Defining Two Chemosensory Arrays in .

has 2 functional chemosensory systems named Che1 and Che3, and 27 chemoreceptors. Che3 is dedicated to chemotaxis while Che1 could be involved in RpoS post-translational regulation. In this study, we have shown that two chemoreceptors Aer2so and McpAso, genetically related to the Che1 system, form distinct core-signaling units and signal to Che1 and Che3, respectively.

The differential expression of PilY1 proteins by the HsfBA phosphorelay allows twitching motility in the absence of exopolysaccharides.

Type Four Pili (T4P) are extracellular appendages mediating several bacterial functions such as motility, biofilm formation and infection. The ability to adhere to substrates is essential for all these functions. In Myxococcus xanthus, during twitching motility, the binding of polar T4P to exopolysaccharides (EPS), induces pilus retraction and the forward cell movement.

The polar Ras-like GTPase MglA activates type IV pilus via SgmX to enable twitching motility in .

Type IV pili (Tfp) are highly conserved macromolecular structures that fulfill diverse cellular functions, such as adhesion to host cells, the import of extracellular DNA, kin recognition, and cell motility (twitching). Outstandingly, twitching motility enables a poorly understood process by which highly coordinated groups of hundreds of cells move in cooperative manner, providing a basis for multicellular behaviors, such as biofilm formation. In the social bacteria , we know that twitching motility is under the dependence of the small GTPase MglA, but the underlying molecular mechanisms remain elusive.

Modulation of bacterial multicellularity via spatio-specific polysaccharide secretion.

The 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 behaviors and the formation of higher-order community structures. Herein, we demonstrate that in the social δ-proteobacterium Myxococcus xanthus, the secretion of a novel biosurfactant polysaccharide (BPS) is 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 (T4P)-inhibited acidic polymer built of randomly acetylated β-linked tetrasaccharide repeats.

How an unusual chemosensory system forms arrays on the bacterial nucleoid.

Chemosensory systems are signaling pathways elegantly organized in hexagonal arrays that confer unique functional features to these systems such as signal amplification. Chemosensory arrays adopt different subcellular localizations from one bacterial species to another, yet keeping their supramolecular organization unmodified. In the gliding bacterium Myxococcus xanthus, a cytoplasmic chemosensory system, Frz, forms multiple clusters on the nucleoid through the direct binding of the FrzCD receptor to DNA.

A divergent CheW confers plasticity to 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.

Cellular targeting and segregation of bacterial chemosensory systems.

The bacterial cytoplasm is not a homogeneous solution of macromolecules, but rather a highly organized and compartmentalized space where the clustering and segregation of macromolecular complexes in certain cell regions confers functional efficiency. Bacterial chemoreceptors represent a versatile model system to study the subcellular localization of macromolecules, as they are present in almost all motile bacterial and archaeal species, where they tend to form highly ordered arrays that occupy distinct positions in cells. The positioning of chemoreceptor clusters, as well as their segregation mechanism on cell division, varies from species to species and probably depends on cells size, environment and speed of movement.

Evolution and Design Governing Signal Precision and Amplification in a Bacterial Chemosensory Pathway.

Understanding the principles underlying the plasticity of signal transduction networks is fundamental to decipher the functioning of living cells. In Myxococcus xanthus, a particular chemosensory system (Frz) coordinates the activity of two separate motility systems (the A- and S-motility systems), promoting multicellular development. This unusual structure asks how signal is transduced in a branched signal transduction pathway.

Functional organization of a multimodular bacterial chemosensory apparatus.

Chemosensory systems (CSS) are complex regulatory pathways capable of perceiving external signals and translating them into different cellular behaviors such as motility and development. In the δ-proteobacterium Myxococcus xanthus, chemosensing allows groups of cells to orient themselves and aggregate into specialized multicellular biofilms termed fruiting bodies. M.

A versatile class of cell surface directional motors gives rise to gliding motility and sporulation in Myxococcus xanthus.

Eukaryotic cells utilize an arsenal of processive transport systems to deliver macromolecules to specific subcellular sites. In prokaryotes, such transport mechanisms have only been shown to mediate gliding motility, a form of microbial surface translocation. Here, we show that the motility function of the Myxococcus xanthus Agl-Glt machinery results from the recent specialization of a versatile class of bacterial transporters.

Cell biology of bacterial sensory modules.

Despite their small size, bacterial cells possess very efficient sensory apparatus that allow them to perceive and respond to the external environment with cell movement. In enteric bacteria, these apparatus are complex lattices of different chemoreceptors working in concert and forming clusters positioned at the cell poles. Since the study of chemotaxis has been expanded to other bacterial species, examples of chemosensory systems regulating functions different than taxis have been described and chemoreceptors localizing in ways divergent from the enteric paradigm have been visualized.

