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At least 253 records · Page 14Linked to original sources
PubMed1999

Phylogenetic Composition, Spatial Structure, and Dynamics of Lotic Bacterial Biofilms Investigated by Fluorescent in Situ Hybridization and Confocal Laser Scanning Microscopy.

> Abstract The phylogenetic composition, three-dimensional structure and dynamics of bacterial communities in river biofilms generated in a rotating annular reactor system were studied by fluorescent in situ hybridization (FISH) and confocal laser scanning microscopy (CLSM). Biofilms grew on independently removable polycarbonate slides exposed in the reactor system with natural river water as inoculum and sole nutrient and carbon source. The microbial biofilm community developed from attached single cells and distinct microcolonies via a more confluent structure characterized by various filamentous bacteria to a mature biofilm rich in polymeric material with fewer cells on a per-area basis after 56 days. During the different stages of biofilm development, characteristic microcolonies and cell morphotypes could be identified as typical features of the investigated lotic biofilms. In situ analysis using a comprehensive suite of rRNA-targeted probes visualized individual cells within the alpha-, beta-, and gamma-Proteobacteria as well as the Cytophaga-Flavobacterium group as major parts of the attached community. The relative abundance of these major groups was determined by using digital image analysis to measure specific cell numbers as well as specific cell area after in situ probing. Within the lotic biofilm community, 87% of the whole bacterial cell area and 79% of the total cell counts hybridized with a Bacteria specific probe. During initial biofilm development, beta-Proteobacteria dominated the bacterial population. This was followed by a rapid increase of alpha-Proteobacteria and bacteria affiliated to the Cytophaga-Flavobacterium group. In mature biofilms, alpha-Proteobacteria and Cytophaga-Flavobacteria continued to be the prevalent bacterial groups. Beta-Proteobacteria constituted the morphologically most diverse group within the biofilm communities, and more narrow phylogenetic staining revealed the importance of distinct phylotypes within the beta1-Proteobacteria for the composition of the microbial community. The presence of sulfate-reducing bacteria affiliated to the Desulfovibrionaceae and Desulfobacteriaceae confirmed the range of metabolic potential within the lotic biofilms.http://link.springer-ny.com/link/service/journals/00248/bibs/37n4p225.html

Journal Article↗
PubMed2004

Fine spatial structure of Atlantic hake (Merluccius merluccius) stocks revealed by variation at microsatellite loci.

Genetic variation at 5 microsatellite loci was analyzed for European hake Merluccius merluccius sampled from 9 different regions in the Atlantic Ocean and the Mediterranean Sea. Significant genetic differentiation was found between samples, suggesting a fine subdivision of Atlantic and Mediterranean hake stocks. These results are discussed in the context of the decline of demersal fish species, probably due to overfishing.

Analysis of Variance↗
PubMed1981

Effects of spatially structured stimulus fields on pattern reversal visual evoked potentials.

Pattern-reversal visual evoked potentials (PRVEPs) were tested in 11 healthy individuals. A photic stimulator for pattern production on a TV monitor, an electroencephalograph for EEG signal amplification and a computer for averaging the potentials and displaying the traces were used in the experiments. The peak latencies and both trough-to-peak and baseline-to-peak amplitudes of the main PRVEP components were found to be closely related to both the check size of checkerboard pattern and the bar width of barred pattern. The latencies decreased exponentially and amplitudes varied non-monotonically with check size or bar width. Most of the amplitudes of these components were greatest when checkerboard patterns with check sizes subtending visual angles of 60--70 min of arc, or barred patterns with bar widths subtending angles of 7--15 min of arc, were presented.

Adult↗
PubMed1983

Oscillating spatial structures of a tissue.

We present a simple mathematical model for the self-controlled growth of a tissue giving rise to an oscillating tissue size under certain conditions. The control is brought about by two substances (two inhibitors or one inhibitor and one nutrient) which influence the cell kinetics locally. The inhibitors are produced by the tissue itself (whereas the nutrient comes from outside but is consumed by the tissue which produces the same effect). Both diffuse freely throughout the tissue, and thus realize a communication between different parts of the tissue. In any case the tissue approaches a self-maintaining space-time structure with properties depending on the parameters of proliferation, death and inhibiting control. We discuss the conditions for this structure not to be time-independent but oscillating.

