The abundance of comammox bacteria was higher than that of ammonia-oxidizing archaea and bacteria in rhizosphere of emergent macrophytes in a typical shallow lake riparian / La abundancia de bacterias comammox fue mayor que la de arqueas y bacterias oxidantes de amoníaco en la rizosfera de macrófitos emergentes en un típico lago ribereño poco profundo

Complete ammonia oxidation (comammox) bacteria can complete the whole nitrification process independently, which not only challenges the classical two-step nitrification theory but also updates long-held perspective of microbial ecological relationship in nitrification process. Although comammox bacteria have been found in many ecosystems in recent years, there is still a lack of research on the comammox process in rhizosphere of emergent macrophytes in lakeshore zone. Sediment samples were collected in this study from rhizosphere, far-rhizosphere, and non-rhizosphere of emergent macrophytes along the shore of Lake Liangzi, a shallow lake. The diversity of comammox bacteria and amoA gene abundance of comammox bacteria, ammonia-oxidizing archaea (AOA), and ammonia-oxidizing bacteria (AOB) in these samples were measured. The results showed that comammox bacteria widely existed in the rhizosphere of emergent macrophytes and fell into clade A.1, clade A.2, and clade B, and clade A was the predominant community in all sampling sites. The abundance of comammox amoA gene (6.52 × 106–2.45 × 108 copies g−1 dry sediment) was higher than that of AOB amoA gene (6.58 × 104–3.58 × 106 copies g−1 dry sediment), and four orders of magnitude higher than that of AOA amoA gene (7.24 × 102–6.89 × 103 copies g−1 dry sediment), suggesting that the rhizosphere of emergent macrophytes is more favorable for the growth of comammox bacteria than that of AOB and AOA. Our study indicated that the comammox bacteria may play important roles in ammonia-oxidizing processes in all different rhizosphere regions.(AU)

Characterization of archaeal and bacterial communities thriving in methane-seeping on-land mud volcanoes, Niigata, Japan / Caracterización de comunidades de arqueas y bacterias que prosperan en volcanes de lodo terrestres que filtran metano, Niigata, Japón

Submarine mud volcanoes (MVs) have attracted significant interest in the scientific community for obtaining clues on the subsurface biosphere. On-land MVs, which are much less focused in this context, are equally important, and they may even provide insights also for astrobiology of extraterrestrial mud volcanism. Hereby, we characterized microbial communities of two active methane-seeping on-land MVs, Murono and Kamou, in central Japan. 16S rRNA gene profiling of those sites recovered the dominant archaeal sequences affiliated with methanogens. Anaerobic methanotrophs (ANME), with the subgroups ANME-1b and ANME-3, were recovered only from the Murono site albeit a greatly reduced relative abundance in the community compared to those of typical submarine MVs. The bacterial sequences affiliated to Caldatribacteriota JS1 were recovered from both sites; on the other hand, sulfate-reducing bacteria (SRB) of Desulfobulbaceae was recovered only from the Murono site. The major difference of on-land MVs from submarine MVs is that the high concentrations of sulfate are not always introduced to the subsurface from above. In addition, the XRD analysis of Murono shows the absence of sulfate-, sulfur-related mineral. Therefore, we hypothesize one scenario of ANME-1b and ANME-3 thriving at the depth of the Murono site independently from SRB, which is similar to the situations reported in some other methane-seeping sites with a sulfate-depleted condition. We note that previous investigations speculate that the erupted materials from Murono and Kamou originate from the Miocene marine strata. The fact that SRB (Desulfobulbaceae) capable of associating with ANME-3 was recovered from the Murono site presents an alternative scenario: the old sea-related juvenile water somehow worked as the source of additional sulfur-related components for the SRB-ANME syntrophic consortium forming at a deeper zone of the site.(AU)

Community structure, distribution pattern, and influencing factors of soil Archaea in the construction area of a large-scale photovoltaic power station / Estructura de la comunidad, patrón de distribución y factores influyentes del suelo Archaea en el área de construcción de una central fotovoltaica a gran escala

