Outer membrane vesicles mediated horizontal transfer of an aerobic denitrification gene between Escherichia coli

Coordination of elemental sulfur and organic carbon source stimulates simultaneous nitrification and denitrification toward low C/N ratio wastewater

The feasibility of inducing simultaneous nitrification and denitrification (SND) by S0 for low carbon to nitrogen (C/N) ratio wastewater remediation was investigated. Compared with S0 and/or organics absent systems (-3.4 %∼5.0 %), the higher nitrogen removal performance (18.2 %∼59.8 %) was achieved with C/N ratios and S0 dosages increasing when S0 and organics added simultaneously. The synergistic effect of S0 and organics stimulated extracellular polymeric substances secretion and weakened intermolecular binding force of S0, facilitating S0 bio-utilization and reducing the external organics requirement. It also promoted microbial metabolism (0.16 ∼ 0.24 μg O2/(g VSS·h)) and ammonia assimilation (5.9 %∼20.5 %), thereby enhancing the capture of organics and providing more electron donors for SND. Furthermore, aerobic denitrifiers (15.91 %∼27.45 %) and aerobic denitrifying (napA and nirS) and ammonia assimilating genes were accumulated by this synergistic effect. This study revealed the mechanism of SND induced by coordination of S0 and organics and provided an innovative strategy for triggering efficient and stable SND.

Chitosan oligosaccharide accelerates the dissemination of antibiotic resistance genes through promoting conjugative plasmid transfer

The dissemination of antibiotic resistance genes (ARGs), especially via plasmid-mediated horizontal gene transfer, poses a pervasive threat to global health. Chitosan-oligosaccharide (COS) is extensively utilized in medicine, plant and animal husbandry. However, their impact on microflora implies the potential to exert selective pressure on plasmid transfer. To explore the role of COS in facilitating the dissemination of ARGs via plasmid conjugation, we established in vitro mating models. The addition of COS to conjugation mixtures significantly enhanced the transfer of RP4 plasmid and mcr-1 positive IncX4 plasmid in both intra- and inter-specific. Phenotypic and transcriptome analysis revealed that COS enhanced intercellular contact by neutralizing cell surface charge and increasing cell surface hydrophobicity. Additionally, COS increased membrane permeability by inhibiting the Tol-Pal system, thereby facilitating plasmid conjugative transfer. Furthermore, COS served as the carbon source and was metabolized by E. coli, providing energy for plasmid conjugation through regulating the expression of ATPase and global repressor factor-related genes in RP4 plasmid. Overall, these findings improve our awareness of the potential risks associated with the presence of COS and the spread of bacterial antibiotic resistance, emphasizing the need to establish guidelines for the prudent use of COS and its discharge into the environment.

Latest Update on Outer Membrane Vesicles and Their Role in Horizontal Gene Transfer: A Mini-Review

Outer membrane vesicles (OMVs) are spherical, lipid-based nano-structures, which are released by Gram-negative bacteria in both in vitro and in vivo conditions. The size and composition of OMVs depend on not only the producer bacterial species but also cells belonging to the same strain. The mechanism of vesicles' biogenesis has a key role in determining their cargo and the pattern of macromolecules exposed on their surface. Thus, the content of proteins, lipids, nucleic acids, and other biomolecules defines the properties of OMVs and their beneficial or harmful effects on human health. Many studies have provided evidence that OMVs can be involved in a plethora of biological processes, including cell-to-cell communication and bacteria-host interactions. Moreover, there is a growing body of literature supporting their role in horizontal gene transfer (HGT). During this process, OMVs can facilitate the spreading of genes involved in metabolic pathways, virulence, and antibiotic resistance, guaranteeing bacterial proliferation and survival. For this reason, a deeper understanding of this new mechanism of genetic transfer could improve the development of more efficient strategies to counteract infections sustained by Gram-negative bacteria. In line with this, the main aim of this mini-review is to summarize the latest evidence concerning the involvement of OMVs in HGT.

