Biophysical Aspects of Resource Acquisition and Competition in Algal Mixotrophs

Mixotrophic organisms combine autotrophic and heterotrophic nutrition and are abundant in both freshwater and marine environments. Recent observations indicate that mixotrophs constitute a large fraction of the biomass, bacterivory, and primary production in oligotrophic environments. While mixotrophy allows greater flexibility in terms of resource acquisition, any advantage must be traded off against an associated increase in metabolic costs, which appear to make mixotrophs uncompetitive relative to obligate autotrophs and heterotrophs. Using an idealized model of cell physiology and community competition, we identify one mechanism by which mixotrophs can effectively outcompete specialists for nutrient elements. At low resource concentrations, when the uptake of nutrients is limited by diffusion toward the cell, the investment in cell membrane transporters can be minimized. In this situation, mixotrophs can acquire limiting elements in both organic and inorganic forms, outcompeting their specialist competitors that can utilize only one of these forms. This advantage can be enough to offset as much as a twofold increase in additional metabolic costs incurred by mixotrophs. This mechanism is particularly relevant for the maintenance of mixotrophic populations and productivity in the highly oligotro phic subtropical oceans.United States. National Aeronautics and Space AdministrationGordon and Betty Moore Foundatio

Selective constraints on global plankton dispersal

Marine microbial communities are highly interconnected assemblages of organisms shaped by ecological drift, natural selection and dispersal. The relative strength of these forces determines how ecosystems respond to environmental gradients, how much diversity is resident in a community or population at any given time, and how populations reorganise and evolve in response to environmental perturbations. In this study we introduce a globally-resolved population-genetic ocean model in order to examine the interplay of dispersal, selection and adaptive evolution, and their effects on community assembly and global biogeography. We find that environmental selection places strong constraints on global dispersal, even in the face of extremely high assumed rates of adaptation. Changing the relative strengths of dispersal, selection and adaptation has pronounced effects on community assembly in the model, and suggests that barriers to dispersal play a key role in the structuring of marine communities, enhancing global biodiversity and the importance of local historical contingencies

A Novel Decision Support System For Optimized Sewer Infrastructure Asset Management

This paper approaches the sewerage asset management challenge from a UK perspective by outlining a comprehensive methodology capable of optimising the performance of sewerage infrastructure networks using a series of Hydroinformatic tools. In order to define, evaluate and forecast the future performance of sewerage assets, a unique deterioration model is established to predict the future condition of the network. The model analyses historic CCTV survey information to identify deterioration trends based on key pipe characteristics. Against, this improved understanding of past, current and future condition, a collapse rate is predicted by correlating historic failures against the observed sewer condition profiles. The result is a novel relationship which is drawn between collapse rate and condition profile. From here, a prioritised inspection programme can be delivered that targets poorly performing and high consequence of failure assets. The survey information gather from these studies feeds into a previously successful sewer rehabilitation optimisation model that has been adapted under this new study to provide a mechanism for engineers to evaluate the trade-offs that exist between different sewer rehabilitation schemes. A series of GIS tools have been integrated within the model to identify the benefits from an operational perspective, thus guiding investment decisions towards those assets predicted to be in poor structural condition as well as causing operational issues, i.e., pollution, blockage and/or flooding events. As a result, the methodology acts as a series of strategic decision support tools which is capable of helping sewerage engineers and planners in the evaluation of different intervention programmes of work. A UK case study is provided to demonstrate the benefits of this approach

When everything is not everywhere but species evolve: an alternative method to model adaptive properties of marine ecosystems

The functional and taxonomic biogeography of marine microbial systems reflects the current state of an evolving system. Current models of marine microbial systems and biogeochemical cycles do not reflect this fundamental organizing principle. Here, we investigate the evolutionary adaptive potential of marine microbial systems under environmental change and introduce explicit Darwinian adaptation into an ocean modelling framework, simulating evolving phytoplankton communities in space and time. To this end, we adopt tools from adaptive dynamics theory, evaluating the fitness of invading mutants over annual timescales, replacing the resident if a fitter mutant arises. Using the evolutionary framework, we examine how community assembly, specifically the emergence of phytoplankton cell size diversity, reflects the combined effects of bottom-up and top-down controls. When compared with a species-selection approach, based on the paradigm that “Everything is everywhere, but the environment selects”, we show that (i) the selected optimal trait values are similar; (ii) the patterns emerging from the adaptive model are more robust, but (iii) the two methods lead to different predictions in terms of emergent diversity. We demonstrate that explicitly evolutionary approaches to modelling marine microbial populations and functionality are feasible and practical in time-varying, space-resolving settings and provide a new tool for exploring evolutionary interactions on a range of timescales in the ocean.France. Agence nationale de la recherche (grant PHYTBACK (ANR-10-BLAN-7109))European Union (EU Micro B3 project)European Research Council (ERC Diatomite project)Gordon and Betty Moore Foundation (Grant #3778

Mesenchymal stromal cell-mediated neuroprotection and functional preservation of retinal ganglion cells in a rodent model of glaucoma

Background aims: Glaucoma is a leading cause of irreversible blindness involving loss of retinal ganglion cells (RGC). Mesenchymal stromal cells (MSC) have shown promise as a paracrine-mediated therapy for compromised neurons. It is, however, unknown whether dental pulp stem cells (DPSC) are effective as a cellular therapy in glaucoma and how their hypothesized influence compares with other more widely researched MSC sources. The present study aimed to compare the efficacy of adipose-derived stem cells, bone marrow-derived MSC (BMSC) and DPSC in preventing the loss of RGC and visual function when transplanted into the vitreous of glaucomatous rodent eyes. Methods: Thirty-five days after raised intraocular pressure (IOP) and intravitreal stem cell transplantation, Brn3a+ RGC numbers, retinal nerve fibre layer thickness (RNFL) and RGC function were evaluated by immunohistochemistry, optical coherence tomography and electroretinography, respectively. Results: Control glaucomatous eyes that were sham-treated with heat-killed DPSC had a significant loss of RGC numbers, RNFL thickness and function compared with intact eyes. BMSC and, to a greater extent, DPSC provided significant protection from RGC loss and RNFL thinning and preserved RGC function. Discussion: The study supports the use of DPSC as a neuroprotective cellular therapy in retinal degenerative disease such as glaucoma