FtsZ-Ring Regulation and Cell Division Are Mediated by Essential EzrA and Accessory Proteins ZapA and ZapJ in Streptococcus pneumoniae

The bacterial FtsZ-ring initiates division by recruiting a large repertoire of proteins (the divisome; Z-ring) needed for septation and separation of cells. Although FtsZ is essential and its role as the main orchestrator of cell division is conserved in most eubacteria, the regulators of Z-ring presence and positioning are not universal. This study characterizes factors that regulate divisome presence and placement in the ovoid-shaped pathogen, Streptococcus pneumoniae (Spn), focusing on FtsZ, EzrA, SepF, ZapA, and ZapJ, which is reported here as a partner of ZapA. Epi-fluorescence microscopy (EFm) and high-resolution microscopy experiments showed that FtsZ and EzrA co-localize during the entire Spn cell cycle, whereas ZapA and ZapJ are late-arriving divisome proteins. Depletion and conditional mutants demonstrate that EzrA is essential in Spn and required for normal cell growth, size, shape homeostasis, and chromosome segregation. Moreover, EzrA(Spn) is required for midcell placement of FtsZ-rings and PG synthesis. Notably, overexpression of EzrA leads to the appearance of extra Z-rings in Spn. Together, these observations support a role for EzrA as a positive regulator of FtsZ-ring formation in Spn. Conversely, FtsZ is required for EzrA recruitment to equatorial rings and for the organization of PG synthesis. In contrast to EzrA depletion, which causes a bacteriostatic phenotype in Spn, depletion of FtsZ results in enlarged spherical cells that are subject to LytA-dependent autolysis. Co-immunoprecipitation and bacterial two-hybrid assays show that EzrA(Spn) is in complexes with FtsZ, Z-ring regulators (FtsA, SepF, ZapA, MapZ), division proteins (FtsK, StkP), and proteins that mediate peptidoglycan synthesis (GpsB, aPBP1a), consistent with a role for EzrA at the interface of cell division and PG synthesis. In contrast to the essentiality of FtsZ and EzrA, ZapA and SepF have accessory roles in regulating pneumococcal physiology. We further show that ZapA interacts with a non-ZapB homolog, named here as ZapJ, which is conserved in Streptococcus species. The absence of the accessory proteins, ZapA, ZapJ, and SepF, exacerbates growth defects when EzrA is depleted or MapZ is deleted. Taken together, these results provide new information about the spatially and temporally distinct proteins that regulate FtsZ-ring organization and cell division in Spn.

Tuning spherical cells into kinking helices in wall-less bacteria

In bacteria, cell shape is determined and maintained through a complex interplay between the peptidoglycan cell wall and cytoplasmic filaments made of polymerized MreB. Spiroplasma species, members of the Mollicutes class, challenge this general understanding because they are characterized by a helical cell shape and motility without a cell wall. This specificity is thought to rely on five MreB isoforms and a specific fibril protein. In this study, combinations of these five MreBs and of the fibril from Spiroplasma citri were expressed in another Mollicutes, Mycoplasma capricolum. Mycoplasma cells that were initially pleomorphic, mostly spherical, turned into helices when MreBs and fibrils were expressed in this heterologous host. The fibril protein was essential neither for helicity nor for cell movements. The isoform MreB5 had a special role as it was sufficient to confer helicity and motility to the mycoplasma cells. Cryo-electron microscopy confirmed the association of MreBs and fibril-based cytoskeleton with the plasma membrane, suggesting a direct effect on the membrane curvature. Finally, the heterologous expression of these proteins, MreBs and fibril, made it possible to reproduce the kink-like motility of spiroplasmas without providing the ability of cell movement in liquid broth. We suggest that other Spiroplasma components, not yet identified, are required for swimming, a hypothesis that could be evaluated in future studies using the same model.

