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Flagella enable bacteria to actively spread within the environment. A number of species possess two separate flagellar systems, where in most cases a primary polar flagellar system is supported by distinct secondary lateral flagella under appropriate conditions. Using functional fluorescence tagging on one of these species, Shewanella putrefaciens, as a model system, we explored how two different flagellar systems can exhibit efficient joint function. The S. putrefaciens secondary flagellar filaments are composed as a mixture of two highly homologous non-glycosylated flagellins, FlaA

The opportunistic pathogen Pseudomonas aeruginosa adapts to solid surfaces to enhance virulence and infect its host. Type IV pili (T4P), long and thin filaments that power surface-specific twitching motility, allow single cells to sense surfaces and control their direction of movement. T4P distribution is polarized to the sensing pole by the chemotaxis-like Chp system via a local positive feedback loop. However, how the initial spatially resolved mechanical signal is translated into T4P polarity is incompletely understood. Here, we demonstrate that the two Chp response regulators PilG and PilH enable dynamic cell polarization by antagonistically regulating T4P extension. By precisely quantifying the localization of fluorescent protein fusions, we show that phosphorylation of PilG by the histidine kinase ChpA controls PilG polarization. Although PilH is not strictly required for twitching reversals, it becomes activated upon phosphorylation and breaks the local positive feedback mechanism established by PilG, allowing forward-twitching cells to reverse. Chp thus uses a main output response regulator, PilG, to resolve mechanical signals in space and employs a second regulator, PilH, to break and respond when the signal changes. By identifying the molecular functions of two response regulators that dynamically control cell polarization, our work provides a rationale for the diversity of architectures often found in non-canonical chemotaxis systems.

The opportunistic pathogenPseudomonas aeruginosaadapts to solid surfaces to enhance virulence and infect its host. Type IV pili (T4P), long and thin filaments that power surface-specific twitching motility, allow single cells to mechanosense surfaces. For example, cells sense T4P attachment to control the direction of twitching motility. In this process, they establish a local positive feedback that polarizes T4P distribution to the sensing pole. A complex chemotaxis-like system called Chp mediates this response. The signalling mechanism allowing for transduction of this spatially-resolved signal is however unresolved. Here we demonstrate that the two Chp response regulators PilG and PilH enable dynamic cell polarization by coupling their antagonistic functions on T4P extension. By precisely quantifying the localization of fluorescent protein fusions, we show that PilG polarizes in response to mechanosensing through phosphorylation by the histidine kinase ChpA. We find that PilH is not inherently required for reversals. However, PilH activation is necessary to break the local positive feedback established by PilG so that forward-twitching cells can reverse. To spatially resolve mechanical signals, Chp thus locally transduces signals with a main output response regulator, PilG. To respond to signal changes, Chp uses its second regulator PilH to break the local feedback. By identifying the molecular functions of two response regulators that dynamically control cell polarization, our work provides a rationale for the diversity of architectures often found in non-canonical chemotaxis systems.

A huge number of bacterial species are motile by flagella, which allow them to actively move toward favorable environments and away from hazardous areas and to conquer new habitats. The general perception of flagellum-mediated movement and chemotaxis is dominated by the Escherichia coli paradigm, with its peritrichous flagellation and its famous run-and-tumble navigation pattern, which has shaped the view on how bacteria swim and navigate in chemical gradients. However, a significant amount—more likely the majority—of bacterial species exhibit a (bi)polar flagellar localization pattern instead of lateral flagella. Accordingly, these species have evolved very different mechanisms for navigation and chemotaxis. Here, we review the earlier and recent findings on the various modes of motility mediated by polar flagella.

ZusammenfassungMit der COVID-19-Pandemie stehen die Notaufnahmen als Schnittstelle der ambulanten und stationären Krankenversorgung vor einer großen Herausforderung. Die Dynamik der Pandemie zwang die Notfallversorgung des Universitätsklinikums Münster zu umfassenden Anpassungsprozessen, die in kürzester Zeit erfolgen mussten. Dazu gehörte die Etablierung einer ambulanten Coronateststelle und einer studentischen Telefonhotline. Innerklinisch wurden neue Isolationskapazitäten in der Notaufnahme sowie eine eigene COVID-19-Station eingerichtet. Der Patientenfluss wurde durch Flussdiagramme sowohl für den ambulanten als auch für den stationären Bereich neu geregelt. Das allgemeine und spezielle Notfallmanagement wurde für die reibungslose Versorgung COVID-19-positiver Patienten optimiert und das Personal in der Benutzung von Schutzausrüstung trainiert. Dieser Erlebnisbericht soll anderen Notaufnahmen in der Vorbereitung auf die COVID-19-Pandemie unterstützen.

Flagella-mediated motility, where propulsion is mediated by a rotating helical filament, is a very widespread and effective means of locomotion for numerous bacteria. Almost half of all species assemble their filament from more than one distinct building block, the flagellin. Here we show how bacteria may use different flagellins to build a filament best suited for different environments and that polarly flagellated bacteria employ a novel way of flagella-mediated motility.

