The surface area-to-volume ratio of cells is one of the key factors affecting fundamental biological processes and, thus, fitness of unicellular organisms. One of the general models for allometric increase in surface-to-volume scaling involves fractal-like elaboration of cellular surfaces. However, specific data illustrating this pattern in natural populations of the unicellular organisms have not previously been available. This study shows that unicellular green algae of the genus Micrasterias (Desmidiales) have positive allometric surface-to-volume scaling caused by changes in morphology of individual species, especially in the degree of cell lobulation. This allometric pattern was also detected within most of the cultured and natural populations analysed. Values of the allometric S:V scaling within individual populations were closely correlated to the phylogenetic structure of the clade. In addition, they were related to species-specific cellular morphology. Individual populations differed in their allometric patterns, and their position in the allometric space was strongly correlated with the degree of allometric S:V scaling. This result illustrates that allometric shape patterns are an important correlate of the capacity of individual populations to compensate for increases in their cell volumes by increasing the surface area. However, variation in allometric patterns was not associated with phylogenetic structure. This indicates that the position of the populations in the allometric space was not evolutionarily conserved and might be influenced by environmental factors.
- Keywords
- Desmidiales, allometry, geometric morphometrics, green algae, surface-to-volume-scaling,
- MeSH
- Phylogeny MeSH
- Micrasterias classification cytology genetics MeSH
- Regression Analysis MeSH
- RNA, Ribosomal, 18S genetics MeSH
- Cell Size MeSH
- Publication type
- Journal Article MeSH
- Names of Substances
- RNA, Ribosomal, 18S MeSH
The metabolic theory of ecology (MTE) predicts the ubiquity of the of 3/4 scaling exponent relating metabolic rate (MR) to body mass, as well as cell-size invariance coupled with body-size dependence of cellular MR in quickly dividing cells. An alternative prediction is that MR scales interspecifically with a coefficient that is between 2/3 and 1, depending on the cell size and cell MR, which is mostly driven by the cell surface-to-volume ratio. We tested (1) the contribution of cell size to interspecific differences in MR and (2) whether the cell size-MR relationship is mediated by genome size (GS), which usually correlates positively with cell size. We tested (1) and (2) using erythrocyte area as a proxy for cell size in 14 eyelid geckos, which belong to a monophyletic group exhibiting large body-size variation. The scaling of standard MR (SMR) was significantly lower than 3/4, whereas mass-specific SMR correlated with erythrocyte area in both phylogenetically adjusted and conventional analyses. This points to cell-size variation as the factor governing metabolic rate scaling, which questions predictions of the MTE. However, the nonsignificance of the correlation between mass-specific SMR and GS undermines the strength of the relation between GS and cell size, at least in these species.
- MeSH
- Ecosystem * MeSH
- Genome MeSH
- Lizards metabolism MeSH
- Cell Size * MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Free energy profiles associated with transfer of chlorinated and brominated halomethane molecules from the gas phase across the water-vapor interface to the aqueous phase were calculated using classical molecular dynamics simulations. The investigated species include chloromethane (CH3Cl), bromomethane (CH3Br), dichloromethane (CH2Cl2), dibromomethane (CH2Br2), chloroform (CHCl3), and bromoform (CHBr3). The employed halomethane force field was tuned by scaling up the atomic charges to reproduce the experimental hydration free energies. The computed free energy profiles have a minimum at the water-vapor interface of about 12-15 kJ·mol(-1) relative to full hydration in the bulk liquid. This implies that the halomethanes exhibit enhanced interfacial concentrations in systems with large surface area per unit volume, such as air bubbles dispersed in water or water droplets dispersed in air. Implications for water treatment as well as for atmospheric chemistry are discussed.
- Publication type
- Journal Article MeSH
A procedure is introduced for measuring the radius of spherical colloid particles from the curvature of upper parts of their central cross-sectional profiles obtained by atomic force microscopy (AFM). To minimize the possible compression and displacement of the spheres, AFM is operated in a mode rendering a constant ultralow pN force on the tip. The procedure allows us to evaluate the mean radius of nearly monodisperse submicrometer spheres of silica in their natively hydrated state in aqueous electrolyte solutions, irrespective of whether they are coagulated or not. A variation in the volume (swelling degree) of layers delimited by the AFM mean radii of these spheres in KCl solutions and their invariable mean radius in vacuum is obtained that follows a scaling power law derived in polymer physics for swellable polyelectrolyte gels and deduced previously by us from coagulation tests. This supports our former suggestion about the existence of soft polyelectrolyte gel-like layer developed spontaneously around silica surfaces and colloids. We discuss this finding in the context of recent knowledge about the structure of the silica/water interface obtained from direct surface force measurements between macroscopic silica surfaces and from particle size measurements of silica colloids and highlight its importance for colloid chemistry and condensed mattter physics.
