A thermophilic syntrophic bacterium, Pelotomaculum thermopropionicum strain SI, was grown in a monoculture or coculture with a hydrogenotrophic methanogen, Methanothermobacter thermautotrophicus strain ⌬H. Microscopic observation revealed that cells of each organism were dispersed in a monoculture independent of the growth substrate. In a coculture, however, these organisms coaggregated to different degrees depending on the substrate; namely, a large fraction of the cells coaggregated when they were grown on propionate, but relatively few cells coaggregated when they were grown on ethanol or 1-propanol. Field emission-scanning electron microscopy revealed that flagellum-like filaments of SI cells played a role in making contact with ⌬H cells. Microscopic observation of aggregates also showed that extracellular polymeric substance-like structures were present in intercellular spaces. In order to evaluate the importance of coaggregation for syntrophic propionate oxidation, allowable average distances between SI and ⌬H cells for accomplishing efficient interspecies hydrogen transfer were calculated by using Fick's diffusion law. The allowable distance for syntrophic propionate oxidation was estimated to be approximately 2 m, while the allowable distances for ethanol and propanol oxidation were 16 m and 32 m, respectively. Considering that the mean cell-to-cell distance in the randomly dispersed culture was approximately 30 m (at a concentration in the mid-exponential growth phase of the coculture of 5 ؋ 10 7 cells ml ؊1 ), it is obvious that close physical contact of these organisms by coaggregation is indispensable for efficient syntrophic propionate oxidation.In anaerobic digestors, organic matter is converted to methane and CO 2 via various intermediates (1, 27). Among the most important intermediate metabolites are volatile fatty acids (VFAs), such as acetate, propionate, and butyrate, and it has been reported that accumulation of VFAs results in a significant decrease in the methane production efficiency in such digestors (16,17,37,38). VFAs are, however, unfavorable substrates for anaerobes, since oxidation of these substrates to H 2 and CO 2 (or formate) is endoergonic under standard conditions (i.e., the changes in the Gibbs free energy are positive [⌬G°Ј Ͼ 0]) (Table 1) and is thermodynamically feasible only when the H 2 partial pressure (or formate concentration) is kept low (3,11,29,34). For instance, thermodynamic estimation has predicted that H 2 partial pressures as low as 10 Pa and 100 Pa are necessary for the oxidation of propionate and butyrate, respectively (29, 34). Since H 2 and formate are scavenged mainly by the carbonate respiration of methanogenic archaea, syntrophic association of VFA-oxidizing bacteria (called syntrophs) and methanogenic archaea is considered indispensable for efficient VFA oxidation (27, 36).As described previously, syntrophic VFA oxidation depends on interspecies electron (as H 2 and formate) transfer. Researchers have suggested that close physical contact between syntro...

Endothelial glycocalyx coats healthy vascular endothelium and plays an important role in vascular homeostasis. Although cerebral capillaries are categorized as continuous, as are those in the heart and lung, they likely have specific features related to their function in the blood brain barrier. To test that idea, brains, hearts and lungs from C57BL6 mice were processed with lanthanum-containing alkaline fixative, which preserves the structure of glycocalyx, and examined using scanning and transmission electron microscopy. We found that endothelial glycocalyx is present over the entire luminal surface of cerebral capillaries. The percent area physically covered by glycocalyx within the lumen of cerebral capillaries was 40.1 ± 4.5%, which is significantly more than in cardiac and pulmonary capillaries (15.1 ± 3.7% and 3.7 ± 0.3%, respectively). Upon lipopolysaccharide-induced vascular injury, the endothelial glycocalyx was reduced within cerebral capillaries, but substantial amounts remained. By contrast, cardiac and pulmonary capillaries became nearly devoid of glycocalyx. These findings suggest the denser structure of glycocalyx in the brain is associated with endothelial protection and may be an important component of the blood brain barrier.

BackgroundSugar-protein glycocalyx coats healthy endothelium, but its ultrastructure is not well described. Our aim was to determine the three-dimensional ultrastructure of capillary endothelial glycocalyx in the heart, kidney, and liver, where capillaries are, respectively, continuous, fenestrated, and sinusoidal.MethodsTissue samples were processed with lanthanum-containing alkaline fixative, which preserves the structure of glycocalyx.ResultsScanning and transmission electron microscopy revealed that the endothelial glycocalyx layer in continuous and fenestrated capillaries was substantially thicker than in sinusoids. In the heart, the endothelial glycocalyx presented as moss- or broccoli-like and covered the entire luminal endothelial cell surface. In the kidney, the glycocalyx appeared to nearly occlude the endothelial pores of the fenestrated capillaries and was also present on the surface of the renal podocytes. In sinusoids of the liver, glycocalyx covered not only the luminal side but also the opposite side, facing the space of Disse. In a mouse lipopolysaccharide-induced experimental endotoxemia model, the capillary endothelial glycocalyx was severely disrupted; that is, it appeared to be peeling off the cells and clumping. Serum concentrations of syndecan-1, a marker of glycocalyx damage, were significantly increased 24 h after administration of lipopolysaccharide.ConclusionsIn the present study, we visualized the three-dimensional ultrastructure of endothelial glycocalyx in healthy continuous, fenestrated, and sinusoidal capillaries, and we also showed their disruption under experimental endotoxemic conditions. The latter may provide a morphological basis for the microvascular endothelial dysfunction associated with septic injury to organs.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-017-1841-8) contains supplementary material, which is available to authorized users.