The Palomar Fiber Nuller (PFN) is a rotating-baseline nulling interferometer that enables high-accuracy near-infrared (NIR) nulling observations with full azimuth coverage. To achieve NIR null-depth accuracies of several x 10-4, the PFN uses a common-mode optical system to provide a high degree of symmetry, single-mode-fiber beam combination to reduce sensitivity to pointing and wavefront errors, extreme adaptive optics to stabilize the fiber coupling and the cross-aperture fringe phase, rapid signal calibration and camera readout to minimize temporal effects, and a statistical null-depth fluctuation analysis to relax the phase stabilization requirement. Here we describe the PFN final design and performance, and provide a demonstration of faint-companion detection by means of nulling-baseline rotation, as originally envisioned for space-based nulling interferometry. Specifically, the Ks-band null-depth rotation curve measured on the spectroscopic binary eta Peg reflects both a secondary star 1.08 +/- 0.06 x 10-2 as bright as the primary, and a null-depth contribution of 4.8 +/- 1.6 x 10-4 due to the size of the primary star. With a 30 mas separation at the time, eta Peg B was well inside both the telescope diffraction-limited beam diameter (88 mas) and typical coronagraphic inner working angles. Finally, we discuss potential improvements that can enable a number of small-angle nulling observations on larger telescopes., 26 pages, 4 figures, accepted for publication in MNRAS

Raman microscopic spectroscopyis a new approach for further characterization and detection of molecular features in many pathological processes. This technique has been successfully applied to scrutinize the spatial distribution of small molecules and proteins within biological systems by in situ analysis. This study uses Raman microscopic spectroscopyto identify any in-depth benefits and drawbacks in diagnosing Staphylococcus epidermidis in human bone grafts.40 non-infected human bone samples and 10 human bone samples infected with Staphylococcus epidermidis were analyzed using Raman microscopic spectroscopy. Reflectance data were collected between 200 cmRaman measurements produced distinct diagnostic spectra that were used to distinguish between non-infected human bone samples and Staphylococcus epidermidis infected human bone samples by spectral and principal component analyses. A substantial loss in bone quality and protein conformation was detected by human bone samples co-cultured with Staphylococcus epidermidis. The mineral-to-matrix ratio using the phosphate/Amide I ratio (p = 0.030) and carbonate/phosphate ratio (p = 0.001) indicates that the loss of relative mineral content in bones upon bacterial infection is higher than in non-infected human bones. Also, an increase of alterations in the collagen network (p = 0.048) and a decrease in the structural organization and relative collagen in infected human bone could be detected. Subsequent principal component analyses identified Staphylococcus epidermidis in different spectral regions, respectively, originating mainly from CHRaman microscopic spectroscopyis presented as a promising diagnostic tool to detect Staphylococcus epidermidis in human bone grafts. Further studies in human tissues are warranted.

Significance Single cells across kingdoms of life explore, prey, escape, or congregate using surface-specific motility. Motile eukaryotic cells use chemotaxis to direct migration on surfaces. However, how bacteria control surface motility remains underexplored. Pseudomonas aeruginosa twitches on surfaces by successive extension and retraction of extracellular filaments called type IV pili. Here, we show that P. aeruginosa directs twitching by sensing mechanical input generated by type IV pili. The Chp sensory system performs spatially resolved mechanosensing by harnessing two response regulators with antagonistic functions. Our results demonstrate that sensory systems, whose input often remains elusive, can sense mechanical signals to actively steer motility. Furthermore, Chp establishes a signaling principle shared with higher-order organisms, identifying a conserved strategy to transduce spatially resolved signals., The opportunistic pathogen Pseudomonas aeruginosa explores surfaces using twitching motility powered by retractile extracellular filaments called type IV pili (T4P). Single cells twitch by sequential T4P extension, attachment, and retraction. How single cells coordinate T4P to efficiently navigate surfaces remains unclear. We demonstrate that P. aeruginosa actively directs twitching in the direction of mechanical input from T4P in a process called mechanotaxis. The Chp chemotaxis-like system controls the balance of forward and reverse twitching migration of single cells in response to the mechanical signal. Collisions between twitching cells stimulate reversals, but Chp mutants either always or never reverse. As a result, while wild-type cells colonize surfaces uniformly, collision-blind Chp mutants jam, demonstrating a function for mechanosensing in regulating group behavior. On surfaces, Chp senses T4P attachment at one pole, thereby sensing a spatially resolved signal. As a result, the Chp response regulators PilG and PilH control the polarization of the extension motor PilB. PilG stimulates polarization favoring forward migration, while PilH inhibits polarization, inducing reversal. Subcellular segregation of PilG and PilH efficiently orchestrates their antagonistic functions, ultimately enabling rapid reversals upon perturbations. The distinct localization of response regulators establishes a signaling landscape known as local excitation–global inhibition in higher-order organisms, identifying a conserved strategy to transduce spatially resolved signals.