Cell Communication↗
PubMed1988

Application of tris(2,2'-bipyridyl)ruthenium(III) for the investigation of DNA spatial structure by a chemical modification method.

It was shown that the treatment of a DNA fragment and a hepta-decanucleotide having a hairpin structure by Ru(2,2'-bipyridyl)3(3+) complex at 15 degrees C in 1 M NaCl for 10-60 min, and subsequent hydrolysis in 1 M piperidine at 95 degrees C led to the specific cleavage of the polynucleotide chain at guanosine residues in the single-stranded regions. This method can be used for the studying of nucleic acids secondary structure.

2,2'-Dipyridyl↗
PubMed1984

A generalized reaction diffusion model for spatial structure formed by motile cells.

A non-linear stability analysis using a multi-scale perturbation procedure is carried out on a model of a generalized reaction diffusion mechanism which involves only a single equation but which nevertheless exhibits bifurcation to non-uniform states. The patterns generated by this model by variation in a parameter related to the scalar dimensions of domain of definition, indicate its capacity to represent certain key morphogenetic features of multicellular systems formed by motile cells.

Animals↗
PubMedDate not supplied

Quantification of spatial structure of human proximal tibial bone biopsies using 3D measures of complexity.

Changes in trabecular bone composition during development of osteoporosis are used as a model for bone loss in microgravity conditions during a space flight. Symbolic dynamics and measures of complexity are proposed and applied to assess quantitatively the structural composition of bone tissue from 3D data sets of human tibia bone biopsies acquired by a micro-CT scanner. In order to justify the newly proposed approach, the measures of complexity of the bone architecture were compared with the results of traditional 2D bone histomorphometry. The proposed technique is able to quantify the structural loss of the bone tissue and may help to diagnose and to monitor changes in bone structure of patients on Earth as well as of the space-flying personnel.

Aged↗
PubMed2003

Effects of disturbances caused by coastal constructions on spatial structure, growth dynamics and photosynthesis of the seagrass Posidonia oceanica.

The light-limitation hypothesis was tested to assess whether water turbidity had caused the decline of a Mediterranean Posidonia oceanica (L.) Delile meadow in an area affected by a harbor. The annual growth, photosynthesis and rhizome starch concentrations of seagrass were measured and related to changes in light availability and dissolved nutrient concentration along a gradient of meadow degradation from areas close to the harbor outwards. Environmental and plant variables were measured in three stations placed along this gradient and compared with a reference station at an undisturbed meadow. The light attenuation coefficient (k) increased toward the inner harbor area, mainly due to sediment resuspension. The shoot density and leaf productivity of P. oceanica shoots were much lower in disturbed stations of the inner harbor area than in the outer, less disturbed station and the reference meadow. However, daily leaf carbon gains, calculated from the photosynthetic rates at saturating irradiance (P(max)) and the daily period in which seagrass receives light higher than its saturating irradiance (H(sat)), suggested positive C-balance in all stations. This was partly explained by photo-acclimatization of seagrass to the reduced light availability at the disturbed harbor stations (inner and intermediate), as indicated by the lengthening of H(sat) and the decrease in saturating irradiance (I(sat)) and respiratory demands. Despite photo-acclimatization, disturbed harbor stations showed less positive C-balance, seen not only in their lower leaf growth and biomass but also in a decrease in rhizome carbohydrate reserves (starch). Our results suggest that light reduction account for the reduced seagrass productivity and abundance. However, meadow decline (in terms of shoot mortality) in the harbor area is well above that predicted from similar light environments of nearby meadows or simulated in shading experiments. Thus, there are other factors than light limitation involved in seagrass mortality, most probably through more complex interactions (e.g. nutrient-epiphytes-grazers, water quality--siltation).

Alismatales↗
PubMed2006

Cytonuclear disequilibria in a spatially structured hybrid zone.

