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1.
Jake V Bailey Verena Salman Gregory W Rouse Heide N Schulz-Vogt Lisa A Levin Victoria J Orphan 《The ISME journal》2011,5(12):1926-1935
We present evidence for a dimorphic life cycle in the vacuolate sulfide-oxidizing bacteria that appears to involve the attachment of a spherical Thiomargarita-like cell to the exteriors of invertebrate integuments and other benthic substrates at methane seeps. The attached cell elongates to produce a stalk-like form before budding off spherical daughter cells resembling free-living Thiomargarita that are abundant in surrounding sulfidic seep sediments. The relationship between the attached parent cell and free-living daughter cell is reminiscent of the dimorphic life modes of the prosthecate Alphaproteobacteria, but on a grand scale, with individual elongate cells reaching nearly a millimeter in length. Abundant growth of attached Thiomargarita-like bacteria on the integuments of gastropods and other seep fauna provides not only a novel ecological niche for these giant bacteria, but also for animals that may benefit from epibiont colonization. 相似文献
2.
Sallie W. Chisholm Sheila L. Frankel Ralf Goericke Robert J. Olson Brian Palenik John B. Waterbury Lisa West-Johnsrud Erik R. Zettler 《Archives of microbiology》1992,157(3):297-300
Several years ago, prochlorophyte picoplankton were discovered in the N. Atlantic. They have since been found to be abundant within the euphotic zone of the world's tropical and temperate oceans. The cells are extremely small, lack phycobiliproteins, and contain divinyl chlorophyll a and b as their primary photosynthetic pigments. Phylogenies constructed from DNA sequence data indicate that these cells are more closely related to a cluster of marine cyanobacteria than to their prochlorophyte relatives Prochlorothrix and Prochloron. Several strains of this organism have recently been brought into culture, and herewith are given the name Prochlorococcus marinus. 相似文献
3.
Description of a new epibiotic relationship (Suctorian–Copepoda) in NE Atlantic waters: from morphological to phylogenetic analyses 下载免费PDF全文
Maria Gregori Gregorio Fernández‐Leborans Álvaro Roura Ángel F. González Santiago Pascual 《Acta zoologica》2016,97(2):165-176
Paraeuchaeta hebes is one of the most important carnivorous copepods in the coastal upwelling system off Galician waters (Ría de Vigo, NE Atlantic). A suctorian epibiont of the genus Pelagacineta was found attached to the surface of these copepods. The abundance and distribution on the copepod surface were analysed, taking into account the sex of the crustacean, revealing some preference for females and also a different attachment point in both sexes. The morphological study allowed us to identify a new species of this Suctoria epibiont as Pelagacineta hebensis. Moreover, the 18S rRNA gene was partially sequenced to inspect the phylogenetic position of Pelagacineta hebensis within the subclass Phyllopharyngea. The maximum‐likelihood (ML) tree obtained was consistent with the morphological and with previous molecular studies and showed that P. hebensis belongs to the order Endogenina, as a sister clade of the few taxa sequenced within this order. Including new genetic data to the Endogenina will allow building new hypothesis about the evolution of the most derived clade of suctorians. 相似文献
4.
Although widely distributed in eukaryotic cells glycoproteins appear to be rare in prokaryotic organisms. The prevalence of the misconception that bacteria do not glycosylate their proteins has been a subject matter of discussion for a long time. Glycoconjugates that are linked to proteins or peptides, generated by the ribosomal translational mechanism have been reported only in the last two to three decades in a few prokaryotic organisms. Most studied prokaryotic glycoproteins are the S-layer glycoproteins of Archeabacteria. Apart from these, membrane-associated, surface-associated, secreted glycoproteins and exoenzymes glycoproteins are also well documented in both, Archea and Eubacteria. From the recent literature, it is now clear that prokaryotes are capable of glycosylating proteins. In general, prokaryotes are deprived of the cellular organelles required for glycosylation. In prokaryotes many different glycoprotein structures have been observed that display much more variation than that observed in eukaryotes. Besides following similar mechanisms in the process of glycosylation, prokaryotes have also been shown to use mechanisms that are different from those found in eukaryotes. The knowledge pertaining to the functional aspects of prokaryotic glycoproteins is rather scarce. This review summarizes developments and understanding relating to characteristics, synthesis, and functions of prokaryotic glycoproteins. An extensive summary of glycosylation that has been reported to occur in bacteria has also been tabulated. Various possible applications of these diverse biomolecules in biotechnology, vaccine development, pharmaceutics and diagnostics are also touched upon. 相似文献
5.
