Cerebrospinal fluid conveys many physiologically important signaling factors through the ventricular cavities of the brain. We investigated the transport of cerebrospinal fluid in the third ventricle of the mouse brain and discovered a highly organized pattern of cilia modules, which collectively give rise to a network of fluid flows that allows for precise transport within this ventricle. We also discovered a cilia-based switch that reliably and periodically alters the flow pattern so as to create a dynamic subdivision that may control substance distribution in the third ventricle. Complex flow patterns were also present in the third ventricles of rats and pigs. Our work suggests that ciliated epithelia can generate and maintain complex, spatiotemporally regulated flow networks.

The rhizosphere-associated bacterium Serratia plymuthica HRO-C48 is not only able to suppress symptoms caused by soil-borne pathogens but is also able to stimulate growth of plants. Detailed knowledge about the underlying mechanisms and regulation are crucial for the application in biocontrol strategies. To analyse the influence of N-acyl homoserine lactone (AHL)-mediated communication on the biocontrol activity, the AHL-degrading lactonase AiiA was heterologously expressed in the strain, resulting in abolished AHL production. The comparative analysis of the wild type and AHL negative mutants led to the identification of new AHL-regulated phenotypes. In the pathosystem Verticillium dahliae-oilseed rape, the essential role of AHL-mediated signaling for disease suppression was demonstrated. In vitro, the regulatory function of AHLs in the synthesis of the plant growth hormone indole-3-acetic acid is shown for the first time. Additionally, swimming motility was found to be negatively AHL regulated. In contrast, production of extracellular hydrolytic enzymes is shown to be positively AHL-regulated. HRO-C48 emits a broad spectrum of volatile organic compounds that are involved in antifungal activity and, interestingly, whose relative abundances are influenced by quorum sensing (QS). This study shows that QS is crucial for biocontrol activity of S. plymuthica and discusses the impact for the application of the strain as a biocontrol agent.

The rapid reorganization of the actin cytoskeleton in response to external stimuli is an essential property of many motile eukaryotic cells. Here, we report evidence that the actin machinery of chemotactic Dictyostelium cells operates close to an oscillatory instability. When averaging the actin response of many cells to a short pulse of the chemoattractant cAMP, we observed a transient accumulation of cortical actin reminiscent of a damped oscillation. At the single-cell level, however, the response dynamics ranged from short, strongly damped responses to slowly decaying, weakly damped oscillations. Furthermore, in a small subpopulation, we observed self-sustained oscillations in the cortical F-actin concentration. To substantiate that an oscillatory mechanism governs the actin dynamics in these cells, we systematically exposed a large number of cells to periodic pulse trains of different frequencies. Our results indicate a resonance peak at a stimulation period of around 20 s. We propose a delayed feedback model that explains our experimental findings based on a time-delay in the regulatory network of the actin system. To test the model, we performed stimulation experiments with cells that express GFP-tagged fusion proteins of Coronin and actin-interacting protein 1, as well as knockout mutants that lack Coronin and actin-interacting protein 1. These actin-binding proteins enhance the disassembly of actin filaments and thus allow us to estimate the delay time in the regulatory feedback loop. Based on this independent estimate, our model predicts an intrinsic period of 20 s, which agrees with the resonance observed in our periodic stimulation experiments.Dictyostelium discoideum | microfluidics | caged cAMP | delay-differential equation T he actin cytoskeleton provides the basis for shape dynamics and motility of eukaryotic cells. Essential biological processes like wound healing, embryonic morphogenesis, or cancer metastasis rely on the rapid rearrangement of the actin cytoskeleton in response to external chemical cues (1). Many of the underlying actin-driven processes have been investigated in cells of the social amoeba Dictyostelium discoideum. Under starvation, the singlecelled amoeba expresses a chemotactic signaling system to aggregate into a multicellular structure, mediated by the chemoattractant cAMP. The corresponding receptor signaling pathway and the downstream cytoskeletal machinery show remarkable similarities to motile cells of higher organisms, in particular neutrophils (2), making Dictyostelium one of the most popular models for eukaryotic cell motility and chemotaxis (3, 4).In earlier studies, it was observed that the actin system of chemotactic Dictyostelium cells shows a complex, nonmonotonic response when exposed to a sudden increase in the extracellular chemoattractant concentration (5-7). Between 5 and 10 s after the stimulus, a first maximum in the filamentous actin content is observed, followed by a second, less intense but prolonged maximum that starts about 30 s after the stimulus and...

Background: Oral biofilm studies based on simplified experimental setups are difficult to interpret. Models are limited mostly by the number of bacterial species observed and the insufficiency of artificial media. Few studies have attempted to overcome these limitations and to cultivate native oral biofilm.Aims: This study aimed to grow oral biofilm in vivo before transfer to a biofilm reactor for ex situ incubation. The in vitro survival of this oral biofilm and the changes in bacterial composition over time were observed.Methods: Six human enamel-dentin slabs embedded buccally in dental splints were used as biofilm carriers. Fitted individually to the upper jaw of 25 non-smoking male volunteers, the splints were worn continuously for 48 h. During this time, tooth-brushing and alcohol-consumption were not permitted. The biofilm was then transferred on slabs into a biofilm reactor and incubated there for 48 h while being nourished in BHI medium. Live/dead staining and confocal laser scanning microscopy were used to observe bacterial survival over four points in time: directly after removal (T0) and after 1 (T1), 24 (T2), and 48 h (T3) of incubation. Bacterial diversity at T0 and T3 was compared with 454-pyrosequencing. Fluorescence in situ hybridization (FISH) was performed to show specific taxa. Survival curves were calculated with a specially designed MATLAB script. Acacia and QIIME 1.9.1 were used to process pyrosequencing data. SPSS 21.0 and R 3.3.1 were used for statistical analysis.Results: After initial fluctuations at T1, survival curves mostly showed approximation of the bacterial numbers to the initial level at T3. Pyrosequencing analysis resulted in 117 OTUs common to all samples. The genera Streptococcus and Veillonella (both Firmicutes) dominated at T0 and T3. They make up two thirds of the biofilm. Genera with lower relative abundance had grown significantly at T3. FISH analysis confirmed the pyrosequencing results, i.e., the predominant staining of Firmicutes.Conclusion: We demonstrate the in vitro survival of native primary oral biofilm in its natural complexity over 48 h. Our results offer a baseline for cultivation studies of native oral biofilms in (phyto-) pharmacological and dental materials research. Further investigations and validation of culturing conditions could also facilitate the study of biofilm-induced diseases.

One contribution of 17 to a Theo Murphy meeting issue 'Unity and diversity of cilia in locomotion and transport'.The brain ventricles are interconnected, elaborate cavities that traverse the brain. They are filled with cerebrospinal fluid (CSF) that is, to a large part, produced by the choroid plexus, a secretory epithelium that reaches into the ventricles. CSF is rich in cytokines, growth factors and extracellular vesicles that glide along the walls of ventricles, powered by bundles of motile cilia that coat the ventricular wall. We review the cellular and biochemical properties of the ventral part of the third ventricle that is surrounded by the hypothalamus. In particular, we consider the recently discovered intricate network of cilia-driven flows that characterize this ventricle and discuss the potential physiological significance of this flow for the directional transport of CSF signals to cellular targets located either within the third ventricle or in the adjacent hypothalamic brain parenchyma. Cilia-driven streams of signalling molecules offer an exciting perspective on how fluid-borne signals are dynamically transmitted in the brain.This article is part of the Theo Murphy meeting issue 'Unity and diversity of cilia in locomotion and transport'.