Pedro Domínguez Morales

The limitations on organic detection in mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the viking results

The failure of Viking Lander thermal volatilization (TV) (without or with thermal degradation)–gas chromatography (GC)–MS experiments to detect organics suggests chemical rather than biological interpretations for the reactivity of the martian soil. Here, we report that TV–GC–MS may be blind to low levels of organics on Mars. A comparison between TV–GC–MS and total organics has been conducted for a variety of Mars analog soils. In the Antarctic Dry Valleys and the Atacama and Libyan Deserts we find 10–90 μg of refractory or graphitic carbon per gram of soil, which would have been undetectable by the Viking TV–GC–MS. In iron-containing soils (jarosites from Rio Tinto and Panoche Valley) and the Mars simulant (palogonite), oxidation of the organic material to carbon dioxide (CO2) by iron oxides and/or their salts drastically attenuates the detection of organics. The release of 50–700 ppm of CO2 by TV–GC–MS in the Viking analysis may indicate that an oxidation of organic material took place. Therefore, the martian surface could have several orders of magnitude more organics than the stated Viking detection limit. Because of the simplicity of sample handling, TV–GC–MS is still considered the standard method for organic detection on future Mars missions. We suggest that the design of future organic instruments for Mars should include other methods to be able to detect extinct and/or extant life.

Forest-to-pasture conversion influences on soil organic carbon dynamics in a tropical deciduous forest

On a global basis, nearly 42% of tropical land area is classified as tropical deciduous forest (TDF) (Murphy and Lugo 1986). Currently, this ecosystem has very high deforestation rates; and its conversion to cattle pasture may result in losses of soil organic matter, decreases in soil fertility, and increases in CO2 flux to the atmosphere. The soil organic matter turnover rate in a TDF after pasture conversion was estimated in Mexico by determining natural abundances of13C. Changes in these values would be induced by vegetation changes from the C3 (forest) to the C4 (pasture) photosynthetic pathway. The rate of loss of remnant forest-soil organic matter (fSOM) was 2.9 t ha−1 year−1 in 7-year-old pasture and decreased to 0.66 t ha−1 year−1 by year 11. For up to 3 years, net fSOM level increased in pastures; this increment can be attributed to decomposition of remnant forest roots. The sand-associated SOM fraction was the most and the silt-associated fraction the least depleted. TDF conversion to pasture results in extremely high rates of loss of remnant fSOM that are higher than any reported for any tropical forest.

Geochemistry of hydrothermal fluids from an intraplate ocean island: Everman volcano, Socorro Island, Mexico

Abstract Socorro Island, Mexico, still volcanically active, is an alkaline and peralkaline volcanic island in the eastern Pacific Ocean located on a mid-ocean ridge spreading center that was abandoned at ∼3.5 Ma. Gas and water samples collected on the island in 1999 from the dome fumaroles and hot springs of Everman volcano have been analyzed for major components, H-O-C-S, He and Ar isotopic composition, and noble gas abundances. The boiling-point-temperature steam vents and low-salinity thermal springs discharge Cl-free meteoric water, and are typical surface manifestations of a high-temperature hydrothermal system. High H 2 and CH 4 contents (up to 14 and 3.5 vol.% in dry gas, respectively) and an enrichment of CH 4 in 13 C (δ 13 C CH 4 =−18‰) may suggest that these reduced gases were at least partially produced by the interaction of ultramafic rocks with water inside volcanic edifice due to serpentinization of olivine. The 3 He/ 4 He ratios (6.0–6.6 R a ) which are lower than the MORB-values, and the high He/Ne ratios (>4000) and He/Ar ratios (up to 4) indicate a contribution of radiogenic He from the oceanic crust or shallow magma chamber like at a low- 3 He hot spot. The maximum of the 40 Ar/ 36 Ar values (311) is close to the maximum value found in the Socorro volcanic rocks. Noble gas abundances are close to values for the partially degassed air-saturated water, however, with some excess Ne concentrations. An enrichment in 132 Xe (or depletion in 84 Kr) of the least air-contaminated gas sample (He/Ne>4000) relative to air-saturated water can be related to the contribution of noble gases from a non-atmospheric source, probably oceanic crustal component assimilated in a shallow magma reservoir.

