Biofilms, flagella, and mechanosensing of surfaces by bacteria

Flagellar stator genes control a trophic shift from obligate to facultative predation and biofilm formation in a bacterial predator

The bacterial predator Bdellovibrio bacteriovorus is considered to be obligatorily prey (host)-dependent (H-D), and thus unable to form biofilms. However, spontaneous host-independent (H-I) variants grow axenically and can form robust biofilms. A screen of 350 H-I mutants revealed that single mutations in stator genes fliL or motA were sufficient to generate flagellar motility-defective H-I strains able to adhere to surfaces but unable to develop biofilms. The variants showed large transcriptional shifts in genes related to flagella, prey-invasion, and cyclic-di-GMP (CdG), as well as large changes in CdG cellular concentration relative to the H-D parent. The introduction of the parental fliL allele resulted in a full reversion to the H-D phenotype, but we propose that specific interactions between stator proteins prevented functional complementation by fliL paralogs. In contrast, specific mutations in a pilus-associated protein (Bd0108) mutant background were necessary for biofilm formation, including secretion of extracellular DNA (eDNA), proteins, and polysaccharides matrix components. Remarkably, fliL disruption strongly reduced biofilm development. All H-I variants grew similarly without prey, showed a strain-specific reduction in predatory ability in prey suspensions, but maintained similar high efficiency in prey biofilms. Population-wide allele sequencing suggested additional routes to host independence. Thus, stator and invasion pole-dependent signaling control the H-D and the H-I biofilm-forming phenotypes, with single mutations overriding prey requirements, and enabling shifts from obligate to facultative predation, with potential consequences on community dynamics. Our findings on the facility and variety of changes leading to facultative predation also challenge the concept of Bdellovibrio and like organisms being obligate predators.

IMPORTANCE

The ability of bacteria to form biofilms is a central research theme in biology, medicine, and the environment. We show that cultures of the obligate (host-dependent) "solitary" predatory bacterium Bdellovibrio bacteriovorus, which cannot replicate without prey, can use various genetic routes to spontaneously yield host-independent (H-I) variants that grow axenically (as a single species, in the absence of prey) and exhibit various surface attachment phenotypes, including biofilm formation. These routes include single mutations in flagellar stator genes that affect biofilm formation, provoke motor instability and large motility defects, and disrupt cyclic-di-GMP intracellular signaling. H-I strains also exhibit reduced predatory efficiency in suspension but high efficiency in prey biofilms. These changes override the requirements for prey, enabling a shift from obligate to facultative predation, with potential consequences on community dynamics.

Quantification of early biofilm growth in microtiter plates through a novel image analysis software

Given the significant impact of biofilms on human health and material corrosion, research in this field urgently needs more accessible techniques to facilitate the testing of new control agents and general understanding of biofilm biology. Microtiter plates offer a convenient format for standardized evaluations, including high-throughput assays of alternative treatments and molecular modulators. This study introduces a novel Biofilm Analysis Software (BAS) for quantifying biofilms from microtiter plate images. We focused on early biofilm growth stages and compared BAS quantification to common techniques: direct turbidity measurement, intrinsic fluorescence detection linked to pyoverdine production, and standard crystal violet staining which enables image analysis and optical density measurement. We also assessed their sensitivity for detecting subtle growth effects caused by cyclic AMP and gentamicin. Our results show that BAS image analysis is at least as sensitive as the standard method of spectrophotometrically quantifying the crystal violet retained by biofilms. Furthermore, we demonstrated that bacteria adhered after short incubations (from 10 min to 4 h), isolated from planktonic populations by a simple rinse, can be monitored until their growth is detectable by intrinsic fluorescence, BAS analysis, or resolubilized crystal violet. These procedures are widely accessible for many laboratories, including those with limited resources, as they do not require a spectrophotometer or other specialized equipment.

The yad and yeh fimbrial loci influence gene expression and virulence in enterohemorrhagic Escherichia coli O157:H7

Fimbriae are essential virulence factors for many bacterial pathogens. Fimbriae are extracellular structures that attach bacteria to surfaces. Thus, fimbriae mediate a critical step required for any pathogen to establish infection by anchoring a bacterium to host tissue. The human pathogen enterohemorrhagic Escherichia coli (EHEC) O157:H7encodes 16 fimbriae that may be important for EHEC to initiate infection and allow for productive expression of virulence traits important in later stages of infection, including a type III secretion system (T3SS) and Shiga toxin; however, the roles of most EHEC fimbriae are largely uncharacterized. Here, we provide evidence that two EHEC fimbriae, Yad and Yeh, modulate expression of diverse genes including genes encoding T3SS and Shiga toxin and that these fimbriae are required for robust colonization of the gastrointestinal tract. These findings reveal a significant and previously unappreciated role for fimbriae in bacterial pathogenesis as important determinants of virulence gene expression.IMPORTANCEFimbriae are extracellular proteinaceous structures whose defining role is to anchor bacteria to surfaces. This is a fundamental step for bacterial pathogens to establish infection in a host. Here, we show that the contributions of fimbriae to pathogenesis are more complex. Specifically, we demonstrate that fimbriae influence expression of virulence traits essential for disease progression in the intestinal pathogen enterohemorrhagic Escherichia coli. Gram-positive and Gram-negative bacteria express multiple fimbriae; therefore, these findings may have broad implications for understanding how pathogens use fimbriae, beyond adhesion, to initiate infection and coordinate gene expression, which ultimately results in disease.

Active interface bulging in Bacillus subtilis swarms promotes self-assembly and biofilm formation

Microbial communities such as biofilms are commonly found at interfaces. However, it is unclear how the physical environment of interfaces may contribute to the development and behavior of surface-associated microbial communities. Combining multimode imaging, single-cell tracking, and numerical simulations, here, we found that activity-induced interface bulging promotes colony biofilm formation in Bacillus subtilis swarms presumably via segregation and enrichment of sessile cells in the bulging area. Specifically, the diffusivity of passive particles is ~50% lower inside the bulging area than elsewhere, which enables a diffusion-trapping mechanism for self-assembly and may account for the enrichment of sessile cells. We also uncovered a quasilinear relation between cell speed and surface-packing density that underlies the process of active interface bulging. Guided by the speed-density relation, we demonstrated reversible formation of liquid bulges by manipulating the speed and local density of cells with light. Over the course of development, the active bulges turned into striped biofilm structures, which eventually give rise to a large-scale ridge pattern. Our findings reveal a unique physical mechanism of biofilm formation at air-solid interface, which is pertinent to engineering living materials and directed self-assembly in active fluids.

Carbon Source and Substrate Surface Affect Biofilm Formation by the Plant-Associated Bacterium Pseudomonas donghuensis P482

The ability of bacteria to colonize diverse environmental niches is often linked to their competence in biofilm formation. It depends on the individual characteristics of a strain, the nature of the colonized surface (abiotic or biotic), or the availability of certain nutrients. Pseudomonas donghuensis P482 efficiently colonizes the rhizosphere of various plant hosts, but a connection between plant tissue colonization and the biofilm formation ability of this strain has not yet been established. We demonstrate here that the potential of P482 to form biofilms on abiotic surfaces and the structural characteristics of the biofilm are influenced by the carbon source available to the bacterium, with glycerol promoting the process. Also, the type of substratum, polystyrene or glass, impacts the ability of P482 to attach to the surface. Moreover, P482 mutants in genes associated with motility or chemotaxis, the synthesis of polysaccharides, and encoding proteases or regulatory factors, which affect biofilm formation on glass, were fully capable of colonizing the root tissue of both tomato and maize hosts. Investigating the role of cellular factors in biofilm formation using these plant-associated bacteria shows that the ability of bacteria to form biofilm on abiotic surfaces does not necessarily mirror its ability to colonize plant tissues. Our research provides a broader perspective on the adaptation of these bacteria to various environments.

