Mechanics limits ecological diversity and promotes heterogeneity in confined bacterial communities.

Multispecies bacterial populations often inhabit confined and densely packed environments where spatial competition determines the ecological diversity of the community. However, the role of mechanical interactions in shaping the ecology is still poorly understood. Here, we study a model system consisting of two populations of nonmotile Escherichia coli bacteria competing within open, monolayer microchannels. The competitive dynamics is observed to be biphasic: After seeding, either one strain rapidly fixates or both strains orient into spatially stratified, stable communities. We find that mechanical interactions with other cells and local spatial constraints influence the resulting community ecology in unexpected ways, severely limiting the overall diversity of the communities while simultaneously allowing for the establishment of stable, heterogeneous populations of bacteria displaying disparate growth rates. Surprisingly, the populations have a high probability of coexisting even when one strain has a significant growth advantage. A more coccus morphology is shown to provide a selective advantage, but agent-based simulations indicate this is due to hydrodynamic and adhesion effects within the microchannel and not from breaking of the nematic ordering. Our observations are qualitatively reproduced by a simple Pólya urn model, which suggests the generality of our findings for confined population dynamics and highlights the importance of early colonization conditions on the resulting diversity and ecology of bacterial communities. These results provide fundamental insights into the determinants of community diversity in dense confined ecosystems where spatial exclusion is central to competition as in organized biofilms or intestinal crypts.

Determining the Young's Modulus of the Bacterial Cell Envelope.

Bacteria experience substantial physical forces in their natural environment, including forces caused by osmotic pressure, growth in constrained spaces, and fluid shear. The cell envelope is the primary load-carrying structure of bacteria, but the mechanical properties of the cell envelope are poorly understood; reports of Young's modulus of the cell envelope of Escherichia coli range from 2 to 18 MPa. We developed a microfluidic system to apply mechanical loads to hundreds of bacteria at once and demonstrated the utility of the approach for evaluating whole-cell stiffness. Here, we extend this technique to determine Young's modulus of the cell envelope of E. coli and of the pathogens Vibrio cholerae and Staphylococcus aureus. An optimization-based inverse finite element analysis was used to determine the cell envelope Young's modulus from observed deformations. The Young's modulus values of the cell envelope were 2.06 ± 0.04 MPa for E. coli, 0.84 ± 0.02 MPa for E. coli treated with a chemical (A22) known to reduce cell stiffness, 0.12 ± 0.03 MPa for V. cholerae, and 1.52 ± 0.06 MPa for S. aureus (mean ± SD). The microfluidic approach allows examination of hundreds of cells at once and is readily applied to Gram-negative and Gram-positive organisms as well as rod-shaped and cocci cells, allowing further examination of the structural causes behind differences in cell envelope Young's modulus among bacterial species and strains.

Challenges for heat stress: Intestinal culturable bacteria of Lohmann Brown chickens.

This study aimed to assess how heat stress, specifically within the range of 35-38 °C, affects the populations of culturable intestinal lactobacilli, enterococci, and Escherichia coli, as well as the expression of Heat Shock Proteins (HSP70), in Lohmann Brown chickens. It also explored the influence of the chickens' blood transferrin and ceruloplasmin genotypes on these responses. Thirty chickens underwent eight hours of heat stress, maintained at an average temperature of 37 °C and a relative humidity of 75-80%, with continuous access to food and water. Behavioral monitoring was conducted throughout to prevent excessive heat-related mortality. The Lohmann Brown chickens from the Yerevan "Arax" poultry farm were initially classified based on their blood transferrin and ceruloplasmin genotypes to investigate potential correlations between intestinal bacterial composition and variations in these polymorphisms. A significant correlation was found between heat stress and the abundance of culturable enterococci within the intestinal microbiota, regardless of chicken TfAB, TfBC, CpAB, CpCC and TfAB, TfBC, CpAB, CpCD genotypes. Heat stress led to nearly double the HSP70 levels in chicken blood, along with a reduction in the culturable enterococci population by at least 10,000-fold in the intestinal microbiota. These findings are significant for targeted management strategies to mitigate heat stress in chicken populations.

