Role of chemotaxis in autoaggregation of Escherichia coli

Many bacteria can communicate with each other, coordinating and synchronizing their behaviour by means of production and sensing of extracellular signal molecules called autoinducers. Most autoinducers modulate intraspecies communication, but autoinducer 2 (AI-2) functions as a universal quorum sensing signal that enables interspecies communication. In this work, we show novel roles of AI-2 in intra- and interspecies interactions of E. coli. We demonstrate that motility and chemotaxis play a crucial role in the collective behaviour – autoaggregation – of E. coli. This provides the first physiologically relevant example of collective behaviour in bacteria being driven by chemotaxis to a self-produced attractant. Equally important is our finding that this self-attraction is mediated by the quorum-sensing signal AI-2. AI-2 is produced by a large number of bacteria including E. coli, but significance of AI-2-mediated signalling remains poorly understood. Using comprehensive whole-population and single-cell analysis, we have conclusively shown that AI-2 import and metabolism represent the only AI-2 uptake-dependent phenotype in E. coli. Nevertheless, our work shows that, by promoting aggregative behaviour via chemotaxis, AI-2 plays a true signalling function in E. coli. Such AI-2-mediated autoaggregation promotes not only bacterial stress resistance but also formation of surface-attached biofilms. Our work thus establishes direct connection between these two forms of bacterial collective behaviour that are normally treated separately. We also demonstrate that autoaggregation behaviour and biofilm formation by E. coli are enhanced in presence of Enterococcus faecalis that naturally co-occurs with E. coli in mammalian gut. We further show that this enhancement is due to the interspecies signalling that is mediated by AI-2, which enables E. coli to maintain activity of its quorum sensing system and promotes its chemotaxis-dependent aggregation at lower cell densities. Formation of such mixed dual-species biofilms increases stress resistance of both E. coli and E. faecalis

Bacterial Quorum Sensing Signals at the Interdomain Interface

Chemical interactions among microorganisms and between microorganisms and their hosts involve bidirectional release and sensing of various signalling molecules. Quorum sensing, mediated by small molecules termed autoinducers, is well known to be used by bacteria to coordinate their collective behaviours. However, there is a growing body of evidence suggesting that autoinducers are involved not only in intraspecies and interspecies communication among bacteria, but also in signalling interactions with eukaryotic hosts and even with phages. Although a clear picture is yet to emerge, in this minireview we briefly summarize recent advances in our understanding of interdomain signalling mediated by the major classes of the bacterial quorum sensing molecules, including its effects on the host cells and its potential physiological relevance.ISSN:0021-2148ISSN:1565-8187ISSN:1869-586

Reply to jobling, “lysogeny of escherichia coli by the obligately lytic bacteriophage t1: Not proven”

ISSN:2150-7511ISSN:2161-212

Role of chemotaxis in autoaggregation of Escherichia coli

Many bacteria can communicate with each other, coordinating and synchronizing their behaviour by means of production and sensing of extracellular signal molecules called autoinducers. Most autoinducers modulate intraspecies communication, but autoinducer 2 (AI-2) functions as a universal quorum sensing signal that enables interspecies communication. In this work, we show novel roles of AI-2 in intra- and interspecies interactions of E. coli. We demonstrate that motility and chemotaxis play a crucial role in the collective behaviour – autoaggregation – of E. coli. This provides the first physiologically relevant example of collective behaviour in bacteria being driven by chemotaxis to a self-produced attractant. Equally important is our finding that this self-attraction is mediated by the quorum-sensing signal AI-2. AI-2 is produced by a large number of bacteria including E. coli, but significance of AI-2-mediated signalling remains poorly understood. Using comprehensive whole-population and single-cell analysis, we have conclusively shown that AI-2 import and metabolism represent the only AI-2 uptake-dependent phenotype in E. coli. Nevertheless, our work shows that, by promoting aggregative behaviour via chemotaxis, AI-2 plays a true signalling function in E. coli. Such AI-2-mediated autoaggregation promotes not only bacterial stress resistance but also formation of surface-attached biofilms. Our work thus establishes direct connection between these two forms of bacterial collective behaviour that are normally treated separately. We also demonstrate that autoaggregation behaviour and biofilm formation by E. coli are enhanced in presence of Enterococcus faecalis that naturally co-occurs with E. coli in mammalian gut. We further show that this enhancement is due to the interspecies signalling that is mediated by AI-2, which enables E. coli to maintain activity of its quorum sensing system and promotes its chemotaxis-dependent aggregation at lower cell densities. Formation of such mixed dual-species biofilms increases stress resistance of both E. coli and E. faecalis

Flagellum-Mediated Mechanosensing and RflP Control Motility State of Pathogenic Escherichia coli

