Biology subjects

Mignot, T.

Publications and source records attributed to Mignot, T..

At least 19 recordsLinked to original sources

bioRxiv2026

Evidence for a central ecological function of predatory Myxococcota in soil ecosystems

Myxococcota is a recently classified phylum including bacteria renowned for their predatory lifestyle. However, ecological functions of these bacteria remain under studied. Here, we examined the ecological position and potential impact of Myxococcota communities across diverse soil habitats using the global geographical collection of 16S microbial communities structured by the Earth Microbiome Project (EMP). First, we found that the abundance of Myxococcota varied greatly from 6.3% to 0.8% across 13 soil habitats. A deeper microbial analysis in two selected habitats showed that Myxococcota was highly abundant (4.9%) ranking 5 in field soil (a grassland planted with switchgrass) than in sand biofilter (an engineered system for water quality production, 1.3% and 11, resp.). Moreover, both Myxococcota and microbial communities displayed a significantly higher -diversity in field soil than in sand biofilter environments, suggesting that diversity of Myxococcota seems to be associated with that of microbial communities in these habitats. Using co-occurrence network analysis, we found that Myxococcota exhibited a high eigenvector centrality (5.1%) and one hub taxon, Polyangiales, in field soil habitat. In contrast, Myxococcota centrality was less pronounced (1.1%) in the sand biofilter, where consistent negative correlations were also detected. Altogether, these results suggest that Myxococcota communities experienced beneficial interactions in field soil environment, whereas they may have faced competitive relationships in sand biofilter habitat. Overall, our findings provide further insights into the status of Myxococcota communities in soil environments, suggesting their fundamental roles in the structure of soil microbial communities.

ecology↗

bioRxiv2025

Tunable simultaneous propulsion by two distinct motility motors drives surface motility in bacteria

Motility allows cells to explore their surroundings, evade threats, and coordinate collective behaviors. Many organisms, from bacteria to animals, encode more than one motility system, yet whether and how mechanistically distinct systems are integrated within individual cells remains largely unresolved. We address this question in the predatory bacterium Myxococcus xanthus, which navigates surfaces using two mechanistically and evolutionarily distinct motors: focal-adhesion-based gliding and type IV pili-driven twitching. For this, we develop an imaging-based quantitative behavioral phenotyping method to show that both motors are simultaneously active within individual cells and jointly power cell movement. Cells engaging both motors move faster and explore space more effectively than cells using either motor alone, expanding locomotion performance. Extracellular calcium tunes their relative contributions, progressively shifting cells from gliding- to twitching-dominated propulsion. Unexpectedly, the gliding motor can boost twitching even without anchoring to the surface, revealing that cooperation between motility systems extends beyond simultaneous force generation. Together, these findings reveal that evolutionarily distinct motility systems can function as components of a single, environmentally tunable propulsion strategy.

microbiology↗

bioRxiv2025

Visualization of peptidoglycan layer isolated from gliding diderm bacteria, Flavobacterium johnsoniae and Myxococcus xanthus, by quick-freeze deep-etch replica electron microscopy

The bacterial peptidoglycan layer plays an important role in protecting the bacteria from turgor pressure, viruses, and predators. However, it also acts as a barrier in transmitting forces generated on the cell membrane to adhesion proteins on the surface during gliding locomotion. In this study, peptidoglycan layers were isolated from two species of gliding diderm, i.e., Gram-negative bacteria, and their structures were visualized by quick-freeze deep-etch replica electron microscopy. The diameter of pores in the peptidoglycan layer of M. xanthus and the area of surface pores were 51 nm and 14.6%, respectively, which were significantly larger than those of E. coli (32 nm and 5.8%) and F. johnsoniae (29 nm and 7.0%). Based on this, we discussed the mechanism by which diderm bacteria transmit forces across the PG layer to the bacterial surface. SignificancePeptidoglycan is a rigid meshwork that protects bacterial cells from turgor stress, virus, and predators. Bacteria move to get nutrients and escape from predators. The force for motility is generated in the cell membrane and transmitted to the surface across the peptidoglycan layer. In this study, the peptidoglycan structures of two representative gliding Gram-negative bacteria were visualized to understand the transmission mechanism.

