Stream water age distributions controlled by storage dynamics and nonlinear hydrologic connectivity : Modeling with high-resolution isotope data

Peer reviewedPublisher PD

Structure and activity investigations of the cell fate determinant, SpoIIE, from Bacillus subtilis

For many years the Gram positive bacterium Bacillus subtilis has been a model organism for prokaryotic cell and molecular biology. The asymmetric cell division which B. subtilis undergoes during sporulation is a simple system by which to study the process of cell differentiation. Sporulation is governed by a series of genetic temporal and spatial controls. Gene regulation brought about by a series of σ factors and transcriptional regulators is coupled to key morphological stages or checkpoints. σF initiates the first step in a cascade of complex genetic control which eventually produces a resilient endospore. The activation of σF, the first compartment-specific sigma factor, in the forespore and its regulation through interaction between three proteins; SpoIIAA, SpoIIAB and SpoIIE, is of particular interest. SpoIIE, a protein phosphatase which binds to the asymmetric division septum, is a crucial factor in the selective activation of σF in the forespore. Of three putative domains in SpoIIE only the C-terminal PP2C phosphatase domain has been structurally characterised. The central domain, domain II, of SpoIIE has been assigned a role in interaction with the cell division machinery; however mutational studies have shown that, in addition, this domain is also responsible for the regulation of phosphatase activity. This work describes the isolation and characterisation of three new fragments of SpoIIE containing elements of the central cytoplasmic domain of SpoIIE. These include a fragment found to accurately represent the N-terminal solubility limit of domain II which shows a high degree of oligomeric character. The fragments isolated show specific phosphatase activity against SpoIIAA~P, albeit at reduced rates compared to the free phosphatase domain, which indicates an inhibitory role for SpoIIE domain II against the PP2C domain. Three ultimately unsuccessful approaches were attempted to isolate a co-complex of SpoIIE and SpoIIAA~P for structural characterisation. A tendency for domain II containing SpoIIE fragments to precipitate in the presence of Mn(2+) is also identified. An in vivo investigation into the sporulation efficiencies of amino acid substitutions in a potential regulatory interface between domains II and III of SpoIIE indicated no strong sporulation defects

Uncoupled continuous-time random walks: Solution and limiting behavior of the master equation

A detailed study is presented for a large class of uncoupled continuous-time random walks (CTRWs). The master equation is solved for the Mittag-Leffler survival probability. The properly scaled diffusive limit of the master equation is taken and its relation with the fractional diffusion equation is discussed. Finally, some common objections found in the literature are thoroughly reviewed.Comment: Preprint version of an already published paper. 8 page

Expression of soluble, active fragments of the morphogenetic protein SpoIIE from Bacillus subtilis using a library-based construct screen

SpoIIE is a dual function protein that plays important roles during sporulation in Bacillus subtilis. It binds to the tubulin-like protein FtsZ causing the cell division septum to relocate from mid-cell to the cell pole, and it dephosphorylates SpoIIAA phosphate leading to establishment of differential gene expression in the two compartments following the asymmetric septation. Its 872 residue polypeptide contains a multiple-membrane spanning sequence at the N-terminus and a PP2C phosphatase domain at the C-terminus. The central segment that binds to FtsZ is unlike domains of known structure or function, moreover the domain boundaries are poorly defined and this has hampered the expression of soluble fragments of SpoIIE at the levels required for structural studies. Here we have screened over 9000 genetic constructs of spoIIE using a random incremental truncation library approach, ESPRIT, to identify a number of soluble C-terminal fragments of SpoIIE that were aligned with the protein sequence to map putative domains and domain boundaries. The expression and purification of three fragments were optimised, yielding multimilligram quantities of the PP2C phosphatase domain, the putative FtsZ-binding domain and a larger fragment encompassing both these domains. All three fragments are monomeric and the PP2C domain-containing fragments have phosphatase activity

Linking high-frequency DOC dynamics to the age of connected water sources

Acknowledgments The authors would like to thank our NRI colleagues for all their help with field and laboratory work, especially Audrey Innes, Jonathan Dick, and Ann Porter. We would like to also thank Iain Malcolm (Marine Scotland Science) for providing AWS data and the European Research Council ERC (project GA 335910 VEWA) for funding the VeWa project. Please contact the authors for access to the data used in this paper. We would also like to thank the Natural Environment Research Council NERC (project NE/K000268/1) for funding.Peer reviewedPublisher PD

Self-Objectification Among Physically Active Women

This article discusses self-objectification among physically active women

Production of high internal phase emulsions using rising air bubbles

High internal phase water in oil emulsions were produced by air sparging the two-phase system. The air sparging provided a mechanism for the incremental addition of the aqueous phase into the oil phase, and in turn the formation of aggregates of the aqueous droplets. Over time, a space-filling network of the droplets developed throughout the whole container. We refer to this critical state as a homogeneous, high internal phase coarse emulsion. Once the coarse emulsion was produced, the air bubbles were forced to perform useful work on the network, causing a refinement in the size of the droplets, with a concomitant increase in the emulsion viscosity. The emulsification process was reliable, however, over only a narrow range of air addition rates. At very low rates, the thin film drainage of the oil from between the aqueous droplets was more extensive, and hence the aqueous droplets coalesced and returned to the lower aqueous zone. At higher rates, the air flow tended to disrupt the droplet network. When expanded metal mesh was inserted into the vessel, with each horizontal layer of mesh separated by 40 mm, the process was found to be significantly more robust. Thus, using higher air rates, it was possible to achieve more than an order of magnitude increase in the emulsification rate. A well-defined coarse emulsion was also generated using gravity, by firstly causing aqueous phase droplets to detach from an upper surface, and secondly sediment to form a bed of droplets below. A given dispersed phase volume fraction was produced by fluidising the bed. Once the required bed concentration was formed, a refined emulsion was readily generated by air sparging