Bacteria-surface interactions: role of impacting bacteria-laden droplets.

Understanding the interactions of pathogenic droplets with surfaces is crucial to biomedical applications. In this study, using E. coli as the model microbe, we investigate the impact of a bacteria-laden droplet on different substrates, both bare and antimicrobial. In doing so, we unveil the significance of kinetic energy and spreading parameters of the impacting droplet in determining the microbes' proliferation capabilities. Our results indicate an inverse relationship between the impact Weber number and the bacterial ability to proliferate. We reveal that the mechanical stress generated during impact impedes the capabilities of microbes present inside the droplet to create their progeny. Following an order analysis of the mechanical stress generated, we argue that the impact does not induce lysis-driven cell death of the bacteria; rather, it promotes a stress-driven transition of viable bacteria to a viable-but-non-culturable (VBNC) state. Furthermore, variations in the concentration of particles on the antimicrobial surfaces revealed the role of the post-impact spreading behaviour in dictating bacterial proliferation capabilities. Contrary to the conventional notion, we demonstrate that during the early stages of interaction, a bare substrate may outperform an antibacterial substrate in the inactivation of the bacterial load. Finally, we present an interaction map illustrating the complex relationship between bacterial colony-forming units, bactericide concentration on the surface, and the impact Weber number. We believe that the inferences of the study, highlighting the effect of mechanical stresses on the soft cell wall of microbes, could be a useful design consideration for the development of antimicrobial surfaces.

Bacterial accumulation in intestinal folds induced by physical and biological factors.

BACKGROUND: The gut microbiota, vital for host health, influences metabolism, immune function, and development. Understanding the dynamic processes of bacterial accumulation within the gut is crucial, as it is closely related to immune responses, antibiotic resistance, and colorectal cancer. We investigated Escherichia coli behavior and distribution in zebrafish larval intestines, focusing on the gut microenvironment. RESULTS: We discovered that E. coli spread was considerably suppressed within the intestinal folds, leading to a strong physical accumulation in the folds. Moreover, a higher concentration of E. coli on the dorsal side than on the ventral side was observed. Our in vitro microfluidic experiments and theoretical analysis revealed that the overall distribution of E. coli in the intestines was established by a combination of physical factor and bacterial taxis. CONCLUSIONS: Our findings provide valuable insight into how the intestinal microenvironment affects bacterial motility and accumulation, enhancing our understanding of the behavioral and ecological dynamics of the intestinal microbiota.

Protective effects of antibiotic resistant bacteria on susceptibles in biofilm: Influential factors, mechanism, and modeling.

In environmental biofilms, antibiotic-resistant bacteria facilitate the persistence of susceptible counterparts under antibiotic stresses, contributing to increased community-level resistance. However, there is a lack of quantitative understanding of this protective effect and its influential factors, hindering accurate risk assessment of biofilm resistance in diverse environment. This study isolated an opportunistic Escherichia coli pathogen from soil, and engineered it with plasmids conferring antibiotic resistance. Protective effects of the ampicillin resistant strain (AmpR) on their susceptible counterparts (AmpS) were observed in ampicillin-stress colony biofilms. The concentration of ampicillin delineated protective effects into 3 zones: continuous protection (<1 MIC of AmpS), initial AmpS/R dependent (1-8 MIC of AmpS), and ineffective (>8 MIC of AmpS). Intriguingly, Zone 2 exhibited a surprising "less is more" phenomenon tuned by the initial AmpS/R ratio, where biofilm with an initially lower AmpR (1:50 vs 50:1) harbored 30-90 % more AmpR after 24 h growth under antibiotic stress. Compared to AmpS, AmpR displayed superiority in adhesion, antibiotic degradation, motility, and quorum sensing, allowing them to preferentially colonize biofilm edge and areas with higher ampicillin. An agent-based model incorporating protective effects successfully simulated tempo-spatial dynamics of AmpR and AmpS influenced by antibiotic stress and initial AmpS/R. This study provides a holistic view on the pervasive but poorly understood protective effects in biofilm, enabling development of better risk assessment and precisely targeted control strategies of biofilm resistance in diverse environment.

