scholarly journals Localized Peptidoglycan Biosynthesis in Chlamydia trachomatis Conforms to the Polarized Division and Cell Size Reduction Developmental Models

2021 ◽  
Vol 12 ◽  
Author(s):  
George W. Liechti
Keyword(s):  
Cell Size ◽  
Cell Envelope ◽  
Bacterial Species ◽  
Imaging Study ◽  
Developmental Cycle ◽  
Average Cell ◽  
Division Plane ◽  
Developmental Models ◽  
Bacterial Membranes ◽  
Average Decrease

Cell size regulation in bacteria is a function of two basic cellular processes: the expansion of the cell envelope and its constriction at spatially defined points at what will eventually become the division plane. In most bacterial species, both cell wall expansion and restriction are dependent on peptidoglycan (PG), a structural polymer comprised of sugars and amino acids that imparts strength and rigidity to bacterial membranes. Pathogenic Chlamydia species are unique in that their cell walls contain very little PG, which is restricted almost entirely to the apparent division plane of the microbe’s replicative forms. Very little is known about the degree to which PG affects the size and shape of C. trachomatis during its division process, and recent studies suggest the process is initiated via a polarized mechanism. We conducted an imaging study to ascertain the dimensions, orientation, and relative density of chlamydial PG throughout the organism’s developmental cycle. Our analysis indicates that PG in replicating C. trachomatis can be associated with four, broad structural forms; polar/septal disks, small/thick rings, large rings, and small/thin rings. We found that PG density appeared to be highest in septal disks and small/thick rings, indicating that these structures likely have high PG synthesis to degradation ratios. We also discovered that as C. trachomatis progresses through its developmental cycle PG structures, on average, decrease in total volume, indicating that the average cell volume of chlamydial RBs likely decreases over time. When cells infected with C. trachomatis are treated with inhibitors of critical components of the microbe’s two distinct PG synthases, we observed drastic differences in the ratio of PG synthesis to degradation, as well as the volume and shape of PG-containing structures. Overall, our results suggest that C. trachomatis PG synthases differentially regulate the expansion and contraction of the PG ring during both the expansion and constriction of the microbe’s cell membrane during cell growth and division, respectively.

Characterization of microstructures of SAN foam core using micro-computed tomography

2021 ◽  
pp. 026248932110068
Author(s):  
Youming Chen ◽  
Raj Das ◽  
Hui Wang ◽  
Mark Battley
Keyword(s):  
Cell Wall ◽  
Cell Size ◽  
Wall Thickness ◽  
Strain Localization ◽  
Cell Wall Thickness ◽  
Micro Computed Tomography ◽  
Average Cell Size ◽  
Average Cell ◽  
3D Images ◽  
Compressive Tests

In this study, the microstructure of a SAN foam was imaged using a micro-CT scanner. Through image processing and analysis, variations in density, cell wall thickness and cell size in the foam were quantitatively explored. It is found that cells in the foam are not elongated in the thickness (or rise) direction of foam sheets, but rather equiaxed. Cell walls in the foam are significantly straight. Density, cell size and cell wall thickness all vary along the thickness direction of foam sheets. The low density in the vicinity of one face of foam sheets leads to low compressive stiffness and strength, resulting in the strain localization observed in our previous compressive tests. For M80, large open cells on the top face of foam sheets are likely to buckle in compressive tests, therefore being another potential contributor to the strain localization as well. The average cell wall thickness measured from 2D slice images is around 1.4 times that measured from 3D images, and the average cell size measured from 2D slice images is about 13.8% smaller than that measured from 3D images. The dispersions of cell wall thickness measured from 2D slice images are 1.16–1.20 times those measured from 3D images. The dispersions of cell size measured from 2D slice images are 1.12–1.36 times those measured from 3D images.

