Imaging flow cytometry reveals a dual role for exopolysaccharides in biofilms: To promote self-adhesion while repelling non-self-community members

Isolation, Identification, and Potential Biotechnological Application on Soil Porosity of the Microbial Exopolysaccharides (EPS) from Bacillus polymyxa

Microbial exopolysaccharides (EPS) exhibit high viscosity, offering significant potential for reducing soil porosity. In this paper, a kind of Bacillus polymyxa producing EPS was selected and its chemical and physical properties, including the morphology, molecular weight, monosaccharide composition, structure, and rheological properties, were studied. Subsequently, the effect of EPS on soil porosity was investigated by the permeability coefficient and X-ray computed tomography (X-CT), and the mechanism by which EPS reduced soil porosity was elucidated. The EPS was a porous ellipsoid with a molecular weight of 7.89 × 104 Da, mainly composed of mannose, galactose, and glucose with a molar ratio of 7.35:1.96:1.00. The rheological properties were fitted using a power law model, and the EPS solution exhibited pseudoplasticity at different concentrations and pH conditions. Compared with the blank group, the permeability coefficient of the microbial group decreased by 66.27% after 504 h, and the porosity measured of the microbial group by X-CT decreased by 68.20% after 240 h. In general, the results suggest that the EPS is a promising natural polymer with great application potential in soil and groundwater remediation, which is conducive to promoting the development and progress of green barrier remediation materials.

Structural characteristics, biotechnological production and applications of exopolysaccharides from Bacillus sp.: A comprehensive review

Exopolysaccharides (EPS) produced by Bacillus species display various biological activities and characteristics such as anti-oxidant, immunomodulatory, anti-bacterial, and bioadhesive effects. These attributes confer Bacillus species broad potential applications in diverse fields such as food, medicine, environment, and agriculture. Moreover, Bacillus-derived EPS are easier to produce and yield higher quantities than plant-derived polysaccharides. Despite these advantages, Bacillus-derived EPS still encounter numerous obstacles in industrial production and commercial applications, including elevated costs, the absence of mature fermentation tank production procedures, and the lack of systematic in vivo and in vitro activity and metabolic evaluation. Therefore, it is essential to gain insight into the current status of structure, production, and applications of Bacillus-derived EPS for facilitating their future broader application. This paper provides a comprehensive overview of the current research on the production, separation, characteristics and applications of these related biological products. Furthermore, this paper summarizes the current challenges impeding industrial production of Bacillus-derived EPS, along with potential solutions, and their prospective applications in enhancing the attributes of beneficial biofilms, laying a solid scientific foundation for the applications of Bacillus-derived EPS in industry and agriculture.

Lignin-Based Mucus-Mimicking Antiviral Hydrogels with Enzyme Stability and Tunable Porosity

Mucus is a complex hydrogel that acts as a defensive and protective barrier in various parts of the human body. The rise in the level of viral infections has underscored the importance of advancing research into mucus-mimicking hydrogels for the efficient design of antiviral agents. Herein, we demonstrate the gram-scale synthesis of biocompatible, lignin-based virus-binding inhibitors that reduce waste and ensure long-term availability. The lignin-based inhibitors are equipped with sulfate moieties, which are known binding partners for many viruses, including SARS-CoV-2 and herpes viruses. In addition, cross-linking the synthesized inhibitors yielded hydrogels that mimicked native mucus concerning surface functionality and rheology. The degree of sulfation exhibits a very strong impact on the mesh size distribution of the hydrogels, which provides a new means to fine-tune the steric and electrostatic contributions of the virus-hydrogel interaction. This feature strongly impacts the sequestration capability of the lignin-based hydrogels, which is demonstrated by infection inhibition assays involving human herpes simplex virus 1, influenza A viruses, and the bacterium Escherichia coli (E. coli). These measurements showed a reduction in plaque-forming units (HSV-1) and colony-forming units (E. coli) by more than 4 orders of magnitude, indicating the potent inhibition by the lignin-based hydrogels.

Redox-Responsive Hydrogels Loaded with an Antibacterial Peptide as Controlled Drug Delivery for Healing Infectious Wounds

Infectious wounds occur when harmful microorganisms such as bacteria or viruses invade a wound site. Its problems associated include delayed healing, increased pain, swelling, and the potential for systemic infections. Therefore, developing new wound dressing materials with antibacterial effects is crucial for improving the healing process. Here a redox-degradable hydrogel loaded with an antibacterial peptide (vancomycin) in a straightforward gram-scale synthesis, is developed. The hydrogel structure consists of a disulfide bond-containing hyperbranched polyglycerol (SS-hPG) that is cross-linked by 4-arm polyethylene glycol-thiol (4-arm PEG-SH). The polymerization mechanism and full characterization of SS-hPG are described as this synthesis is reported for the first time. Rheology is used to ascertain the hydrogel's mechanical characteristics, such as stiffness, and self-healing, determining these properties for different ratios and concentrations of both gel components. The incorporation of disulfide bonds in the hydrogel is proved by conducting degradation experiments in reductive environments. Fluorescein isothiocyanate-albumin (FITC-BSA) and vancomycin both are loaded into the gel, and the guest release kinetics is assessed for both slow and on-demand releases. Finally, the in vitro and in vivo experiments prove that the vancomycin-loaded hydrogel acts as an antibacterial barrier for wound dressing and accelerates the healing of infectious wounds in a mouse model.

