1,721,081 research outputs found
Characterization of methanotrophic microbial community in a soil sample from Terre Calde di Medolla (Italy)
No full textMethane-oxidizing bacteria (methanotrophs) have a ubiquitous distribution in the environment and play an important role in global climate warming by lowering methane emission into the atmosphere. “Terre Calde di Medolla” (literally, “Warm Earths of Medolla”) refers to a farming area, located near the town of Modena (Emilia-Romagna region, northern Italy), which has always been known for the relatively high temperatures of the soil. After the 2012 Emilia earthquake that affected this area, soil temperatures of 44°C were revealed (20–25°C above the local background value) together with diffuse soil fluxes of methane (CH4) and minor, though significant, of carbon dioxide (CO2). Ground heating and gas seepage appeared to be spatially correlated, thus suggesting a close relationship between the two phenomena.The aim of this work was to characterize the methanotrophic microbial community present in soil samples collected from this area using a cultivation-independent approach. We performed clone library analysis and terminal restriction fragment length polymorphism (T-RFLP) fingerprinting of the 16S rDNA and pmoA gene (coding for the alpha-subunit of the particulate methane monooxygenase). Results from 16S rDNA analysis showed that methanotrophic bacteria represented around 10% of the entire microbial community. In particular, bacteria belonging to Acidobacteria and Actinobacteria phyla were detected as well as members of Ammonifex, Sphingomonas and Bacillus genera.
Through the analysis of pmoA gene, Methylococcus, Methylocaldum and Methylomonas were found to be the dominant genera (around 90%) of the methanotrophic community under analysis. In addition to these Gammaproteobacteria, Methylocystis spp. were detected which belong to Alphaproteobacteria class. Further studies will define the correlation between the composition and the role of the methanotrophic microbial community and the peculiar characteristics of “Terre Calde di Medolla” soil
Diversity of methane-oxidizing bacteria in soils from “hot lands of medolla” (Italy) featured by anomalous high-temperatures and biogenic CO2 emission
Full text link“Terre Calde di Medolla” (TCM) (literally, “Hot Lands of Medolla”) refers to a farming area in Italy with anomalously high temperatures and diffuse emissions of biogenic CO2, which has been linked to CH4 oxidation processes from a depth of 0.7 m to the surface. We herein assessed the composition of the total bacterial community and diversity of methane-oxidizing bacteria (MOB) in soil samples collected at a depth at which the peak temperature was detected (0.6 m). Cultivation independent methods were used, such as: i) a clone library analysis of the 16S rRNA gene and pmoA (coding for the α-subunit of the particulate methane monooxygenase) gene, and ii) Terminal Restriction Fragment Length Polymorphism (T-RFLP) fingerprinting. The 16S rRNA gene analysis assessed the predominance of Actinobacteria, Acidobacteria, Proteobacteria, and Bacillus in TCM samples collected at a depth of 0.6 m along with the presence of methanotrophs (Methylocaldum and Methylobacter) and methylotrophs (Methylobacillus). The phylogenetic analysis of pmoA sequences showed the presence of MOB affiliated with Methylomonas, Methylocystis, Methylococcus, and Methylocaldum in addition to as yet uncultivated and uncharacterized methanotrophs. Jaccard’s analysis of T-RFLP profiles at different ground depths revealed a similar MOB composition in soil samples at depths of 0.6 m and 0.7 m, while this similarity was weaker between these samples and those taken at a depth of 2.5 m, in which the genus Methylocaldum was absent. These results correlate the anomalously high temperatures of the farming area of “Terre Calde di Medolla” with the presence of microbial methane-oxidizing bacteria
Microbial geomorphologies in modern salt flats and their astrobiological significance
No full textFollowing the discovery of Martian mineral deposits with an assumed evaporite origin (especially sulfates), salt flat areas from hot and cold arid environments (such as sabkhas and playa lakes) are currently investigated for comparative analysis between terrestrial salt-bearing settings and their Martian environmental analogs. Similarly to the Earth, evaporite deposits seem widespread on Mars where their stratigraphic setting and composition suggest relationships with aqueous environments and, therefore, they represent a useful indicator of habitability.
