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11.
12.
Summary In phenotype the mycoplasmas are very different from ordinary bacteria. However, genotypically (i.e., phylogenetically) they are not. On the basis of ribosomal RNA homologies the mycoplasmas belong with the clostridia, and indeed havespecific clostridial relatives. Mycoplasmas are, however, unlike almost all other bacteria in the evolutionary characteristics of their ribosomal RNAs. These RNAs contain relatively few of the highly conserved oligonucleotide sequences characteristic of normal eubacterial ribosomal RNAs. This is interpreted to be a reflection of an elevated mutation rate in mycoplasma lines of descent. A general consequence of this would be that the variation associated with a mycoplasma population is augmented both in number and kind, which in turn would lead to an unusual evolutionary course, one unique in all respects. Mycoplasmas, then, are actually tachytelic bacteria. The unusual evolutionary characteristics of their ribosomal RNAs are the imprints of their rapid evolution. 相似文献
13.
14.
John W. Brown 《Journal of experimental marine biology and ecology》1984,80(2):197-206
The classification of lysine biosynthetic pathways in various organisms have been used to investigate their descent in evolution. We have attempted these determinations in the diatoms Amphora coffeaeformis var:perpusilla (Grunow Cleve.) and Phaeodactylum tricornutum (Bohlin). Additionally, we have verified earlier results of Vogel in a green alga, Chlorella pyrenoidosa strain Tx 71105 (Texas Culture Collection). Our research indicates that the diaminopimelic acid route is involved in all three organisms. While these studies do not exclude the possible co-existence of the α-aminoadipic acid route, the results imply a closer evolutionary relationship of pennate diatoms to bacteria and “classical” photosynthetic plants rather than to heterotrophic or mixotrophic fungi and atypical algal strains such as the Euglenophyta. 相似文献
15.
The activity of 5′-nucleotidase and ouabain-sensitive Na/K ATPase was determined in seven different mouse melanoma cell lines. Ouabain-sensitive Na/K ATPase activity was found in NP40-treated cell homogenates of all cell lines. However, 5′-nucleotidase activity was found in only one mouse melanoma cell line—JB/RH. The absence of expression of 5′-nucleotidase activity in the other six cell lines is not associated with pigmentation in melanoma cells, nor is the gene switched off in all transformed melanocytes of C57BL/6 origin. 相似文献
16.
Susana Benlloch Francisco Rodríguez-Valera Silvia G. Acinas Antonio J. Martínez-Murcia 《Hydrobiologia》1996,329(1-3):3-17
Activity and numbers of heterotrophic bacteria have indicated that, as expected, Prevost Lagoon is more eutrophic than Arcachon Bay. Amplification and sequence analysis of the 16S rRNA genes from DNA samples extracted directly from the environment allow the determination of phylogenetic relationships among members of microbial communities in natural ecosystems without the need for cultivation. Analysis of partial 16S rRNA gene sequences obtained from Stations A and 11 revealed that, in both environments, a relatively large number of clones related to Cytophaga/FlexibacterBacteroides as well as to -Proteobacteria were found. One hundred percent similarity with the sequences of the data bases were not found for any of the more than a hundred clones studied. In fact for most clones maximum similarity was below 95% for the nucleotide series sequenced. Similarity was not higher with any of the sequences found for the 14 isolates (pure cultures) obtained from the same samples. Redundancy, i.e. number of identical sequences, was higher in the samples from Arcachon. In addition, sequences related to representatives of ten major phylogenetic branches of Eubacteria were obtained from Prevost Lagoon, however only five branches were represented by the data from Arcachon. These findings indicate a higher bacterial diversity in Prévost Lagoon. 相似文献
17.
Bacterial host specificity of Lucinacea endosymbionts: Interspecific variation in 16S rRNA sequences 总被引:2,自引:0,他引:2
Abstract Three tropical lucinid clams ( Codakia orbiculata, Codakia pectinella and Lucina nassula ) from a shallow coastal environment have been studied regarding to their thioautotrophic bacterial endosymbionts. The 16S rRNA genes (rDNA) from these three endosymbionts were amplified using PCR. Phylogenetic analysis by distance matrix and parsimony methods always placed the newly examined symbionts within the monophyletic group composed of symbionts of the bivalve superfamily Lucinacea. A same single 16S rRNA sequence was found in C. orbiculata and C. pectinella and was identical to that found in C. orbicularis and Linga pensylvanica , two other lucinids living in the same type of environment. These data indicate that a same symbiont species may be associated with different host species. Lucina nassula hosts a symbiont with a distinct 16S rDNA sequence, but very closely related to the former. 相似文献
18.