Effect of the Processing Parameters on the Fabrication of MgAl2O4 Foams

Stable MgAl2O4 foams (7–21 vol.%) were manufactured using a natural extract from the pericarp of the soap-nut fruit, saponin being the main component, as the foaming agent. The soap-nut extract is soluble in water, biodegradable, non-toxic, and has similar properties to commercial tensoactives. The stability and characteristics of the porous structure of the ceramic foams were evaluated in terms of the amount of foaming agent, content of MgAl2O4 particles, time and speed of stirring of the slurry, type of agitator, and drying temperature. It was found that the foaming capacity decreased with the percent of foaming agent and ceramic, whereas the time and speed of stirring enhanced the foamability. Foaming trials showed that stirring aqueous slurries with 3 wt.% of soap-nut extract for 2 min at 1070 or 2120 rpm, depending on the type of agitator, produced stable MgAl2O4 foams when drying at 60 °C. The mechanism of foaming is discussed. The foams were sintered at 1400 °C for 1 h under an Ar atmosphere. Observation of the sintered foam structures in the scanning electron microscope revealed nearly spherical cells with very good interconnectivity and strength to be manipulated, making them suitable as preforms for manufacturing Al-based composites by pressureless infiltration.

SEM Analyses of Fossilized Chondrocytes in the Extinct Birds Yanornis and Confuciusornis: Insights on Taphonomy and Modes of Preservation in the Jehol Biota

Calcified cartilage is a vertebrate tissue that has unique characteristics, such as a high percentage of calcification, avascularity and cells with apparently delayed autolytic processes after death. All of these factors suggest that fossilized cartilage may be favorable to exceptional cellular preservation, but little is known about chondrocyte fossilization overall in vertebrate paleontology. To further understand the spectrum of cellular preservation in this tissue, we analyze the morphology and the chemistry of some intralacunar content seen in previously published avian cartilage from the Early Cretaceous Jehol biota (in Yanornis and Confuciusornis). For this, we combine standard paleohistology with Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). To better identify some fossilized structures, we compare them with experimentally decayed and biofilm-invaded avian cartilage. Histological images of the cartilage of Yanornis show structures that resemble cell nuclei within chondrocyte lacunae. An SEM analysis on this cartilage shows that some lacunae are filled with a type of in vivo mineralization (similar to micropetrotic lacunae) and others are filled with small and spherical silicified cells surrounded by an amorphous carbonaceous material. These silicified cells apparently underwent postmortem cell shrinkage and do not constitute cell nuclei. Confuciusornis shows filamentous, non-spherical cells that are mostly made of silicon and carbon. This cell morphology does not resemble that of typical healthy chondrocytes, but based on comparison with decaying, biofilm-infiltrated chondrocyte lacunae from extant material, the most plausible conclusion is that the cells of Confuciusornis were partially autolyzed prior to their mineralization. In Yanornis and Confuciusornis respectively, silicification and alumino-silicification were responsible for chondrocyte preservation; while alumino-silicification and ironization occurred in their soft tissues. This shows that alumino-silicification is quite a common mechanism of cellular and soft-tissue preservation in the Jehol biota. Moreover, the two different chondrocyte morphologies (spherical and filamentous) apparently reflect two taphonomical histories, including different timings of postmortem permineralization (one rapid and one much more delayed). This type of analysis paired with more actuotaphonomy experiments will be needed in the future to better understand the preservation potential of chondrocytes and other cell types in the fossil record.

Histological Study of the Male Internal Genital Tract of Dwarf Caiman (Paleosuchus palpebrosus Cuvier, 1807)

