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      Historia en tiempo real de las bacterias del siglo XXI: gigantes y marcianas Translated title: Real time history of 21st century bacteria: giants and martians

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          Abstract

          Resumen Hemos denominado bacterias del siglo XXI a dos tipos de extrañas y maravillosas criaturas del Reino Protista, descubiertas entre los últimos años del siglo pasado y los días que hoy vivimos: las bacterias gigantes y las de un posible origen marciano. En su búsqueda, audaces investigadores han viajado a tierras distantes y peligrosas, acampando en lugares desolados y descendiendo a las profundidades marinas, actividades que llamamos investigación aventura. Presentamos como ejemplos una expedición al Mar Rojo, buscando el gigantesco Epulopiscium; una temporada en el lago Mono, California, en pos de una bacteria con arsénico en su ADN; un patrullaje en el Ártico, para encontrar bacterias petrificadas en un meteorito marciano; sin olvidar que el tranquilo laboratorio también puede ser un lugar peligroso, porque toda investigación es una aventura.

          Translated abstract

          We denominate “21st century bacteria” two types of strange and amazing creatures from the kingdom Protista, discovered between the last years of the twentieth and the present days: the giant bacteria and those with a possible Martian origin. Searching for them, bold investigators have travelled to distant and hostile lands, desolate places and deep waters, performing a kind of investigation that we only can describe as “investigation-adventure”. This paper presents expeditions to the Red Sea, fishing the Epulopiscium; to Lake Mono, searching a bacteria able to growth with arsenic; to the Antarctic Circle, finding a meteorite with petrified alien microorganisms; and… to the quiet laboratory, a not less dangerous place.

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          Most cited references17

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          Dense populations of a giant sulfur bacterium in Namibian shelf sediments.

          A previously unknown giant sulfur bacterium is abundant in sediments underlying the oxygen minimum zone of the Benguela Current upwelling system. The bacterium has a spherical cell that exceeds by up to 100-fold the biovolume of the largest known prokaryotes. On the basis of 16S ribosomal DNA sequence data, these bacteria are closely related to the marine filamentous sulfur bacteria Thioploca, abundant in the upwelling area off Chile and Peru. Similar to Thioploca, the giant bacteria oxidize sulfide with nitrate that is accumulated to
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            Extreme polyploidy in a large bacterium.

            Cells rely on diffusion to move metabolites and biomolecules. Diffusion is highly efficient but only over short distances. Although eukaryotic cells have broken free of diffusion-dictated constraints on cell size, most bacteria and archaea are forced to remain small. Exceptions to this rule are found among the bacterial symbionts of surgeonfish; Epulopiscium spp. are cigar-shaped cells that reach lengths in excess of 600 mum. A large Epulopiscium contains thousands of times more DNA than a bacterium such as Escherichia coli, but the composition of this DNA is not well understood. Here, we present evidence that Epulopiscium contains tens of thousands of copies of its genome. Using quantitative, single-cell PCR assays targeting single-copy genes, we have determined that copy number is positively correlated with Epulopiscium cell size. Although other bacteria are known to possess multiple genomes, polyploidy of the magnitude observed in Epulopiscium is unprecedented. The arrangement of genomes around the cell periphery may permit regional responses to local stimuli, thus allowing Epulopiscium to maintain its unusually large size. Surveys of the sequences of single-copy genes (dnaA, recA, and ftsZ) revealed genetic homogeneity within a cell consistent with only a small amount ( approximately 1%) of the parental DNA being transferred to the next generation. The results also suggest that the abundance of genome copies in Epulopiscium may allow for an unstable genetic feature, a long mononucleotide tract, in an essential gene. With the evolution of extreme polyploidy and large cell size, Epulopiscium has acquired some of the advantages of eukaryotic cells.
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              The largest bacterium.

              The large, morphologically peculiar microorganism Epulopiscium fishelsoni inhabits the intestinal tract of Acanthurus nigrofuscus, a brown surgeonfish (family Acanthuridae) from the Red Sea. Similar microorganisms have been found in surgeonfish species from the Great Barrier Reef. As these microorganisms have only been seen in surgeonfish and no free-living forms have been found, they are considered to be specific symbionts of surgeonfish, although the nature of the symbiosis is unclear. Initial reports considered them to be eukaryotic protists, based primarily on their size, with individuals being larger than 600 microns by 80 microns. But their cellular morphology in the electron microscope is more like that of bacterial than eukaryotic cells. To resolve the nature of these symbionts, we have isolated the genes encoding the small subunit ribosomal RNA from two morphotypes and used them in a phylogenetic analysis. In situ hybridization with oligonucleotide probes based on the cloned rRNA sequences confirmed the source of the rRNA genes. Our result identify the symbionts as members of the low-(G+C) Gram-positive group of bacteria. They are therefore the largest bacteria to be described so far.
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                Author and article information

                Contributors
                Role: ND
                Journal
                rci
                Revista chilena de infectología
                Rev. chil. infectol.
                Sociedad Chilena de Infectología (Santiago, , Chile )
                0716-1018
                February 2019
                : 36
                : 1
                : 92-98
                Affiliations
                [1] orgnameCentro de Estudios Humanistas Julio Prado Chile
                Article
                S0716-10182019000100092
                1b42e9e5-edf3-4099-b5f4-fa16b1f2b9f9

                This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

                History
                : 16 January 2019
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 23, Pages: 7
                Product

                SciELO Chile

                Categories
                NOTA HISTORICA

                adventure investigation,investigación aventura,bacteria marciana,Bacteria gigante,Giant bacteria,mars bacteria

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