Enhanced cavitation dose and reactive oxygen species production in microbubble-mediated sonodynamic therapy for inhibition of Escherichia coli and biofilm.

Sonodynamic therapy (SDT) is an emerging antibacterial therapy. This work selected hematoporphyrin monomethyl ether (HMME) as the sonosensitizer, and studied the enhanced inhibition effect of Escherichia coli and biofilm by microbubble-mediated cavitation in SDT. Firstly, the influence of microbubble-mediated cavitation effect on different concentrations of HMME (10 µg/ml, 30 µg/ml, 50 µg/ml) was studied. Using 1,3-diphenylisobenzofuran (DPBF) as an indicator, the effect of microbubble-mediated cavitation on the production of reactive oxygen species (ROS) was studied by absorption spectroscopy. Secondly, using agar medium, laser confocal microscopy and scanning electron microscopy, the effect of microbubble-mediated cavitation on the activity and morphology of bacteria was studied. Finally, the inhibitory effect of cavitation combined with SDT on biofilm was evaluated by laser confocal microscopy. The research results indicate that: (1) Microbubble-mediated ultrasound cavitation can significantly increase cavitation intensity and production of ROS. (2) Microbubble-mediated acoustic cavitation can alter the morphological structure of bacteria. (3) It can significantly enhance the inhibition of SDT on the activity of Escherichia coli and its biofilm. Compared with the control group, the addition of microbubbles resulted in an increase in the number of dead bacteria by 61.7 %, 71.6 %, and 76.2 %, respectively. The fluorescence intensity of the biofilm decreased by 27.1 %, 80.3 %, and 98.2 %, respectively. On the basis of adding microbubbles to ensure antibacterial and biofilm inhibition effects, this work studied the influence of cavitation effect in SDT on bacterial structure, providing a foundation for further revealing the intrinsic mechanism of SDT.

Interplay between environmental yielding and dynamic forcing modulates bacterial growth.

Many bacterial habitats-ranging from gels and tissues in the body to cell-secreted exopolysaccharides in biofilms-are rheologically complex, undergo dynamic external forcing, and have unevenly distributed nutrients. How do these features jointly influence how the resident cells grow and proliferate? Here, we address this question by studying the growth of Escherichia coli dispersed in granular hydrogel matrices with defined and highly tunable structural and rheological properties, under different amounts of external forcing imposed by mechanical shaking, and in both aerobic and anaerobic conditions. Our experiments establish a general principle: that the balance between the yield stress of the environment that the cells inhabit, σy, and the external stress imposed on the environment, σ, modulates bacterial growth by altering transport of essential nutrients to the cells. In particular, when σy<σ, the environment is easily fluidized and mixed over large scales, providing nutrients to the cells and sustaining complete cellular growth. By contrast, when σy>σ, the elasticity of the environment suppresses large-scale fluid mixing, limiting nutrient availability and arresting cellular growth. Our work thus reveals a new mechanism, beyond effects that change cellular behavior via local forcing, by which the rheology of the environment may modulate microbial physiology in diverse natural and industrial settings.

Biofilm exopolysaccharides alter sensory-neuron-mediated sickness during lung infection.