Dairi T Motohira Y Kuzuyama T Takahashi S Itoh N Seto H 《Molecular & general genetics : MGG》2000,262(6):957-964
We have isolated a mutant lacking 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase activity from a terpenoid antibiotic
(terpentecin) producer, Streptomyces griseolosporeus MF730-N6, which uses both the mevalonate and nonmevalonate pathways for the formation of isopentenyl diphosphate, by screening
terpentecin non-producing mutants. Terpentecin is known to be synthesized via the mevalonate pathway. The gene encoding HMG-CoA
reductase (hmgg) was cloned and identified by complementation of the mutant, using a self-cloning system developed in this study for strain
MF730-N6. The corresponding hmgs gene for HMG-CoA reductase was also cloned from Streptomyces sp. KO-3988, which produces the terpenoid antibiotic furaquinocin. Sequence analysis of hmgg and hmgs showed that both genes encode polypeptides of 353 amino acids which are 84% identical to each other. A search of protein
sequence databases revealed that both gene products were also similar to HMG-CoA reductases from a variety of other organisms,
including Streptomyces sp. CL190 (hmgg is 89% and hmgs 85% identical to its CL190 homolog), sea urchin (40.3 and 40.5%), German cockroach (37.6 and 38.4%), and Camptotheca acuminata (39.7 and 40.8%).
Received: 17 May 1999 / Accepted: 10 September 1999 相似文献
6.
1. The distribution and location of the ciliated protozoan Lagenophrys aselli on the freshwater isopod Asellus aquaticus were studied in relation to water flow over the third pleopod surface. 2. At low densities L. aselli had a significant preference for the anterior centre of the pleopod; however, at the highest densities this preference was no longer significant. The distribution ranged from closer than random at low densities to further than random at the highest densities, and may have been a product of feeding and reproduction of L. aselli as well as the short intermoult period of the host. 3. An individual L. aselli has an effective area of both the lorica and the ciliated feeding disc. The ciliated feeding disc, when extended, may contribute to the presence of a small anterior–posterior gap being left between individuals. 相似文献
7.
Base Composition Skews, Replication Orientation, and Gene Orientation in 12 Prokaryote Genomes 总被引:21,自引:0,他引:21
Michael J. McLean Kenneth H. Wolfe Kevin M. Devine 《Journal of molecular evolution》1998,47(6):691-696
Variation in GC content, GC skew and AT skew along genomic regions was examined at third codon positions in completely sequenced
prokaryotes. Eight out of nine eubacteria studied show GC and AT skews that change sign at the origin of replication. The
leading strand in DNA replication is G-T rich at codon position 3 in six eubacteria, but C-T rich in two Mycoplasma species. In M. genitalium the AT and GC skews are symmetrical around the origin and terminus of replication, whereas its GC content variation has been
shown to have a centre of symmetry elsewhere in the genome. Borrelia burgdorferi and Treponema pallidum show extraordinary extents of base composition skew correlated with direction of DNA replication. Base composition skews
measured at third codon positions probably reflect mutational biases, whereas those measured over all bases in a sequence
(or at codon positions 1 and 2) can be strongly affected by protein considerations due to the tendency in some bacteria for
genes to be transcribed in the same direction that they are replicated. Consequently in some species the direction of skew
for total genomic DNA is opposite to that for codon position 3.
Received: 2 February 1998 / Accepted: 15 June 1998 相似文献
8.