The photovoltaic power station in Qinghai has been built for 8 years; however, its impact on the regional soil ecological environment has not been studied in depth. To reveal the structure and distribution pattern of archaeal communities in desert soil under the influence of a large photovoltaic power station, a comparative study was carried out between the soil affected by photovoltaic panels and the bare land samples outside the photovoltaic station in Gonghe, Qinghai Province. The abundance, community structure, diversity, and distribution characteristics of archaea were analyzed by quantitative PCR and Illumina-MiSeq high-throughput sequencing, and the main environmental factors affecting the variation in soil archaeal community were identified by RDA. The contribution rate of environmental factors and human factors to microbial community diversity was quantitatively evaluated by VPA. The results showed that there was no significant difference in soil nutrients and other physicochemical factors between the photovoltaic power station and bare land. Thaumarchaeota was the dominant archaeal phylum in the area, accounting for more than 99% of archaeal phylum, while at the level of genus, Nitrososphaera was the dominant archaeal genera. There was no significant difference in archaeal community structure between and under different types of PV panels. The analysis has shown that the construction of a photovoltaic station has little effect on the community structure of soil archaea in a desert area, and it was speculated that the selection of niche played a leading role in the distribution pattern of soil archaeal community. This study provides the basis for a scientific understanding of the characteristics and distribution patterns of soil archaeal communities affected by the construction of a photovoltaic power station.(AU)

Induction of the antioxidant defense system using long-chain carotenoids extracted from extreme halophilic archaeon, Halovenus aranensis / Inducción del sistema de defensa antioxidante utilizando carotenoides de cadena larga extraídos de arqueas halofílicas extremas, Halovenus aranensis

The field of microbial pigments is an emerging area in natural products science. Carotenoids form a major class of such pigments and are found to be diversely synthesized by microorganisms that reside in hypersaline ecosystems to provide resistance against oxidative stress. Human cells can benefit from compounds such as carotenoids as antioxidant agents through either their capability to quench free radicals or their effect on promoting the antioxidant defense pathway. In this study, the antioxidant effectiveness of carotenoid extract from an extremely halophilic archaeon Halovenus aranensis strain EB27T has been evaluated using different approaches. Finally, the ability of the extracted pigment to induce the antioxidant defense pathway of human primary skin fibroblast cells was studied. Hvn. aranensis carotenoid extract exhibited strong effectiveness such that at 2 µg/ml, the carotenoid extract fully neutralized the oxidative stress of hydrogen peroxide at its EC50 based on MTT assay. Results from real-time PCR of relevant genes, luciferase bioreporter of oxidative stress, and the western blot analysis further confirmed the antioxidant capability of the carotenoids. It was also shown the carotenoid extract had more antioxidant activity compared to β-carotene the same concentration. Results suggest the carotenoid extract from this archaeon to have high potential for clinical and industrial applications.(AU)

Microbiota dispersion in the Uyuni salt flat (Bolivia) as determined by community structure analyses

Soil microbial communities are an important component of biological diversity and terrestrial ecosystems which is responsible for processes such as decomposition, mineralization of nutrients, and accumulation of organic matter. One of the factors that provide information on the mechanisms regulating biodiversity is spatial scaling. We characterized the microbial communities using 16S rRNA gene sequences from DNA isolated from halite at various locations and correlated these to geographic distance in the Uyuni salt flat (Bolivia). Sequences from each site were analyzed to determine any spatial patterns of diversity, as well as to describe the microbial communities. Results suggest that different taxa are able to disperse over Uyuni's surface crust regardless of distance. As expected, ubiquitous taxa included members of Halobacteriaceae such as Haloarcula, Halorubrum, Halorhabdus, Halolamina, and halophilic bacteria Salinibacter, Halorhodospira, and unclassified members of the Gammaproteobacteria. Archaeal communities were homogeneous across the salt flat. In contrast, bacterial communities present strong local variations which could be attributed to external factors. Likely sources for these variations are the Rio Grande river influent in the south shore and the Tunupa volcano influencing the northern area