Infections of the lung cause observable sickness thought to be secondary to inflammation. Signs of sickness are crucial to alert others via behavioral-immune responses to limit contact with contagious individuals. Gram-negative bacteria produce exopolysaccharide (EPS) that provides microbial protection; however, the impact of EPS on sickness remains uncertain. Using genome-engineered Pseudomonas aeruginosa (P. aeruginosa) strains, we compared EPS-producers versus non-producers and a virulent Escherichia coli (E. coli) lung infection model in male and female mice. EPS-negative P. aeruginosa and virulent E. coli infection caused severe sickness, behavioral alterations, inflammation, and hypothermia mediated by TLR4 detection of the exposed lipopolysaccharide (LPS) in lung TRPV1+ sensory neurons. However, inflammation did not account for sickness. Stimulation of lung nociceptors induced acute stress responses in the paraventricular hypothalamic nuclei by activating corticotropin-releasing hormone neurons responsible for sickness behavior and hypothermia. Thus, EPS-producing biofilm pathogens evade initiating a lung-brain sensory neuronal response that results in sickness.

Microbial profile of broiler carcasses processed at a university scale mobile poultry processing unit.

Chicken and chicken products have been associated with foodborne pathogens such as Salmonella, Campylobacter, and Escherichia coli (E. coli). Poultry comprises an important segment of the agricultural economy (75 million birds processed as of 2019) in West Virginia (WV). The risk of pathogens on processed chickens has risen with the increased popularity of mobile poultry processing units (MPPUs). This study evaluated the microbial safety of broilers processed in a MPPU in WV. This study assessed aerobic plate counts (APCs), E. coli counts and the presence/absence of Salmonella and Campylobacter on 96 broiler carcasses following each MPPU step of scalding, eviscerating, and chilling. Samples were either chilled in ice water only (W) or ice water with 5 ppm chlorine (CW). The highest number of bacteria recovered from carcasses were APCs (4.21 log10CFU/mL) and E. coli (3.77 log10CFU/mL; P = 0.02). A total reduction of 0.30 (P = 0.10) and 0.63 (P = 0.01) log10CFU/mL for APCs and E. coli, respectively, occurred from chilling carcasses in CW. Overall, results show that E. coli, Salmonella, and Campylobacter were significantly (P < 0.05) reduced from the initial scalding to the chilling step. However, Salmonella frequency doubled (15.63-34.38%) after the evisceration step, indicating that washing carcasses after evisceration may be a critical control point in preventing cross-contamination by Salmonella. Proper chilling is also an important microbial mitigation step in MPPU processing. Results indicate that Campylobacter was more resistant to chilling than Salmonella. Campylobacter was not completely inactivated until carcasses were chilled in CW, whereas W was sufficient to reduce Salmonella on carcasses. The results led to the conclusion that although 5 ppm chlorine (Cl2) achieved more bacterial reductions than water alone, the reductions were not always significant (P > 0.05). Further MPPU studies are needed to verify more effective chilling and processing strategies.

Bacteriophage specificity is impacted by interactions between bacteria.

Predators play a central role in shaping community structure, function, and stability. The degree to which bacteriophage predators (viruses that infect bacteria) evolve to be specialists with a single bacterial prey species versus generalists able to consume multiple types of prey has implications for their effect on microbial communities. The presence and abundance of multiple bacterial prey types can alter selection for phage generalists, but less is known about how interactions between prey shape predator specificity in microbial systems. Using a phenomenological mathematical model of phage and bacterial populations, we find that the dominant phage strategy depends on prey ecology. Given a fitness cost for generalism, generalist predators maintain an advantage when prey species compete, while specialists dominate when prey are obligately engaged in cross-feeding interactions. We test these predictions in a synthetic microbial community with interacting strains of Escherichia coli and Salmonella enterica by competing a generalist T5-like phage able to infect both prey against P22vir, an S. enterica-specific phage. Our experimental data conform to our modeling expectations when prey species are competing or obligately mutualistic, although our results suggest that the in vitro cost of generalism is caused by a combination of biological mechanisms not anticipated in our model. Our work demonstrates that interactions between bacteria play a role in shaping ecological selection on predator specificity in obligately lytic bacteriophages and emphasizes the diversity of ways in which fitness trade-offs can manifest. IMPORTANCE: There is significant natural diversity in how many different types of bacteria a bacteriophage can infect, but the mechanisms driving this diversity are unclear. This study uses a combination of mathematical modeling and an in vitro system consisting of Escherichia coli, Salmonella enterica, a T5-like generalist phage, and the specialist phage P22vir to highlight the connection between bacteriophage specificity and interactions between their potential microbial prey. Mathematical modeling suggests that competing bacteria tend to favor generalist bacteriophage, while bacteria that benefit each other tend to favor specialist bacteriophage. Experimental results support this general finding. The experiments also show that the optimal phage strategy is impacted by phage degradation and bacterial physiology. These findings enhance our understanding of how complex microbial communities shape selection on bacteriophage specificity, which may improve our ability to use phage to manage antibiotic-resistant microbial infections.

