Live Bacterial Cells Research Articles

Visualizing the Replisome, Chromosome Breaks, and Replication Restart in Bacillus subtilis.

Research over the last two decades has revealed that bacterial genomes are highly organized and that bacteria have sophisticated mechanisms in place to ensure their correct replication and segregation into progeny cells. Here we discuss techniques that can be used with live bacterial cells to analyze DNA replisome dynamics, double-strand chromosome breaks, and restart of repaired replication forks.

Dairy Lactic Acid Bacteria and Their Potential Function in Dietetics: The Food-Gut-Health Axis.

Fermented dairy products are the good source of different species of live lactic acid bacteria (LAB), which are beneficial microbes well characterized for their health-promoting potential. Traditionally, dietary intake of fermented dairy foods has been related to different health-promoting benefits including antimicrobial activity and modulation of the immune system, among others. In recent years, emerging evidence suggests a contribution of dairy LAB in the prophylaxis and therapy of non-communicable diseases. Live bacterial cells or their metabolites can directly impact physiological responses and/or act as signalling molecules mediating more complex communications. This review provides up-to-date knowledge on the interactions between LAB isolated from dairy products (dairy LAB) and human health by discussing the concept of the food–gut-health axis. In particular, some bioactivities and probiotic potentials of dairy LAB have been provided on their involvement in the gut–brain axis and non-communicable diseases mainly focusing on their potential in the treatment of obesity, cardiovascular diseases, diabetes mellitus, inflammatory bowel diseases, and cancer.

EVALUATION OF PATHOGENICITY OF NODULE BACTERIA STRAIN RHIZOBIUM LEGUMINOSARUM G 222

Objective. Investigate pathogenic (non-pathogenic) properties of a new strain of nodule bacteria Rhizobium leguminosarum G 222. Methods. Microbiological (obtaining a suspension of R. leI guminosarum G 222, determination of its titre by opacity optical standard and by seeding on a digest medium; microscopy of stained imprint smears of internal organs of experimental animals and seeding of tissue samples on a digest medium), pathoanatomical (to determine possible invasiveness and dissemination of bacteria in the tissues of internal organs of animals — in the model of outbred white mice after administration of a suspension of live bacterial cells (oral doses from 0.5 × 109 to 5 × 109 CFU in 0.5 cm3 of sterile isotonic sodium chloride solution per mouse and intraperitoneal doses from 1 × 109 to 5 × 109 CFU/0.5 cm3) and statistical. Results. Over 15 days of observations after administration of a suspension of live bacterial cells, no death of experimental animals was registered. The strain did not lead to any changes in the general condition of the mice. No changes in their behaviour were reported. Fifteen days after the start of the study, it was found that this strain is non-infective (non-invasive), does not disseminate and does not reproduce in the body of experimental animals. Oral and intraperitoneal doses of a suspension of live bacterial cells did not result in bacterial invasion of animal internal organs. No retrocultures were registered. Gross examination did not find characteristic changes in the internal organs of the experimental animals. The obtained results indicate the avirulence of the strain for the studied warm-blooded animals (intraperitoneal LD50 > 5 billion cells/mouse, oral LD50 > 5 billion cells/mouse). Conclusion: According to the results regarding the lack of virulence and according to regulations, the new strain R. leguminosarum G 222 belongs to the group of avirulent microorganisms that are not able to invade the internal organs of studied warm-blooded laboratory animals and can be considered nonpathogenic and used as a basis for microbial preparations to increase crop yields.

Systematic Assessment of Accessibility to the Surface of Staphylococcus aureus.

Proteins from bacterial foes, antimicrobial peptides, and host immune proteins must navigate past a dense layer of bacterial surface biomacromolecules to reach the peptidoglycan (PG) layer of Gram-positive bacteria. A subclass of molecules (e.g., antibiotics with intracellular targets) also must permeate through the PG (in a molecular sieving manner) to reach the cytoplasmic membrane. Despite the biological and therapeutic importance of surface accessibility, systematic analyses in live bacterial cells have been lacking. We describe a live cell fluorescence assay that is robust, shows a high level of reproducibility, and reports on the permeability of molecules to and within the PG scaffold. Moreover, our study shows that teichoic acids impede the permeability of molecules of a wide range of sizes and chemical composition.