Flagella and motility are widespread virulence factors among pathogenic bacteria. Motility enhances the initial host colonization, but the flagellum is a major antigen targeted by the host immune system. Here, we demonstrate that pathogenic E. coli strains employ a mechanosensory function of the flagellar motor to activate flagellar expression under high loads, while repressing it in liquid culture. We hypothesize that this mechanism allows pathogenic E. coli to regulate its motility dependent on the stage of infection, activating flagellar expression upon initial contact with the host epithelium, when motility is beneficial, but reducing it within the host to delay the immune response.Bacterial flagellar motility plays an important role in many processes that occur at surfaces or in hydrogels, including adhesion, biofilm formation, and bacterium-host interactions. Consequently, expression of flagellar genes, as well as genes involved in biofilm formation and virulence, can be regulated by the surface contact. In a few bacterial species, flagella themselves are known to serve as mechanosensors, where an increased load on flagella experienced during surface contact or swimming in viscous media controls gene expression. In this study, we show that gene regulation by motility-dependent mechanosensing is common among pathogenic Escherichia coli strains. This regulatory mechanism requires flagellar rotation, and it enables pathogenic E. coli to repress flagellar genes at low loads in liquid culture, while activating motility in porous medium (soft agar) or upon surface contact. It also controls several other cellular functions, including metabolism and signaling. The mechanosensing response in pathogenic E. coli depends on the negative regulator of motility, RflP (YdiV), which inhibits basal expression of flagellar genes in liquid. While no conditional inhibition of flagellar gene expression in liquid and therefore no upregulation in porous medium was observed in the wild-type commensal or laboratory strains of E. coli, mechanosensitive regulation could be recovered by overexpression of RflP in the laboratory strain. We hypothesize that this conditional activation of flagellar genes in pathogenic E. coli reflects adaptation to the dual role played by flagella and motility during infection

Multiple functions of flagellar motility and chemotaxis in bacterial physiology

Most swimming bacteria are capable of following gradients of nutrients, signaling molecules and other environmental factors that affect bacterial physiology. This tactic behavior became one of the most-studied model systems for signal transduction and quantitative biology, and underlying molecular mechanisms are well characterized in Escherichia coli and several other model bacteria. In this review, we focus primarily on less understood aspect of bacterial chemotaxis, namely its physiological relevance for individual bacterial cells and for bacterial populations. As evident from multiple recent studies, even for the same bacterial species flagellar motility and chemotaxis might serve multiple roles, depending on the physiological and environmental conditions. Among these, finding sources of nutrients and more generally locating niches that are optimal for growth appear to be one of the major functions of bacterial chemotaxis, which could explain many chemoeffector preferences as well as flagellar gene regulation. Chemotaxis might also generally enhance efficiency of environmental colonization by motile bacteria, which involves intricate interplay between individual and collective behaviors and trade-offs between growth and motility. Finally, motility and chemotaxis play multiple roles in collective behaviors of bacteria including swarming, biofilm formation and autoaggregation, as well as in their interactions with animal and plant hosts.ISSN:0168-6445ISSN:1574-697

Silicon Nitride, a Bioceramic for Bone Tissue Engineering: A Reinforced Cryogel System With Antibiofilm and Osteogenic Effects

Silicon nitride (SiN [Si3N4]) is a promising bioceramic for use in a wide variety of orthopedic applications. Over the past decades, it has been mainly used in industrial applications, such as space shuttle engines, but not in the medical field due to scarce data on the biological effects of SiN. More recently, it has been increasingly identified as an emerging material for dental and orthopedic implant applications. Although a few reports about the antibacterial properties and osteoconductivity of SiN have been published to date, there have been limited studies of SiN-based scaffolds for bone tissue engineering. Here, we developed a silicon nitride reinforced gelatin/chitosan cryogel system (SiN-GC) by loading silicon nitride microparticles into a gelatin/chitosan cryogel (GC), with the aim of producing a biomimetic scaffold with antibiofilm and osteogenic properties. In this scaffold system, the GC component provides a hydrophilic and macroporous environment for cells, while the SiN component not only provides antibacterial properties and osteoconductivity but also increases the mechanical stiffness of the scaffold. This provides enhanced mechanical support for the defect area and a better osteogenic environment. First, we analyzed the scaffold characteristics of SiN-GC with different SiN concentrations, followed by evaluation of its apatite-forming capacity in simulated body fluid and protein adsorption capacity. We further confirmed an antibiofilm effect of SiN-GC against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as well as enhanced cell proliferation, mineralization, and osteogenic gene upregulation for MC3T3-E1 pre-osteoblast cells. Finally, we developed a bioreactor to culture cell-laden scaffolds under cyclic compressive loading to mimic physiological conditions and were able to demonstrate improved mineralization and osteogenesis from SiN-GC. Overall, we confirmed the antibiofilm and osteogenic effect of a silicon nitride reinforced cryogel system, and the results indicate that silicon nitride as a biomaterial system component has a promising potential to be developed further for bone tissue engineering applications.ISSN:2296-418