Rediversification following ecotype isolation reveals hidden adaptive potential.

Microbial communities play a critical role in ecological processes, and their diversity is key to their functioning. However, little is known about whether communities can regenerate ecological diversity following ecotype removal or extinction and how the rediversified communities would compare to the original ones. Here, we show that simple two-ecotype communities from the E. coli long-term evolution experiment (LTEE) consistently rediversified into two ecotypes following the isolation of one of the ecotypes, coexisting via negative frequency-dependent selection. Communities separated by more than 30,000 generations of evolutionary time rediversify in similar ways. The rediversified ecotype appears to share a number of growth traits with the ecotype it replaces. However, the rediversified community is also different from the original community in ways relevant to the mechanism of ecotype coexistence-for example, in stationary phase response and survival. We found substantial variation in the transcriptional states between the two original ecotypes, whereas the differences within the rediversified community were comparatively smaller, although the rediversified community showed unique patterns of differential expression. Our results suggest that evolution may leave room for alternative diversification processes even in a maximally reduced community of only two strains. We hypothesize that the presence of alternative evolutionary pathways may be even more pronounced in communities of many species where there are even more potential niches, highlighting an important role for perturbations, such as species removal, in evolving ecological communities.

Klebsiella aerogenes ingestion elicits behavioral changes and innate immunity in the host, Caenorhabditis elegans.

Klebsiella aerogenes (previously known as Enterobacter aerogenes) is a common opportunistic pathogen that infect the respiratory tract and central nervous system. However, how it interferes the host regulatory mechanism has not been previously described. When C. elegans were exposed to K. aerogenes, they exhibited a shorter lifespan compared to those fed with E. coli OP50. The time required for 50 % of L4 hermaphrodite nematodes to die when exposed to K. aerogenes was approximately 9 days, whereas it was about 18 days when fed with E. coli OP50. The interaction with K. aerogenes also affected the physical activity of C. elegans. Parameters like pharyngeal pumping, head thrashing, body bending, and swimming showed a gradual decline during infection. The expression of serotonin-mediated axon regeneration K. aerogenes infection led to increased levels of reactive oxygen species (ROS) in C. elegans compared to E. coli OP50-fed worms. The nematodes activated antioxidant mechanisms, including the expression of SODs, to counteract elevated ROS levels. The interaction with K. aerogenes activated immune regulatory pathways in C. elegans, including the mTOR signaling pathway downstream player SGK-1. Lifespan regulatory pathways, such as pha-4 and pmk-1, were also affected, likely contributing to the nematode ability to survive in a pathogenic environment. K. aerogenes infection has a detrimental impact on the healthspan and lifespan of C. elegans, affecting physical activity, intestinal health, serotonin regulation, ROS levels, and immune responses. These findings provide insights into the complex interactions between K. aerogenes and host organisms.

Chemical basis of microbiome preference in the nematode C. elegans.