Impact of Zinc Oxide Nanoparticles on the Composition of Gut Microbiota in Healthy and Autism Spectrum Disorder Children.

Autism spectrum disorder (ASD) seriously affects children’s health, while the gut microbiome has been widely hypothesized to be involved in the regulation of ASD behavior. This study investigated and compared the number, diversity, and population structure of gut microbiota between healthy and ASD children and their susceptibility to zinc oxide nanoparticles (ZnONPs) based on the measurement of live cell number, living/dead bacterial staining test, flow cytometry observation and bacterial community analysis using 16S rRNA gene amplicon sequencing. The result of this present study revealed that ASD children not only significantly reduced the live cell number and the community diversity of gut bacteria, but also changed the gut bacterial community composition compared to the healthy children. In addition, this result revealed that ZnONPs significantly reduced the number of live bacterial cells in the gut of healthy children, but not in that of ASD children. In contrast, ZnONPs generally increased the gut bacterial community diversity in both ASD and healthy children, while a greater increase was found in ASD children than that of healthy children. Furthermore, this study successfully isolated and identified some representative nanoparticle-resistant bacteria based on the color, shape, and edge of colony as well as the 16S rDNA sequence analysis. The community of nanoparticle-resistant bacteria differed in between healthy and ASD children. Indeed, the representative strains 6-1, 6-2, 6-3 and 6-4 from healthy children were identified as Bacillus anthracis, Escherichia coli, Bacillus cereus and Escherichia coli with sequence similarity of 97.86%, 99.86%, 99.03% and 99.65%, respectively, while the representative strains 8-1, 8-2 and 8-3 from ASD children were identified as Bacillus cereus, with sequence similarities of 99.58%, 99.72% and 99.72%, respectively. Overall, this study demonstrated that ZnONPs caused a change in number, diversity, and species composition of gut bacteria, but differed in healthy and ASD children.

Development and Application of a Loop-Mediated Isothermal Amplification (LAMP) Assay for the Detection of Pseudomonas syringae Pathovars pisi and syringae

Pseudomonas syringae causes bacterial blight (BB) disease worldwide on economically important fruit and vegetable crops including field pea (Pisum sativum L.). The two pathovars responsible for BB in field pea are Pseudomonas syringae pathovar pisi (Psp) and syringae (Pss). In the field, both pathovars cause indistinguishable symptoms on field pea and require laboratory diagnosis to determine the causal pathovar. To aid in-field and laboratory diagnosis, accurate, and robust loop-mediated isothermal amplification (LAMP) assays for Psp and Pss were developed. The assays were able to detect Psp or Pss on live or heat-killed bacterial cells, plant exudates, seeds, and DNA extracts with no inhibitory effects. The two specific LAMP assays developed detected Psp and Pss accurately in less than 20 min and no cross-reaction was observed with 18 strains of closely related species of Pseudomonas syringae. Compared to the conventional PCR assays, the two LAMP assays were equally specific but have advantages of producing quicker and visual live results, enabling early detection and differentiation of Psp and Pss. Our results suggested a potential use of LAMP assays for laboratory testing and can be applied for in-field surveys.