Noriko Usui Kouji Matsushima Anne M. Pilaro Dan L. Longo Robert H. Wiltrout 《Biotherapy》1996,9(4):199-208
Recombinant human interleukin 1α (rh IL-1α) and etoposide (VP-16) synergize for direct growth inhibition of several human
tumor cell linesin vitro. Our previous studies demonstrated that VP-16 increased the number of membrane-associated IL-1 receptors (IL-1Rs) and also
enhanced the internalization of receptor-bound rh IL-1α. The purposes of this study were to test our hypothess that these
events were critical to the synergy between rhIL-1α and VP-16, to determine whether rhIL-1α and VP-16 synergize to increase
superoxide (SO) anion radical productionin vitro since SO anion has been implicated in the toxic effects of IL-1, and to investigate the antitumor efficacy of the combinaton
against tumors in vivo. A375/C6 melanoma cells and OVCAR-3 ovarian carcinoma cells were tested with IL-1 receptor antagonist
(IL-1ra) before exposure to rhIL-1α, VP-16 and rhIL-1α plus VP-16. The synergistic or antagonistic effects were assessed by
MTT assay. SO production was measured by reduction of cytochrome C. Athymic female mice bearing the A375/C6 melanoma were
treated by rhIL-1α, VP-16, and rhIL-1α+VP-16. The antitumor effects were evaluated by quantitating tumor growth and survival
time. Pretreatment with the IL-1ra abrogated the synergistic effects of rhIL-1α and VP-16. The production of SO radical by
A375/C6 cells was increased 2.5 fold by the combination of rhIL-1α and VP-16, and the addition of exogenous SOD blocked the
synergy between rhIL-1α and VP-16. However, when A375/S0D15 cells which over-expressed manganese superoxide dismutase (MnSOD)
after MnSOD cDNA transfecton were exposed to rhIL-1α and VP-16, in vitro antagonism was observed. In vivo studies demonstrated
that the combination of rhIL-1α and VP-16 delayed tumor growth better than either agent alone, although long-term survival
was not improved because of substantial toxicity. Our results suggest that the synergistic antitumor effects of IL-1α and
VP-16 may be due to IL-1R modulation and increased internalization of IL-1-IL-1R complex by VP-16 treatment, as well as to
a subsequent increase in SO anion radical production from the tumor cells exposed to both drugs. Thus, the combnation of IL-1α
and VP-16 might prove useful for the treatment of malignant diseasein vivo, if the increased toxicity can be reduced or managed.
The US Government’s right to retain a non-exclusive royalty-free license on and to any copyright is acknowledged. 相似文献
19.
Isolation of an anaerobic bacterium which reductively dechlorinates tetrachloroethene and trichloroethene 总被引:5,自引:0,他引:5
Strain TEA, a strictly anaerobic, motile rod with one to four lateral flagella and a crystalline surface layer was isolated from a mixed culture that completely reduces chlorinated ethenes to ethene. The organism coupled reductive dehalogenation of tetrachloroethene or trichloroethene to cis-1,2-dichloroethene to growth, using molecular hydrogen as the electron donor. It was unable to grow fermentatively or in the presence of tri- or tetrachloroethene with glucose, pyruvate, lactate, acetate or formate. The 16S rDNA sequence of strain TEA was 99.7% identical to that of Dehalobacter restrictus. The two organisms thus are representatives of the same species or the same genus within the Bacillus/Clostridium subphylum of the gram-positive bacteria. 相似文献
20.
Sulfur-oxidizing chemoautotrophic (thioautotrophic) bacteria are now known to occur as endosymbionts in phylogenetically diverse
bivalve hosts found in a wide variety of marine environments. The evolutionary origins of these symbioses, however, have remained
obscure. Comparative 16S rRNA sequence analysis was used to investigate whether thioautotrophic endosymbionts are monophyletic
or polyphyletic in origin and to assess whether phylogenetic relationships inferred among these symbionts reflect those inferred
among their hosts. 16S rRNA gene sequences determined for endosymbionts from nine newly examined bivalve species from three
families (Vesicomyidae, Lucinidae, and Solemyidae) were compared with previously published 16S rRNA sequences of thioautotrophic
symbionts and free-living bacteria. Distance and parsimony methods were used to infer phylogenetic relationships among these
bacteria. All newly examined symbionts fall within the gamma subdivision of the Proteobacteria, in clusters containing previously
examined symbiotic thioautotrophs. The closest free-living relatives of these symbionts are bacteria of the genus Thiomicrospira. Symbionts of the bivalve superfamily Lucinacea and the family Vesicomyidae each form distinct monophyletic lineages which
are strongly supported by bootstrap analysis, demonstrating that host phylogenies inferred from morphological and fossil evidence
are congruent with phylogenies inferred for their respective symbionts by molecular sequence analysis. The observed congruence
between host and symbiont phylogenies indicates shared evolutionary history of hosts and symbiont lineages and suggests an
ancient origin for these symbioses.
Correspondence to: D.L. Distel 相似文献