Animals are exposed to many microbes in their environment, some of which have been shown to colonize various tissues including the intestine. The composition of the intestinal microbiota affects many aspects of the host's physiology and health. Despite this, very little is known about whether host behavior contributes to the colonization. We approach this question in the nematode C. elegans, which feeds on bacteria and also harbors an intestinal microbiome. We examined the behavior of C. elegans towards CeMbio, a simplified microbiome consisting of twelve strains that represent the bacteria found in the animal's natural environment. We observed that C. elegans raised on E. coli shows a strong preference for three members of CeMbio (Lelliottia amnigena JUb66, Enterobacter hormaechei CEent1, and Pantoea nemavictus BIGb0393) compared to E. coli. Previously, these three bacterial strains have been shown to support faster C. elegans development time than E. coli OP50 and are low colonizers compared to eight other members of CeMbio. We then used gas chromatography coupled to mass spectrometry to identify that these three bacteria release isoamyl alcohol, a previously described C. elegans chemoattractant. We suggest that C. elegans seeks bacteria that release isoamyl alcohol and support faster growth.

Interfacial coupling of CuFe2O4 induced hotspots over self-assembled g-C3N4 nanosheets as an efficient photocatalytic bacterial disinfectant.

Most bacterial disinfectants contain high levels of extremely toxic and environmental hazardous chemicals, which pose a significant threat to the ecosystem. Semiconductor photocatalysis exhibits attractive prospects as an emerging greener technology for waste water disinfection. However, the fast recombination of charge carriers limits its practical application. Herein, self-assembled polymeric feather-like g-C3N4 (GCN) nanosheets modified with ferromagnetic CuFe2O4 (CFO) nanospheres were successfully applied as a reusable visible light photocatalytic disinfectant. As expected, the g-C3N4/CuFe2O4 (GCF) nanohybrid displayed superior photocatalytic inactivation efficiency of 0.157log within 120 min towards Escherichia coli DH5α (E. coli) compared with pristine GCN and CFO. The characterization results revealed the synergistic heterostructure interfaces, high surface area, and the transformative self-assembly of GCN to feather-like structure providing a rich active site for improved charge separation efficiency, and wide spectral response, therefore the superior performance of GCF. The radical trapping assay proclaimed that both O2•- and •OH radical played major role in the photocatalytic inactivation among the other reactive oxygen species (ROS). Furthermore, the chemical oxygen demand (COD), protein estimation, and DNA estimation assay results validated the cell damage caused by the photocatalyst. Besides that, GCN showed applicability in real-time wastewater samples with improved efficiency than in the saline solution. The excellent magnetic characteristics facilitated the recycling of the catalyst with insignificant leaching, magnetic induction, and distinguished separation. The results of this work signify the well-designed GCF as a high-performance and reusable photocatalyst for real-world pathogenic bacterial disinfection operations.

Comparative transcriptome analysis of E. coli & Staphylococcus aureus infected goat mammary epithelial cells reveals genes associated with infection.

Mastitis, an inflammatory disease of the mammary gland, imposes a significant financial burden on the dairy sector. However, the specific molecular mechanisms underlying their interactions with goat mammary epithelial cells (GMECs) remain poorly understood. This study aimed to investigate the transcriptomic response of GMECs during infection with E. coli and S. aureus, providing insights into the host-pathogen interactions. Differential expression of gene (DEGs) analysis was done to find genes and pathways dysregulated in the wake of infection. E. coli infection triggered a robust upregulation of immune response genes, including pro-inflammatory chemokines and cytokines as well as genes involved in tissue repair and remodeling. Conversely, S. aureus infection showed a more complex pattern, involving the activation of immune-related gene as well as those involved in autophagy, apoptosis and tissue remodeling. Furthermore, several key pathways, such as Toll-like receptor signaling and cytokine-cytokine receptor interaction, were differentially modulated in response to each pathogen. Understanding the specific responses of GMECs to these pathogens will provide a foundation for understanding the complex dynamics of infection and host response, offering potential avenues for the development of novel strategies to prevent and treat bacterial infections in both animals and humans.