The Path from the RNA World 总被引:1,自引:0,他引:1
We describe a sequential (step by step) Darwinian model for the evolution of life from the late stages of the RNA world through
to the emergence of eukaryotes and prokaryotes. The starting point is our model, derived from current RNA activity, of the
RNA world just prior to the advent of genetically-encoded protein synthesis. By focusing on the function of the protoribosome
we develop a plausible model for the evolution of a protein-synthesizing ribosome from a high-fidelity RNA polymerase that
incorporated triplets of oligonucleotides. With the standard assumption that during the evolution of enzymatic activity, catalysis
is transferred from RNA → RNP → protein, the first proteins in the ``breakthrough organism' (the first to have encoded protein
synthesis) would be nonspecific chaperone-like proteins rather than catalytic. Moreover, because some RNA molecules that pre-date
protein synthesis under this model now occur as introns in some of the very earliest proteins, the model predicts these particular
introns are older than the exons surrounding them, the ``introns-first' theory. Many features of the model for the genome
organization in the final RNA world ribo-organism are more prevalent in the eukaryotic genome and we suggest that the prokaryotic
genome organization (a single, circular genome with one center of replication) was derived from a ``eukaryotic-like' genome
organization (a fragmented linear genome with multiple centers of replication). The steps from the proposed ribo-organism
RNA genome → eukaryotic-like DNA genome → prokaryotic-like DNA genome are all relatively straightforward, whereas the transition
prokaryotic-like genome → eukaryotic-like genome appears impossible under a Darwinian mechanism of evolution, given the assumption
of the transition RNA → RNP → protein. A likely molecular mechanism, ``plasmid transfer,' is available for the origin of
prokaryotic-type genomes from an eukaryotic-like architecture. Under this model prokaryotes are considered specialized and
derived with reduced dependence on ssRNA biochemistry. A functional explanation is that prokaryote ancestors underwent selection
for thermophily (high temperature) and/or for rapid reproduction (r selection) at least once in their history.
Received: 14 January 1997 / Accepted: 19 May 1997 相似文献
9.
A number of proteins have been identified that contain prominent sequence signatures that are uniquely shared by the members
of the Deinococcus-Thermus genera and the cyanobacterial species but which are not found in any of the other eubacterial or archaebacterial homologs.
The proteins containing such sequence signatures include (1) the DnaJ/Hsp40 family of proteins, (2) DNA polymerase I, (3)
the protein synthesis elongation factor EF-Tu, and (4) the elongation factor EF-Ts. A strong affinity of the Deinococcus-Thermus species to cyanobacteria is also seen in the phylogenetic trees based on Hsp70 and DnaJ sequences. These results provide
strong evidence of a close and specific evolutionary relationship between species belonging to these two eubacterial divisions.
Received: 10 September 1997 / Accepted: 15 December 1997 相似文献
10.
Roberts TH Hejgaard J Saunders NF Cavicchioli R Curmi PM 《Journal of molecular evolution》2004,59(4):437-447
Most serpins irreversibly inactivate specific serine proteinases of the chymotrypsin family. Inhibitory serpins are unusual proteins in that their native structure is metastable, and rapid conversion to a relaxed state is required to trap target enzymes in a covalent complex. The evolutionary origin of the serpin fold is unresolved, and while serpins in animals are known to be involved in the regulation of a remarkable diversity of metabolic processes, the physiological functions of homologues from other phyla are unknown. Addressing these questions, here we analyze serpin genes identified in unicellular eukaryotes: the green alga Chlamydomonas reinhardtii, the dinoflagellate Alexandrium tamarense, and the human pathogens Entamoeba spp., Eimera tenella, Toxoplasma gondii, and Giardia lamblia. We compare these sequences to others, particularly those in the complete genome sequences of Archaea, where serpins were found in only 4 of 13 genera, and Bacteria, in only 9 of 56 genera. The serpins from unicellular organisms appear to be phylogenetically distinct from all of the clades of higher eukaryotic serpins. Most of the sequences from unicellular organisms have the characteristics of inhibitory serpins, and where multiple serpin genes are found in one genome, variability is displayed in the region of the reactive-center loop important for specificity. All the unicellular eukaryotic serpins have large hydrophobic or positively charged residues at the putative P1 position. In contrast, none of the prokaryotic serpins has a residue of these types at the predicted P1 position, but many have smaller, neutral residues. Serpin evolution is discussed.[Reviewing Editor: Dr. Peer Bork] 相似文献