microbiology↗

bioRxiv2024

Cell polarity control by an unconventional G-protein complex in bacteria

In Myxococcus xanthus, cell polarity and motility are regulated by the small GTPase MglA and its associated regulators, MglB, a potential GTPase Activating Protein and the RomRX complex, a potential Guanine nucleotide Exchange Factor. However, recent results have questioned the exact function of these regulators. Using a new type of fluorescent nucleotides for fluorescence-based anisotropy, we first demonstrate that RomRX does not function as a GEF but as an effector that binds strictly to MglAGTP. Secondly, based on an enzymology model, we found that MglB functions as a weak catalyst, unlike typical GAPs, and requires additional factors to dissociate from MglA. We demonstrate that RomRX, and specifically RomR, effectively competes with MglA by sequestering MglB. This low affinity interaction is still permissive for GAP activity but sufficient to partition these proteins in vivo as indicated by a biomimetic assay in oil emulsion droplets reconstituting these interactions in a cell-sized environment. These results suggest a new model for cell polarity where RomRX exerts a dual function, targeting MglAGTP to the pole via its effector function and preventing its accumulation at the lagging pole by destabilizing the MglA-MglB complex.

biochemistry↗

bioRxiv2024

The mechanism of spatial pattern transition in motile bacterial collectives

Understanding how individual behaviours contribute to collective actions is key in biological systems. In Myxococcus xanthus, a bacterial predator, swarming shifts to rippling patterns due to changes in the local environment near prey colonies. Through high-resolution microscopy and theoretical analysis, we demonstrate that two key properties drive this shift: local cellular alignment guided by an extracellular matrix and the ability of cells to reverse to resolve congestion. A tunable refractory period in the reversal system enables collective adaptation, allowing cells to synchronise in rippling and resolve congestion in swarming. These transitions occur without changes in genetic regulation but create stable spatial domains that promote local differentiation, a mechanism of spatial sorting that may be widespread in biology.

microbiology↗

bioRxiv2024

Di-HAMP domains of a cytoplasmic chemoreceptor modulate nucleoid array formation and downstream signalling

In bacterial chemosensing, environmental cues are typically sensed by bacterial transmembrane receptors known as methyl accepting chemotaxis proteins (MCPs). MCPs form highly organized arrays using the bacterial membrane as a scaffold, which amplify the signals and transduce them into a cellular response. The FrzCD cytoplasmic receptor from Myxococcus xanthus is unique due to its ability to bind DNA and use the nucleoid as a scaffold to form arrays. In this study, we identified two HAMP (histidine kinase, adenylyl cyclase, MCP and phosphatase) domains located between the DNA binding and signaling domains of FrzCD. In vitro experiments demonstrate that these HAMP domains restrict FrzCD to a dimeric form in solution and modulate FrzCDs affinity for DNA, whereas the signaling domain stabilizes higher-order oligomeric assemblies upon DNA binding. Through fluorescence microscopy and analyses on Myxococcus social behavior, we demonstrate that the impact of FrzCD HAMP domains on DNA binding and oligomerization significantly influences group motility and development. Our results suggest that HAMP domains might have roles not only in signal transduction but also in the plasticity of chemosensory arrays. These observations illustrate mechanisms of regulation of a DNA-bound cytoplasmic array formed by a diffusible MCP. Significance StatementOur study identifies the presence of tandem HAMP domains in a cytoplasmic chemoreceptor, FrzCD, from Myxococcus xanthus, and highlights their role in dynamic receptor oligomerization on a DNA scaffold. By controlling receptor oligomerization and subsequently the array formation on the nucleoid, the tandem HAMP domains impart plasticity to the receptor arrays. Such plasticity governs cellular responses to external signals and dictate bacterial social behavior in group motility and multicellular structure formation.

microbiology↗

bioRxiv2023

Fatty Acid Metabolism and The Oxidative Stress Response Support Bacterial Predation

Despite growing awareness of their importance in soil ecology, the genetic and physiological traits of bacterial predators are still relatively poorly understood. In the course of a Myxococcus xanthus predator evolution experiment, we discovered a class of genotypes leading to enhanced predation against diverse species. RNA-seq analysis demonstrated that this phenotype is linked to the constitutive activation of a predation-specific program. Functional analysis of the mutations accumulated across the evolutionary time in a two- component system and Acyl-CoA-manipulating enzymes revealed the critical roles of fatty acid metabolism and antioxidant gene induction. The former likely adapts the predator to metabolites derived from the prey while the latter protects predatory cells from reactive oxygen species (ROS) generated by prey cells under stress and released upon lysis during predation. These findings reveal interesting parallels between bacterial predator-prey dynamics and pathogen-host cell interactions. Significance StatementThis study illuminates the largely unexplored genetic and metabolic strategies used by bacterial predators in soil ecosystems. Through experimental evolution in Myxococcus xanthus, we discovered that more efficient predators accumulate mutations that activate a genetic program for predation. This program simultaneously triggers a metabolic shift favoring fatty acid degradation for energy production and upregulates antioxidant gene expression, enhancing protection against reactive oxygen species generated during prey cell lysis. This adaptive mechanism proves advantageous across a wide range of prey species, suggesting that metabolic adaptation plays a crucial role in the evolutionary trajectory of bacterial predators within their natural ecological niche.