Elimination of Pathogen Biofilms via Postbiotics from Lactic Acid Bacteria: A Promising Method in Food and Biomedicine

Pathogenic biofilms provide a naturally favorable barrier for microbial growth and are closely related to the virulence of pathogens. Postbiotics from lactic acid bacteria (LAB) are secondary metabolites and cellular components obtained by inactivation of fermentation broth; they have a certain inhibitory effect on all stages of pathogen biofilms. Postbiotics from LAB have drawn attention because of their high stability, safety dose parameters, and long storage period, which give them a broad application prospect in the fields of food and medicine. The mechanisms of eliminating pathogen biofilms via postbiotics from LAB mainly affect the surface adhesion, self-aggregation, virulence, and QS of pathogens influencing interspecific and intraspecific communication. However, there are some factors (preparation process and lack of target) which can limit the antibiofilm impact of postbiotics. Therefore, by using a delivery carrier and optimizing process parameters, the effect of interfering factors can be eliminated. This review summarizes the concept and characteristics of postbiotics from LAB, focusing on their preparation technology and antibiofilm effect, and the applications and limitations of postbiotics in food processing and clinical treatment are also discussed.

Convergence of flow cytometry and bacteriology. Current and future applications: a focus on food and clinical microbiology

Since its development in the 1960s, flow cytometry (FCM) was quickly revealed a powerful tool to analyse cell populations in medical studies, yet, for many years, was almost exclusively used to analyse eukaryotic cells. Instrument and methodological limitations to distinguish genuine bacterial signals from the background, among other limitations, have hampered FCM applications in bacteriology. In recent years, thanks to the continuous development of FCM instruments and methods with a higher discriminatory capacity to detect low-size particles, FCM has emerged as an appealing technique to advance the study of microbes, with important applications in research, clinical and industrial settings. The capacity to rapidly enumerate and classify individual bacterial cells based on viability facilitates the monitoring of bacterial presence in foodstuffs or clinical samples, reducing the time needed to detect contamination or infectious processes. Besides, FCM has stood out as a valuable tool to advance the study of complex microbial communities, or microbiomes, that are very relevant in the context of human health, as well as to understand the interaction of bacterial and host cells. This review highlights current developments in, and future applications of, FCM in bacteriology, with a focus on those related to food and clinical microbiology.

Nutrient Availability and Biofilm Polysaccharide Shape the Bacillaene-Dependent Antagonism of Bacillus subtilis against Salmonella Typhimurium

Salmonella enterica is one of the most common foodborne pathogens and, due to the spread of antibiotic resistance, new antimicrobial strategies are urgently needed to control it. In this study, we explored the probiotic potential of Bacillus subtilis PS-216 and elucidated the mechanisms that underlie the interactions between this soil isolate and the model pathogenic strain S. Typhimurium SL1344. The results reveal that B. subtilis PS-216 inhibits the growth and biofilm formation of S. Typhimurium through the production of the pks cluster-dependent polyketide bacillaene. The presence of S. Typhimurium enhanced the activity of the PpksC promoter that controls bacillaene production, suggesting that B. subtilis senses and responds to Salmonella. The level of Salmonella inhibition, overall PpksC activity, and PpksC induction by Salmonella were all higher in nutrient-rich conditions than in nutrient-depleted conditions. Although eliminating the extracellular polysaccharide production of B. subtilis via deletion of the epsA-O operon had no significant effect on inhibitory activity against Salmonella in nutrient-rich conditions, this deletion mutant showed an enhanced antagonism against Salmonella in nutrient-depleted conditions, revealing an intricate relationship between exopolysaccharide production, nutrient availability, and bacillaene synthesis. Overall, this work provides evidence on the regulatory role of nutrient availability, sensing of the competitor, and EpsA-O polysaccharide in the social outcome of bacillaene-dependent competition between B. subtilis and S. Typhimurium. IMPORTANCE Probiotic bacteria represent an alternative for controlling foodborne disease caused by Salmonella enterica, which constitutes a serious concern during food production due to its antibiotic resistance and resilience to environmental stress. Bacillus subtilis is gaining popularity as a probiotic, but its behavior in biofilms with pathogens such as Salmonella remains to be elucidated. Here, we show that the antagonism of B. subtilis is mediated by the polyketide bacillaene and that the production of bacillaene is a highly dynamic trait which depends on environmental factors such as nutrient availability and the presence of competitors. Moreover, the production of extracellular polysaccharides by B. subtilis further alters the influence of these factors. Hence, this work highlights the inhibitory effect of B. subtilis, which is condition-dependent, and the importance of evaluating probiotic strains under conditions relevant to the intended use.