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Flagellated protozoa detected in Dermatophagoides by light microscopy

House dust mites (HDM) are arthropods of medical importance due to their relationship with allergic diseases. House dust provides a detrital habitat for these organisms, in which human skin scales are a primary food source. For digestion, wall gut cells elaborate potent proteases. Nevertheless, the observation of flagellated protozoa in intestinal extracts of HDM by light microscopy might contribute to digestive processes in mites, opening a new avenue of research regarding the ecological interactions between mites and these microorganisms in the utilisation of such substrates, as well as with regard to allergic diseases

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Spatial homogeneity of bacterial and archaeal communities in the deep eastern Mediterranean Sea surface sediments

The diversity of microorganisms inhabiting the deep sea surface sediments was investigated in 9 stations (700-1900 m depth) in the Levantine basin by 454 massive tag sequencing of the 16S rDNA V4 region using universal primers. In total, 108,811 reads (an average of 10,088 per sample) were assigned to 5014 bacterial and 966 archaeal operational taxonomic units (OTUs; at 97% cut off). The 55% of the reads were of archaea, indicating dominance of archaea over bacteria at eight of the stations. The diversity and estimated richness values were high (e.g., H´ ranged from 5.66 to 7.41 for bacteria). The compositions of the microorganisms at all stations were remarkably similar, with Bray-Curtis similarities of 0.53-0.91 and 0.74-0.99 for bacterial and archaeal orders respectively. At two stations, very high abundances of only a few genera (Marinobacterium, Bacillus, Vibrio, Photobacterium) were accountable for the dissimilarities documented compared to the other deep sea stations. Half of the bacterial reads (51%) belonged to the phylum Proteobacteria, comprising mainly Gammaproteobacteria (41-72% of the proteobacterial reads per sample), Deltaproteobacteria (12-29%), Alphaproteobacteria (7-18%) and Betaproteobacteria (3-14%). The most abundant bacterial family was Sinobacteraceae (order Xanthomonadales) with 5-10% of total bacterial reads per sample. Most abundant reads (15.4% of all microbial reads) were affiliated with Marine Group 1 archaea, putatively capable of ammonia oxidation (213 OTUs), and bacteria involved in nitrification were found in all samples. The data point to the significant role that chemolithotrophic carbon assimilation and nitrification fill in the oligotrophic deep sea Levant sediments (AU)

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Archaeal and bacterial diversity in two hot springs from geothermal regions in Bulgaria as demostrated by 16S rRNA and GH-57 genes

Archaeal and bacterial diversity in two Bulgarian hot springs, geographically separated with different tectonic origin and different temperature of water was investigated exploring two genes, 16S rRNA and GH-57. Archaeal diversity was significantly higher in the hotter spring Levunovo (LV) (82°C); on the contrary, bacterial diversity was higher in the spring Vetren Dol (VD) (68°C). The analyzed clones from LV library were referred to twenty eight different sequence types belonging to five archaeal groups from Crenarchaeota and Euryarchaeota. A domination of two groups was observed, Candidate Thaumarchaeota and Methanosarcinales. The majority of the clones from VD were referred to HWCG (Hot Water Crenarchaeotic Group). The formation of a group of thermophiles in the order Methanosarcinales was suggested. Phylogenetic analysis revealed high numbers of novel sequences, more than one third of archaeal and half of the bacterial phylotypes displayed similarity lower than 97% with known ones. The retrieved GH-57 gene sequences showed a complex phylogenic distribution. The main part of the retrieved homologous GH-57 sequences affiliated with bacterial phyla Bacteroidetes, Deltaproteobacteria, Candidate Saccharibacteria and affiliation of almost half of the analyzed sequences is not fully resolved. GH-57 gene analysis allows an increased resolution of the biodiversity assessment and in depth analysis of specific taxonomic groups (AU)