Gliding motility revisited: how do the myxobacteria move without flagella?

In bacteria, motility is important for a wide variety of biological functions such as virulence, fruiting body formation, and biofilm formation. While most bacteria move by using specialized appendages, usually external or periplasmic flagella, some bacteria use other mechanisms for their movements that are less well characterized. These mechanisms do not always exhibit obvious motility structures.

A multi-protein complex from Myxococcus xanthus required for bacterial gliding motility.

Myxococcus xanthus moves by gliding motility powered by Type IV pili (S-motility) and a second motility system, A-motility, whose mechanism remains elusive despite the identification of approximately 40 A-motility genes. In this study, we used biochemistry and cell biology analyses to identify multi-protein complexes associated with A-motility. Previously, we showed that the N-terminal domain of FrzCD, the receptor for the frizzy chemosensory pathway, interacts with two A-motility proteins, AglZ and AgmU.

Bacterial motility complexes require the actin-like protein, MreB and the Ras homologue, MglA.

Gliding motility in the bacterium Myxococcus xanthus uses two motility engines: S-motility powered by type-IV pili and A-motility powered by uncharacterized motor proteins and focal adhesion complexes. In this paper, we identified MreB, an actin-like protein, and MglA, a small GTPase of the Ras superfamily, as essential for both motility systems. A22, an inhibitor of MreB cytoskeleton assembly, reversibly inhibited S- and A-motility, causing rapid dispersal of S- and A-motility protein clusters, FrzS and AglZ.

AglZ regulates adventurous (A-) motility in Myxococcus xanthus through its interaction with the cytoplasmic receptor, FrzCD.

Myxococcus xanthus moves by gliding motility powered by type IV pili (S-motility) and distributed motor complexes (A-motility). The Frz chemosensory pathway controls reversals for both motility systems. However, it is unclear how the Frz pathway can communicate with these different systems.

Localization of a bacterial cytoplasmic receptor is dynamic and changes with cell-cell contacts.

Directional motility in the gliding bacterium Myxococcus xanthus requires controlled cell reversals mediated by the Frz chemosensory system. FrzCD, a cytoplasmic chemoreceptor, does not form membrane-bound polar clusters typical for most bacteria, but rather cytoplasmic clusters that appear helically arranged and span the cell length. The distribution of FrzCD in living cells was found to be dynamic: FrzCD was localized in clusters that continuously changed their size, number, and position.

Chemotaxis mediated by NarX-FrzCD chimeras and nonadapting repellent responses in Myxococcus xanthus.

Myxococcus xanthus requires gliding motility for swarming and fruiting body formation. It uses the Frz chemosensory pathway to regulate cell reversals. FrzCD is a cytoplasmic chemoreceptor required for sensing effectors for this pathway.

Germination-independent induction of cellular immune response by Bacillus subtilis spores displaying the C fragment of the tetanus toxin.

Bacillus subtilis spores displaying the tetanus toxin fragment C (TTFC) on their surface have been previously shown to induce the production of specific IgG and secretory IgA in mice immunized through the oral or nasal route. Aim of this study was to analyze whether these spores were also able to induce cellular immunity, and whether such immune response was dependent on spore germination in the animal gastro-intestinal tract (GIT). We first developed a germination defective strain of B.

The lrp gene and its role in type I fimbriation in Citrobacter rodentium.

Citrobacter rodentium is a murine pathogen that is now widely used as an in vivo model for gastrointestinal infections due to its similarities with human enteropathogens, such as the possession of a locus for enterocyte effacement (the LEE island). We studied the lrp gene of C. rodentium and found that it encodes a product highly similar to members of the Lrp (leucine-responsive regulatory protein) family of transcriptional regulators, able to recognize leucine as an effector and to repress the expression of its own structural gene.

Display of heterologous antigens on the Bacillus subtilis spore coat using CotC as a fusion partner.

We report the use of CotC, a major component of the Bacillus subtilis spore coat, as a fusion partner for the expression of two heterologous antigens on the spore coat. Recombinant spores expressing tetanus toxin fragment C (TTFC) of Clostridium tetani or the B subunit of the heat-labile toxin of Escherichia coli (LTB) were used for oral dosing and shown to generate specific systemic and mucosal immune responses in a murine model. This report, expanding the previously described expression of TTFC on the spore surface by fusion to CotB [J Bacteriol 183 (2001) 6294] and its use for oral vaccination [Infect Immun 71 (2003) 2810] shows that different antigens can be successfully presented on the spore coat and supports the use of the spore as an efficient vehicle for mucosal immunisation.