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Mitochondrial cristae expand the surface area of respiratory membranes and ultimately allow for the evolutionary scaling of respiration with cell volume across eukaryotes. The discovery of Mic60 homologs among alphaproteobacteria, the closest extant relatives of mitochondria, suggested that cristae might have evolved from bacterial intracytoplasmic membranes (ICMs). Here, we investigated the predicted structure and function of alphaproteobacterial Mic60, and a protein encoded by an adjacent gene Orf52, in two distantly related purple alphaproteobacteria, Rhodobacter sphaeroides and Rhodopseudomonas palustris. In addition, we assessed the potential physical interactors of Mic60 and Orf52 in R. sphaeroides. We show that the three α helices of mitochondrial Mic60's mitofilin domain, as well as its adjacent membrane-binding amphipathic helix, are present in alphaproteobacterial Mic60. The disruption of Mic60 and Orf52 caused photoheterotrophic growth defects, which are most severe under low light conditions, and both their disruption and overexpression led to enlarged ICMs in both studied alphaproteobacteria. We also found that alphaproteobacterial Mic60 physically interacts with BamA, the homolog of Sam50, one of the main physical interactors of eukaryotic Mic60. This interaction, responsible for making contact sites at mitochondrial envelopes, has been conserved in modern alphaproteobacteria despite more than a billion years of evolutionary divergence. Our results suggest a role for Mic60 in photosynthetic ICM development and contact site formation at alphaproteobacterial envelopes. Overall, we provide support for the hypothesis that mitochondrial cristae evolved from alphaproteobacterial ICMs and have therefore improved our understanding of the nature of the mitochondrial ancestor.
- Keywords
- Cereibacter, MICOS, Rhodobacter, Rhodopseudomonas, chromatophores, endosymbosis, eukaryogenesis, eukaryote, purple bacteria,
- MeSH
- Alphaproteobacteria * genetics metabolism MeSH
- Biological Evolution MeSH
- Mitochondrial Membranes metabolism MeSH
- Mitochondrial Proteins * metabolism MeSH
- Mitochondria metabolism MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Names of Substances
- Mitochondrial Proteins * MeSH
The presence of a multitude of bioactive organic pollutants collectively classified as pharmaceuticals and personal care products (PPCPs) in freshwaters is of concern, considering that ecological assessments of their potential impacts on natural systems are still scarce. In this field experiment we tested whether a single pulse exposure to a mixture of 12 pharmaceuticals and personal care products, which are commonly found in European inland waters, can influence the size distributions of natural lake phytoplankton communities. Size is one of the most influential determinants of community structure and functioning, particularly in planktonic communities and food webs. Using an in-situ microcosm approach, phytoplankton communities in two lakes with different nutrient levels (mesotrophic and eutrophic) were exposed to a concentration gradient of the PPCPs mixture at five levels. We tested whether sub-lethal PPCPs doses affect the scaling of organisms' abundances with their size, and the slope of these size spectra, which describe changes in the abundances of small relative to large phytoplankton. Our results showed that a large proportion (approximately 80%) of the dataset followed a power-law distribution, thus suggesting evidence of scale invariance of abundances, as expected in steady state ecosystems. PPCPs were however found to induce significant changes in the size spectra and community structure of natural phytoplankton assemblages. The two highest treatment levels of PPCPs were associated with decreased abundance of the most dominant size class (nano-phytoplankton: 2-5 μm), leading to a flattening of the size spectra slope. These results suggest that a pulse exposure to PPCPs induce changes that potentially lead to unsteady ecosystem states and cascading effects in the aquatic food webs, by favoring larger non-edible algae at the expense of small edible species. We propose higher susceptibility due to higher surface to volume ratio in small species as the likely cause of these structural changes.
- Keywords
- Field experiment, Micropollutants, Pharmaceutical and personal care products (PPCPs), Phytoplankton communities, Scaling law, Size abundance relationship,
- MeSH
- Water Pollutants, Chemical analysis MeSH
- Ecosystem * MeSH
- Phytoplankton physiology MeSH
- Lakes chemistry MeSH
- Environmental Monitoring * MeSH
- Food Chain MeSH
- Publication type
- Journal Article MeSH
- Names of Substances
- Water Pollutants, Chemical MeSH
The secretory cells of the ampullar part of bovine oviduct are characterized by the secretory granules in cytoplasm. Their apical surface is covered with a small amount of micro-villi. Among the organellae, the Golgi apparatus is well-marked: during the sexual cycle it produces several centres. Its volume and surface reach their maxima before ovulation. The mitochondria are large and have a smaller amount of cristae. Their number culminates in pro-oestrus and their volume and surface area in metoestrus. The tubuli of granulated endoplasmic reticulum dilate during pro-oestrus and oestrus and some of them later disintegrate. They reach the largest volume and surface in pro-oestrus when the highest number of polyribosomes also occurs. Secretory granules are produced throughout the cycle as low-density spherical corpuscles covered with a simple membrane: in the course of maturation they change into high-density corpuscles and some of them break down. Their number and volume culminate in metoestrus when they are secreted on a mass scale. The population of secretory cells is heterogeneous. Besides dense and light cells, thin granules. Some cells lose contact with the basal membrane and their extrusion occurs mainly during metoestrus.