Influence of volcanic activity on spring water chemistry at Popocatepetl Volcano, Mexico

Abstract The results of the 7 years (1994–2000) of monthly monitoring of spring water before and during eruptions show response to volcanic activity. Low salinity and temperature characterize most of the springs, which are located on the flanks of Popocatepetl Volcano. The pH ranges from 5.8 to 7.8 and temperature from 3 to 36 °C. Oxygen and hydrogen isotopic data show that the water is of meteoric origin, but SO 4 2− , Cl − , F − , HCO 3 − , B, and SO 4 2− /Cl − variations precede main eruptive activity, which is considered linked to influx of magmatic gases and acid fluids that react with sublimates and host rock and mix with the large water system. Na + , Ca 2+ , SiO 2 and Mg 2+ concentrations in the water also increased before eruptive activity. The computed partial pressure of CO 2 in equilibrium with spring waters shows values higher than air-saturated water (ASW), with the highest values up to 0.73 bar of pCO 2 . Boron is detected in the water only preceding the larger eruptions. When present, boron concentration is normally under health standard limits, but in two cases the concentration was slightly above. Other components are within health standard limits, except for F − in one spring.

Carbon isotopic composition of Mexican honey

SUMMARYWe characterized Mexican honey from the main production regions, using the internal stable carbon isotope ratio (ISIRA) of the honey and its protein. We found the average δ13C given by White for American honey is very close to the corresponding value for Mexican honey even though clear evidence that C4 and CAM plants are visited by bees. We found adulteration of Mexican commercial samples using the criterium of −1.00 ‰ difference also given by White. Two pyrolysis methods were tested to optimize the accuracy of the carbon isotope ratio analysis of honey. We found that the quartz method showed smaller variation in the data due to a complete combustion of the honey. The honey protein was isolated and purified using the protein dialysis procedure recommended by the Association of Official Analytical Chemists. We found that the direct precipitation method without dialysis is not useful for samples which are adulterated by more than 50%.

Carbon stable isotopes ratios of pelagic and littoral communities in Alchichica crater-lake, Mexico

Carbon stable isotope ratios were determined in dominant biotic components of pelagic and littoral systems in Alchichica crater-lake. Results showed that carbon signatures were significantly different between both systems. The pelagic environment was more depleted (−26.15 to −15.14 per mille) than the littoral zone (−21.03 to −17.91 per mille). The potential source end-point in the simplified pelagic community was established to be diatomaceous phytoplankton; its predicted value was −21.7 per mille. There is a clear evidence that Nodularia does not sustain the pelagic food chain. In contrast, the highly diverse littoral community was sustained by epiphytes. No allochthonous sources seemed to influence this food web. 13C enrichment was observed along the components of both systems with fractionations of 0.8 to 1.4 per mille. The contribution of the seagrass Ruppia maritima is probably associated with the detritus pathway. Carbon source partitioning between both systems was not recorded. The δ13C in Alchichica crater-lake was more enriched than in other saline lakes and could be attributed to different salinity and CO2 concentrations among lakes.