Identification of a multi-modal mechanism for Se(VI) reduction and Se(0) allotropic transition by Stenotrophomonas bentonitica

Microorganisms can play a key role in selenium (Se) bioremediation and the fabrication of Se-based nanomaterials by reducing toxic forms (Se(VI) and Se(IV)) into Se(0). In recent years, omics have become a useful tool in understanding the metabolic pathways involved in the reduction process. This paper aims to elucidate the specific molecular mechanisms involved in Se(VI) reduction by the bacterium Stenotrophomonas bentonitica. Both cytoplasmic and membrane fractions were able to reduce Se(VI) to Se(0) nanoparticles (NPs) with different morphologies (nanospheres and nanorods) and allotropes (amorphous, monoclinic, and trigonal). Proteomic analyses indicated an adaptive response against Se(VI) through the alteration of several metabolic pathways including those related to energy acquisition, synthesis of proteins and nucleic acids, and transport systems. Whilst the thioredoxin system and the Painter reactions were identified to play a crucial role in Se reduction, flagellin may also be involved in the allotropic transformation of Se. These findings suggest a multi-modal reduction mechanism is involved, providing new insights for developing novel strategies in bioremediation and nanoparticle synthesis for the recovery of critical materials within the concept of circular economy.

Mechanisms of microbial co-aggregation in mixed anaerobic cultures

Co-aggregation of anaerobic microorganisms into suspended microbial biofilms (aggregates) serves ecological and biotechnological functions. Tightly packed aggregates of metabolically interdependent bacteria and archaea play key roles in cycling of carbon and nitrogen. Additionally, in biotechnological applications, such as wastewater treatment, microbial aggregates provide a complete metabolic network to convert complex organic material. Currently, experimental data explaining the mechanisms behind microbial co-aggregation in anoxic environments is scarce and scattered across the literature. To what extent does this process resemble co-aggregation in aerobic environments? Does the limited availability of terminal electron acceptors drive mutualistic microbial relationships, contrary to the commensal relationships observed in oxygen-rich environments? And do co-aggregating bacteria and archaea, which depend on each other to harvest the bare minimum Gibbs energy from energy-poor substrates, use similar cellular mechanisms as those used by pathogenic bacteria that form biofilms? Here, we provide an overview of the current understanding of why and how mixed anaerobic microbial communities co-aggregate and discuss potential future scientific advancements that could improve the study of anaerobic suspended aggregates. KEY POINTS: • Metabolic dependency promotes aggregation of anaerobic bacteria and archaea • Flagella, pili, and adhesins play a role in the formation of anaerobic aggregates • Cyclic di-GMP/AMP signaling may trigger the polysaccharides production in anaerobes.

A flagellar accessory protein links chemotaxis to surface sensing

Bacteria find suitable locations for colonization by sensing and responding to surfaces. Complex signaling repertoires control surface colonization, and surface contact sensing by the flagellum plays a central role in activating colonization programs. Caulobacter crescentus adheres to surfaces using a polysaccharide adhesin called the holdfast. In C. crescentus, disruption of the flagellum through interactions with a surface or mutation of flagellar genes increases holdfast production. Our group previously identified several C. crescentus genes involved in flagellar surface sensing. One of these, called fssF, codes for a protein with homology to the flagellar C-ring protein FliN. We show here that a fluorescently tagged FssF protein localizes to the flagellated pole of the cell and requires all components of the flagellar C-ring for proper localization, supporting the model that FssF associates with the C-ring. Deleting fssF results in a severe motility defect that we show is due to a disruption of chemotaxis. Epistasis experiments demonstrate that fssF promotes adhesion through a stator-dependent pathway when late-stage flagellar mutants are disrupted. Separately, we find that disruption of chemotaxis through deletion of fssF or other chemotaxis genes results in a hyperadhesion phenotype. Key genes in the surface sensing network (pleD, motB, and dgcB) contribute to both ∆flgH-dependent and ∆fssF-dependent hyperadhesion, but these genes affect adhesion differently in the two hyperadhesive backgrounds. Our results support a model in which the stator subunits of the flagella incorporate both mechanical and chemical signals to regulate adhesion.

Tannic acid inhibits Escherichia coli biofilm formation and underlying molecular mechanisms: Biofilm regulator CsgD

Biofilms often engender persistent infections, heightened antibiotic resistance, and the recurrence of infections. Therefor, infections related to bacterial biofilms are often chronic and pose challenges in terms of treatment. The main transcription regulatory factor, CsgD, activates csgABC-encoded curli to participate in the composition of extracellular matrix, which is an important skeleton for biofilm development in enterobacteriaceae. In our previous study, a wide range of natural bioactive compounds that exhibit strong affinity to CsgD were screened and identified via molecular docking. Tannic acid (TA) was subsequently chosen, based on its potent biofilm inhibition effect as observed in crystal violet staining. Therefore, the aim of this study was to investigate the specific effects of TA on the biofilm formation of clinically isolated Escherichia coli (E. coli). Results demonstrated a significant inhibition of E. coli Ec032 biofilm formation by TA, while not substantially affecting the biofilm of the ΔcsgD strain. Moreover, deletion of the csgD gene led to a reduction in Ec032 biofilm formation, alongside diminished bacterial motility and curli synthesis inhibition. Transcriptomic analysis and RT-qPCR revealed that TA repressed genes associated with the csg operon and other biofilm-related genes. In conclusion, our results suggest that CsgD is one of the key targets for TA to inhibit E. coli biofilm formation. This work preliminarily elucidates the molecular mechanisms of TA inhibiting E. coli biofilm formation, which could provide a lead structure for the development of future antibiofilm drugs.

Transcriptomic and proteomic analysis of the virulence inducing effect of ciprofloxacin on enterohemorrhagic Escherichia coli

Enterohemorrhagic E. coli (EHEC) is considered to be the most dangerous pathotype of E. coli, as it causes severe conditions such as hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS). Antibiotic treatment of EHEC infections is generally not recommended since it may promote the production of the Shiga toxin (Stx) and lead to worsened symptoms. This study explores how exposure to the fluoroquinolone ciprofloxacin reorganizes the transcriptome and proteome of EHEC O157:H7 strain EDL933, with special emphasis on virulence-associated factors. As expected, exposure to ciprofloxacin caused an extensive upregulation of SOS-response- and Stx-phage proteins, including Stx. A range of other virulence-associated factors were also upregulated, including many genes encoded by the LEE-pathogenicity island, the enterohemolysin gene (ehxA), as well as several genes and proteins involved in LPS production. However, a large proportion of the genes and proteins (17 and 8%, respectively) whose expression was upregulated upon ciprofloxacin exposure (17 and 8%, respectively) are not functionally assigned. This indicates a knowledge gap in our understanding of mechanisms involved in EHECs response to antibiotic-induced stress. Altogether, the results contribute to better understanding of how exposure to ciprofloxacin influences the virulome of EHEC and generates a knowledge base for further studies on how EHEC responds to antibiotic-induced stress. A deeper understanding on how EHEC responds to antibiotics will facilitate development of novel and safer treatments for EHEC infections.

