Influence of growth and high mould concentration on the pressure drop in solid state fermentations

#Aspergillus niger$ was grown on Amberlite IRA-900 imbibed with a solution containing high concentrations of sucrose (Si = 100, 200, 300 and 400 g/litre) in static aerated fermentors. Growth was followed in dry biomass, biomass protein, CO2 production and pressure drop (DP). The DP allowed the monitoring of germination, vegetative growth, militation and the onset of sporulation for the four concentrations of sucrose studied. Concentrations up to 103 mg dry biomass/g dry support were obtained with Si = 400 g/litre and these reduced the relative intrinsic permeability to 0.0125. Under this condition the mould occupies 34 % of the free space. DP increase was related to CO2 production. (Résumé d'auteur

Phenomenological model of fungal biofilters for the abatement of hydrophobic VOCs

This work describes the growth of filamentous fungi in biofilters for the degradation of hydrophobic VOCs. The study system was n-hexane and Fusarium solani B1. The system is mathematically described and the main physical, kinetic data and morphological parameters were obtained by independent experiments and validated with data from laboratory experiments. The model describes the increase in the transport area by the growth of the filamentous cylindrical mycelia and its relation with n-hexane elimination in quasi-stationary state in a biofilter. The model describing fungal growth includes Monod-Haldane kinetic and hyphal elongation and ramification. A specific surface area of transport (SSAT) of 1.91 × 105 m2 m-3 and a maximum elimination capacity (EC) of 248 g m-3 h-1 were obtained by the mathematical model simulation, with a 10% of error with respect to the experimental EC

Caracterización morfológica de hifas aéras y simulación del crecimiento de Fusarium solani bajo diferentes fuentes de carbono para su aplicación en la biofiltración de COVs hidrofóbicos

Publicado por la Academia Mexicana de Investigación y Docencia en Ingeniería Química A.C.This work presents the e ect of di erent carbon sources (glycerol, 1-hexanol and n-hexane)over the morphology of the aerial hyphae of the filamentous fungus Fusarium solani for its application in the biofiltration of volatile organic compounds (VOCs). A mathematical model was developed and further verified that combines microscopic and macroscopic parameters describing the mycelial fungal growth. Image analysis of microcultures and culture in agar dishes was performed to determine the morphological parameters. The results show that the hydrophobic and volatile carbon sources modified the morphology of Fusarium solani, this is associated with the better utilization of the volatile carbon source. The main morphology changes observed with glycerol and n-hexane, were the reduction in both the hyphal diameter (from 2.99 um to 2.01 um) and the average hyphal length (from 603.8 um to 280.1 um). These results indicate an increase in the transport area for the same amount of biomass as an adaptation response to increase the uptake of volatile hydrophobic substrates.Este trabajo presenta el efecto de diferentes fuentes de carbono (glicerol, 1-hexanol y n-hexano) sobre la morfología de las hifas aéreas del hongo filamentoso Fusarium solani para su aplicación en la biofiltración de compuestos orgánicos volátiles (COVs). Un modelo matemático que combina parámetros microscópicos y macroscópicos que describen el crecimiento del micelio del hongo fue desarrollado y verificado. Análisis de imágenes de los microcultivos y cultivos en placas de agar fue realizado para determinar los parámetros morfológicos. Los resultados muestran que las fuentes de carbono hidrofóbicas y volátiles modifican la morfología de Fusarium solani, esto está asociado con la mejor utilización de la fuente de carbono volátil. Los principales cambios morfológicos observados con glicerol y n-hexano, fueron la reducción en ambos diámetros de las hifas (desde 2.99 um a 2.01 um) y la longitud promedio de la hifa (desde 603.8 um a 280.1 um). Estos resultados indican un aumento en el área de transporte para la misma cantidad de biomasa como una respuesta de adaptación para aumentar la captación de los sustratos hidrofóbicos volátiles

Elimination of hydrophobic volatile organic compounds in fungal biofilters: Reducing start-up time using different carbon sources

Fungal biofilters have been recently studied as an alternative to the bacterial systems for the elimination of hydrophobic volatile organic compounds (VOC). Fungi foster reduced transport limitation of hydrophobic VOCs due to their hydrophobic surface and extended gas exchange area associated to the hyphal growth. Nevertheless, one of their principal drawbacks is their slow growth, which is critical in the start-up of fungal biofilters. This work compares the use of different carbon sources (glycerol, 1-hexanol, wheat bran, and n-hexane) to reduce the start-up period and sustain high n-hexane elimination capacities (EC) in biofilters inoculated with Fusarium solani. Four parallel experiments were performed with the different media and the EC, the n-hexane partition coefficient, the biomass production and the specific consumption rate were evaluated. Biofilters were operated with a residence time of 1.3min and an inlet n-hexane load of 325gm-3reactorh-1. The time to attain maximum EC once gaseous n-hexane was fed was reduced in the three experiments with alternate substrates, as compared to the 36 days needed with the control where only n-hexane was added. The shortest adaptation period was 7 days when wheat bran was initially used obtaining a maximum EC of 160gm-3reactorh-1 and a critical load of 55gm-3reactorh-1. The results were also consistent with the pressure drop, the amount of biomass produced and its affinity for the gaseous n-hexane, as represented by its partition coefficient. © 2010 Wiley Periodicals, Inc

