Novel imaging technologies for characterization of microbial extracellular polysaccharides

Preparation, structural characterization, antioxidant activity and protection against cisplatin-induced acute kidney injury by polysaccharides from the lateral root of Aconitum carmichaelii

Response surface methodology (RSM) and Box- Behnken design (BBD) based on one-way experiments were used to optimize the extraction parameters of the lateral root polysaccharides of Aconitum carmichaelii. The extracted polysaccharides were named as refined fucose polysaccharide. The optimal conditions included a water to raw material ratio of 43, an extraction time of 2 h, and an extraction temperature of 90°C. The shape of RFP was shown by infrared spectroscopy (IR) and scanning electron microscopy (SEM) analysis. The monosaccharide composition and molecular weight of RFP was determined by high-performance liquid chromatography (HPLC). Furthermore, RFP exhibited moderate antioxidant activity by analyzing the scavenging rates of 2,2-diphenyl-1-picrylhydrazyl radical, superoxide anion radical, hydroxyl radical, and ABTS + radical. RFP exerted cytoprotective effects against hydrogen peroxide (H2O2)-induced injury in the rat renal tubular epithelial cell line rat renal tubular epithelial cells (NRK-52E) and inhibited apoptosis. In addition, researches found that RFP could alleviate cisplatin-induced acute kidney injury in mice by enhancing the levels of glutathione (GSH) and glutathione peroxidase-4 (GPX-4), decreasing the levels of malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), reducing lipid peroxidation, and thus inhibiting ferroptosis. In conclusion, this study provides a good strategy for obtaining bioactive polysaccharides from Fuzi.

Two Distinct Bacterial Biofilm Components Trigger Metamorphosis in the Colonial Hydrozoan Hydractinia echinata

In marine environments, the bacterially induced metamorphosis of larvae is a widespread cross-kingdom communication phenomenon that is critical for the persistence of many marine invertebrates. However, the majority of inducing bacterial signals and underlying cellular mechanisms remain enigmatic. The marine hydroid Hydractinia echinata is a well-known model system for investigating bacterially stimulated larval metamorphosis, as larvae transform into the colonial adult stage within 24 h of signal detection. Although H. echinata has served as a cell biological model system for decades, the identity and influence of bacterial signals on the morphogenic transition remained largely unexplored. Using a bioassay-guided analysis, we first determined that specific bacterial (lyso)phospholipids, naturally present in bacterial membranes and vesicles, elicit metamorphosis in Hydractinia larvae in a dose-response manner. Lysophospholipids, as single compounds or in combination (50 μM), induced metamorphosis in up to 50% of all larvae within 48 h. Using fluorescence-labeled bacterial phospholipids, we demonstrated that phospholipids are incorporated into the larval membranes, where interactions with internal signaling cascades are proposed to occur. Second, we identified two structurally distinct exopolysaccharides of bacterial biofilms, the new Rha-Man polysaccharide from Pseudoalteromonas sp. strain P1-9 and curdlan from Alcaligenes faecalis, to induce metamorphosis in up to 75% of tested larvae. We also found that combinations of (lyso)phospholipids and curdlan induced transformation within 24 h, thereby exceeding the morphogenic activity observed for single compounds and bacterial biofilms. Our results demonstrate that two structurally distinct, bacterium-derived metabolites converge to induce high transformation rates of Hydractinia larvae and thus may help ensure optimal habitat selection. IMPORTANCE Bacterial biofilms profoundly influence the recruitment and settlement of marine invertebrates, critical steps for diverse marine processes such as the formation of coral reefs, the maintenance of marine fisheries, and the fouling of submerged surfaces. However, the complex composition of biofilms often makes the characterization of individual signals and regulatory mechanisms challenging. Developing tractable model systems to characterize these coevolved interactions is the key to understanding fundamental processes in evolutionary biology. Here, we characterized two types of bacterial signaling molecules, phospholipids and polysaccharides, that induce the morphogenic transition. We then analyzed their abundance and combinatorial activity. This study highlights the general importance of multiple bacterial signal converging activity in development-related cross-kingdom signaling and poses the question of whether complex lipids and polysaccharides are general metamorphic cues for cnidarian larvae.