Interspecies surfactants serve as public goods enabling surface motility in Pseudomonas aeruginosa

In most natural environments, bacteria live in polymicrobial communities where secreted molecules from neighboring species alter bacterial behaviors including motility, but such interactions are understudied. Pseudomonas aeruginosa is a motile opportunistic pathogen that exists in diverse multispecies environments such as the soil and is frequently found in human wound and respiratory tract co-infections with other bacteria including Staphylococcus aureus. Here we show that P. aeruginosa can co-opt secreted surfactants from other species for flagellar-based surface motility. We found that exogenous surfactants from S. aureus, other bacteria, and interkingdom species enabled P. aeruginosa to switch from swarming to an alternative surface spreading motility on semi-solid surfaces and allowed for the emergence of surface motility on hard agar where P. aeruginosa was otherwise unable to move. This motility was distinct from the response of other motile bacteria in the presence of exogenous surfactants. Mutant analysis indicated that this P. aeruginosa motility was similar to a previously described mucin-based motility, 'surfing', albeit with divergent regulation. Thus, our study demonstrates that secreted surfactants from the host as well as neighboring bacterial and interkingdom species act as public goods facilitating P. aeruginosa flagella-mediated surfing-like surface motility, thereby allowing it to access different environmental niches.

Emerging Approaches for Mitigating Biofilm-Formation-Associated Infections in Farm, Wild, and Companion Animals

The importance of addressing the problem of biofilms in farm, wild, and companion animals lies in their pervasive impact on animal health and welfare. Biofilms, as resilient communities of microorganisms, pose a persistent challenge in causing infections and complicating treatment strategies. Recognizing and understanding the importance of mitigating biofilm formation is critical to ensuring the welfare of animals in a variety of settings, from farms to the wild and companion animals. Effectively addressing this issue not only improves the overall health of individual animals, but also contributes to the broader goals of sustainable agriculture, wildlife conservation, and responsible pet ownership. This review examines the current understanding of biofilm formation in animal diseases and elucidates the complex processes involved. Recognizing the limitations of traditional antibiotic treatments, mechanisms of resistance associated with biofilms are explored. The focus is on alternative therapeutic strategies to control biofilm, with illuminating case studies providing valuable context and practical insights. In conclusion, the review highlights the importance of exploring emerging approaches to mitigate biofilm formation in animals. It consolidates existing knowledge, highlights gaps in understanding, and encourages further research to address this critical facet of animal health. The comprehensive perspective provided by this review serves as a foundation for future investigations and interventions to improve the management of biofilm-associated infections in diverse animal populations.

Where bacteria and eukaryotes meet

The international workshop "Interdisciplinary life of microbes: from single cells to multicellular aggregates," following a virtual preassembly in November 2021, was held in person in Dresden, from 9 to 13 November 2022. It attracted not only prominent experts in biofilm research but also researchers from broadly neighboring disciplines, such as medicine, chemistry, and theoretical and experimental biophysics, both eukaryotic and prokaryotic. Focused brainstorming sessions were the special feature of the event and are at the heart of this commentary.

Quorum Sensing Enhances Direct Interspecies Electron Transfer in Anaerobic Methane Production

Direct interspecies electron transfer (DIET) provides an innovative way to achieve efficient methanogenesis, and this study proposes a new approach to upregulate the DIET pathway by enhancing quorum sensing (QS). Based on long-term reactor performance, QS enhancement achieved more vigorous methanogenesis with 98.7% COD removal efficiency. In the control system, methanogenesis failure occurred at the accumulated acetate of 7420 mg of COD/L and lowered pH of 6.04, and a much lower COD removal of 41.9% was observed. The more significant DIET in QS-enhancing system was supported by higher expression of conductive pili and the c-Cyts cytochrome secretion-related genes, resulting in 12.7- and 10.3-fold improvements. Moreover, QS enhancement also improved the energy production capability, with the increase of F-type and V/A-type ATPase expression by 6.3- and 4.2-fold, and this effect probably provided more energy for nanowires and c-Cyts cytochrome secretion. From the perspective of community structure, QS enhancement increased the abundance of Methanosaeta and Geobacter from 54.3 and 17.6% in the control to 63.0 and 33.8%, respectively. Furthermore, the expression of genes involved in carbon dioxide reduction and alcohol dehydrogenation increased by 0.6- and 7.1-fold, respectively. Taken together, this study indicates the positive effects of QS chemicals to stimulate DIET and advances the understanding of the DIET methanogenesis involved in environments such as anaerobic digesters and sediments.

Flagella-mediated adhesion of Escherichia coli O157:H7 to surface of stainless steel, glass and fresh produces during sublethal injury and recovery

E. coli O157:H7 can be induced into sublethally injured (SI) state by lactic acid (LA) and regain activity in nutrient environments. This research clarified the role of flagella-related genes (fliD, fliS, cheA and motA) in adhesion of E. coli O157:H7 onto stainless steel, glass, lettuce, spinach, red cabbage and cucumber during LA-induced SI and recovery by plate counting. Results of adhesion showed improper flagellar rotation caused by the deletion of motA resulting in the decreased adhesion. Motility of wildtype determined by diameter of motility halo decreased in SI state and repaired with recovery time increasing, lagging behind changes in expression of flagella-related genes. Flagellar function-impaired strains all exhibited non-motile property. Thus, we speculated that flagella-mediated motility is critical in early stage of adhesion. We also found the effects of Fe2+, Ca2+ and Mn2+ on adhesion or motility of wildtype was independent of bacterial states. However, the addition of Ca2+ and Mn2+ did not affect motility of flagellar function-impaired strains as they did on wildtype. This research provides new insights to understand the role of flagella and cations in bacterial adhesion, which will aid in development of anti-adhesion agents to reduce bio-contamination in food processing.

Driving forces shaping the microbial ecology in meat packing plants

Meat production is a complex system, continually receiving animals, water, air, and workers, all of which serve as carriers of bacteria. Selective pressures involved in different meat processing stages such as antimicrobial interventions and low temperatures, may promote the accumulation of certain residential microbiota in meat cutting facilities. Bacteria including human pathogens from all these sources can contaminate meat surfaces. While significant advancements have been made in enhancing hygienic standards and pathogen control measures in meat plants, resulting in a notable reduction in STEC recalls and clinical cases, STEC still stands as a predominant contributor to foodborne illnesses associated with beef and occasionally with pork. The second-and third-generation sequencing technology has become popular in microbiota related studies and provided a better image of the microbial community in the meat processing environments. In this article, we reviewed the potential factors influencing the microbial ecology in commercial meat processing facilities and conducted a meta-analysis on the microbiota data published in the last 10 years. In addition, the mechanisms by which bacteria persist in meat production environments have been discussed with a focus on the significant human pathogen E. coli O157:H7 and generic E. coli, an indicator often used for the hygienic condition in food production.

Viscosity-dependent determinants of Campylobacter jejuni impacting the velocity of flagellar motility

IMPORTANCE

Bacteria can adapt flagellar motor output in response to the load that the extracellular milieu imparts on the flagellar filament to enable propulsion. Bacteria can adapt flagellar motor output in response to the load that the extracellular milieu imparts on the flagellar filament to enable propulsion through diverse environments. These changes may involve increasing power and torque in high-viscosity environments or reducing power and flagellar rotation upon contact with a surface. C. jejuni swimming velocity in low-viscosity environments is comparable to other bacterial flagellates and increases significantly as external viscosity increases. In this work, we provide evidence that the mechanics of the C. jejuni flagellar motor has evolved to naturally promote high swimming velocity in high-viscosity environments. We found that C. jejuni produces VidA and VidB as auxiliary proteins to specifically affect flagellar motor activity in low viscosity to reduce swimming velocity. Our findings provide some of the first insights into different mechanisms that exist in bacteria to alter the mechanics of a flagellar motor, depending on the viscosity of extracellular environments.