The effect of organofluorine additives on the morphology, thermal conductivity and mechanical properties of rigid polyurethane and polyisocyanurate foams

2021 ◽  
pp. 0021955X2098715
Author(s):  
Cosimo Brondi ◽  
Ernesto Di Maio ◽  
Luigi Bertucelli ◽  
Vanni Parenti ◽  
Thomas Mosciatti
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Cell Size ◽  
Flexural Properties ◽  
Anisotropy Ratio ◽  
Cell Content ◽  
Average Cell Size ◽  
Average Cell ◽  
Thermal Insulating ◽  
Liquid Type

This study investigates the effect of liquid-type organofluorine additives (OFAs) on the morphology, thermal conductivity and mechanical properties of rigid polyurethane (PU) and polyisocyanurate (PIR) foams. Foams were characterized in terms of their morphology (density, average cell size, anisotropy ratio, open cell content), thermal conductivity and compressive as well as flexural properties. Based on the results, we observed that OFAs efficiently reduced the average cell size of both PU and PIR foams, leading to improved thermal insulating and mechanical properties.

scholarly journals RNA G-Quadruplex Structures Mediate Gene Regulation in Bacteria

mBio ◽  
2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Xiaolong Shao ◽  
Weitong Zhang ◽  
Mubarak Ishaq Umar ◽  
Hei Yuen Wong ◽  
Zijing Seng ◽  
...  
Keyword(s):  
Gene Regulation ◽  
Cell Envelope ◽  
Bacterial Species ◽  
Virulence Gene ◽  
Content Type ◽  
Cellular Processes ◽  
Wide Range ◽  
G Quadruplex ◽  
Eukaryotic Organisms

ABSTRACT Guanine (G)-rich sequences in RNA can fold into diverse RNA G-quadruplex (rG4) structures to mediate various biological functions and cellular processes in eukaryotic organisms. However, the presence, locations, and functions of rG4s in prokaryotes are still elusive. We used QUMA-1, an rG4-specific fluorescent probe, to detect rG4 structures in a wide range of bacterial species both in vitro and in live cells and found rG4 to be an abundant RNA secondary structure across those species. Subsequently, to identify bacterial rG4 sites in the transcriptome, the model Escherichia coli strain and a major human pathogen, Pseudomonas aeruginosa, were subjected to recently developed high-throughput rG4 structure sequencing (rG4-seq). In total, 168 and 161 in vitro rG4 sites were found in E. coli and P. aeruginosa, respectively. Genes carrying these rG4 sites were found to be involved in virulence, gene regulation, cell envelope synthesis, and metabolism. More importantly, biophysical assays revealed the formation of a group of rG4 sites in mRNAs (such as hemL and bswR), and they were functionally validated in cells by genetic (point mutation and lux reporter assays) and phenotypic experiments, providing substantial evidence for the formation and function of rG4s in bacteria. Overall, our study uncovers important regulatory functions of rG4s in bacterial pathogenicity and metabolic pathways and strongly suggests that rG4s exist and can be detected in a wide range of bacterial species. IMPORTANCE G-quadruplex in RNA (rG4) mediates various biological functions and cellular processes in eukaryotic organisms. However, the presence, locations, and functions of rG4 are still elusive in prokaryotes. Here, we found that rG4 is an abundant RNA secondary structure across a wide range of bacterial species. Subsequently, the transcriptome-wide rG4 structure sequencing (rG4-seq) revealed that the model E. coli strain and a major human pathogen, P. aeruginosa, have 168 and 161 in vitro rG4 sites, respectively, involved in virulence, gene regulation, cell envelope, and metabolism. We further verified the regulatory functions of two rG4 sites in bacteria (hemL and bswR). Overall, this finding strongly suggests that rG4s play key regulatory roles in a wide range of bacterial species.