Atomic Force Microscopy (AFM) As a Surface Mapping Tool in Microorganisms Resistant Toward Antimicrobials: A Mini-Review

The worldwide emergence of antimicrobial resistance (AMR) in pathogenic microorganisms, including bacteria and viruses due to a plethora of reasons, such as genetic mutation and indiscriminate use of antimicrobials, is a major challenge faced by the healthcare sector today. One of the issues at hand is to effectively screen and isolate resistant strains from sensitive ones. Utilizing the distinct nanomechanical properties (e.g., elasticity, intracellular turgor pressure, and Young’s modulus) of microbes can be an intriguing way to achieve this; while atomic force microscopy (AFM), with or without modification of the tips, presents an effective way to investigate such biophysical properties of microbial surfaces or an entire microbial cell. Additionally, advanced AFM instruments, apart from being compatible with aqueous environments—as often is the case for biological samples—can measure the adhesive forces acting between AFM tips/cantilevers (conjugated to bacterium/virion, substrates, and molecules) and target cells/surfaces to develop informative force-distance curves. Moreover, such force spectroscopies provide an idea of the nature of intercellular interactions (e.g., receptor-ligand) or propensity of microbes to aggregate into densely packed layers, that is, the formation of biofilms—a property of resistant strains (e.g., Staphylococcus aureus, Pseudomonas aeruginosa). This mini-review will revisit the use of single-cell force spectroscopy (SCFS) and single-molecule force spectroscopy (SMFS) that are emerging as powerful additions to the arsenal of researchers in the struggle against resistant microbes, identify their strengths and weakness and, finally, prioritize some future directions for research.

Differences in Production, Composition, and Antioxidant Activities of Exopolymeric Substances (EPS) Obtained from Cultures of Endophytic Fusarium culmorum Strains with Different Effects on Cereals

Exopolymeric substances (EPS) can determine plant-microorganism interactions and have great potential as bioactive compounds. The different amounts of EPS obtained from cultures of three endophytic Fusarium culmorum strains with different aggressiveness-growth promoting (PGPF), deleterious (DRMO), and pathogenic towards cereal plants-depended on growth conditions. The EPS concentrations (under optimized culture conditions) were the lowest (0.2 g/L) in the PGPF, about three times higher in the DRMO, and five times higher in the pathogen culture. The EPS of these strains differed in the content of proteins, phenolic components, total sugars, glycosidic linkages, and sugar composition (glucose, mannose, galactose, and smaller quantities of arabinose, galactosamine, and glucosamine). The pathogen EPS exhibited the highest total sugar and mannose concentration. FTIR analysis confirmed the β configuration of the sugars. The EPS differed in the number and weight of polysaccharidic subfractions. The EPS of PGPF and DRMO had two subfractions and the pathogen EPS exhibited a subfraction with the lowest weight (5 kDa). The three EPS preparations (ethanol-precipitated EP, crude C, and proteolysed P) had antioxidant activity (particularly high for the EP-EPS soluble in high concentrations). The EP-EPS of the PGPF strain had the highest antioxidant activity, most likely associated with the highest content of phenolic compounds in this EPS.

Quantitative imaging and spectroscopic technologies for microbiology

Light microscopy has enabled the observation of the structure and organisation of biofilms. Typically, the contrast in an image obtained from light microscopy is given by the time-averaged intensity that is effective in visualising the overall structure. Technological advancements in light microscopy have led to the creation of techniques that not only provide a static intensity image of the biofilm, but also enable one to quantify various dynamic physicochemical properties of biomolecules in microbial biofilms. Such light microscopy-based techniques can be grouped into two main classes, those that are based on luminescence and those that are based on scattering. Here, we review the fundamentals and applications of luminescence and scattering-based techniques, specifically, fluorescence lifetime imaging, Förster resonance energy transfer, fluorescence correlation spectroscopy, fluorescence recovery after photobleaching, single-particle tracking, transient state imaging, and Brillouin and Raman microscopy. These techniques provide information about the abundance, interactions and mobility of various molecules in the biofilms and also properties of the local microenvironment at optical resolution. Further, one could use any of these techniques to probe the real-time changes in these physical parameters upon the addition of external agents or at different stages during the growth of biofilms.

Critical review on biofilm methods

Biofilms are widespread in nature and constitute an important strategy implemented by microorganisms to survive in sometimes harsh environmental conditions. They can be beneficial or have a negative impact particularly when formed in industrial settings or on medical devices. As such, research into the formation and elimination of biofilms is important for many disciplines. Several new methodologies have been recently developed for, or adapted to, biofilm studies that have contributed to deeper knowledge on biofilm physiology, structure and composition. In this review, traditional and cutting-edge methods to study biofilm biomass, viability, structure, composition and physiology are addressed. Moreover, as there is a lack of consensus among the diversity of techniques used to grow and study biofilms. This review intends to remedy this, by giving a critical perspective, highlighting the advantages and limitations of several methods. Accordingly, this review aims at helping scientists in finding the most appropriate and up-to-date methods to study their biofilms.