Flagella are required to coordinately activate competition and host colonization factors in response to a mechanical signal

Bacteria employ antagonistic strategies to eliminate competitors of an ecological niche. Contact-dependent mechanisms, such as the type VI secretion system (T6SS), are prevalent in host-associated bacteria, yet we know relatively little about how T6SS+ strains make contact with competitors in highly viscous environments, such as host mucus. To better understand how cells respond to and contact one another in such environments, we performed a genome-wide transposon mutant screen of the T6SS-wielding beneficial bacterial symbiont, Vibrio fischeri, and identified two sets of genes that are conditionally required for killing. LPS/capsule and flagellar-associated genes do not affect T6SS directly and are therefore not required for interbacterial killing when cell contact is forced yet are necessary for killing in high-viscosity liquid (hydrogel) where cell-cell contact must be biologically mediated. Quantitative transcriptomics revealed that V. fischeri significantly increases expression of both T6SS genes and cell surface modification factors upon transition from low- to high-viscosity media. Consistent with coincubation and fluorescence microscopy data, flagella are not required for T6SS expression in hydrogel. However, flagella play a key role in responding to the physical environment by promoting expression of the surface modification genes identified in our screen, as well as additional functional pathways important for host colonization including uptake of host-relevant iron and carbon sources, and nitric oxide detoxification enzymes. Our findings suggest that flagella may act as a mechanosensor for V. fischeri to coordinately activate competitive strategies and host colonization factors, underscoring the significance of the physical environment in directing complex bacterial behaviors.

Sensitivity of Legionella pneumophila to phthalates and their substitutes

Phthalates constitute a family of anthropogenic chemicals developed to be used in the manufacture of plastics, solvents, and personal care products. Their dispersion and accumulation in many environments can occur at all stages of their use (from synthesis to recycling). However, many phthalates together with other accumulated engineered chemicals have been shown to interfere with hormone activities. These compounds are also in close contact with microorganisms that are free-living, in biofilms or in microbiota, within multicellular organisms. Herein, the activity of several phthalates and their substitutes were investigated on the opportunistic pathogen Legionella pneumophila, an aquatic microbe that can infect humans. Beside showing the toxicity of some phthalates, data suggested that Acetyl tributyl citrate (ATBC) and DBP (Di-n-butyl phthalate) at environmental doses (i.e. 10-6 M and 10-8 M) can modulate Legionella behavior in terms of motility, biofilm formation and response to antibiotics. A dose of 10-6 M mostly induced adverse effects for the bacteria, in contrast to a dose of 10-8 M. No perturbation of virulence towards Acanthamoeba castellanii was recorded. These behavioral alterations suggest that L. pneumophila is able to sense ATBC and DBP, in a cross-talk that either mimics the response to a native ligand, or dysregulates its physiology.

Biofilm formation and cell plasticity drive diazotrophy in an anoxygenic phototrophic bacterium

IMPORTANCE

The contribution of non-cyanobacterial diazotrophs (NCDs) to total N2 fixation in the marine water column is unknown, but their importance is likely constrained by the limited availability of dissolved organic matter and low O2 conditions. Light could support N2 fixation and growth by NCDs, yet no examples from bacterioplankton exist. In this study, we show that the phototrophic NCD, Rhodopseudomonas sp. BAL398, which is a member of the diazotrophic community in the surface waters of the Baltic Sea, can utilize light. Our study highlights the significance of biofilm formation for utilizing light and fixing N2 under oxic conditions and the role of cell plasticity in regulating these processes. Our findings have implications for the general understanding of the ecology and importance of NCDs in marine waters.

Myxococcus xanthus PilB interacts with c-di-GMP and modulates motility and biofilm formation

The regulation of biofilm and motile states as alternate bacterial lifestyles has been studied extensively in flagellated bacteria, where the second messenger cyclic-di-GMP (cdG) plays a crucial role. However, much less is known about the mechanisms of such regulation in motile bacteria without flagella. The bacterial type IV pilus (T4P) serves as a motility apparatus that enables Myxococcus xanthus to move on solid surfaces. PilB, the T4P assembly ATPase, is, therefore, required for T4P-dependent motility in M. xanthus. Interestingly, T4P is also involved in the regulation of exopolysaccharide as the biofilm matrix material in this bacterium. A newly discovered cdG-binding domain, MshEN, is conserved in the N-terminus of PilB (PilBN) in M. xanthus and other bacteria. This suggests that cdG may bind to PilB to control the respective outputs that regulate biofilm development and T4P-powered motility. In this study, we aimed to validate M. xanthus PilB as a cdG effector protein. We performed a systematic mutational analysis of its cdG-binding domain to investigate its relationship with motility, piliation, and biofilm formation. Excluding those resulting in low levels of PilB protein, all other substitution mutations in PilBN resulted in pilB mutants with distinct and differential phenotypes in piliation and biofilm levels in M. xanthus. This suggests that the PilBN domain plays dual roles in modulating motility and biofilm levels, and these two functions of PilB can be dependent on and independent of each other in M. xanthus. IMPORTANCE The regulation of motility and biofilm by cyclic-di-GMP in flagellated bacteria has been extensively investigated. However, our knowledge regarding this regulation in motile bacteria without flagella remains limited. Here, we aimed to address this gap by investigating a non-flagellated bacterium with motility powered by bacterial type-IV pilus (T4P). Previous studies hinted at the possibility of Myxococcus xanthus PilB, the T4P assembly ATPase, serving as a cyclic-di-GMP effector involved in regulating both motility and biofilm. Our findings strongly support the hypothesis that PilB directly interacts with cyclic-di-GMP to act as a potential switch to promote biofilm formation or T4P-dependent motility. These results shed light on the bifurcation of PilB functions and its pivotal role in coordinating biofilm formation and T4P-mediated motility.

Microbiome recognition of virulence-factor-governed interfacial mechanisms in antibiotic resistance and pathogenicity removal by functionalized microbubbles

The frequent occurrence of epidemics around the world gives rise to increasing concerns of the pollution of pathogens and antibiotic resistant bacteria in water. This study investigated the impacts of virulence factors (VFs) on the removal of antibiotic resistant and pathogenic bacteria from municipal wastewater by ozone-free or ozone-encapsulated Fe(III)-coagulant-modified colloidal microbubbles (O3_free-CCMBs or O3-CCMBs). The highly interface-dependent process was initiated with cell-capture on the microbubble surface where the as-collected cells could be further inactivated with the bubble-released ozone and oxidative species if O3-CCMBs were used. The microbiome sequencing analyses denote that the O3_free-CCMB performance of antibiotic resistant and pathogenic bacteria removal was dependent on the virulence phenotypes related to cell-surface properties or structures. The adhesion-related VFs facilitated the effective attachment between cells and the coagulant-modified bubble-surface, which further enhanced cell inactivation by bubble-released ozone. On the contrary, the motility-related VFs might help cells to escape from the bubble capture by locomotion; however, this could be overcome by O3-CCMB-induced oxidative demolition of the movement structures. Besides, the microbubble performance was also impacted with the cell-membrane structure related to antibiotic resistance (i.e., efflux pumps) and the dissolved organic matter through promoting the surface-capture and decreasing the oxidation efficacy. The ozone-encapsulated microbubbles with surface functionalization are robust and promising tools in hampering antibiotic resistance and pathogenicity dissemination from wastewater to surface water environment; and awareness should be raised for the influence of virulence signatures on its performance.

Mechanism of 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT) in controlling microbial problems in aircraft fuel systems

This research investigated the potential use of 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT) as a biocide in aircraft fuel systems, which is rarely studied due to the unique properties of such systems. The study assessed the effectiveness of CMIT against three microbial isolates using minimum inhibitory concentrations and bacteriostatic tests, and showed that CMIT had good activity against them. Electrochemical studies were conducted to determine the impact of CMIT on the 7B04 aluminum alloy, which demonstrated that CMIT acted as a cathodic inhibitor and exhibited certain levels of short-term and long-term corrosion inhibition effects at concentrations of 100 mg L^-1 and 60 mg L^-1, respectively. Additionally, the research provided insights into the mechanisms governing microbial problems by studying the reaction of CMIT with glutathione and sulfate. Overall, the study suggested that CMIT may be a useful biocide in aircraft fuel systems and provided important information on its efficacy and mechanism of action.