- MeSH
- Cytoplasmic Granules ultrastructure MeSH
- Epithelium ultrastructure MeSH
- Estrus * MeSH
- Cattle anatomy & histology MeSH
- Pregnancy MeSH
- Fallopian Tubes ultrastructure MeSH
- Animals MeSH
- Check Tag
- Cattle anatomy & histology MeSH
- Pregnancy MeSH
- Female MeSH
- Animals MeSH
- Publication type
- English Abstract MeSH
- Journal Article MeSH
Tri-beam microscopes comprising a fs-laser beam, a Xe+ plasma focused ion beam (PFIB) and an electron beam all in one chamber open up exciting opportunities for site-specific correlative microscopy. They offer the possibility of rapid ablation and material removal by fs-laser, subsequent polishing by Xe-PFIB milling and electron imaging of the same area. While tri-beam systems are capable of probing large (mm) volumes providing high resolution microscopical characterisation of 2D and 3D images across exceptionally wide range of materials and biomaterials applications, presenting high quality/low damage surfaces to the electron beam can present a significant challenge, especially given the large parameter space for optimisation. Here the optimal conditions and artefacts associated with large scale volume milling, mini test piece manufacture, serial sectioning and surface polishing are investigated, both in terms of surface roughness and surface quality for metallic, ceramic, mixed complex phase, carbonaceous, and biological materials. This provides a good starting place for those wishing to examine large areas or volumes by tri-beam microscopy across a range of materials.
The aim of this study was to determine whether capillarity in the denervated and reinnervated rat extensor digitorum longus muscle (EDL) is scaled by muscle fiber oxidative potential. We visualized capillaries adjacent to a metabolically defined fiber type and estimated capillarity of fibers with very high oxidative potential (O) vs fibers with very low oxidative potential (G). Capillaries and muscle fiber types were shown by a combined triple immunofluorescent technique and the histochemical method for NADH-tetrazolium reductase. Stacks of images were captured by a confocal microscope. Applying the Ellipse program, fibers were outlined, and the diameter, perimeter, cross-sectional area, length, surface area, and volume within the stack were calculated for both fiber types. Using the Tracer plug-in module, capillaries were traced within the three-dimensional (3D) volume, the length of capillaries adjacent to individual muscle fibers was measured, and the capillary length per fiber length (Lcap/Lfib), surface area (Lcap/Sfib), and volume (Lcap/Vfib) were calculated. Furthermore, capillaries and fibers of both types were visualized in 3D. In all experimental groups, O and G fibers significantly differed in girth, Lcap/Sfib, and Lcap/Vfib, but not in Lcap/Lfib. We conclude that capillarity in the EDL is scaled by muscle fiber size and not by muscle fiber oxidative potential.
- MeSH
- Muscle Denervation MeSH
- Histocytochemistry MeSH
- Capillaries anatomy & histology MeSH
- Microscopy, Confocal MeSH
- Muscle Fibers, Skeletal metabolism MeSH
- Muscle, Skeletal blood supply innervation metabolism MeSH
- Rats MeSH
- Oxidation-Reduction MeSH
- Rats, Wistar MeSH
- Imaging, Three-Dimensional MeSH
- Animals MeSH
- Check Tag
- Rats MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Fluid manipulation on the micro-scale (microfluidics) is bringing new potential applications in a number of fields, including chemistry, biology and medicine. At sub-millimeter channel scale, some phenomena, unimportant at the macroscale, become an important force to consider when designing a microfluidics system. For example, the decrease in fluid mass causes the effects of viscosity to overcome the influence of inertia. Turbulent flow cannot be achieved at any realistic fluid velocity, making mixing a challenging task. The only phenomenon capable of blending liquids at microscale is diffusion and liquid streams can be flowed side-by-side for tens of minutes before they completely fuse together. The decrease in the channel size also leads to an increased surface-to-volume ratio, which increases the importance of surface effects, including adsorption, capillary action and surface wetting and/or electric double layer formation with related electrokinetic phenomena. While rivers cannot flow uphill, a stream of liquid can easily flow up against gravity inside a capillary. Similarly, the formation of electric double layer near the charged surface of a micro-channel or capillary can be applied for electrokinetic actuating. This review summarizes selected physical phenomena related to liquid-based (water solutions) microfluidics as described recently.
- Keywords
- Electrokinetics, Micro-mixers, Microfluidics, Surface effects,
- MeSH
- Adsorption MeSH
- Diffusion MeSH
- Capillary Action MeSH
- Microfluidics * MeSH
- Water chemistry MeSH
- Publication type
- Journal Article MeSH
- Review MeSH
- Names of Substances
- Water MeSH