Diet and health at Chinikihá, Chiapas, Mexico: some preliminary results

Abstract This study reports stable nitrogen, and carbon isotopic analyses (δ13 C and δ15 N) from bone collagen and enamel apatite for eight human samples at the site of Chinikihá, Mexico, during the Late Classic (AD 650–850). It has been proposed that, during this time period, an increase in maize consumption combined with a decrease in meat consumption could have been the result of an environmental collapse, reflected in a generalised poor diet and health. However, recent studies demonstrate that there is great intrasite variability, and that access to maize and animal protein may relate more to changes in the distribution of foods among social groups. Data from chemical analyses are combined with other variables, such as health status and mortuary patterns to determine differences among the inhabitants of an upper-class household. Our results indicate that, while the basic staple of all the inhabitants of Chinikihá was maize, access to other wild plants and animal protein may have depended on sex, age and other social factors, and not necessarily be the consequence of an environmental depletion of resources. This article provides more data to the growing body of literature that support local variation and internal differences, and expands our knowledge on differential access to resources within the members of a higher-class unit.

Rhodococcus erythropolis as a host for expression, secretion and glycosylation of Mycobacterium tuberculosis proteins

BackgroundGlycosylation is one of the most abundant posttranslational polypeptide chain modification in nature. Although carbohydrate modification of protein antigens from many microbial pathogens constitutes important components of B cell epitopes, the role in T cell immunity is not completely understood. There is growing evidence about the importance of these modifications in host bacteria interactions in tuberculosis. It is known, that the sugars present in some Mycobacterium tuberculosis glycoproteins play an important role in both humoral and cellular immune response against the pathogen. Since this modification is lost in the recombinant proteins expressed in Escherichia coli, it is fundamental to search for host bacteria with the capacity to modify the foreign proteins. Amongst the bacteria that are likely to have this possibility are some members of Rhodococcus genus which are Gram-positive bacteria, with high GC-content and genetically very close related to M. tuberculosis.ResultsIn this work, apa, pstS1 and lprG genes that coding for M. tuberculosis glycoproteins were cloned and expressed in Rhodococcus erythropolis. All recombinant proteins were mannosylated as demonstrated by their interaction with mannose binding lectin Concanavalin A. In addition, as native proteins recombinants Apa and PstS1 were secreted to the culture medium in contrast with LprG that was retained in the cell wall.ConclusionsTogether these results, point out R. erythropolis, as a new host for expression of M. tuberculosis glycoproteins.

Climate change and peopling of the Neotropics during the Pleistocene-Holocene transition

espanolLa cueva de Santa Marta, Chiapas, es uno de los pocos sitios de los Neotropicos con alta resolucion cronologica que presenta ocupacion humana continua desde 12500 cal BP. En este trabajo se correlacionan los datos de actividad humana con las condiciones climaticas inferidas mediante analisis sedimentarios, palinologicos, arqueozoologicos y de isotopos estables en caracoles de rio con el fin de evaluar las condiciones ambientales del Pleistoceno final y el Holoceno temprano a las que se enfrentaron los primeros pobladores de las regiones tropicales de America. Los resultados sugieren que los dos principales periodos de cambio climatico abrupto (CCA) del Pleistoceno final y el Holoceno temprano (Younger Dryas y evento 8.2 ka) estan registrados en el abrigo y coinciden con los dos principales periodos de ocupacion humana. Los resultados sugieren que estos periodos CCA fueron frios y humedos; mientras que la actividad humana muestra un impacto limitado al nivel local o regional, sobre un entorno cambiante durante la transicion Pleistoceno-Holoceno y la probable introduccion de especies aloctonas. EnglishSanta Marta cave, Chiapas, is a unique archaeological site with high-resolution chronological control and continuous human occupation since 12500 cal BP. In this work we report a correlation between human activity and climate conditions inferred from sedimentological, palynological, archaeozoological and stable isotopic analyses with the aim of assessing the late Pleistocene and early Holocene environmental conditions faced by the first settlers in tropical America. Results suggest that the late Pleistocene and early Holocene periods of abrupt climatic change (ACC), the Younger Dryas and the 8.2 ka event, are recorded in the rock shelter, and coincide with the two main periods of human occupation. The data suggest that these ACC periods were both cold and moist. Human activity had a limited impact at the local or regional level, over a changing environment during the Pleistocene-Holocene transition, though there is some evidence for the introduction of exotic species.