Microfluidics for Biofilm Studies

Biofilms are multicellular communities held together by a self-produced extracellular matrix and exhibit a set of properties that distinguish them from free-living bacteria. Biofilms are exposed to a variety of mechanical and chemical cues resulting from fluid motion and mass transport. Microfluidics provides the precise control of hydrodynamic and physicochemical microenvironments to study biofilms in general. In this review, we summarize the recent progress made in microfluidics-based biofilm research, including understanding the mechanism of bacterial adhesion and biofilm development, assessment of antifouling and antimicrobial properties, development of advanced in vitro infection models, and advancement in methods to characterize biofilms. Finally, we provide a perspective on the future direction of microfluidics-assisted biofilm research.

Textiles as fomites in the healthcare system

Nosocomial infections or healthcare-associated infections (HAIs) are acquired under medical care in healthcare facilities. In hospital environments, the transmission of infectious diseases through textiles such as white coats, bed linen, curtains, and towels are well documented. Textile hygiene and infection control measures have become more important in recent years due to the growing concerns about textiles as fomites in healthcare settings. However, systematic research in this area is lacking; the factors contributing to the transmission of infections through textiles needs to be better understood. The review aims to critically explore textiles as contaminants in healthcare systems, and to identify potential risks they may pose to patients and healthcare workers. It delineates different factors affecting bacterial adherence on fabrics, such as surface properties of bacteria and fabrics, and environmental factors. It also identifies areas that require further research to reduce the risk of HAIs and improve textile hygiene practices. Finally, the review elaborates on the strategies currently employed, and those that can be employed to limit the spread of nosocomial infections through fabrics. Implementing textile hygiene practices effectively in healthcare facilities requires a thorough analysis of factors affecting fabric-microbiome interactions, followed by designing newer fabrics that discourage pathogen load. KEY POINTS: • Healthcare textiles act as a potential reservoir of nosocomial pathogens • Survival of pathogens is affected by surface properties of fabric and bacteria • Guidelines required for fabrics that discourage microbial load, for hospital use.

Contact Area and Deformation of Escherichia coli Cells Adhered on a Cationic Surface

When bacteria adhere to surfaces, the chemical and mechanical character of the cell-substrate interface guides cell function and the development of microcolonies and biofilms. Alternately on bactericidal surfaces, intimate contact is critical to biofilm prevention. The direct study of the buried cell-substrate interfaces at the heart of these behaviors is hindered by the small bacterial cell size and inaccessibility of the contact region. Here, we present a total internal reflectance fluorescence depletion approach to measure the size of the cell-substrate contact region and quantify the gap separation and curvature near the contact zone, providing an assessment of the shapes of the near-surface undersides of adhered bacterial cells. Resolution of the gap height is about 10%, down to a few nanometers at contact. Using 1 and 2 μm silica spheres as calibration standards we report that, for flagella-free Escherichia coli (E. coli) adhering on a cationic poly-l-lysine layer, the cell-surface contact and apparent cell deformation vary with adsorbed cell configuration. Most cells adhere by their ends, achieving small contact areas of 0.15 μm2, corresponding to about 1-2% of the cell's surface. The altered Gaussian curvatures of end-adhered cells suggest the flattening of the envelope within the small contact region. When cells adhere by their sides, the contact area is larger, in the range 0.3-1.1 μm2 and comprising up to ∼12% of the cell's total surface. A region of sharper curvature, greater than that of the cells' original spherocylindrical shape, borders the flat contact region in cases of side-on or end-on cell adhesion, suggesting envelope stress. From the measured curvatures, precise stress distributions over the cell surface could be calculated in future studies that incorporate knowledge of envelope moduli. Overall the small contact areas of end-adhered cells may be a limiting factor for antimicrobial surfaces that kill on contact rather than releasing bactericide.

Different cellular fatty acid pattern and gene expression of planktonic and biofilm state Listeria monocytogenes under nutritional stress

Listeria monocytogenes is a Gram-positive bacterium frequently involved in food-borne disease outbreaks and is widely distributed in the food-processing environment. This work aims to depict the impact of nutrition deficiency on the survival strategy of L. monocytogenes both in planktonic and biofilm states. In the present study, cell characteristics (autoaggression, hydrophobicity and motility), membrane fatty acid composition of MRL300083 (Lm83) in the forms of planktonic and biofilm-associated cells cultured in TSB-YE and 10-fold dilutions of TSB-YE (DTSB-YE) were investigated. Additionally, the relative expression of related genes were also determined by RT-qPCR. It was observed that cell growth in different bacterial life modes under nutritional stress rendered the cells a distinct phenotype. The higher autoaggression (AAG) and motility of the planktonic cells in DTSB-YE is associated with better biofilm formation. An increased proportion of unsaturated fatty acid/saturated fatty acid (USFA/SFA) indicates more fluidic biophysical properties for cell membranes of L. monocytogenes in planktonic and biofilm cells in DTSB-YE. Biofilm cells produced a higher percentage of USFA and straight fatty acids than the corresponding planktonic cells. An appropriate degree of membrane fluidity is crucial for survival, and alteration of membrane lipids is an essential adaptive response. The adaptation of bacteria to stress is a multifactorial cellular process, the expression of flagella-related genes fliG, fliP, flgE and the two-component chemotactic system cheA/Y genes of planktonic cells in DTSB-YE significantly increased compared to that in TSB-YE (p < 0.05). This study provides new information on the role of the physiological adaptation and gene expression of L. monocytogenes for planktonic and biofilm growth under nutritional stress.

The Determination, Monitoring, Molecular Mechanisms and Formation of Biofilm in E. coli

Biofilms are cell assemblies embedded in an exopolysaccharide matrix formed by microorganisms of a single or many different species. This matrix in which they are embedded protects the bacteria from external influences and antimicrobial effects. The biofilm structure that microorganisms form to protect themselves from harsh environmental conditions and survive is found in nature in many different environments. These environments where biofilm formation occurs have in common that they are in contact with fluids. The gene expression of bacteria in complex biofilm differs from that of bacteria in the planktonic state. The differences in biofilm cell expression are one of the effects of community life. Means of quorum sensing, bacteria can act in coordination with each other. At the same time, while biofilm formation provides many benefits to bacteria, it has positive and negative effects in many different areas. Depending on where they occur, biofilms can cause serious health problems, contamination risks, corrosion, and heat and efficiency losses. However, they can also be used in water treatment plants, bioremediation, and energy production with microbial fuel cells. In this review, the basic steps of biofilm formation and biofilm regulation in the model organism Escherichia coli were discussed. Finally, the methods by which biofilm formation can be detected and monitored were briefly discussed.

Diving into the complexity of the spirochetal endoflagellum

Spirochaetes, a phylum that includes medically important pathogens such as the causative agents of Lyme disease, syphilis, and leptospirosis, are in many ways highly unique bacteria. Their cell morphology, subcellular organization, and metabolism reveal atypical features. Spirochetal motility is also singular, dependent on the presence of periplasmic flagella or endoflagella, inserted subterminally at cell poles and not penetrating the outer membrane and elongating outside the cell as in enterobacteria. In this review we present a comprehensive comparative genomics analysis of endoflagellar systems in spirochetes, highlighting recent findings on the flagellar basal body and filament. Continued progress in understanding the function and architecture of spirochetal flagella is uncovering paradigm-shifting mechanisms of bacterial motility.

