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881.
Whole cell absorption spectra of the Eustigmatophycean algae Nannochloropsis salina Bourrelly and Nannochloropsis sp. reveal the presence of a distinct absorption peak at 490 nm. The lack of chlorophylls b and c in these species indicates that this peak must be attributed to carotenoid absorption. In vivo fluorescence excitation spectra for chlorophyll a emission show a corresponding maximum at 490 nm. This peak is more clearly resolved than carotenoid maxima in other algal classes due to the absence of accessory chlorophylls. The carotenoid composition of the two Nannochloropsis species shows that violaxanthin and vaucheriaxanthin are the main contributors to 490 nm absorption. Violaxanthin accounts for approximately 60% of the total carotenoid in both clones. We conclude that light absorption by violaxanthin, and possibly by vaucheriaxanthin, is coupled in energy transfer to chlorophyll a and that violaxanthin is the major light-harvesting pigment in the Eustigmatophyceae. This is the first report of the photosynthetic light-harvesting function of this carotenoid. 相似文献
882.
Kurt Mendgen 《Archives of microbiology》1979,122(2):129-135
A new species of anaerobic bacterium that degrades the even-numbered carbon fatty acids, butyrate, caproate and caprylate, to acetate and H2 and the odd-numbered carbon fatty acids, valerate and heptanoate, to acetate, propionate and H2 was obtained in coculture with either an H2-utilizing methanogen or H2-utilizing desulfovibrio. The organism could be grown only in syntrophic association with the H2-utilizer and no other energy sources or combination of electron donor and acceptors were utilized. It was a Gram-negative helical rod with 2 to 8 flagella, about 20 nm in diameter, inserted in a linear fashion about 130 nm or more apart along the concave side of the cell. It grew with a generation time of 84 h in co-culture with Methanospirillum hungatii and was present in numbers of at least 4.5×10-6 per g of anaerobic digestor sludge. 相似文献
883.
All cellular proteins are synthesized by the ribosome, an intricate molecular machine that translates the information of protein coding genes into the amino acid alphabet. The linear polypeptides synthesized by the ribosome must generally fold into specific three-dimensional structures to become biologically active. Folding has long been recognized to begin before synthesis is complete. Recently, biochemical and biophysical studies have shed light onto how the ribosome shapes the folding pathways of nascent proteins. Here, we discuss recent progress that is beginning to define the role of the ribosome in the folding of newly synthesized polypeptides. 相似文献
884.
Bruno Mesmin Frederick R. Maxfield 《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》2009,1791(7):636-645
We review the cellular mechanisms implicated in cholesterol trafficking and distribution. Recent studies have provided new information about the distribution of sterols within cells, including analysis of its transbilayer distribution. The cholesterol interaction with other lipids and its engagement in various trafficking processes will determine its proper level in a specific membrane; making the cholesterol distribution uneven among the various intracellular organelles. The cholesterol content is important since cholesterol plays an essential role in membranes by controlling their physicochemical properties as well as key cellular events such as signal transduction and protein trafficking. Cholesterol movement between cellular organelles is highly dynamic, and can be achieved by vesicular and non-vesicular processes. Various studies have analyzed the proteins that play a significant role in these processes, giving us new information about the relative importance of these two trafficking pathways in cholesterol transport. Although still poorly characterized in many trafficking routes, several potential sterol transport proteins have been described in detail; as a result, molecular mechanisms for sterol transport among membranes start to be appreciated. 相似文献
885.
An individual-based model (IbM) for bacterial adaptation and evolution, COSMIC-Rules, has been employed to simulate interactions of virtual temperate bacteriophages (phages) and their bacterial hosts. Outcomes of infection mimic those of a phage such as lambda, which can enter either the lytic or lysogenic cycle, depending on the nutritional status of the host. Infection of different hosts possessing differing restriction and modification systems is also simulated. Phages restricted upon infection of one restricting host can be adapted (by host-controlled modification of the phage genome) and subsequently propagate with full efficiency on this host. However, such ability is lost if the progeny phages are passaged through a new host with a different restriction and modification system before attempted re-infection of the original restrictive host. The simulations show that adaptation and re-adaptation to a particular host-controlled restriction and modification system result in lower efficiency and delayed lysis of bacterial cells compared with infection of non-restricting host bacteria. 相似文献
886.
Seishiro Aoki Tetsuya Kondo Danielle Prévost Sayuri Nakata Tadashi Kajita Motomi Ito 《Systematic and applied microbiology》2010
Sixty-one rhizobial strains from Lathyrus japonicus nodules growing on the seashore in Japan were characterized and compared to two strains from Canada. The PCR-based method was used to identify test strains with novel taxonomic markers that were designed to discriminate between all known Lathyrus rhizobia. Three genomic groups (I, II, and III) were finally identified using RAPD, RFLP, and phylogenetic analyses. Strains in genomic group I (related to Rhizobium leguminosarum) were divided into two subgroups (Ia and Ib) and subgroup Ia was related to biovar viciae. Strains in subgroup Ib, which were all isolated from Japanese sea pea, belonged to a distinct group from other rhizobial groups in the recA phylogeny and PCR-based grouping, and were more tolerant to salt than the isolate from an inland legume. Test strains in genomic groups II and III belonged to a single clade with the reference strains of R. pisi, R. etli, and R. phaseoli in the 16S rRNA phylogeny. The PCR-based method and phylogenetic analysis of recA revealed that genomic group II was related to R. pisi. The analyses also showed that genomic group III harbored a mixed chromosomal sequence of different genomic groups, suggesting a recent horizontal gene transfer between diverse rhizobia. Although two Canadian strains belonged to subgroup Ia, molecular and physiological analyses showed the divergence between Canadian and Japanese strains. Phylogenetic analysis of nod genes divided the rhizobial strains into several groups that reflected the host range of rhizobia. Symbiosis between dispersing legumes and rhizobia at seashore is discussed. 相似文献
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