Brazil has six species of crocodiles belonging to the subfamily Caimaninae,one of them being Paleosuchus palpebrosus (Cuvier, 1807) (dwarf caiman).It is considered one of the smallest crocodilian species, and is sensitive toenvironmental changes. The anatomical and histological descriptions ofthe reproductive tract of reptiles are scarce, so it is important to study themorphology of the genital tract of caimans for a better understanding of thereproduction of these species. We performed the histological analysis of thetestis, epididymis, and deferent duct of the dwarf caiman Paleosuchus palpebrosus. Structures of the genital tract were collected from euthanized animals. Testes, epididymis, and deferent ducts were separated and preparedaccording to routine histological techniques for morphological characterization. The testis is covered by a capsule of fibromuscular connective tissue.Spermatogonia are observed as spherical cells with round nuclei and loosechromatin, and primary spermatocytes show dark cytoplasm, round nuclei,and pale chromatin. Spermatids are seen as cylindrical or filamentous cellswith nuclei that may be highly condensed, ranging from round to oval. Theepididymis is observed as a coiled duct lined by a tall cuboidal epitheliumwith stereocilia; the deferent duct shows ciliated pseudostratified cylindrical epithelium. The adrenal gland is found in the dorsomedial portion of thetestis. The histological structure of the reproductive tract of Paleosuchuspalpebrosus is similar to that of other reptiles’species.

Effect of Precursor Design on Preparing Open-Cell Aluminum Foam Fabricated by Space-Holder Method

Open-cell aluminum foams with spherical cells have great potential application due to their reliable structural and functional performance. However, a problem of poor cell connectivity always arises during fabrication. Three precursor designs were explored to optimize the cell structure. The results showed that the lack of the treatment of the space holders caused poor cell connectivity and a lower porosity, which could be resolved by introducing alcohol as a binder or hot-pressing space holders in precursor designs. Nevertheless, a poor fluid of the granules in the former had a negative effect on porosity improvement, whereas the latter created a precursor with strong bonding between the granules with good flow characteristics and led to a significant improvement in cell connectivity and porosity. This work could provide an approach to designing precursor structures in order to tailor the structure of the final open-cell aluminum foam.

К ВОПРОСУ ФИЗИЧЕСКОГО ОБОСНОВАНИЯ КРИТЕРИЕВ ЕДИНОЙ ТЕОРИИ ФИЗИКИ

With the help of harmonic analysis of different-scale finite element models of cubic and spherical cells, a physical substantiation of possible criteria for a unified theory of physics is presented, which consists in the fact that both with a decrease in cells from macroscopic to mesostatic and down to microscopic levels of deformation, and with an increase in cells from macroscopic to megascopic level, periodic changes in the number of resonance peaks of the deformation parameters of the cells are observed, which can explain various characteristic physical phenomena at different scale levels of deformation.

Microfluidic capillary networks are more sensitive than ektacytometry to the decline of red blood cell deformability induced by storage

Ektacytometry has been the primary method for evaluating deformability of red blood cells (RBCs) in both research and clinical settings. This study was designed to test the hypothesis that the flow of RBCs through a network of microfluidic capillaries could provide a more sensitive assessment of the progressive impairment of RBC deformability during hypothermic storage than ektacytometry. RBC units (n = 9) were split in half, with one half stored under standard (normoxic) conditions and the other half stored hypoxically, for up to 6 weeks. RBC deformability was measured weekly using two microfluidic devices, an artificial microvascular network (AMVN) and a multiplexed microcapillary network (MMCN), and two commercially available ektacytometers (RheoScan-D and LORRCA). By week 6, the elongation indexes measured with RheoScan-D and LORRCA decreased by 5.8–7.1% (5.4–6.9% for hypoxic storage). Over the same storage duration, the AMVN perfusion rate declined by 27.5% (24.5% for hypoxic) and the MMCN perfusion rate declined by 49.0% (42.4% for hypoxic). Unlike ektacytometry, both AMVN and MMCN measurements showed statistically significant differences between the two conditions after 1 week of storage. RBC morphology deteriorated continuously with the fraction of irreversibly-damaged (spherical) cells increasing significantly faster for normoxic than for hypoxic storage. Consequently, the number of MMCN capillary plugging events and the time MMCN capillaries spent plugged was consistently lower for hypoxic than for normoxic storage. These data suggest that capillary networks are significantly more sensitive to both the overall storage-induced decline of RBC deformability, and to the differences between the two storage conditions, than ektacytometry.