Cell Density-Regulated Adhesins Contribute to Early Disease Development and Adhesion in Ralstonia solanacearum

Adhesins (adhesive proteins) help bacteria stick to and colonize diverse surfaces and often contribute to virulence. The genome of the bacterial wilt pathogen Ralstonia solanacearum (Rs) encodes dozens of putative adhesins, some of which are upregulated during plant pathogenesis. Little is known about the role of these proteins in bacterial wilt disease. During tomato colonization, three putative Rs adhesin genes were upregulated in a ΔphcA quorum-sensing mutant that cannot respond to high cell densities: radA (Ralstonia adhesin A), rcpA (Ralstonia collagen-like protein A), and rcpB. Based on this differential gene expression, we hypothesized that adhesins repressed by PhcA contribute to early disease stages when Rs experiences a low cell density. During root colonization, Rs upregulated rcpA and rcpB, but not radA, relative to bacteria in the stem at mid-disease. Root attachment assays and confocal microscopy with ΔrcpA/B and ΔradA revealed that all three adhesins help Rs attach to tomato seedling roots. Biofilm assays on abiotic surfaces found that Rs does not require RadA, RcpA, or RcpB for interbacterial attachment (cohesion), but these proteins are essential for anchoring aggregates to a surface (adhesion). However, Rs did not require the adhesins for later disease stages in planta, including colonization of the root endosphere and stems. Interestingly, all three adhesins were essential for full competitive fitness in planta. Together, these infection stage-specific assays identified three proteins that contribute to adhesion and the critical first host-pathogen interaction in bacterial wilt disease. IMPORTANCE Every microbe must balance its need to attach to surfaces with the biological imperative to move and spread. The high-impact plant-pathogenic bacterium Ralstonia solanacearum can stick to biotic and abiotic substrates, presumably using some of the dozens of putative adhesins encoded in its genome. We confirmed the functions and identified the biological roles of multiple afimbrial adhesins. By assaying the competitive fitness and the success of adhesin mutants in three different plant compartments, we identified the specific disease stages and host tissues where three previously cryptic adhesins contribute to success in plants. Combined with tissue-specific regulatory data, this work indicates that R. solanacearum deploys distinct adhesins that help it succeed at different stages of plant pathogenesis.

Motility Control as a Possible Link Between Quorum Sensing to Surface Attachment in Vibrio Species

In this chapter, we discuss motility control as a possible link between quorum sensing (QS) to surface attachment in Vibrio species. QS regulates a variety of behaviors that are important for the life cycle of many bacterial species, including virulence factor production, biofilm formation, or metabolic homeostasis. Therefore, without QS, many species of bacteria cannot survive in their natural environments. Here, we summarize several QS systems in different Vibrio species and discuss some of emerging features that suggest QS is intimately connected to motility control. Finally, we speculate the connection between motility and QS is critical for Vibrio species to detect solid surfaces for surface attachment.

Dichotomous Role of Humic Substances in Modulating Transformation of Antibiotic Resistance Genes in Mineral Systems

Widespread antibiotic resistance genes (ARGs) have emerged as a focus of attention for public health. Transformation is essential for ARGs dissemination in soils and associated environments; however, the mechanisms of how soil components contribute to the transformation of ARGs remain elusive. Here we demonstrate that three representative mineral-humic acid (HA) composites exert contrasting influence on the transformation of plasmid-borne ARGs in Bacillus subtilis. Mineral surface-bound HA facilitated transformation in kaolinite and montmorillonite systems, while an inhibitory effect of HA was observed for goethite. The elevated transformation by HA-coated kaolinite was mainly attributed to the enhanced activity of competence-stimulating factor (CSF), while increased transformation by montmorillonite-HA composites was assigned to the weakened adsorption affinity of DNA and enhanced gene expression induced by flagella-driven cell motility. In goethite system, HA played an overriding role in suppressing transformation via alleviation of cell membrane damage. The results obtained offer insights into the divergent mechanisms of humic substances in modulating bacterial transformation by soil minerals. Our findings would help for a better understanding on the fate of ARGs in soil systems and provide potentials for the utilization of soil components, particularly organic matter, to mitigate the spread of ARGs in a range of settings.

Role of Bacteriophages in the Evolution of Pathogenic Vibrios and Lessons for Phage Therapy

Viruses of bacteria, i.e., bacteriophages (or phages for short), were discovered over a century ago and have played a major role as a model system for the establishment of the fields of microbial genetics and molecular biology. Despite the relative simplicity of phages, microbiologists are continually discovering new aspects of their biology including mechanisms for battling host defenses. In turn, novel mechanisms of host defense against phages are being discovered at a rapid clip. A deeper understanding of the arms race between bacteria and phages will continue to reveal novel molecular mechanisms and will be important for the rational design of phage-based prophylaxis and therapies to prevent and treat bacterial infections, respectively. Here we delve into the molecular interactions of Vibrio species and phages.

Citric Acid in Rice Root Exudates Enhanced the Colonization and Plant Growth-Promoting Ability of Bacillus altitudinis LZP02

Exploration of the underlying mechanisms of plant-microbe interactions is very important. In the present study, citric acid in the root exudates of rice significantly enhanced the colonization of Bacillus altitudinis LZP02 in the rhizosphere. According to the results of transcriptome and reverse transcription-quantitative PCR or analyses, citric acid increased the expression of several genes involved in bacterial chemotaxis and biofilm formation in B. altitudinis LZP02. In addition, citric acid also increased the expression of several genes associated with S-adenosylmethionine biosynthesis and metabolism. Interestingly, the secretion of citric acid by rice roots could be increased by inoculation with B. altitudinis LZP02. The result indicated that citric acid might be a vital signal in the interaction between rice and B. altitudinis LZP02. Further verification showed that citric acid enhanced the plant growth-promoting ability of B. altitudinis LZP02. IMPORTANCE In a previous study, the mechanism by which citric acid in rice root exudates enhanced the colonization of Bacillus altitudinis LZP02 was discovered. The present study verified that citric acid increased the recruitment and rice growth-promoting ability of B. altitudinis LZP02. These findings serve as an interesting case for explaining the underlying mechanisms of plant-microbe interactions. Henceforth, citric acid and B. altitudinis LZP02 could be exploited for the development of sustainable agronomy.

Fabrication, control, and modeling of robots inspired by flagella and cilia

Flagella and cilia are slender structures that serve important functionalities in the microscopic world through their locomotion induced by fluid and structure interaction. With recent developments in microscopy, fabrication, biology, and modeling capability, robots inspired by the locomotion of these organelles in low Reynolds number flow have been manufactured and tested on the micro-and macro-scale, ranging from medicalin vivomicrobots, microfluidics to macro prototypes. We present a collection of modeling theories, control principles, and fabrication methods for flagellated and ciliary robots.

Getting to the root of Ralstonia invasion

Plant diseases caused by soilborne pathogens are a major limiting factor in crop production. Bacterial wilt disease, caused by soilborne bacteria in the Ralstonia solanacearum Species Complex (Ralstonia), results in significant crop loss throughout the world. Ralstonia invades root systems and colonizes plant xylem, changing plant physiology and ultimately causing plant wilting in susceptible varieties. Elucidating how Ralstonia invades and colonizes plants is central to developing strategies for crop protection. Here we review Ralstonia pathogenesis from root detection and attachment, early root colonization, xylem invasion and subsequent wilting. We focus primarily on studies in tomato from the last 5-10 years. Recent work has identified elegant mechanisms Ralstonia uses to adapt to the plant xylem, and has discovered new genes that function in Ralstonia fitness in planta. A picture is emerging of an amazingly versatile pathogen that uses multiple strategies to make its surrounding environment more hospitable and can adapt to new environments.

What Glues the Glue to the Cell Surface?

In the Caulobacterales , a highly adhesive polysaccharide called the holdfast mediates attachment to exogenous surfaces. The mechanism by which this polysaccharide is anchored to the cell envelope is not well defined.