Three-dimensional label-free visualization and quantification of polyhydroxyalkanoates in individual bacterial cell in its native state

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters that are intracellularly accumulated as distinct insoluble granules by various microorganisms. PHAs have attracted much attention as sustainable substitutes for petroleum-based plastics. However, the formation of PHA granules and their characteristics, such as localization, volume, weight, and density of granules, in an individual live bacterial cell are not well understood. Here, we report the results of three-dimensional (3D) quantitative label-free analysis of PHA granules in individual live bacterial cells through measuring the refractive index distributions by optical diffraction tomography (ODT). The formation and growth of PHA granules in the cells of Cupriavidus necator, the best-studied native PHA producer, and recombinant Escherichia coli harboring C. necator poly(3-hydroxybutyrate) (PHB) biosynthesis pathway are comparatively examined. Through the statistical ODT analyses of the bacterial cells, the distinctive characteristics for density and localization of PHB granules in vivo could be observed. The PHB granules in recombinant E. coli show higher density and localization polarity compared with those of C. necator, indicating that polymer chains are more densely packed and granules tend to be located at the cell poles, respectively. The cells were investigated in more detail through real-time 3D analyses, showing how differently PHA granules are processed in relation to the cell division process in native and nonnative PHA-producing strains. We also show that PHA granule-associated protein PhaM of C. necator plays a key role in making these differences between C. necator and recombinant E. coli strains. This study provides spatiotemporal insights into PHA accumulation inside the native and recombinant bacterial cells.

The Effect of the Addition of Chokeberry Fiber on the Quality of Sheep's Milk Fermented by Lactobacillus rhamnosus and Lactobacillus acidophilus.

The global market for sheep's milk and its products is increasing due to higher demand for cheese and traditional dairy products, and as a novelty, sheep's milk is an ingredient in infant formulas and nutraceuticals. The aim of this study was to determine the properties of fermented sheep's milk, which combines probiotic benefits with increased dietary fiber content. The influence of the applied dose of chokeberry fiber on the growth of living cells of Lactobacillus acidophilus and Lactobacillus rhamnosus in fermented sheep's milk was also evaluated. Sheep milk with the addition of 0% (control sample), 1.5%, and 3.0% chokeberry fiber was fermented by two different probiotic monocultures L. acidophilus and L. rhamnosus. In the fermented milk, pH value, syneresis (%), color, and texture were determined. Furthermore, the microbiological analysis and an organoleptic evaluation were performed. With the increasing dose of chokeberry fiber, the pH value decreased already before the fermentation process. After fermentation, the milk's pH values with fiber were still lower than those in the control sample. Presumably, more acidic metabolites were produced by L. acidophilus, causing a more intense reduction of the pH value than L. rhamnosus both in control milk and in milk with the addition of fiber. The addition of chokeberry fiber affected the stimulation of the growth of both types of bacteria. In the milk sample without fiber addition, a more significant number of viable cells were counted for L. acidophilus by 0.5 log CFU g−1 more than the milk fermented with L. rhamnosus. Furthermore, in milk fermented by L. acidophilus with 1.5% chokeberry fiber (LA1), the number of viable bacterial cells was higher than that in milk fermented by L. rhamnosus with the same addition of fiber (LR1). However, in sample LA3, the number of viable bacterial cells was lower than that in sample LR3. Tested fermented sheep milk met the Recommendation of the International Dairy Federation's requirements regarding the number of live bacterial cells for dairy probiotics. The addition of chokeberry fiber increased syneresis in each fermented milk group, regardless of the bacteria used for fermentation. Moreover, the use of fiber caused a significant reduction in brightness L∗, an increase of red color, and a decrease of yellow color. Milk fermented with L. acidophilus was characterized by a harder gel, compared to their analogues fermented with L. rhamnosus. The addition of fiber intensified the sour taste and the taste of the additive in both types of fermented sheep milk.

Evaluation of the Potential Role of Bacillus altitudinis MT422188 in Nickel Bioremediation from Contaminated Industrial Effluents