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Phylogenetic characterization and quantification of ammonia-oxidizing archaea and bacteria from Lake Kivu in a long-term microcosm incubation

A microcosm cultivation-based method was set up to investigate the growth of ammonia-oxidizing archaea (AOA), isolated from a water sample acquired at a depth of 50 m from the northern basin of Lake Kivu. For this purpose, both CARD-FISH and qPCR targeting of archaeal 16S rRNA and amoA genes were used. Archaeal cell growth at the end of the 246-day microcosm experiment accounted for 35% of the SybrGold-stained cells, which corresponded to 6.61 x 10(6) cells/ml and 1.76 +/- 0.09 x 10(6) archaeal 16S rRNA gene copies/ml. Clone libraries and DGGE fingerprinting confirmed the dominance of AOA phylotypes in the archaeal community microcosm. The majority of the identified archaeal 16S rRNA gene sequences in the clone libraries were affiliated with Thaumarchaeota Marine Group 1 .1a. Subsequent cultivation of the AOA community on deep-well microtiter plates in medium containing different carbon sources to stimulate archaeal growth failed to show significant differences in archaeal abundance (ANOVA t14 = -1.058, P = 0.308 and ANOVA t14= 1.584, P = 0.135 for yeast extract and simple organic acids, respectively). The lack of growth stimulation by organic compounds is in concordance with the oligotrophic status of Lake Kivu. Finally, the addition of antibiotics to the growth medium resulted in archaeal cell counts that were significantly lower than those obtained from cultures in antibiotic-free medium (ANOVA t14 = 12.12, P < 0.001) (AU)

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Comparative analysis of the microbial communities inhabiting halite evaporites of the Atacama Desert

Molecular biology and microscopy techniques were used to characterize the microbial communities inside halite evaporites from different parts of the Atacama Desert. Denaturing gradient gel electrophoresis (DGGE) analysis revealed that the evaporite rocks harbor communities predominantly made up of cyanobacteria, along with heterotrophic bacteria and archaea. Different DGGE profiles were obtained for the different sites, with the exception of the cyanobacterial profile, in which only one phylotype was detected across the three sites examined. Chroococcidiopsis-like cells were the only cyanobacterial components of the rock samples, although the phylogenetic study revealed their closer genetic affinity to Halothece genera. Gene sequences of the heterotrophic bacteria and archaea indicated their proximity to microorganisms found in other hypersaline environments. Microorganisms colonizing these halites formed microbial aggregates in the pore spaces between halite crystals, where microbial interactions occur. In this exceptional, salty, porous halite rock habitat, microbial consortia with a community structure probably conditioned by the environmental conditions occupy special microhabitats with physical and chemical properties that promote their survival (AU)

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Presence of structural homologs of ubiquitin in haloalkaliphilic Archaea

Ubiquitin, a protein widely conserved in eukaryotes, is involved in many cellular processes, including proteolysis. While sequences encoding ubiquitin-like proteins have not been identified in prokaryotic genomes sequenced so far, they have revealed the presence of structural and functional homologs of ubiquitin in Bacteria and Archaea. This work describes the amplification and proteomic analysis of a 400-bp DNA fragment from the haloalkaliphilic archaeon Natrialba magadii. The encoded polypeptide, P400, displayed structural homology to ubiquitin-like proteins such as those of the ThiS family and Urm1. Expression of the P400 DNA sequence in Escherichia coli cells yielded a recombinant polypeptide that reacted with anti-ubiquitin antibodies. In addition, a putative open reading frame encoding P400 was identified in the recently sequenced genome of N. magadii. Together, these results evidence the presence in Archaea of structural homologs of ubiquitin- related proteins (AU)

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Two faces of the prokaryote concept / La doble cara del concepto de procariota