Surface-Induced cAMP Signaling Requires Multiple Features of the Pseudomonas aeruginosa Type IV Pili

Pseudomonas aeruginosa type IV pili (TFP) are important for twitching motility and biofilm formation. TFP have been implicated in surface sensing, a process whereby surface-engaged cells upregulate the synthesis of the second messenger cAMP to propagate a signaling cascade leading to biofilm initiation and repression of motility. Here, we showed that mutations in PilA impairing proteolytic processing of the prepilin into mature pilin as well as the disruption of essential TFP components, including the PilC platform protein and PilB assembly motor protein, fail to induce surface-dependent cAMP signaling. We showed that TFP retraction by surface-engaged cells was required to induce signaling and that the retractile motor PilT was both necessary and sufficient to power surface-specific induction of cAMP. Furthermore, full TFP function required to support twitching motility is not required for robust cAMP signalling. The PilU retraction motor, in contrast, was unable to support full signaling in the absence of PilT. Finally, while we confirmed that PilA and PilJ interacted by bacterial two-hybrid analysis, our data do not support the current model that PilJ-PilA interaction drives cAMP signaling. IMPORTANCE Surface sensing by P. aeruginosa requires TFP. TFP plays a critical role in the induction of the second messenger cAMP upon surface contact; this second messenger is part of a larger cascade involved in the transition from a planktonic to a biofilm lifestyle. Here, we showed that TFP must be deployed and actively retracted by the PilT motor for the full induction of cAMP signaling. Furthermore, the mechanism whereby TFP retraction triggers cAMP induction is not well understood, and our data argue against one of the current models in the field proposed to address this knowledge gap.

A multi-state dynamic process confers mechano-adaptation to a biological nanomachine

Adaptation is a defining feature of living systems. The bacterial flagellar motor adapts to changes in the external mechanical load by adding or removing torque-generating (stator) units. But the molecular mechanism behind this mechano-adaptation remains unclear. Here, we combine single motor eletrorotation experiments and theoretical modeling to show that mechano-adaptation of the flagellar motor is enabled by multiple mechanosensitive internal states. Dwell time statistics from experiments suggest the existence of at least two bound states with a high and a low unbinding rate, respectively. A first-passage-time analysis of a four-state model quantitatively explains the experimental data and determines the transition rates among all four states. The torque generated by bound stator units controls their effective unbinding rate by modulating the transition between the bound states, possibly via a catch bond mechanism. Similar force-mediated feedback enabled by multiple internal states may apply to adaptation in other macromolecular complexes.

Combining experiments with modeling, Wadhwa et al. propose a model for mechano-adaptation in the bacterial flagellar motor, finding that load-dependent transitions between multiple internal states govern the binding and unbinding of subunits.

Regulation of flagellar motility and biosynthesis in enterohemorrhagic Escherichia coli O157:H7

ABSTARCTEnterohemorrhagic Escherichia coli (EHEC) O157:H7 is a human pathogen that causes a variety of diseases, such as hemorrhagic colitis and lethal hemolytic uremic syndrome. Flagellum-dependent motility plays diverse roles in the pathogenesis of EHEC O157:H7, including its migration to an optimal host site, adherence and colonization, survival at the infection site, and post-infection dispersal. However, it is very expensive for cellular economy in terms of the number of genes and the energy required for flagellar biosynthesis and functioning. Furthermore, the flagellar filament bears strong antigenic properties that induce a strong host immune response. Consequently, the flagellar gene expression and biosynthesis are highly regulated to occur at the appropriate time and place by different regulatory influences. The present review focuses on the regulatory mechanisms of EHEC O157:H7 motility and flagellar biosynthesis, especially in terms of flagellar gene regulation by environmental factors, regulatory proteins, and small regulatory RNAs.

Motility Increases the Numbers and Durations of Cell-Surface Engagements for Escherichia coli Flowing near Poly(ethylene glycol)-Functionalized Surfaces

Bacteria are keenly sensitive to properties of the surfaces they contact, regulating their ability to form biofilms and initiate infections. This study examines how the presence of flagella, interactions between the cell body and the surface, or motility itself guides the dynamic contact between bacterial cells and a surface in flow, potentially enabling cells to sense physicochemical and mechanical properties of surfaces. This work focuses on a poly(ethylene glycol) biomaterial coating, which does not retain cells. In a comparison of four Escherichia coli strains with different flagellar expressions and motilities, cells with substantial run-and-tumble swimming motility exhibited increased flux to the interface (3 times the calculated transport-limited rate which adequately described the non-motile cells), greater proportions of cells engaging in dynamic nanometer-scale surface associations, extended times of contact with the surface, increased probability of return to the surface after escape and, as evidenced by slow velocities during near-surface travel, closer cellular approach. All these metrics, reported here as distributions of cell populations, point to a greater ability of motile cells, compared with nonmotile cells, to interact more closely, forcefully, and for greater periods of time with interfaces in flow. With contact durations of individual cells exceeding 10 s in the window of observation and trends suggesting further interactions beyond the field of view, the dynamic contact of individual cells may approach the minute timescales reported for mechanosensing and other cell recognition pathways. Thus, despite cell translation and the dynamic nature of contact, flow past a surface, even one rendered non-cell arresting by use of an engineered coating, may produce a subpopulation of cells already upregulating virulence factors before they arrest on a downstream surface and formally initiate biofilm formation.

Metatranscriptome sequencing identifies Escherichia are major contributors to pathogenic functions and biofilm formation in diabetes related foot osteomyelitis

Osteomyelitis in the feet of persons with diabetes is clinically challenging and is associated with high rates of amputation. In this study RNA-sequencing was employed to explore microbial metatranscriptomes with a view to understand the relative activity and functions of the pathogen/s responsible for diabetes foot osteomyelitis (DFO). We obtained 25 intraoperative bone specimens from persons with confirmed DFO, observing that Escherichia spp. (7%), Streptomyces spp. (7%), Staphylococcus spp. (6%), Klebsiella spp. (5%) and Proteus spp. (5%) are the most active taxa on average. Data was then subset to examine functions associated with pathogenesis (virulence and toxins), biofilm formation and antimicrobial/multi-drug resistance. Analysis revealed Escherichia spp. are the most active taxa relative to pathogenic functions with K06218 (mRNA interferase relE), K03699 (membrane damaging toxin tlyC) and K03980 (putative peptidoglycan lipid II flippase murJ), K01114 (membrane damaging toxin plc) and K19168 (toxin cptA) being the most prevalent pathogenic associated transcripts. The most abundant transcripts associated with biofilm pathways included components of the biofilm EPS matrix including glycogen synthesis, cellulose synthesis, colonic acid synthesis and flagella synthesis. We further observed enrichment of a key enzyme involved in the biosynthesis of L-rhamnose (K01710 -dTDP-glucose 4,6-dehydratase rfbB, rmlB, rffG) which was present in all but four patients with DFO.

Bacterial Proprioception: Can a Bacterium Sense Its Movement?

The evolution of the bacterial flagellum gave rise to motility and repurposing of a signaling network, now termed the chemotaxis network, enabled biasing of cell movements. This made it possible for the bacterium to seek out favorable chemical environments. To enable chemotaxis, the chemotaxis network sensitively detects extracellular chemical stimuli and appropriately modulates flagellar functions. Additionally, the flagellar motor itself is capable of detecting mechanical stimuli and adapts its structure and function in response, likely triggering a transition from planktonic to surface-associated lifestyles. Recent work has shown a link between the flagellar motor's response to mechanical stimuli and the chemotactic output. Here, we elaborate on this link and discuss how it likely helps the cell sense and adapt to changes in its swimming speeds in different environments. We discuss the mechanism whereby the motor precisely tunes its chemotaxis output under different mechanical loads, analogous to proprioception in higher order organisms. We speculate on the roles bacterial proprioception might play in a variety of phenomena including the transition to surface-associated lifestyles such as swarming and biofilms.