microbiology↗

bioRxiv2023

Integrin-like adhesin CglD confers traction and stabilizes bacterial focal adhesions involved in myxobacterial gliding motility

AO_SCPLOWBSTRACTC_SCPLOWIntegrins are crucial for eukaryotic cell attachment and motility within the extracellular matrix (ECM) via focal-adhesion formation, with their evolutionary emergence important for the development of multicellularity. Intriguingly, single gliding cells of the predatory deltaproteobacterium Myxococcus xanthus form bacterial focal-adhesion (bFA) sites; therein, helically-trafficked motors become immobilized at anchored locations through Glt apparatus association with cell-surface integrin I-domain-like adhesin CglB. Using traction-force, bead-force, and total internal reflection-fluorescence microscopies combined with biochemical approaches, we herein identify the von Willebrand A domain-containing cell-surface lipoprotein CglD to be a {beta}-integrin-like outer-membrane lipoprotein that functionally associates with and anchors the trans-envelope Glt-CglB gliding apparatus, stabilizing and efficiently anchoring this assembly at bFAs. Calcium dependence governs CglD importance, consistent with its integrated ECM eukaryotic cartilage oligomeric matrix protein domains. CglD thus confers mechanosensory and mechanotransductory capabilities to the gliding apparatus, helping explain bFA-mediated trans-envelope force transduction, from inner-membrane-embedded motors to the cell surface.

microbiology↗

bioRxiv2021

Dynamic proton-dependent motors power Type IX secretion and gliding adhesin movement in Flavobacterium

Motile bacteria usually rely on external apparatus like flagella for swimming or pili for twitching. By contrast, gliding bacteria do not rely on obvious surface appendages to move on solid surfaces. Flavobacterium johnsoniae and other bacteria in the Bacteroidetes phylum use adhesins whose movement on the cell surface supports motility. In F. johnsoniae, secretion and helicoidal motion of the main adhesin SprB are intimately linked and depend on the type IX secretion system (T9SS). Both processes necessitate the proton motive force (PMF), which is thought to fuel a molecular motor that comprises the GldL and GldM cytoplasmic membrane proteins. Here we show that F. johnsoniae gliding motility is powered by the pH gradient component of the PMF. We further delineate the interaction network between the GldLM transmembrane helices (TMH) and show that conserved glutamate residues in GldL TMH are essential for gliding motility, although having distinct roles in SprB secretion and motion. We then demonstrate that the PMF and GldL trigger conformational changes in the GldM periplasmic domain. We finally show that multiple GldLM complexes are distributed in the membrane suggesting that a network of motors may be present to move SprB along a helical path on the cell surface. Altogether, our results provide evidence that GldL and GldM assemble dynamic membrane channels that use the proton gradient to power both T9SS-dependent secretion of SprB and its motion at the cell surface.

microbiology↗

bioRxiv2021

A Tad-like apparatus is required for contact-dependent prey killing in predatory social bacteria

Myxococcus xanthus, a soil bacterium, predates collectively using motility to invade prey colonies. Prey lysis is mostly thought to rely on secreted factors, cocktails of antibiotics and enzymes, and direct contac with Myxococcus cells. In this study, we show that on surfaces the coupling of A-motility and contact-dependent killing is the central predatory mechanism driving effective prey colony invasion and consumption. At the molecular level, contact-dependent killing involves a newly discovered type IV filament-like machinery (Kil) that both promotes motility arrest and prey cell plasmolysis. In this process, Kil proteins assemble at the predator-prey contact site, suggesting that they allow tight contact with prey cells for their intoxication. Kil-like systems form a new class of Tad-like machineries in predatory bacteria, suggesting a conserved function in predator-prey interactions. This study further reveals a novel cell-cell interaction function for bacterial pili-like assemblages.

microbiology↗

bioRxiv2020

MiSiC, a general deep learning-based method for the high-throughput cell segmentation of complex bacterial communities