Bacteria had remained undefined when, in 1962, Roger Y. Stanier and C.B. van Niel published their famed paper «The concept of a bacterium». The articulation of the prokaryote–eukaryote dichotomy was a vital moment in the history of biology. This article provides a brief overview of the context in which the prokaryote concept was successfully launched in the 1960s, and what it was meant to connote. Two concepts were initially distinguished within the prokaryote-eukaryote dichotomy at that time. One was organizational and referred to comparative cell structure; the other was phylogenetic and referred to a «natural» classification. Here, I examine how the two concepts became inseparable; how the prokaryotes came to signify a monophyletic group that preceded the eukaryotes, and how this view remained unquestioned for 15 years, until the birth of molecular evolutionary biology and coherent methods for bacteria phylogenetics based on 16S rRNA. Today, while microbial phylogeneticists generally agree that the prokaryote is a polyphyletic group, there is no agreement on whether the term should be maintained in an organizational sense (AU)

Hasta que en 1962 Roger Y. Stanier y C.B. van Niel publicaron su famoso artículo «The concept of a bacterium», las bacterias habían carecido de definición. La articulación de la dicotomía procariota-eucariota representó un momento crucial en la historia de la biología. La finalidad de esta revisión es ofrecer una breve perspectiva del contexto en el cual hizo aparición satisfactoriamente el concepto de procariota en la década de 1960 y de lo que iba a significar. En aquel tiempo, se incluían dos conceptos en la dicotomía procariota-eucariota. Uno, de tipo organizativo, se refería a la estructura celular comparativa; el otro, filogenético, se refería a una clasificación natural. Este trabajo describe cómo ambos conceptos se hicieron inseparables; cómo el concepto procariota llegó a significar un grupo monofilético que precedió a los eucariotas, y cómo se mantuvo indiscutible este enfoque durante 15 años, hasta el nacimiento de la biología molecular evolutiva y el desarrollo de métodos coherentes en filogenética bacteriana basados en el rRNA 16S. Hoy en día, si bien los expertos en filogenia microbiana están generalmente de acuerdo en que los procariotas forman un grupo polifilético, no hay acuerdo sobre si el término debería mantenerse en un sentido organizativo (AU)

Diversity and biosynthesis of compatible solutes in hyper/thermophiles / Diversidad y biosíntesis de solutos compatibles en hiper/termófilos

The accumulation of compatible solutes, either by uptake from the medium or by de novo synthesis, is a general response of microorganisms to osmotic stress. The diversity of compatible solutes is large but falls into a few major chemical categories, such as carbohydrates or their derivatives and amino acids or their derivatives. This review deals with compatible solutes found in thermophilic or hyperthermophilic bacteria and archaea that have not been commonly identified in microorganisms growing at low and moderate temperatures. The response to NaCl stress of Thermus thermophilus is an example of how a thermophilic bacterium responds to osmotic stress by compatible solute accumulation. Emphasis is made on the pathways leading to the synthesis of mannosylglycerate and glucosylglycerate that have been recently elucidated in several hyper/thermophilic microorganisms. The role of compatible solutes in the thermoprotection of these fascinating microorganisms is also discussed (AU)

La acumulación de solutos compatibles por incorporación del medio o mediante síntesis de novo es una respuesta general de los microorganismos al estrés osmótico. La diversidad de solutos compatibles es grande pero cae en unas pocas categorías químicas importantes tales como carbohidratos o sus derivados y aminoácidos o sus derivados. Esta revisión trata de los solutos compatibles encontrados en bacterias y en arqueas termófilas o hipertermófilas y que no se han identificado en microorganismos que viven a temperaturas bajas y moderadas. La respuesta de Thermus thermophilus al estrés causado por el NaCl es un ejemplo de cómo responde una bacteria termófila al estrés osmótico mediante la acumulación de solutos compatibles. Se destacan las vías que conducen a la síntesis del manosilglicerato y del glucosilglicerato que se han descubierto recientemente en varios microorganismos hiper/thermófilos. Se describe también la función de los solutos compatibles en la termoprotección de estos apasionantes microorganismos (AU)