Role of Legionella pneumophila outer membrane vesicles in host-pathogen interaction

Legionella pneumophila is an opportunistic intracellular pathogen that inhabits artificial water systems and can be transmitted to human hosts by contaminated aerosols. Upon inhalation, it colonizes and grows inside the alveolar macrophages and causes Legionnaires' disease. To effectively control and manage Legionnaires' disease, a deep understanding of the host-pathogen interaction is crucial. Bacterial extracellular vesicles, particularly outer membrane vesicles (OMVs) have emerged as mediators of intercellular communication between bacteria and host cells. These OMVs carry a diverse cargo, including proteins, toxins, virulence factors, and nucleic acids. OMVs play a pivotal role in disease pathogenesis by helping bacteria in colonization, delivering virulence factors into host cells, and modulating host immune responses. This review highlights the role of OMVs in the context of host-pathogen interaction shedding light on the pathogenesis of L. pneumophila. Understanding the functions of OMVs and their cargo provides valuable insights into potential therapeutic targets and interventions for combating Legionnaires' disease.

Physical Properties and Shifting of the Extracellular Membrane Vesicles Attached to Living Bacterial Cell Surfaces

Bacterial cells release nanometer-sized extracellular membrane vesicles (MVs) to deliver cargo molecules for use in mediating various biological processes. However, the detailed processes of transporting these cargos from MVs to recipient cells remain unclear because of the lack of imaging techniques to image nanometer-sized fragile vesicles in a living bacterial cell surface. Herein, we quantitatively demonstrated that the direct binding of MV to the cell surface significantly promotes hydrophobic quorum-sensing signal (C16-HSL) transportation to the recipient cells. Moreover, we analyzed the MV-binding process in the Paracoccus denitrificans cell surface using high-speed atomic force microscopy phase imaging. Although MV shapes were unaltered after binding to the cell surface, the physical properties of a group of single MV particles were shifted. Additionally, the phase shift values of MVs were higher than that of the cell's surfaces upon binding, whereas the phase shift values of the group of MVs were decreased during observation. The shifting physical properties occurred irreversibly only once for each MV during the observations. The decreasing phase shift values indicated alterations of chemical components in the MVs as well, thereby suggesting the dynamic process in which single MV particles deliver their hydrophobic cargo into the recipient cell. IMPORTANCE Compared to the increasing knowledge about MV release mechanisms from donor cells, the mechanism by which recipient cells receive cargo from MVs remains unknown. Herein, we have successfully imaged single MV-binding processes in living bacterial cell surfaces. Accordingly, we confirmed the shift in the MV hydrophobic properties after landing on the cell surface. Our results showed the detailed states and the attaching process of a single MV into the cell surface and can aid the development of a new model for MV reception into Gram-negative bacterial cell surfaces. The insight provided by this study is significant for understanding MV-mediated cell-cell communication mechanisms. Moreover, the AFM technique presented for nanometer-scaled mapping of dynamic physical properties alteration on a living cell could be applied for the analyses of various biological phenomena occurring on the cell surface, and it gives us a new view into the understanding of the phenotypes of the bacterial cell surface.

Recent developments in horizontal gene transfer with the adaptive innovation of fermented foods

Horizontal gene transfer (HGT) has contributed significantly to the adaptability of bacteria, yeast and mold in fermented foods, whose evidence has been found in several fermented foods. Although not every HGT has biological significance, it plays an important role in improving the quality of fermented foods. In this review, how HGT facilitated microbial domestication and adaptive evolution in fermented foods was discussed. HGT can assist in the industrial innovation of fermented foods, and this adaptive evolution strategy can improve the quality of fermented foods. Additionally, the mechanism underlying HGT in fermented foods were analyzed. Furthermore, the critical bottlenecks involved in optimizing HGT during the production of fermented foods and strategies for optimizing HGT were proposed. Finally, the prospect of HGT for promoting the industrial innovation of fermented foods was highlighted. The comprehensive report on HGT in fermented foods provides a new trend for domesticating preferable starters for food fermentation, thus optimizing the quality and improving the industrial production of fermented foods.