The incessant pervasiveness of heavy metals in the environment is one of the precursory factors of pollution. This research study was endeavored upon to investigate the bioremediation potential of a nickel (Ni)-resistant bacterial isolate, identified as Bacillus altitudinis MT422188, whose optimum growth parameters were demonstrated at pH 7, temperature 32 °C, and 1 mM phosphate. Minimal Inhibitory Concentration (MIC) and EC50 for Ni were observed to be 20 and 11.5 mM, respectively, whereas the cross heavy-metal resistance was discerned as Cu2+ (25 mM) > Zn2+ (15 mM) > Cr6+ (10 mM) > Pb2+ (5 mM) > Co2+ (8 mM) > Cd2+ (3 mM) > Hg2+ (0 mM). Ni biosorption studies by live and heat-killed bacterial cells were suggestive of Ni uptake being facilitated by an ATP-independent efflux system. A pilot-scale study displayed the effective removal of Ni (70 mg/L and 85 mg/L) at 4- and 8-day intervals, respectively. Moreover, chemotaxis and motility assays indicated the role of Ni as a chemoattractant for bacterial cells. The presence of Ni reduced the GR (0.001 ± 0.003 Ug−1FW), POX (0.001 ± 0.001 Ug−1FW), and SOD (0.091 ± 0.003 Ug−1FW) activity, whereas Sodium dodecyl sulphate—Polyacrylamide gel electrophoresis (SDS-PAGE) revealed the presence of metallothionein (60 kDa). Kinetic and isotherm studies suggested a pseudo second-order and Freundlich model to be better fitted for our study. The thermodynamic parameters (∆H° = 3.0436 kJ/mol, ∆S° = 0.0224 kJ/mol/K) suggested the process to be endothermic, spontaneous, and favorable in nature. FTIR analysis elucidated the interaction of hydroxyl and carboxyl groups with Ni. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS) demonstrated changes in the morphological and elemental composition of the bacterial cells, which affirmed their interaction with Ni during biosorption. In summary, our study concludes the efficient role of Bacillus altitudinis MT422188 in removing Ni from polluted industrial effluents.

Single-molecule localisation microscopy: accounting for chance co-localisation between foci in bacterial cells

Using single-molecule fluorescence microscopes, individual biomolecules can be observed within live bacterial cells. Using differently coloured probes, physical associations between two different molecular species can be assessed through co-localisation measurements. However, bacterial cells are finite and small (~ 1 μm) relative to the resolution limit of optical microscopes (~ 0.25 μm). Furthermore, the images produced by optical microscopes are typically two-dimensional projections of three-dimensional objects. These limitations mean that a certain proportion of object pairs (molecules) will inevitably be assigned as being co-localised, even when they are distant at molecular distance scales (nm). What is this proportion? Here, we attack this problem, theoretically and computationally, by creating a model of the co-localisation expected purely due to chance. We thus consider a bacterial cell wherein objects are distributed at random and evaluate the co-localisation in a fashion that emulates an experimental analysis. We consider simplified geometries where we can most transparently investigate the effect of a finite size of the cell and the effect of probing a three-dimensional cell in only two dimensions. Coupling theory to simulations, we also study the co-localisation expected due to chance using parameters relevant to bacterial cells. Overall, we show that the co-localisation expected purely due to chance can be quite substantial and describe the parameters that it depends upon.

