Extrusion of transmitter, water and ions generates forces to close fusion pore

AbstractDuring exocytosis the fusion pore opens rapidly, then dilates gradually, and may subsequently close completely, but what controls its dynamics is not well understood. In this study we focus our attention on forces acting on the pore wall, and which are generated solely by the passage of transmitter, ions and water through the open fusion pore. The transport through the charged cylindrical nano-size pore is simulated using a coupled system of Poisson–Nernst–Planck and Navier–Stokes equations and the forces that act radially on the wall of the fusion pore are then estimated. Four forces are considered: a) inertial force, b) pressure, c) viscotic force, and d) electrostatic force. The inertial and viscotic forces are small, but the electrostatic force and the pressure are typically significant. High vesicular pressure tends to open the fusion pore, but the pressure induced by the transport of charged particles (glutamate, ions), which is predominant when the pore wall charge density is high tends to close the pore. The electrostatic force, which also depends on the charge density on the pore wall, is weakly repulsive before the pore dilates, but becomes attractive and pronounced as the pore dilates. Given that the vesicular concentration of free transmitter can change rapidly due to the release, or owing to the dissociation from the gel matrix, we evaluated how much and how rapidly a change of the vesicular K+–glutamate− concentration affects the concentration of glutamate− and ions in the pore and how such changes alter the radial force on the wall of the fusion pore. A step-like rise of the vesicular K+–glutamate− concentration leads to a chain of events. Pore concentration (and efflux) of both K+ and glutamate− rise reaching their new steady-state values in less than 100 ns. Interestingly within a similar time interval the pore concentration of Na+ also rises, whereas that of Cl− diminishes, although their extra-cellular concentration does not change. Finally such changes affect also the water movement. Water efflux changes bi-phasically, first increasing before decreasing to a new, but lower steady-state value. Nevertheless, even under such conditions an overall approximate neutrality of the pore is maintained remarkably well, and the electrostatic, but also inertial, viscotic and pressure forces acting on the pore wall remain constant. In conclusion the extrusion of the vesicular content generates forces, primarily the force due to the electro-kinetically induced pressure and electrostatic force (both influenced by the pore radius and even more by the charge density on the pore wall), which tend to close the fusion pore

Oxygen transfer of microbubble clouds in aqueous solutions: application to wastewater

This study aims at improving the knowledge on the effects of gas injection, bubbles sizes and contaminants on oxygen transfer in microbubble clouds. First the effects of gas injection on oxygen transfer are studied and linked to several parameters that change together with changes in flow rate, namely bubble sizes and rise velocities. Oxygen transfer is then studied in the presence of contaminants that are shown to affect bubble size distribution, modify bubble dynamics and interfacial mass transfer. Oxygen transfer efficiencies are also measured in wastewater and compared with those obtained in aqueous solutions. The agreement between contaminated water in the lab (Triton X100) and wastewater experiments is emphasised as this offers the possibility to develop fundamental understanding relevant to wastewater under laboratory conditions. The role of the surfactants on the volumetric oxygen transfer coefficient is further analysed in terms of specific interfacial area and transfer coefficients, respectively. Interestingly, this shows that the increase in oxygen transfer efficiency as the concentration in Pentanol increases is due to the increase in interfacial area while the transfer coefficients decrease

Pilot scale study: first demonstration of hydrophobic membranes for the removal of ammonia molecules from rendering condensate wastewater

Hydrophobic membrane contactors represent a promising solution to the problem of recycling ammoniacal nitrogen (N-NH4) molecules from waste, water or wastewater resources. The process has been shown to work best with wastewater streams that present high N-NH4 concentrations, low buffering capacities and low total suspended solids. The removal of N-NH4 from rendering condensate, produced during heat treatment of waste animal tissue, was assessed in this research using a hydrophobic membrane contactor. This study investigates how the molecular composition of rendering condensate wastewater undergo changes in its chemistry in order to achieve suitability to be treated using hydrophobic membranes and form a suitable product. The main objective was to test the ammonia stripping technology using two types of hydrophobic membrane materials, polypropylene (PP) and polytetrafluoroethylene (PTFE) at pilot scale and carry out: (i) Process modification for NH3 molecule removal and (ii) product characterization from the process. Theresults demonstrate that PP membranesarenotcompatiblewiththecondensate wasteasit caused wetting. The PTFE membranes showed potential and had a longer lifetime than the PP membranes and removed upto64%ofNH3 moleculesfromthecondensate waste. The product formed contained a 30%concentrated ammonium sulphate salt which has a potential application as a fertilizer. This is the first demonstration of hydrophobic membrane contactors for treatment of condensate wastewate

Genomics of Rhodococcus

Members of the genus Rhodococcus have metabolic versatility and unique adaptation capacities to fluctuating environmental conditions, enabling the colonization of a wide variety of environments; they also play an important role in nutrient cycling and have potential applications in bioremediation, biotransformations and biocatalysis. Rhodococcus spp. are mainly distributed in soil, water and marine sediments, although some of them are also pathogens for humans, animals and plants. Consistent with the wide catabolic diversity, Rhodococcus spp. possess large and complex genomes (up to 10.1 Mbp), which contain a multiplicity of catabolic genes, high genetic redundancy of biosynthetic pathways and large catabolic plasmids, the latter encoding peculiar metabolic and physiological traits. Recently, the progress in sequencing technology led to a dramatic increase in the number of sequenced Rhodococcus genomes, which have been investigated through diverse bioinformatic approaches. In particular, whole-genome comparative and genome-based functional studies were associated to omic technologies for the study of the global Rhodococcus cell response with the aim of providing insight into the genetic basis of specific catabolic capacities and phenotypic traits. Lastly, genome-based advances in Rhodococcus engineering led to the first design of molecular toolkits for tunable and targeted genome editing. Besides this, genome-based metabolic models were developed to make metabolic predictions of the Rhodococcus cell response to specific growth conditions. Both the synthetic and system approaches offered new opportunities for genome-scale rational design of Rhodococcus cell for environmental and industrial applications