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  • 1
    ISSN: 1432-1432
    Keywords: Key words: Intergenic spacer region — Intervening sequences — 16S–23S rRNA gene spacer — Concerted evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The ribosomal RNA multigene family in Escherichia coli comprises seven rrn operons of similar, but not identical, sequence. Four operons (rrnC, B, G, and E) contain genes in the 16S–23S intergenic spacer region (ISR) for tRNAGlu-2 and three (rrnA, D, and H) contain genes for tRNAIle-1 and tRNAAla-1B. To increase our understanding of their molecular evolution, we have determined the ISR sequence of the seven operons in a set of 12 strains from the ECOR collection. Each operon was specifically amplified using polymerase chain reaction primers designed from genes or open reading frames located upstream of the 16S rRNA genes in E. coli K12. With a single exception (ECOR 40), ISRs containing one or two tRNA genes were found at the same respective loci as those of strain K12. Intercistronic heterogeneity already found in K12 was representative of most variation among the strains studied and the location of polymorphic sites was the same. Dispersed nucleotide substitutions were very few but 21 variable sites were found grouped in a stem-loop, although the secondary structure was conserved. Some regions were found in which a stretch of nucleotides was substituted in block by one alternative, apparently unrelated, sequence (as illustrated by the known putative insertion of rsl in K12). Except for substitutions of different sizes and insertions/deletions found in the ISR, the pattern of nucleotide variation is very similar to that found for the 16S rRNA gene in E. coli. Strains K12 and ECOR 40 showed the highest intercistronic heterogeneity. Most strains showed a strong tendency to homogenization. Concerted evolution could explain the notorious conservation of this region that is supposed to have low functional restrictions.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 36 (1986), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract By using 3 different methods for the detection of antagonism, complex patterns of this type of interaction were evident within a group comprising 79 halobacterial strains, which included the most divergent types of culture collection strains available, as well as freshly isolated ones. The experiments carried out showed that such interactions are not due to phages, but to the effects of bacteriocin-like substances, known as halocins. With the exception of only 2 strains, all the remainder caused inhibition to a greater or lesser degree, showing a wide variety of activity spectra. Comparative numerical analysis of these spectra revealed the existence of at least 15 different groups of halocins.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 231 (2004), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The enormous sequencing capabilities of our times might be reaching the point of overflowing the possibilities to analyse data and allow for a feedback on where to focus the available resources. We have now a foreseeable future in which most bacterial species will have an annotated genome. However, we know also that most prokaryotic diversity would not be included there. On the one hand, there is the problem of many groups not being easily amenable to culture and hence not represented in culture-centred microbial taxonomy. On the other hand, the gene pools present in one species can be orders of magnitude larger that the genome of one strain (selected for genome sequencing). Contrasting with eukaryotic genomes, the repertoire of genes present in one prokaryotic cell genome does not correlate stringently with its taxonomic identity. Hence gene catalogues from one environment might provide more meaningful information than the classical species catalogues. Metagenomics or microbial environmental genomics provide a different tool that gravitates around the habitat rather than the species. Such tool could be just the right way to complement ‘organismal genomics’. Its potential to advance our understanding of microbial ecology and prokaryotic diversity and evolution is discussed.
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Phylogenetic information from ribosomal RNA genes directly amplified from the environment changed our view of the biosphere, revealing an extraordinary diversity of previously undetected prokaryotic lineages. Using ribosomal RNA genes from marine picoplankton, several new groups of bacteria and ...