Ecological Aspect of Antibiotic Batumin Synthesis by Pseudomonas batumici

The species Pseudomonas batumici, isolated from the rhizosphere of eucalyptus in the humid subtropical zone, is a producer of the polyketide antibiotic batumin with highly selective activity against staphylococci. Batumin biosynthesis operon includes 28 genes or 74 151 bp. According to modern notions, the biosynthesis of energy-intensive metabolites, which probably includes batumin, is justified in the case of its multifunctionality for producers. The species P. batumici, as a representative of rhizosphere bacteria, must interact with plants and compete with the surrounding microbiota. Aim. To determine the role of batumin in the ecology of the rhizosphere producer strain P. batumici UCM B-321. Methods. The batumin producing strain P. batumici UCM B-321T was obtained from the Ukrainian Collection of Microorganisms. Antibiotic batumin was obtained by fermentation of P. batumici UCM B-321. Extraction was carried out from acidified P. batumici fermentation broth by chloroform (1:2). Chromatographic analysis of fermentation broth obtained after centrifugation was carried out by HPLC using liquid chromatograph Agilent 1200 with mass spectrometric detector Agilent G1956B. Batumin derivatives were obtained after the extraction of the fermentation broth of P. batumici using thin layer chromatography (TLC) on silica gel plates (Merck, USA) in the benzene-isopropanol system (5:1). Disc-diffusion method on phytopathogenic test-strains was used for bioautography. Biofilm formation by P. batumici strain was studied according to O’Toole by growing strain B-321 at 25 0C for 48 hours in 96-well plates on LB medium. Batumin effect upon bacterial mobility was studied using Volf and Berg method in Petri dishes with 0.5% semisolid bacterial agar. To research chemotaxis the soil strain Bacillus subtilis IMV B-7023 and the following concentrations of batumin were used: 20, 50, and 150 μg/mL. The studies were performed using Tso and Adler method. Results. Growth inhibition zones for phytopathogenic bacteria strains were the following (in mm): Pseudomonas syringae pv. syringae UCM B-1027T – 19±3, P. fluorescens IMV 8573 – 22±3, Pectobacterium carotovorum UCM B-1075T – 17±2. Activity against Xantomonas campestris pv. campestris UCM B-1049, Clavibacter michiganensis subsp. michiganensis IMV 102, Agrobacterium tumefaciens UCM B-1000 was not detected. Minimum inhibitory concentrations (MIC) in the range from 8 to 64 μg/mL for P. carotovorum UCM B-1075T, Erwinia aroidea IMV 1058, Proteus vulgaris UCM B-905 and P. fluorescens IMV 8573 are hardly comparable with the discovered against staphylococci. TLC analysis of its broth extract revealed five separate compounds with different values of retention factors: Rf1=0.42; Rf2=0.38; Rf3=0.31; Rf4=0.28; Rf5=0.25. The main component of extract was batumin, other four substances were present in minor quantities. All found substances had similar absorption maxima with the minimum differences between isomeric forms: descarbamoyl batumin-enol (Mr=505, λ=226 nm), descarbamoyl batumin-keto (Mr=505, λ=231 nm), batumin (Mr=548, λ=231 nm), batumin-enol (Mr=548, λ=228 nm) and 17-hydroxy-batumin (Mr=550, λ=229 nm). The largest inhibition zone (P. carotovorum UCM B-1075T) was on the third compound placement which represents of batumin, tiny inhibition zones were found around keto and enol form of descarbamoyl batumin. Observation of live bacterial cells in light microscope confirmed a serious disruption of motility in all these bacteria by batumin in the concentration far lower than the MIC for these organisms. Proteus actively moved in the control, but in presence of 10 μg/mL of batumin was almost no growth. The biofilm formation by P. batumici UCM B-321 was stimulated by supplementing batumin into the medium. The stimulation effect by batumin on the biofilm formation was equally strong when the compound was applied in the concentrations of 1 and 10 μg/mL. Batumin was not an attractant of the producer strain. However, in one of our experiments batumin has shown the properties of positive effector (attractant) for B. subtilis UCM B-7023 strain. Conclusion. The discovered features allow to consider the antibiotic batumin synthesized by P. batumici UCM B-321 as the essential tool for survival and competition of the producer strain in a natural habitat.

Multimodal real-time frequency tracking of cantilever arrays in liquid environment for biodetection: Comprehensive setup and performance analysis.

We present a nanomechanical platform for real-time quantitative label-free detection of target biomolecules in a liquid environment with mass sensitivity down to few pg. Newly fabricated arrays of up to 18 cantilevers are integrated in a micromachined fluidic chamber, connected to software-controlled fluidic pumps for automated sample injections. We discuss two functionalization approaches to independently sensitize the interface of different cantilevers. A custom piezo-stack actuator and optical readout system enable the measurement of resonance frequencies up to 2MHz. We implement a new measurement strategy based on a phase-locked loop (PLL), built via in-house developed software. The PLL allows us to track, within the same experiment, the evolution of resonance frequency over time of up to four modes for all the cantilevers in the array. With respect to the previous measurement technique, based on standard frequency sweep, the PLL enhances the estimated detection limit of the device by a factor of 7 (down to 2pg in 5min integration time) and the time resolution by more than threefold (below 15s), being on par with commercial gold-standard techniques. The detection limit and noise of the new setup are investigated via Allan deviation and standard deviation analysis, considering different resonance modes and interface chemistries. As a proof-of-concept, we show the immobilization and label-free in situ detection of live bacterial cells (E. coli), demonstrating qualitative and quantitative agreement in the mechanical response of three different resonance modes.