The maturing of microbial ecology / La madurez de la ecología microbiana

A.J. Kluyver and C.B. van Niel introduced many scientists to the exceptional metabolic capacity of microbes and their remarkable ability to adapt to changing environments in The Microbe’s Contribution to Biology. Beyond providing an overview of the physiology and adaptability of microbes, the book outlined many of the basic principles for the emerging discipline of microbial ecology. While the study of pure cultures was highlighted, provided a unifying framework for understanding the vast metabolic potential of microbes and their roles in the global cycling of elements, extrapolation from pure cultures to natural environments has often been overshadowed by microbiologists’ inability to culture many of the microbes seen in natural environments. A combination of genomic approaches is now providing a culture-independent view of the microbial world, revealing a more diverse and dynamic community of microbes than originally anticipated. As methods for determining the diversity of microbial communities become increasingly accessible, a major challenge to microbial ecologists is to link the structure of natural microbial communities with their functions. This article presents several examples from studies of aquatic and terrestrial microbial communities in which culture and culture-independent methods are providing an enhanced appreciation for the microbe’s contribution to the evolution and maintenance of life on Earth, and offers some thoughts about the graduate-level educational programs needed to enhance the maturing field of microbial ecology (AU)

Con su libro The Microbe’s Contribution to Biology, A.J. Kluyver y C.B. van Niel mostraron a muchos científicos la capacidad metabólica excepcional de los microbios y su notable habilidad para adaptarse a los cambios ambientales. Además de una descripción de la fisiología y de la adaptabilidad de los microbios, el libro destacaba muchos de los principios básicos de la ecología microbiana, que era entonces una disciplina emergente. Mientras el estudio de los cultivos puros ocupaba un lugar destacado, proporcionando un marco unitario para la comprensión del amplio potencial metabólico de los microbios, y de su función en el ciclo global de los elementos, la extrapolación de cultivos puros a ambientes naturales fue eclipsada a menudo por la incapacidad de los microbiólogos de cultivar muchos de los microbios observados en ambientes naturales. La combinación de enfoques genómicos está proporcionando una visión del mundo microbiano independiente del cultivo, lo que revela una comunidad de microbios más diversa y más dinámica de lo que se había considerado originalmente. A medida que los métodos para determinar la diversidad de las comunidades microbianas se hacen más accesibles, un reto importante para los ecólogos microbianos es relacionar la estructura de las comunidades microbianas naturales con sus funciones. Este artículo presenta varios ejemplos que provienen de estudios de comunidades microbianas acuáticas y terrestres, en los cuales tanto los métodos dependientes de cultivo como los que no lo son, amplían la apreciación de la contribución de los microbios a la evolución y al mantenimiento de la vida en la Tierra. También ofrece algunas reflexiones sobre la necesidad de que las licenciaturas realcen el campo ya maduro de la ecología microbiana (AU)

Happy microbes in hostile niches. A symposium on extremophiles

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IS200: an old and still bacterial transposon / IS200: un antiguo y tranquilo transposón bacteriano

IS200 is a mobile element found in a variety of eubacterial genera, such as Salmonella, Escherichia, Shigella, Vibrio, Enterococcus, Clostridium, Helicobacter, and Actinobacillus. In addition, IS200-like elements are found in archaea. IS200 elements are very small (707-711 bp) and contain a single gene. Cladograms constructed with IS200 DNA sequences suggest that IS200 has not spread among eubacteria by horizontal transfer; thus it may be an ancestral component of the bacterial genome. Self-restraint may have favored this evolutionary endurance; in fact, unlike typical mobile elements, IS200 transposes rarely. Tight repression of transposase synthesis is achieved by a combination of mechanisms: inefficient transcription, protection from impinging transcription by a transcriptional terminator, and repression of translation by a stem-loop mRNA structure. A consequence of IS200 self-restraint is that the number and distribution of IS200 elements remain fairly constant in natural populations of bacteria. This stability makes IS200 a suitable molecular marker for epidemiological and ecological studies, especially when the number of IS200 copies is high. In Salmonella enterica, IS200 fingerprinting is extensively used for strain discrimination (AU)