Growth and Cell-Size Distribution of Marine Planktonic Algae in Batch and Dialysis Cultures

1973 ◽  
Vol 30 (2) ◽  
pp. 143-155 ◽  
Author(s):  
A. Prakash ◽  
Liv Skoglund ◽  
Britt Rystad ◽  
Arne Jensen
Keyword(s):  
Size Distribution ◽  
Cell Size ◽  
Growth Cycle ◽  
Exponential Growth Phase ◽  
Average Cell Size ◽  
Cell Size Distribution ◽  
Average Cell ◽  
Planktonic Algae ◽  
Maximum Cell ◽  
Dialysis Culture

An extended exponential growth phase and a higher maximum population characterized growth of planktonic algae in a dialysis system compared with that in a batch system. Algal cells grown in a dialysis culture had higher chlorophyll content and a larger average cell size than those grown in a batch culture. In both types of culture, changes in cell-size distribution were related to the phases of the growth cycle with maximum cell-size during the stationary phase. Various interactions of the component reactions of photosynthesis leading to changes in growth pattern and cell-size distribution are discussed.

scholarly journals Mycobacterium tuberculosis Rv2700 Contributes to Cell Envelope Integrity and Virulence

2019 ◽  
Vol 201 (19) ◽  
Author(s):  
Edward R. Ballister ◽  
Marie I. Samanovic ◽  
K. Heran Darwin
Keyword(s):  
Growth Rate ◽  
Mycobacterium Tuberculosis ◽  
Cell Envelope ◽  
Bacterial Species ◽  
Transmembrane Helix ◽  
Antibiotic Sensitivity ◽  
Uncharacterized Protein ◽  
Content Type ◽  
Cell Envelopes ◽  
Envelope Functions

ABSTRACT The cell envelope of Mycobacterium tuberculosis is a key target for antibiotics, yet its assembly and maintenance remain incompletely understood. Here we report that Rv2700, a previously uncharacterized M. tuberculosis gene, contributes to envelope integrity. Specifically, an Rv2700 mutant strain had a decreased growth rate, increased sensitivity to antibiotics that target peptidoglycan crosslinking, and increased cell envelope permeability. We propose that Rv2700 be named a “cell envelope integrity” gene (cei). Importantly, a cei mutant had attenuated virulence in mice. Cei shares predicted structural homology with another M. tuberculosis protein, VirR (Rv0431), and we found that a virR mutant had growth rate, antibiotic sensitivity, and envelope permeability phenotypes similar to those of the cei mutant. Both Cei and VirR are predicted to consist of a transmembrane helix and an extracellular LytR_C domain. LytR_C domains have no known function, but they are also found in a family of proteins, the LytR-Cps2A-Psr (LCP) enzymes, that perform important cell envelope functions in a range of bacteria. In mycobacteria, LCP enzymes attach arabinogalactan to peptidoglycan, and mycobacterial LCP enzyme mutants have phenotypes similar to those of virR- and cei-deficient strains. Collectively, our results suggest that LytR_C domain proteins may contribute to the cell envelope functions performed by LCP proteins. This study provides a framework for further mechanistic investigations of LytR_C proteins and, more broadly, for advancing our understanding of the cell envelopes of mycobacteria and other medically and economically important genera. IMPORTANCE Mycobacterium tuberculosis causes about 1.5 million deaths per year. The unique composition of the Mycobacterium tuberculosis cell envelope is required for this bacterium to cause disease and is the target for several critical antibiotics. By better understanding the mechanisms by which mycobacteria assemble and maintain their cell envelope, we might uncover new therapeutic targets. In this work, we show that a previously uncharacterized protein, Rv2700, is important for cell envelope integrity in Mycobacterium tuberculosis and that loss of Rv2700 attenuates virulence in mice. This family of proteins is found in a broad group of bacterial species, so our work provides a first insight into their potential functions in many species important to the environment, industry, and human health.

scholarly journals Antimicrobial Mechanism of pBD2 against Staphylococcus aureus

Molecules ◽  
2020 ◽  
Vol 25 (15) ◽  
pp. 3513 ◽  
Author(s):  
Kun Zhang ◽  
Heng Zhang ◽  
Chunyu Gao ◽  
Ruibo Chen ◽  
Chunli Li
Keyword(s):  
Staphylococcus Aureus ◽  
Antibacterial Activity ◽  
Morphological Changes ◽  
Bacterial Species ◽  
Resistant Bacteria ◽  
Quantitative Real Time Pcr ◽  
Bacterial Membranes ◽  
Qrt Pcr ◽  
High Antibacterial Activity ◽  
Therapeutic Substance