An autonomous bioluminescent bacterial biosensor module for outdoor sensor networks, and its application for the detection of buried explosives

We describe a miniaturized field-deployable biosensor module, designed to function as an element in a sensor network for standoff monitoring and mapping of environmental hazards. The module harbors live bacterial sensor cells, genetically engineered to emit a bioluminescent signal in the presence of preselected target materials, which act as its core sensing elements. The module, which detects and processes the biological signal, composes a digital record that describes its findings, and can be transmitted to a remote receiver. The module is an autonomous self-contained unit that can function either as a standalone sensor, or as a node in a sensor network. The biosensor module can potentially be used for detecting any target material to which the sensor cells were engineered to respond. The module described herein was constructed to detect the presence of buried landmines underneath its footprint. The demonstrated detection sensitivity was 0.25 mg 2,4-dinitrotoluene per Kg soil.

Expression and purification of the native C-amidated antimicrobial peptide maculatin 1.1.

Maculatin 1.1 (Mac1) is an antimicrobial peptide (AMP) from an Australian tree frog and exhibits low micromolar activity against Gram-positive bacteria. The antimicrobial properties of Mac1 are linked to its disruption of bacterial lipid membranes, which has been studied extensively by in vitro nuclear magnetic resonance (NMR) spectroscopy and biophysical approaches. Although in vivo NMR has recently proven effective in probing peptide-lipid interplay in live bacterial cells, direct structural characterisation of AMPs has been prohibited by low sensitivity and overwhelming background noise. To overcome this issue, we report a recombinant expression protocol to produce isotopically enriched Mac1. We utilized a double-fusion construct to alleviate toxicity against the Escherichia coli host and generate the native N-free and C-amidated termini Mac1 peptide. The SUMO and intein tags allowed native N-terminus and C-terminal amidation, respectively, to be achieved in a one-pot reaction. The protocol yielded 0.1mg/L of native, uniformly 15 N-labelled, Mac1, which possessed identical structure and activity to peptide obtained by solid-phase peptide synthesis.

Direct Measurements of Erythromycin’s Effect on Protein Synthesis Kinetics in Living Bacterial Cells

Macrolide antibiotics, such as erythromycin, bind to the nascent peptide exit tunnel (NPET) of the bacterial ribosome and modulate protein synthesis depending on the nascent peptide sequence. Whereas in vitro biochemical and structural methods have been instrumental in dissecting and explaining the molecular details of macrolide-induced peptidyl-tRNA drop-off and ribosome stalling, the dynamic effects of the drugs on ongoing protein synthesis inside live bacterial cells are far less explored. In the present study, we used single-particle tracking of dye-labeled tRNAs to study the kinetics of mRNA translation in the presence of erythromycin, directly inside live Escherichia coli cells. In erythromycin-treated cells, we find that the dwells of elongator tRNAPhe on ribosomes extend significantly, but they occur much more seldom. In contrast, the drug barely affects the ribosome binding events of the initiator tRNAfMet. By overexpressing specific short peptides, we further find context-specific ribosome binding dynamics of tRNAPhe, underscoring the complexity of erythromycin’s effect on protein synthesis in bacterial cells.

Dynamic interactions between the RNA chaperone Hfq, small regulatory RNAs, and mRNAs in live bacterial cells.