A hybrid zone model was developed that uses a stepping-stone model of population structure along with both nuclear and cytoplasmic genotypes to evaluate the effect that migration has on random mating organisms when no selection is present. Numerical simulations indicate that a number of different allele frequency and cytonuclear disequilibrium patterns can be found across the hybrid zone when it has reached equilibrium, and these results are discussed in the context of relative migration rates of the two sexes and the two source populations. The importance of numbers of subpopulations sampled, census time, and the persistence of pure species individuals into the hybrid zone are also discussed. Although this model does not consider selection or assortative mating in the hybrid zone, it should provide a useful baseline for evaluating joint cytonuclear genetic data from a structurally complex hybrid zone.

Animals↗
PubMed2005

The detection of motion in chromatic stimuli: first-order and second-order spatial structure.

This study provides evidence for the existence of a low-level chromatic motion mechanism and further elucidates the conditions under which its operation becomes measurable in an experimental stimulus. Observers discriminated the direction of motion of amplitude modulated (AM) gratings that were defined by luminance or chromatic variation and masked with spatiotemporally broadband luminance or chromatic noise. The size and retinal location of the stimuli were varied and the effects of broadband noise and grating masks were both compared with the cohort of stimuli. Some significant disparities in the published literature were well explained by the results. In conclusion, evidence for a chromatically sensitive motion mechanism that evades the, detrimental effects of a luminance mask was found only at the fovea and only when the stimulus was small and centrally placed.

Color Perception↗
PubMed1986

A part of codon bias in genes protects protein spatial structures from destabilization by random single point mutations.

Relationships are examined, using a primitive approximation, between the known general codon bias in genes and resistance of protein tertiary structure to destabilization by random single point mutations. A correlation of these two properties is found in the case of the first codon position while the second and third codon positions are evidently used for other purposes. This study suggests a separation of roles of the particular codon positions in the translation of the genetic message.

Base Sequence↗
PubMed1999

Spatial structures of the bradykinin potentiating peptide F from Agkistrodon piscivorus piscivoris venom.

Bradykinin potentiating peptides usually show two different activities, potentiation of bradykinin and inhibition of angiotensin converting enzyme (ACE). Exceptions of this rule have been found suggesting that both effects occur independently. This study of peptide F by means of NMR spectroscopy shows clearly two different main conformations of the molecule. These different conformations may be the reason for the different activities.

Agkistrodon↗
PubMed2006

Spatial structure of Au8: Importance of basis set completeness and geometry relaxation.

The relative stabilities of the lowest energy structures are calculated for the gold octamer, Au8, employing highly correlated ab initio methods. The question of dimensionality of these clusters is addressed, and a guideline for future structural studies of such systems is provided. In particular, the importance of geometry relaxation beyond the MP2 level of theory as well as the need for basis sets toward the complete limit (CBS) are discussed. The planar D(4h) symmetric structure of Au8 is the lowest energy structure. At the CCSD(T)/CBS limit, it is separated by 16 kJ mol(-1) from the next higher Td symmetric isomer.

Journal Article↗
PubMed2003

Influence of spatial structure on genetic isolation in Plebejus argus populations (Lepidoptera: Lycaenidae).

Populations of Plebejus argus were sampled in southwest Finland, both on the mainland and on islands, and in and around the Doñana National Park in southwest Spain. A total of 453 individuals coming from 14 locations were investigated using allozyme electrophoresis on a total of 10 polymorphic allozyme loci. Contrary to earlier studies, all conducted in Britain, our samples showed little differentiation between sampled locations. In Spain, the populations of the Donaña area showed no differentiation despite being up to 36 km apart; only the population to the south of the Guadalquivir river showed a significant difference to the others. In Finland the population on one island showed marked genetic differentiation from all the others, which showed little or no difference from each other. No isolation-by-distance effect could be detected in either system. We hypothesise that emigration-immigration events are more frequent in the Spanish and Finnish populations than in the British ones. We did, however, find two isolated populations, one in Spain and one in Finland; both were small and geographically isolated and shared evident drift.

Animals↗