Bacteria Use Type IV Pili to Walk Upright and Detach from Surfaces

1. Department of Bioengineering, California Nano Systems Institute,University of California, Los Angeles, CA 90024, USA. 2. Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204, USA. 3. Department of Materials Science and Engineering, University of Illinois, Urbana-Champaign, IL 61801, USA. 4. Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA.Bacterial biofilms are structured multicellular communities involved in a broad range of infections. Knowing how free-swimming bacteria adapt their motility mechanisms near surfaces is crucial for understanding the transition between planktonic and biofilm phenotypes. By translating microscopy movies into searchable databases of bacterial behavior, we identified fundamental type IV pili–driven mechanisms for Pseudomonas aeruginosa surface motility involved in distinct foraging strategies. Bacteria stood upright and “walked” with trajectories optimized for two-dimensional surface exploration. Vertical orientation facilitated surface detachment and could influence biofilm morphology.Center for Nonlinear Dynamic

Cyclotrons as Drivers for Precision Neutrino Measurements

As we enter the age of precision measurement in neutrino physics, improved flux sources are required. These must have a well-defined flavor content with energies in ranges where backgrounds are low and cross section knowledge is high. Very few sources of neutrinos can meet these requirements. However, pion/muon and isotope decay-at-rest sources qualify. The ideal drivers for decay-at-rest sources are cyclotron accelerators, which are compact and relatively inexpensive. This paper describes a scheme to produce decay-at-rest sources driven by such cyclotrons, developed within the DAEdALUS program. Examples of the value of the high precision beams for pursuing Beyond Standard Model interactions are reviewed. New results on a combined DAEdALUS--Hyper-K search for CP-violation that achieve errors on the mixing matrix parameter of 4 degrees to 12 degrees are presented.Comment: This paper was invited by the journal Advances in High Energy Physics for their upcoming special issue on "Neutrino Masses and Oscillations," which will be published on the 100th anniversary of Pontecorvo's birt

Synchronization in a ring of pulsating oscillators with bidirectional couplings

We study the dynamical behavior of an ensemble of oscillators interacting through short range bidirectional pulses. The geometry is 1D with periodic boundary conditions. Our interest is twofold. To explore the conditions required to reach fully synchronization and to invewstigate the time needed to get such state. We present both theoretical and numerical results.Comment: Revtex, 4 pages, 2 figures. To appear in Int. J. Bifurc. and Chao

Aquatic polymers can drive pathogen transmission in coastal ecosystems.

Gelatinous polymers including extracellular polymeric substances (EPSs) are fundamental to biophysical processes in aquatic habitats, including mediating aggregation processes and functioning as the matrix of biofilms. Yet insight into the impact of these sticky molecules on the environmental transmission of pathogens in the ocean is limited. We used the zoonotic parasite Toxoplasma gondii as a model to evaluate polymer-mediated mechanisms that promote transmission of terrestrially derived pathogens to marine fauna and humans. We show that transparent exopolymer particles, a particulate form of EPS, enhance T. gondii association with marine aggregates, material consumed by organisms otherwise unable to access micrometre-sized particles. Adhesion to EPS biofilms on macroalgae also captures T. gondii from the water, enabling uptake of pathogens by invertebrates that feed on kelp surfaces. We demonstrate the acquisition, concentration and retention of T. gondii by kelp-grazing snails, which can transmit T. gondii to threatened California sea otters. Results highlight novel mechanisms whereby aquatic polymers facilitate incorporation of pathogens into food webs via association with particle aggregates and biofilms. Identifying the critical role of invisible polymers in transmission of pathogens in the ocean represents a fundamental advance in understanding and mitigating the health impacts of coastal habitat pollution with contaminated runoff

Spatial epidemiological patterns suggest mechanisms of land-sea transmission for Sarcocystis neurona in a coastal marine mammal.