Studies of microbial communities by live imaging require new tools for the robust identification of bacterial cells in dense and often inter-species populations, sometimes over very large scales. Here, we developed MiSiC, a general deep-learning-based segmentation method that automatically segments a wide range of spatially structured bacterial communities with very little parameter adjustment, independent of the imaging modality. Using a bacterial predator-prey interaction model, we demonstrate that MiSiC enables the analysis of interspecies interactions, resolving processes at subcellular scales and discriminating between species in millimeter size datasets. The simple implementation of MiSiC and the relatively low need in computing power make its use broadly accessible to fields interested in bacterial interactions and cell biology.

microbiology↗

bioRxiv2020

CglB adhesins secreted at bacterial focal adhesions mediate gliding motility

AO_SCPLOWBSTRACTC_SCPLOWThe predatory deltaproteobacterium Myxococcus xanthus uses a helically-trafficked motor at bacterial focal adhesion (bFA) sites to power gliding motility. Using TIRF and force microscopy, we herein identify the integrin I-domain-like outer-membrane (OM) lipoprotein CglB as an essential substratum-coupling protein of the gliding motility complex. Similar to most known OM lipoproteins, CglB is anchored on the periplasmic side of the OM and thus a mechanism must exist to secrete it to the cell surface in order for it to interact with the underlying substratum. We reveal this process to be mediated by a predicted OM {beta}-barrel structure of the gliding complex. This OM platform was found to regulate the conformational activation and secretion of CglB across the OM. These data suggest that the gliding complex promotes surface exposure of CglB at bFAs, thus explaining the manner by which forces exerted by inner-membrane motors are transduced across the cell envelope to the substratum; they also uncover a novel protein secretion mechanism, highlighting the ubiquitous connection between secretion and bacterial motility.

microbiology↗

bioRxiv2020

Modulation of bacterial multicellularity via spatiotemporal polysaccharide secretion

AO_SCPLOWBSTRACTC_SCPLOWThe development of multicellularity is a key evolutionary transition allowing for differentiation of physiological functions across a cell population that confers survival benefits; among unicellular bacteria, this can lead to complex developmental behaviours and the formation of higher-order community structures. Herein, we demonstrate that in the social {delta}-proteobacterium Myxococcus xanthus, the secretion of a novel secreted biosurfactant polysaccharide (BPS) is temporally and spatially modulated within communities, mediating swarm migration as well as the formation of multicellular swarm biofilms and fruiting bodies. BPS is a type IV pilus-inhibited acidic polymer built of randomly-acetylated {beta}-linked tetrasaccharide repeats. Both BPS and the "shared good" EPS are produced by dedicated Wzx/Wzy-dependent polysaccharide assembly pathways distinct from that responsible for spore coat assembly. To our knowledge, such pathways have never-before been explicitly shown to synthesize a biosurfactant. Together, these data reveal the central role of secreted polysaccharides in the intricate behaviours coordinating bacterial multicellularity.

microbiology↗

bioRxiv2019

Establishing Rod-Shape from Spherical, Peptidoglycan-Deficient Bacterial Spores

Chemical-induced spores of the Gram-negative bacterium Myxococcus xanthus are peptidoglycan (PG)-deficient. It is unclear how these spherical spores germinate into rod-shaped, walled cells without preexisting PG templates. We found that germinating spores first synthesize PG randomly on spherical surfaces. MglB, a GTPase-activating protein, forms a cluster that surveys the status of PG growth and stabilizes at one future cell pole. Following MglB, the Ras family GTPase MglA localizes to the second pole. MglA directs molecular motors to transport the bacterial actin homolog MreB and the Rod PG synthesis complexes away from poles. The Rod system establishes rod-shape by elongating PG at nonpolar regions. Thus, the interaction between GTPase, cytoskeletons and molecular motors provides a mechanism for the de novo establishment of rod-shape in bacteria. SignificanceSpheres and rods are among the most common shapes adopted by walled bacteria, in which the peptidoglycan (PG) cell wall largely determines cell shape. When induced by chemicals, rod-shaped vegetative cells of the Gram-negative bacterium Myxococcus xanthus thoroughly degrade their PG and shrink into spherical spores. As these spores germinate, rod-shaped cells are rebuilt without preexisting templates, which provides a rare opportunity to visualize de novo PG synthesis and bacterial morphogenesis. In this study, we investigated how spherical spores germinate into rods and elucidated a system for rod-shape morphogenesis that includes the Rod PG synthesis system, a GTPase-GAP pair, the MreB cytoskeleton and a molecular motor.

microbiology↗

bioRxiv2019

Chitosan films for microfluidic studies of single bacteria and perspectives for antibiotics susceptibility testing