Differential induction of NF-κB pathways by non-pathogenic and pathogenic bacteria in Helicoverpa armigera is critical for an efficient immune response and survival.

Following pathogen infection in a host, extensive changes occur in the host's gene expression pattern to suppress infection and increase the chance of host survival. Likewise, many pathogens have evolved to evade/suppress host immunity and increase their survival within the host. In this study, we assessed the NF-κB (Imd and Toll) essential gene expression response of Helicoverpa armigera to an entomopathogenic Serratia marcescens and non-pathogenic Escherichia coli. Bacterial cells of S. marcescens or E. coli were injected into the haemocoel of fifth-instar larvae of H. armigera, whereas distilled water was injected into control insects. Our results showed that the expression levels of the Imd and Toll pathway genes (i.e., Relish, imd, spätzle and dif) and the antimicrobial peptides (i.e., gloverin, transferin, gallerimycin, and galiomicin) were differentially expressed following the bacterial injections while control larvae showed no differences. The E. coli injection induced higher and longer-lasted gene expression than the S. marcescens injected larvae, in which the gene expressions were diminished from 24 h post injection. Transcript Knockdown of Relish increased the replication rates of S. marcescens and E. coli, and lowered the infected larvae survival rates. These results showed that H. armigera NF-κB immunity pathways (particularly Imd pathway) play a vital role in immunity against bacterial infections, and S. marcescens might modulate these pathways to survive and replicate in the host.

Multiflagellarity leads to the size-independent swimming speed of peritrichous bacteria.

To swim through a viscous fluid, a flagellated bacterium must overcome the fluid drag on its body by rotating a flagellum or a bundle of multiple flagella. Because the drag increases with the size of bacteria, it is expected theoretically that the swimming speed of a bacterium inversely correlates with its body length. Nevertheless, despite extensive research, the fundamental size-speed relation of flagellated bacteria remains unclear with different experiments reporting conflicting results. Here, by critically reviewing the existing evidence and synergizing our own experiments of large sample sizes, hydrodynamic modeling, and simulations, we demonstrate that the average swimming speed of Escherichia coli, a premier model of peritrichous bacteria, is independent of their body length. Our quantitative analysis shows that such a counterintuitive relation is the consequence of the collective flagellar dynamics dictated by the linear correlation between the body length and the number of flagella of bacteria. Notably, our study reveals how bacteria utilize the increasing number of flagella to regulate the flagellar motor load. The collective load sharing among multiple flagella results in a lower load on each flagellar motor and therefore faster flagellar rotation, which compensates for the higher fluid drag on the longer bodies of bacteria. Without this balancing mechanism, the swimming speed of monotrichous bacteria generically decreases with increasing body length, a feature limiting the size variation of the bacteria. Altogether, our study resolves a long-standing controversy over the size-speed relation of flagellated bacteria and provides insights into the functional benefit of multiflagellarity in bacteria.

Indole produced during dysbiosis mediates host-microorganism chemical communication.

An imbalance of the gut microbiota, termed dysbiosis, has a substantial impact on host physiology. However, the mechanism by which host deals with gut dysbiosis to maintain fitness remains largely unknown. In Caenorhabditis elegans, Escherichia coli, which is its bacterial diet, proliferates in its intestinal lumen during aging. Here, we demonstrate that progressive intestinal proliferation of E. coli activates the transcription factor DAF-16, which is required for maintenance of longevity and organismal fitness in worms with age. DAF-16 up-regulates two lysozymes lys-7 and lys-8, thus limiting the bacterial accumulation in the gut of worms during aging. During dysbiosis, the levels of indole produced by E. coli are increased in worms. Indole is involved in the activation of DAF-16 by TRPA-1 in neurons of worms. Our finding demonstrates that indole functions as a microbial signal of gut dysbiosis to promote fitness of the host.