IS200 es un elemento móvil presente en una variedad de géneros de eubacterias como Salmonella, Escherichia, Shigella, Vibrio, Enterococcus, Clostridium, Helicobacter y Actinobacillus. También se encuentran elementos similares a IS200 en arqueas. Los elementos IS200 son muy pequeños (707-711 pb) y contienen un solo gen. Los cladogramas construidos a partir de las secuencias de DNA de IS200 sugieren que este elemento no ha sufrido transferencia horizontal dentro de las eubacterias; por tanto, IS200 puede ser un componente ancestral del genoma bacteriano. La longevidad evolutiva de IS200 puede haber sido favorecida por su baja frecuencia de transposición, que contrasta con el comportamiento de muchos elementos móviles. En IS200, la síntesis de transposasa está reprimida por varios mecanismos: transcripción ineficaz, terminación de los transcritos iniciados en promotores foráneos y represión de la traducción por una estructura secundaria («tallo-lazo») de mRNA. Como consecuencia de este autocontrol, tanto el número como la distribución de elementos IS200 se mantienen relativamente constantes en las poblaciones naturales de bacterias. Esta estabilidad convierte a IS200 en un marcador adecuado para estudios epidemiológicos o ecológicos, especialmente cuando el número de copias de IS200 es alto. En Salmonella enterica, los perfiles de IS200 se usan habitualmente para la tipificación y discriminación de cepas (AU)

Hyperthermophily and the origin and earliest evolution of life / La hipertermofilia y el origen y evolución temprana de la vida

The possibility of a high-temperature origin of life has gained support based on indirect evidence of a hot, early Earth and on the basal position of hyperthermophilic organisms in rRNA-based phylogenies. However, although the availability of more than 80 completely sequenced cellular genomes has led to the identification of hyperthermophilic-specific traits, such as a trend towards smaller genomes, reduced protein-encoding gene sizes, and glutamic-acid-rich simple sequences, none of these characteristics are in themselves an indication of primitiveness. There is no geological evidence for the physical setting in which life arose, but current models suggest that the Earth's surface cooled down rapidly. Moreover, at 100 degrees C the half-lives of several organic compounds, including ribose, nucleobases, and amino acids, which are generally thought to have been essential for the emergence of the first living systems, are too short to allow for their accumulation in the prebiotic environment. Accordingly, if hyperthermophily is not truly primordial, then heat-loving lifestyles may be relics of a secondary adaptation that evolved after the origin of life, and before or soon after separation of the major lineages (AU)

Distintos autores han propuesto la posibilidad de un origen de la vida hipertermófilo, hipótesis que ha ganado credibilidad debido a las pruebas indirectas de un ambiente primitivo caliente y a la posición basal que muestran los microorganismos hipertermófilos en las filogenias basadas en el rRNA. Aunque el estudio de más de 80 genomas totalmente secuenciados ha permitido la identificación de características específicas de los hipertermófilos, como pueden ser la tendencia a tamaños de genoma pequeños, genes codificadores de proteínas de menor tamaño, y secuencias sencillas abundantes en ácido glutámico, ninguna de estas características indica por sí misma lo primitivo que es el microorganismo. No hay evidencia geológica que indique el lugar donde se originó la vida, pero los modelos actuales sugieren que la superficie del planeta se enfrió rápidamente. Además, a una temperatura de 100 ?C la vida media de compuestos orgánicos como la ribosa, las bases nucleicas o los aminoácidos, moléculas que se consideran esenciales para la aparición de los primeros sistemas vivos, es demasiado corta para permitir su acumulación en el medio prebiótico. Entonces, si la hipertermofilia no es realmente el estado primordial, los microorganismos hipertermófilos podrían ser vestigios de una adaptación secundaria posterior al origen de la vida, y anterior o inmediatamente posterior a la separación de los principales linajes. (AU)