Among the traces of biological activity retained in salt flat settings those produced by surface to near surface microbial activity deserve a special astrobiological interest. These microbial geomorphologies derive from the interaction between physical and biological agents, and can impact on the development and stabilization of surface morphologies with some fossilization potential. Therefore, once established a clear relationship between micro-geomorphologies and micro-biota, their recognition at the surface on Martian terrains may represent unambiguous indicators of biogenicity.
In the sabkha Oum Dba, near the Atlantic coast of the Western Sahara (southern Morocco), thick microbial mats and mineral precipitations (carbonates and sulfates) are in progress and actively interact in an ecosystem where living and fossilized sectors coexist. It, therefore, represents an ideal natural site for detecting type, evolution, and stabilization of microbial geomorphologies in a typical arid salt flat area
Gas Chromatographic-Mass Spectrometric Analysis of Hydrocarbons and other Neutral Organic Compounds in Volcanic Gases using SPME for Sample Preparation
Full text linkKnowledge of the chemical composition of volcanic exhalation is important in providing information on volcanic feeding systems and on the characteristics of the gaseous compounds emitted into the atmosphere. This paper reports a novel analytical method that makes use of capillary gas chromatography coupled to mass spectrometry, preceded by solid-phase micro extraction for sample enrichment. Such an approach enables considerable expansion of the number of neutral organic compounds that can be positively identified in volcanic exhalation. Data obtained from analysis of real samples are also reported
Geochemistry and geophysics of active volcanic lakes: An introduction
No full textSCOPUS: ar.kinfo:eu-repo/semantics/publishe
Geothermal exploration in Central and Southern Sector of the Sula Graben (Honduras, Central America)
No full textGeochemistry of thermal fluids in NW Honduras: New perspectives for exploitation of geothermal areas in the southern Sula graben
No full textThe results of a geochemical survey on thermal waters and, for the first time for this site, gas discharges in five
geothermal sites (Azacualpa “La Cueva”, Río Ulua, Río Gualcarque, El Olivar and Laguna de Agua Caliente) in
NW Honduras are here presented and discussed. El Olivar and Laguna de Agua Caliente, in the southern part of
the Sula graben are very close to a Quaternary basaltic field, whereas Azacualpa “La Cueva”, Río Ulua and Río
Gualcarque, located to the southwest of the Yojoa Lake, direcly emerge from the Cretaceous limestone deposits.
The measured temperatures range between 37.5 and 104.8 °C. “Mature”, alkaline, Na-SO4 thermal waters
discharge from Azacualpa “La Cueva”, while those from El Olivar and Laguna de Agua Caliente are “immature”
and show a Na-HCO3 composition. Chemical equilibria of waters and gases from the Azacualpa “La Cueva”
thermal springs indicate temperatures ranging from 150 to 200 °C. Conversely, gas discharges from El Olivar
and Laguna de Agua Caliente have attained a partial chemical equilibrium in the liquid phase at slightly higher
temperatures (200–250 °C), although gas–gas faster reactions involving COseemto be adjusted in an isothermally
separated vapor phase. Unlike Azacualpa, SiO2 geothermometer at El Olivar and Laguna de Agua Caliente indicates
equilibrium temperatures for the liquid phase much lower than those calculated for the gas phase (≤120 °C).
We conclude that thermal waters from the Azacualpa area likely represent the direct emergence of a water
dominated reservoir having temperatures ≤150–200 °C. By contrast, at El Olivar and Laguna de Agua Caliente
hot springs are supplied by a boiling shallow aquifer fed by a vapor phase rising from a steam-dominated
zone. The above geochemical model is consistent with a geothermal reservoir hosted within the Cretaceous
carbonate sequences of the Yojoa Group in the whole investigated sites. The reservoir extensively crops out
in the Azacualpa area whereas the geothermal sites of the southern Sula graben (Laguna de Agua Caliente and
El Olivar) are covered by the Oligocene–Miocene volcano–sedimentary sequences of the Matagalpa formation,
possibly acting as efficient impermeable cap rocks.
These results significantly differ from those reported by previous studies and emphasize that the southern Sula
graben, in particular the El Olivar area, can represent among the investigated thermal springs, themost promising
site for the exploitation of a high-enthalpy geothermal field
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