Single cell microfluidics is powerful to study bacteria and determine their susceptibility to antibiotics treatment. Glass treatment by adhesive molecules is a potential solution to immobilize bacterial cells and perform microscopy but traditional cationic polymers such as poly-lysine deeply affect bacterial physiology. In this work, we chemically characterized a class of chitosan polymers for their biocompatibility when adsorbed to glass. Chitosan chains of known length and composition allowed growth of Escherichia coli cells without any deleterious effects on cell physiology. Combined with a machine-learning approach, this method could measure the antibiotics susceptibility of a diversity of clinical strains in less than 1 hour and with higher accuracy than current methods. Last, chitosan polymers also supported growth of Klebsiella pneumoniae, another bacterial pathogen of clinical significance. The low cost of chitosan slides and their simple implementation makes them highly versatile for research as well as clinical use.

microbiology↗

bioRxiv2019

MglA functions as a three-state GTPase to control movement reversals of Myxococcus xanthus

In Myxococcus xanthus, directed movement is controlled by inter-dependent pole-to-pole oscillations of the small GTPase MglA, its GAP MglB and the RomR protein. However, these proteins have strikingly different oscillatory regimes such that MglA is segregated from MglB and RomR at reversal activation. The molecular mechanism whereby information is exchanged between the lagging and leading poles resulting in MglA detachment from the leading pole during reversals has remained unknown. Here, we show that MglA has two GTP-bound forms, one of which is insensitive to MglB (MglA-GTP*) and is re-sensitized to MglB by a feedback mechanism operated by MglA-GDP. By identifying the region of MglB that is critical for its association to the lagging pole, we demonstrate that MglA-GTP* is functional in vivo. These data suggest that MglA-GDP acts as a soluble messenger to convert polar MglA-GTP* into a diffusible MglA-GTP species, explaining MglA re-localization to the opposite pole during reversals.

microbiology↗

bioRxiv2017

A divergent CheW stabilizes nucleoid-associated chemosensory arrays

Chemosensory systems are highly organized signaling pathways that allow bacteria to adapt to environmental changes. The Frz chemosensory system from M. xanthus possesses two CheW-like proteins, FrzA (the core CheW) and FrzB. We found that FrzB does not interact with FrzE (the cognate CheA) as it lacks the amino acid region responsible for this interaction. FrzB, instead, acts upstream of FrzCD in the regulation of M. xanthus chemotaxis behaviors and activates the Frz pathway by allowing the formation and distribution of multiple chemosensory clusters on the nucleoid. These results, together, show that the lack of the CheA-interacting region in FrzB confers new functions to this small protein.\n\nAUTHOR SUMMARYChemosensory systems are signaling complexes that are widespread in bacteria and allow the modulation of different cellular functions, such as taxis and development, in response to the environment. We show that the Myxococcus xanthus FrzB is a divergent CheW lacking the region involved in the interaction with the histidine kinase FrzE. Instead, it acts upstream of FrzCD to allow the formation of multiple distributed Frz chemosensory arrays at the nucleoid. The loss of the CheA-interacting region in FrzB might have been selected to confer plasticity to nucleoid-associated chemosensory systems. By unraveling a new accessory protein and its function, this work opens new insights into the knowledge of the regulatory potentials of bacterial chemosensory systems.

microbiology↗

bioRxiv2017

The nucleoid as a scaffold for the assembly of bacterial signaling complexes

The FrzCD chemoreceptor from the gliding bacterium Myxococcus xanthus forms cytoplasmic clusters that occupy a large central region of the cell body also occupied by the nucleoid. In this work, we show that FrzCD directly binds to the nucleoid with its N-terminal positively charged tail and recruits active signaling complexes at this location. The FrzCD binding to the nucleoid occur in a DNA-sequence independent manner and leads to the formation of multiple distributed clusters that explore constrained areas. This organization might be required for cooperative interactions between clustered receptors as observed in membrane-bound chemosensory arrays.\n\nAUTHOR SUMMARYIn this work, we show that the cytoplasmic chemoreceptor of the Frz chemosensory system, FrzCD, does not bind the cytoplasmic membrane like most MCPs but bind the bacterial nucleoid directly, thus forming distributed protein clusters also containing the Frz kinase. In vitro and in vivo experiments show that DNA-binding is not sequence-specific and is mediated by a basic aminoacid sequence of the FrzCD N-terminal domain. The deletion of this motif abolishes FrzCD DNA-binding and cooperativity in the response to signals. This work shows the importance of the nucleoid in the organization and functioning of cytoplasmic signaling systems in bacteria.

microbiology↗