RNA-binding proteins play myriad roles in regulating RNAs and RNA-mediated functions. In bacteria, the RNA chaperone Hfq is an important post-transcriptional gene regulator. Using live-cell super-resolution imaging, we can distinguish Hfq binding to different sizes of cellular RNAs. We demonstrate that under normal growth conditions, Hfq exhibits widespread mRNA-binding activity, with the distal face of Hfq contributing mostly to the mRNA binding in vivo. In addition, sRNAs can either co-occupy Hfq with the mRNA as a ternary complex, or displace the mRNA from Hfq in a binding face-dependent manner, suggesting mechanisms through which sRNAs rapidly access Hfq to induce sRNA-mediated gene regulation. Finally, our data suggest that binding of Hfq to certain mRNAs through its distal face can recruit RNase E to promote turnover of these mRNAs in a sRNA-independent manner, and such regulatory function of Hfq can be decoyed by sRNA competitors that bind strongly at the distal face.

Live-Cell Single-Molecule Tracking of the Translation Machinery

The use of single-molecule fluorescence microscopy makes it possible to observe molecules of interest in their native environment, one at a time. In this presentation we show how methods recently developed in our lab are applied to study different aspects of protein synthesis kinetics in live bacterial cells.

Treadmilling FtsZ polymers drive the directional movement of sPG-synthesis enzymes via a Brownian ratchet mechanism

The FtsZ protein is a central component of the bacterial cell division machinery. It polymerizes at mid-cell and recruits more than 30 proteins to assemble into a macromolecular complex to direct cell wall constriction. FtsZ polymers exhibit treadmilling dynamics, driving the processive movement of enzymes that synthesize septal peptidoglycan (sPG). Here, we combine theoretical modelling with single-molecule imaging of live bacterial cells to show that FtsZ’s treadmilling drives the directional movement of sPG enzymes via a Brownian ratchet mechanism. The processivity of the directional movement depends on the binding potential between FtsZ and the sPG enzyme, and on a balance between the enzyme’s diffusion and FtsZ’s treadmilling speed. We propose that this interplay may provide a mechanism to control the spatiotemporal distribution of active sPG enzymes, explaining the distinct roles of FtsZ treadmilling in modulating cell wall constriction rate observed in different bacteria.

Removal of aflatoxin b1 and t-2 toxin by bacteria isolated from commercially available probiotic dairy foods.

This study isolated lactic acid bacteria from commercially available probiotic foods to determine their capacity to remove aflatoxin B1 (AFB1) and trichothecene-2 (T-2). The removal rates by original live and heat-treated cells of lactic acid bacteria (LAB) were compared to test the effect of heat treatment on efficacy. LAB is capable to remove up to 46% of AFB1 and up to 45% of T-2 toixn. The toxin removal capability increased as toxin concentration increased despite bacterial cell viability declining. Surprisingly, the denatured LAB removed greater percentages of AFB1 (up to 62%) and T-2 (up to 52%) than live bacterial cells (P < 0.05), lending support to the hypothesis that there is higher binding of toxins to the cell membrane of nonviable cells. The research provided practical evidences, which suggest that when ingested into the gut biota, LAB could likely reduce absorption of AFB1 and T-2 from contaminated foods.

Measurement of the interconnected turgor pressure and envelope elasticity of live bacterial cells.

Turgor pressure and envelope elasticity of bacterial cells are two mechanical parameters that play a dominant role in cellular deformation, division, and motility. However, a clear understanding of these two properties is lacking because of their strongly interconnected mechanisms. This study established a nanoindentation method to precisely measure the turgor pressure and envelope elasticity of live bacteria. The indentation force-depth curves of Klebsiella pneumoniae bacteria were recorded with atomic force microscopy. Through combination of dimensional analysis and numerical simulations, an explicit expression was derived to decouple the two properties of individual bacteria from the nanoindentation curves. We show that the Young's modulus of bacterial envelope is sensitive to the external osmotic environment, and the turgor pressure is significantly dependent on the external osmotic stress. This method can not only quantify the turgor pressure and envelope elasticity of bacteria, but also help resolve the mechanical behaviors of bacteria in different environments.