Sarcocystis neurona was recognised as an important cause of mortality in southern sea otters (Enhydra lutris nereis) after an outbreak in April 2004 and has since been detected in many marine mammal species in the Northeast Pacific Ocean. Risk of S. neurona exposure in sea otters is associated with consumption of clams and soft-sediment prey and is temporally associated with runoff events. We examined the spatial distribution of S. neurona exposure risk based on serum antibody testing and assessed risk factors for exposure in animals from California, Washington, British Columbia and Alaska. Significant spatial clustering of seropositive animals was observed in California and Washington, compared with British Columbia and Alaska. Adult males were at greatest risk for exposure to S. neurona, and there were strong associations with terrestrial features (wetlands, cropland, high human housing-unit density). In California, habitats containing soft sediment exhibited greater risk than hard substrate or kelp beds. Consuming a diet rich in clams was also associated with increased exposure risk. These findings suggest a transmission pathway analogous to that described for Toxoplasma gondii, with infectious stages traveling in freshwater runoff and being concentrated in particular locations by marine habitat features, ocean physical processes, and invertebrate bioconcentration

Extravehicular activities limitations study. Volume 1: Physiological limitations to extravehicular activity in space

This report contains the results of a comprehensive literature search on physiological aspects of EVA. Specifically, the topics covered are: (1) Oxygen levels; (2) Optimum EVA work; (3) Food and Water; (4) Carbon dioxide levels; (5) Repetitive decompressions; (6) Thermal, and (7) Urine collection. The literature was assessed on each of these topics, followed by statements on conclusions and recommended future research needs

Ether Cleavage Re-Investigated: Elucidating the Mechanism of BBr3- Facilitated Demethylation of Aryl Methyl Ethers

Boron tribromide is a versatile reagent utilized in diverse areas ranging from polymer chemistry to natural product synthesis.[1] Owing its high reactivity to the Lewis acidic boron center, BBr3 reactions include haloborylation,[2] boron–silicon exchange,[3] and rearrangement of 7,7-diphenylhydromorphone derivatives.[4] While there is no shortage in the diversity of BBr3-mediated reactions, many of the mechanisms for these transformations have not been fully elucidated. In this report we investigate the mechanism of ether cleavage by BBr3 [5–10] in anisole. Conceptually, demethylation of anisole is initiated by the formation of an ether adduct 1 followed by the loss of bromide. Free bromide nucleophilically attacks the methyl group of the cationic intermediate (2) cleaving the C–O bond and producing PhOBBr2, which undergoes hydrolysis upon aqueous work-up. While this pathway (Scheme 1) at first appears to be viable, we calculated that the formation of 2 and bromide in dichloromethane is thermodynamically inaccessible (ΔG = +38.9 kcal/mol). Recently, alternative mechanisms for ether cleavage were proposed by Sousa and Silva that involve unimolecular or bimolecular rate-determining steps that circumvent formation of bromide in solution (Scheme 2).[11] While a unimolecular process is kinetically favored for ethers containing one or more substituents (e.g. branched alkyl) that stabilize carbocation character in an SN1-like transition state, this barrier for demethylation of primary C atoms, like in the methyl group of anisole, lies too high on the potential energy surface to be accessible under reported reaction conditions. They found that a bimolecular process (Scheme 2, bottom) decreases the kinetic barrier for anisole demethylation significantly. During this reaction pathway, one of the bromides of the first ether adduct nucleophilically attacks the methyl group of the second ether adduct. This is analogous to an SN2 reaction with 180o attack of the methyl group by a bromide in the nucleophilic ether adduct. However, this bimolecular pathway produces two highly charged intermediates 2 and 3 that Sousa and Silva did not investigate. Their computational investigation stopped with the calculation of the initial kinetic barrier.[11] We speculate that these charged intermediates may undergo a similar bimolecular reaction to yield two equivalents of PhOBBr2 and MeBr. Moreover, if charged intermediates are formed then we believe an important set of mechanistic pathways may have been overlooked, namely, those where Lewis acidic BBr3 abstracts bromide from the ether complex to form BBr4 – in a mechanism related to the pathway introduced in Scheme 1