Antimicrobial peptides (AMPs) show high antibacterial activity against pathogens, which makes them potential new therapeutics to prevent and cure diseases. Porcine beta defensin 2 (pBD2) is a newly discovered AMP and has shown antibacterial activity against different bacterial species including multi-resistant bacteria. In this study, the functional mechanism of pBD2 antibacterial activity against Staphylococcus aureus was investigated. After S. aureus cells were incubated with different concentrations of pBD2, the morphological changes in S. aureus and locations of pBD2 were detected by electron microscopy. The differentially expressed genes (DEGs) were also analyzed. The results showed that the bacterial membranes were broken, bulging, and perforated after treatment with pBD2; pBD2 was mainly located on the membranes, and some entered the cytoplasm. Furthermore, 31 DEGs were detected and confirmed by quantitative real-time PCR (qRT-PCR). The known functional DEGs were associated with transmembrane transport, transport of inheritable information, and other metabolic processes. Our data suggest that pBD2 might have multiple modes of action, and the main mechanism by which pBD2 kills S. aureus is the destruction of the membrane and interaction with DNA. The results imply that pBD2 is an effective bactericide for S. aureus, and deserves further study as a new therapeutic substance against S. aureus.

Molecular Simulations of Gram-Negative Bacterial Membranes Come of Age

2020 ◽  
Vol 71 (1) ◽  
pp. 171-188
Author(s):  
Wonpil Im ◽  
Syma Khalid
Keyword(s):  
Recent Progress ◽  
Cell Envelope ◽  
Molecular Simulations ◽  
Molecular Architecture ◽  
Future Directions ◽  
Gram Negative ◽  
Bacterial Membranes ◽  
Antibiotic Development ◽  
Multiple Cell ◽  
Made In

Gram-negative bacteria are protected by a multicompartmental molecular architecture known as the cell envelope that contains two membranes and a thin cell wall. As the cell envelope controls influx and efflux of molecular species, in recent years both experimental and computational studies of such architectures have seen a resurgence due to the implications for antibiotic development. In this article we review recent progress in molecular simulations of bacterial membranes. We show that enormous progress has been made in terms of the lipidic and protein compositions of bacterial systems. The simulations have moved away from the traditional setup of one protein surrounded by a large patch of the same lipid type toward a more bio-logically representative viewpoint. Simulations with multiple cell envelope components are also emerging. We review some of the key method developments that have facilitated recent progress, discuss some current limitations, and offer a perspective on future directions.

Shear Induced Low- and High-Angle Boundary Characterization Using Kikuchi Bands in Transmission Electron Microscopy

2008 ◽  
Vol 584-586 ◽  
pp. 293-299 ◽  
Author(s):  
Marcello Cabibbo
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Cell Size ◽  
Grain Structure ◽  
Structure Evolution ◽  
High Angle ◽  
Boundary Misorientation ◽  
Average Cell Size ◽  
Average Cell ◽  
Transmission Electron

Microstructure evolution with equal channel angular pressing (ECAP) using route Bc, that is a 90° axial rotation of the billet between passes, up to 8 passes, was investigated by transmission electron microscopy. The study has been focused on the induced development of boundary misorientation and spacing toward microstructure refinement. Cell (low-angle) and grain (high-angle) misorientation and spacing were determined from about 250 boundaries per pass of ECAP, systematically using whether Kikuchi patterns or Moiré fringes, these latter where possible. The average cell size and misorientation saturate within the first two passes. Misorientation and spacing of high-angle boundaries decrease with the number of passes. After 8 passes, mean cell size is ≈ 1.3 µm and the fraction of high-angle boundaries is ≈ 0.7. Differences in rate of grain structure evolution per pass are linked to differences in ability of dislocations introduced in new passes to recombine with the existing ones. As ECAP strain rises, the misorientation distribution develops strong deviations from the MacKenzie distribution for statistical grain orientation. This is interpreted as a result of the tendency to form equiaxed grains in a textured grain structure.