Quorum Sensing and Metabolic State of the Host Control Lysogeny-Lysis Switch of Bacteriophage T1

The dynamics of microbial communities are heavily shaped by bacterium-bacteriophage interactions. But despite the apparent importance of bacteriophages, our understanding of the mechanisms controlling phage dynamics in bacterial populations, and particularly of the differences between the decisions that are made in the dormant lysogenic and active lytic states, remains limited. In this report, we show that enterobacterial phage T1, previously described as a lytic phage, is able to undergo lysogeny. We further demonstrate that the lysogeny-to-lysis decision occurs in response to changes in the density of the bacterial population, mediated by interspecies quorum-sensing signal AI-2, and in the metabolic state of the cell, mediated by cAMP receptor protein. We hypothesize that this strategy enables the phage to maximize its chances of self-amplification and spreading in bacterial population upon induction of the lytic cycle and that it might be common in phage-host interactions.Bacterial viruses, or bacteriophages, are highly abundant in the biosphere and have a major impact on microbial populations. Many examples of phage interactions with their hosts, including establishment of dormant lysogenic and active lytic states, have been characterized at the level of the individual cell. However, much less is known about the dependence of these interactions on host metabolism and signal exchange within bacterial communities. In this report, we describe a lysogenic state of the enterobacterial phage T1, previously known as a classical lytic phage, and characterize the underlying regulatory circuitry. We show that the transition from lysogeny to lysis depends on bacterial population density, perceived via interspecies autoinducer 2. Lysis is further controlled by the metabolic state of the cell, mediated by the cyclic-3′,5′-AMP (cAMP) receptor protein (CRP) of the host. We hypothesize that such combinations of cell density and metabolic sensing may be common in phage-host interactions

The Mobilizable Plasmid P3 of Salmonella enterica Serovar Typhimurium SL1344 Depends on the P2 Plasmid for Conjugative Transfer into a Broad Range of Bacteria In Vitro and In Vivo

The global rise of drug-resistant bacteria is of great concern. Conjugative transfer of antibiotic resistance plasmids contributes to the emerging resistance crisis. Despite substantial progress in understanding the molecular basis of conjugation in vitro, the in vivo dynamics of intra- and interspecies conjugative plasmid transfer are much less understood. In this study, we focused on the streptomycin resistance-encoding mobilizable plasmid pRSF1010SL1344 (P3) of Salmonella enterica serovar Typhimurium strain SL1344. We show that P3 is mobilized by interacting with the conjugation machinery of the conjugative plasmid pCol1B9SL1344 (P2) of SL1344. Thereby, P3 can be transferred into a broad range of relevant environmental and clinical bacterial isolates in vitro and in vivo. Our data suggest that S. Typhimurium persisters in host tissues can serve as P3 reservoirs and foster transfer of both P2 and P3 once they reseed the gut lumen. This adds to our understanding of resistance plasmid transfer in ecologically relevant niches, including the mammalian gut. IMPORTANCE S. Typhimurium is a globally abundant bacterial species that rapidly occupies new niches and survives unstable environmental conditions. As an enteric pathogen, S. Typhimurium interacts with a broad range of bacterial species residing in the mammalian gut. High abundance of bacteria in the gut lumen facilitates conjugation and spread of plasmid-carried antibiotic resistance genes. By studying the transfer dynamics of the P3 plasmid in vitro and in vivo, we illustrate the impact of S. Typhimurium-mediated antibiotic resistance spread via conjugation to relevant environmental and clinical bacterial isolates. Plasmids are among the most critical vehicles driving antibiotic resistance spread. Further understanding of the dynamics and drivers of antibiotic resistance transfer is needed to develop effective solutions for slowing down the emerging threat of multidrug-resistant bacterial pathogens.ISSN:0021-9193ISSN:1098-553

Chemotaxis and autoinducer-2 signalling mediate colonization and contribute to co-existence of Escherichia coli strains in the murine gut

Bacteria communicate and coordinate their behaviour at the intra- and interspecies levels by producing and sensing diverse extracellular small molecules called autoinducers. Autoinducer 2 (AI-2) is produced and detected by a variety of bacteria and thus plays an important role in interspecies communication and chemotaxis. Although AI-2 is a major autoinducer molecule present in the mammalian gut and can influence the composition of the murine gut microbiota, its role in bacteria-bacteria and bacteria-host interactions during gut colonization remains unclear. Combining competitive infections in C57BL/6 mice with microscopy and bioinformatic approaches, we show that chemotaxis (cheY) and AI-2 signalling (via lsrB) promote gut colonization by Escherichia coli, which is in turn connected to the ability of the bacteria to utilize fructoselysine (frl operon). We further show that the genomic diversity of E. coli strains with respect to AI-2 signalling allows ecological niche segregation and stable co-existence of different E. coli strains in the mammalian gut.ISSN:2058-527