Expression of the PA1131-rhlC operon was dependent on the P. aeruginosa rhl quorum-sensing system, and a well-conserved lux box was identified in the promoter region. The genetic regulation of rhlC by RpoN and RhlR was in agreement with the observed increasing RhlC rhamnosyltransferase activity during the stationary phase of growth. This is the first report of a rhamnosyltransferase gene responsible for the biosynthesis of di-rhamnolipid.

Movements and Population Structure of Humpback Whales in the North Pacific

Abstract: Despite the extensive use of photographic identification methods to investigate humpback whales in the North Pacific, few quantitative analyses have been conducted. We report on a comprehensive analysis of interchange in the North Pacific among three wintering regions (Mexico, Hawaii, and Japan) each with two to three subareas, and feeding areas that extended from southern California to the Aleutian Islands. Of the 6,413 identification photographs of humpback whales obtained by 16 independent research groups between 1990 and 1993 and examined for this study, 3,650 photographs were determined to be of suitable quality. A total of 1,241 matches was found by two independent matching teams, identifying 2,712 unique whales in the sample (seen one to five times). Site fidelity was greatest at feeding areas where there was a high rate of resightings in the same area in different years and a low rate of interchange among different areas. Migrations between winter regions and feeding areas did not follow a simple pattern, although highest match rates were found for whales that moved between Hawaii and southeastern Alaska, and between mainland and Baja Mexico and California. Interchange among subareas of the three primary wintering regions was extensive for Hawaii, variable (depending on subareas) for Mexico, and low for Japan and reflected the relative distances among subareas. Interchange among these primary wintering regions was rare. This study provides the first quantitative assessment of the migratory structure of humpback whales in the entire North Pacific basin.

A conserved RNA structure (thi box) is involved in regulation of thiamin biosynthetic gene expression in bacteria

Abstract: The thiCOGE genes of Rhizobium etli code for enzymes involved in thiamin biosynthesis. These genes are transcribed with a 211-base untranslated leader that contains the thi box, a 38-base sequence highly conserved in the 5′ regions of thiamin biosynthetic and transport genes of Gram-positive and Gram-negative organisms. A deletion analysis of thiC-lacZ fusions revealed an unexpected relationship between the degree of repression shown by the deleted derivatives and the length of the thiC sequences present in the transcript. Three regions were found to be important for regulation: (i) the thi box sequence, which is absolutely necessary for high-level expression of thiC; (ii) the region immediately upstream to the translation start codon of thiC, which can be folded into a stem-loop structure that would mask the Shine-Dalgarno sequence; and (iii) the proximal part of the coding region of thiC, which was shown to contain a putative Rho-independent terminator. A comparative phylogenetic analysis revealed a possible folding of the thi box sequence into a hairpin structure composed of a hairpin loop, two helixes, and an interior loop. Our results show that thiamin regulation of gene expression involves a complex posttranscriptional mechanism and that the thi box RNA structure is indispensable for thiCOGE expression.