Effect of Nanoclay on the Physical-Mechanical and Thermal Properties and Microstructure of Extruded Noncross-Linked LDPE Nanocomposite Foams

2011 ◽  
Vol 471-472 ◽  
pp. 751-756 ◽  
Author(s):  
F. Zandi ◽  
M. Rezaei ◽  
A. Kasiri
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Cell Size ◽  
Flame Retardancy ◽  
Image Analyzer ◽  
Mechanical And Thermal Properties ◽  
Average Cell Size ◽  
Cell Size Distribution ◽  
Average Cell ◽  
Nanocomposite Foams

Novel noncross-linked low density polyethylene (LDPE) foams were produced by extrusion process. In this study the effects of Organophilic Montmorillonite (OMMT) nanoclay (DK1) on thermal conductivity, flame retardancy, morphological and mechanical properties of LDPE foams have been investigated. Nanoclay dispersion in LDPE foam structure was examined by X-ray diffraction (XRD), microstructure was observed by an optical microscope and analyzed by Bel View image analyzer, thermal conductivity was studied by a simple transient method, mechanical properties was investigated using a tensile-compression Zwick-Roell machine as well as the flame retardancy of the samples was examined by flammability test. The optimum nanoclay content was determined by comparison of the properties in nanocomposite and neat LDPE foams. Due to the presence of nanoclay in the foam and decreasing the cell nucleation energy around the nanoclay, the average cell size was decreased as well as the cell density and microstructure uniformity was increased. In XRD patterns of LDPE nanocomposite foams, OMMT (DK1) characteristic peak was not observed as evidence of nanoclay intercalation-exfoliation in the polymer matrix, which led to the production of foams with homogenous microstructure. Furthermore, this nanocomposites showed lower thermal conductivity compared to neat LDPE foam, which can be attributed to the cell size reduction as well as narrow cell size distribution in nanocomposite foams. Compression test results demonstrated that LDPE nanocomposite foams with proper clay contents have improved mechanical properties (Young’s modulus, compressive strength). Furthermore due to the presence of DK1 nanoclay, LDPE foam showed a good char formation as an evidence of their flame retardancy.

Characterization of LDMMs

MRS Bulletin ◽  
1990 ◽  
Vol 15 (12) ◽  
pp. 41-43
Keyword(s):  
Spatial Scale ◽  
Cell Size ◽  
Three Dimensional ◽  
Morphological Properties ◽  
Sem Images ◽  
Average Cell Size ◽  
Cell Size Distribution ◽  
Average Cell ◽  
Process Step ◽  
Size Standard

The previous sections of this article described the synthesis, morphologies, and properties of a variety of low-density microcellular materials. This section discusses several of the analytical methods used and developed at the DOE laboratories to characterize these state-of-the-art materials.In some LDMM applications, quantitative measurements of the material's average cell size and cell size distribution are desired. Indeed, the term “microcellular” has little meaning without such information. As seen throughout this article, however, most LDMMs do not have a readily defined cellular character. The more general problem is to quantify the spatial scale(s) of the foam. For this purpose it is necessary to define one or more “measures” of the spatial scale. The possibilities are many and include not only single numbers (e.g., cell size and cell size standard deviation, where “cell size” is meaningful) but also functional descriptions (e.g., correlation functions).SEM provides direct images and, therefore, is the most popular technique for examining LDMM morphology. SEM, however, suffers from at least three limitations: (1) SEM examines only a very small volume of material, and thus is impractical for obtaining average morphological properties; (2) SEM requires that nonconductive LDMMs be coated, a process step that can alter the structure and introduce artifacts (particularly with delicate structures); and (3) SEM images are only two-dimensional projections of real three-dimensional structures.

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