A Flagella Hook Coding Gene flgE Positively Affects Biofilm Formation and Cereulide Production in Emetic Bacillus cereus

Bacillus cereus, an important foodborne pathogen, poses a risk to food safety and quality. Robust biofilm formation ability is one of the key properties that is responsible for the food contamination and food poisoning caused by B. cereus, especially the emetic strains. To investigate the mechanism of biofilm formation in emetic B. cereus strains, we screened for the mutants that fail to form biofilms by using random mutagenesis toward B. cereus 892-1, an emetic strain with strong biofilm formation ability. When knocking out flgE, a flagellar hook encoding gene, the mutant showed disappearance of flagellar structure and swimming ability. Further analysis revealed that both pellicle and ring presented defects in the null mutant compared with the wild-type and complementary strains. Compared with the flagellar paralytic strains ΔmotA and ΔmotB, the inhibition of biofilm formation by ΔflgE is not only caused by the inhibition of motility. Interestingly, ΔflgE also decreased the synthesis of cereulide. To our knowledge, this is the first report showing that a flagellar component can both affect the biofilm formation and cereulide production in emetic B. cereus, which can be used as the target to control the biohazard of emetic B. cereus.

Arcobacter butzleri Biofilms: Insights into the Genes Beneath Their Formation

Arcobacter butzleri, the most prevalent species of the genus, has the demonstrated ability to adhere to various surfaces through biofilm production. The biofilm formation capability has been related to the expression of certain genes, which have not been characterized in A. butzleri. In order to increase the knowledge of this foodborne pathogen, the aim of this study was to assess the role of six biofilm-associated genes in campylobacteria (flaA, flaB, fliS, luxS, pta and spoT) in the biofilm formation ability of A. butzleri. Knockout mutants were constructed from different foodborne isolates, and static biofilm assays were conducted on polystyrene (PS), reinforced glass and stainless steel. Additionally, motility and Congo red binding assays were performed. In general, mutants in flaAB, fliS and luxS showed a decrease in the biofilm production irrespective of the surface; mutants in spoT showed an increase on stainless steel, and mutants in pta and spoT showed a decrease on reinforced glass but an increase on PS. Our work sheds light on the biofilm-related pathogenesis of A. butzleri, although future studies are necessary to achieve a satisfactory objective.

The Bacterial Flagellar Motor: Insights Into Torque Generation, Rotational Switching, and Mechanosensing

The flagellar motor is a bidirectional rotary nanomachine used by many bacteria to sense and move through environments of varying complexity. The bidirectional rotation of the motor is governed by interactions between the inner membrane-associated stator units and the C-ring in the cytoplasm. In this review, we take a structural biology perspective to discuss the distinct conformations of the stator complex and the C-ring that regulate bacterial motility by switching rotational direction between the clockwise (CW) and counterclockwise (CCW) senses. We further contextualize recent in situ structural insights into the modulation of the stator units by accessory proteins, such as FliL, to generate full torque. The dynamic structural remodeling of the C-ring and stator complexes as well as their association with signaling and accessory molecules provide a mechanistic basis for how bacteria adjust motility to sense, move through, and survive in specific niches both outside and within host cells and tissues.

Metagenomic analysis of pioneer biofilm-forming marine bacteria with emphasis on Vibrio gigantis adhesion dynamics

Marine biofilms occur frequently and spontaneously in seawater, on almost any submerged solid surface. At the early stages of colonization, it consists of bacteria and evolves into a more complex community. Using 16S rRNA amplicon sequencing and comparative metagenomics, the composition and predicted functional potential of one- to three-day old bacterial communities in surface biofilms were investigated and compared to that of seawater. This confirmed the autochthonous marine bacterium Vibrio gigantis as an early and very abundant biofilm colonizer, also functionally linked to the genes associated with cell motility, surface attachment, and communication via signaling molecules (quorum sensing), all crucial for biofilm formation. The dynamics of adhesion on a solid surface of V. gigantis alone was also monitored in controlled laboratory conditions, using a newly designed and easily implementable protocol. Resulting in a calculated percentage of bacteria-covered surface, a convincing tendency of spontaneous adhering was confirmed. From the multiple results, its quantified and reproducible adhesion dynamics will be used as a basis for future experiments involving surface modifications and coatings, with the goal of preventing adhesion.

Chronic Rhinosinusitis, S. aureus Biofilm and Secreted Products, Inflammatory Responses, and Disease Severity

Chronic rhinosinusitis (CRS) is a persistent inflammation of the nasal cavity and paranasal sinuses associated with tissue remodelling, dysfunction of the sinuses’ natural defence mechanisms, and induction of different inflammatory clusters. The etiopathogenesis of CRS remains elusive, and both environmental factors, such as bacterial biofilms and the host’s general condition, are thought to play a role. Bacterial biofilms have significant clinical relevance due to their potential to cause resistance to antimicrobial therapy and host defenses. Despite substantial medical advances, some CRS patients suffer from recalcitrant disease that is unresponsive to medical and surgical treatments. Those patients often have nasal polyps with tissue eosinophilia, S. aureus-dominant mucosal biofilm, comorbid asthma, and a severely compromised quality of life. This review aims to summarise the contemporary knowledge of inflammatory cells/pathways in CRS, the role of bacterial biofilm, and their impact on the severity of the disease. Here, an emphasis is placed on S. aureus biofilm and its secreted products. A better understanding of these factors might offer important diagnostic and therapeutic perceptions for recalcitrant disease.

Mechanisms Underlying Vibrio cholerae Biofilm Formation and Dispersion

Biofilms are a widely observed growth mode in which microbial communities are spatially structured and embedded in a polymeric extracellular matrix. Here, we focus on the model bacterium Vibrio cholerae and summarize the current understanding of biofilm formation, including initial attachment, matrix components, community dynamics, social interactions, molecular regulation, and dispersal. The regulatory network that orchestrates the decision to form and disperse from biofilms coordinates various environmental inputs. These cues are integrated by several transcription factors, regulatory RNAs, and second-messenger molecules, including bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP). Through complex mechanisms, V. cholerae weighs the energetic cost of forming biofilms against the benefits of protection and social interaction that biofilms provide. Expected final online publication date for the Annual Review of Microbiology, Volume 76 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Lactobacillus spp. derived biosurfactants effect on expression of genes involved in Proteus mirabilis biofilm formation

Nosocomial infections (NIs) have been defined as infections ocuurring shortly after hospitalization or discharging from the hospital. It is associated with increased morbidities and mortalities. Proteus mirabilis considered as the hospital-acquired pathogen. The purpose of this study was to investigate the effect of Lactobacillus acidophilus-derived biosurfactant on P. mirabilis biofilm formation and flhDC/rsmA expression level (P. mirabilis standard strain ATCC 7002 and urinary infection isolated P. mirabilis strains). One of the potential strategies for the prevention of nosocomial infections is the use of probiotics. L. acidophilus was selected as a probiotic strain to produce biosurfactants. A biosurfactant reduces the adhesion of strains to microtiter plate and glass slide surfaces due to the reduction of surface tension. By using Real time PCR quantitation method we showed that biosurfactant significantly reduced rsmA expression whereas increased flhDC expression in P. mirabilis isolates. Several properties of P. mirabilis cells (biofilm formation, adhesion, and gene expression) were changed after L. acidophilus- derived biosurfactant treatment. In this study we showed that biosurfacant treatment can pave the way for a possible control of biofilm development. Based on our findings, we suggest that the prepared biosurfactant may interfere with adhesion of P. mirabilis to catheters and other devices.