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 39 (1986), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract There exists a wide diversity of halophilic eubacteria with chemoorganotrophic-aerobic metabolism. Most of them have a more moderate salt response than halophilic archaebacteria, falling into the category of moderately halophilic bacteria. Although mostly isolated from salted food, their natural habitats are hypersaline waters of intermediate levels of salt concentration, and hypersaline soils. In hypersaline waters, the taxonomic groups found are the ones that also predominate in ocean waters, such as representatives of the genera Vibrio, Pseudomonas and Flavobacterium. However, in hypersaline soils, the taxonomic groups present are those typical of normal soils, such as Pseudomonas, Bacillus and Gram-positive cocci. The halophilic bacteria from soils are also more resistant to exposure to low salt concentrations than the organisms isolated from waters. Therefore, it seems that the general characteristics of the hypersaline environments drastically affect the types of halophilic bacteria present, and that the halophilic character has arisen in many phylogenetic groups of eubacteria.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 14 (1982), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 103 (1992), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
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  • 8
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We have applied a simple methodology based on restriction endonuclease digestion of the total bacterial and archaeal 16S rDNA amplified from sea water samples to compare the prokaryotic diversity present along a transect from coastal to offshore waters in the Mediterranean basin (from Barcelona to the Balearic Islands). Samples from the surface and deep-chlorophyll maximum (DCM) were obtained. Temporal variation during a short span was also investigated by repeating the sampling after 48 h. The patterns of digestion bands from the samples were compared to detect major changes in the bacterial or archaeal groups present. For bacteria the main difference was found between the free-living community and that retained by the eukaryotic filter and assumed to be particle attached. By contrast Archaea collected by the same means did not appear as a separate group. The other main variation was depth-related, with remarkably different communities at the surface, at the DCM, and a single sample taken at 400 m depth. On the other hand, the variation along the transect from the continental platform to an offshore (2000 m maximum depth) station was relatively small. Temporal (48 h) and small scale spatial (a few km) variation was minimal.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 36 (2001), S. 0 
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Analysis of the pigments extracted from solar saltern crystallizer ponds in Santa Pola near Alicante and on the Balearic island of Mallorca, Spain, showed that 5–7.5% of the total prokaryotic pigment absorbance could be attributed to a novel carotenoid or carotenoid-like compound. This unidentified pigment was identical to the sole pigment present in Salinibacter ruber, the only described member of a newly discovered genus of red halophilic Bacteria related to the Cytophaga-Flavobacterium-Bacteroides group. On the basis of fluorescence in situ hybridization experiments it has been shown that Salinibacter is an important component of the microbial community of Spanish saltern ponds. The red color of saltern crystallizer ponds may thus not only be due to red halophilic Archaea and to β-carotene-rich Dunaliella cells as previously assumed, but may contain a bacterial contribution as well. The Salinibacter pigment was not detected in samples collected from crystallizer ponds of the salterns of Eilat, Israel, and only traces of it may have been present in the Newark, CA, USA, salterns. The community structure of the prokaryote community inhabiting saltern crystallizers thus shows significant geographic variations. Polar lipid analyses of the biomass collected from the Santa Pola salterns showed that the total contribution of Salinibacter and other Bacteria to the total biomass was minor, the most important component of the community being halophilic Archaea.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 14 (1996), S. 0 
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Abstract Molecular methods allow an extremely fine strain typing that can be used to establish the population structure of bacterial species. This methodology has been used to characterize a collection of 74 uropathogenic Escherichia coli obtained from three hospitals located in geographically distant towns in Spain, some representatives of the ECOR collection and other reference strains. Genomic DNA was analyzed by RAPD (Random Amplified Polymorphic DNA) that can characterize a bacterial strain to the level of defining individual clones. The 16S rDNA-23S rDNA spacers were amplified by PCR and submitted to restriction analysis. Finally, the presence or absence of G adhesins in Escherichia coli as well as the type of adhesin (three types are known) have been shown by PCR amplification followed by digestion with restriction enzymes. As expected a wide diversity was shown by RAPD and identical patterns were only found in the case of strains isolated from the same individual, an obvious case of relapse. Analysis of the spacers' restriction patterns showed the presence of two markedly differentiated clusters that we have named α and ß. Both RAPD and spacer restriction patterns originated similar clusters of strains showing a consistency in the evolution of the global genome with the sequence variation of the ribosomal spacers. Furthermore, most of the strains having G-adhesin, with only a few exceptions, corresponded to the α rRNA spacer group. The two spacer types detected were also consistent with some phenotypic markers such as sucrose and raffinose utilization. The α and β clusters could be intraspecific groups produced by partial sexual isolation or other barriers that are originating a divergent evolution.
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