Effects of inoculum type, packing material and operating conditions on pentane biofiltration

Biofilters are an interesting alternative to treat airstreams polluted with gaseous alkanes from industrial activities. These hydrophobic compounds are difficult to treat by bacterial communities which are generally used in biofiltration. In this work, four fungal populations (3 consortia and Fusarium solani) were used as inocula in biofilters for treating pentane and hexane. The biofilters were packed with inorganic and organic materials (perlite and peat) and operated with the periodic addition of mineral medium at pH 4 supplemented with antibacterial agents to favor the development of fungi. To reduce the lag phase, the biofilters were inoculated with active mycelia. Lower performance was obtained with the peat biofilters. Sustained 100 % removal efficiencies were obtained with biofilters at an operation pentane load of = 32.9 ± 8.1 g m-3 h-1. Maximum elimination capacity of Cmax = 100 g m-3 h-1 was obtained with one of the fungal consortia; this value is higher than those usually reported for pentane degrading bacterial biofilters

Questioning Glutamate Excitotoxicity in Acute Brain Damage: The Importance of Spreading Depolarization

Background: Within 2 min of severe ischemia, spreading depolarization (SD) propagates like a wave through compromised gray matter of the higher brain. More SDs arise over hours in adjacent tissue, expanding the neuronal damage. This period represents a therapeutic window to inhibit SD and so reduce impending tissue injury. Yet most neuroscientists assume that the course of early brain injury can be explained by glutamate excitotoxicity, the concept that immediate glutamate release promotes early and downstream brain injury. There are many problems with glutamate release being the unseen culprit, the most practical being that the concept has yielded zero therapeutics over the past 30 years. But the basic science is also flawed, arising from dubious foundational observations beginning in the 1950s Methods: Literature pertaining to excitotoxicity and to SD over the past 60 years is critiqued. Results: Excitotoxicity theory centers on the immediate and excessive release of glutamate with resulting neuronal hyperexcitation. This instigates poststroke cascades with subsequent secondary neuronal injury. By contrast, SD theory argues that although SD evokes some brief glutamate release, acute neuronal damage and the subsequent cascade of injury to neurons are elicited by the metabolic stress of SD, not by excessive glutamate release. The challenge we present here is to find new clinical targets based on more informed basic science. This is motivated by the continuing failure by neuroscientists and by industry to develop drugs that can reduce brain injury following ischemic stroke, traumatic brain injury, or sudden cardiac arrest. One important step is to recognize that SD plays a central role in promoting early neuronal damage. We argue that uncovering the molecular biology of SD initiation and propagation is essential because ischemic neurons are usually not acutely injured unless SD propagates through them. The role of glutamate excitotoxicity theory and how it has shaped SD research is then addressed, followed by a critique of its fading relevance to the study of brain injury. Conclusions: Spreading depolarizations better account for the acute neuronal injury arising from brain ischemia than does the early and excessive release of glutamate.Grants to RDA from the Canadian Heart & Stroke Foundation, National Science Engineering and Research Council and the New Frontiers in Research Fund, to E.F from the National Research, Development and Innovation Office of Hungary, grant no. K134377; and the EU’s Horizon 2020 research and innovation program under grant agreement No. 739593, and to JPD from the DFG (German research Council) (DFG DR323/5-1,DFG DR 323/10-1) BMBF Bundesministerium fuer Bildung und Forschung (Era-Net Neuron EBio2, with funds from BMBF 01EW2004)

A Hydrophobic Gate in an Ion Channel: The Closed State of the Nicotinic Acetylcholine Receptor

The nicotinic acetylcholine receptor (nAChR) is the prototypic member of the `Cys-loop' superfamily of ligand-gated ion channels which mediate synaptic neurotransmission, and whose other members include receptors for glycine, gamma-aminobutyric acid, and serotonin. Cryo-electron microscopy has yielded a three dimensional structure of the nAChR in its closed state. However, the exact nature and location of the channel gate remains uncertain. Although the transmembrane pore is constricted close to its center, it is not completely occluded. Rather, the pore has a central hydrophobic zone of radius about 3 A. Model calculations suggest that such a constriction may form a hydrophobic gate, preventing movement of ions through a channel. We present a detailed and quantitative simulation study of the hydrophobic gating model of the nicotinic receptor, in order to fully evaluate this hypothesis. We demonstrate that the hydrophobic constriction of the nAChR pore indeed forms a closed gate. Potential of mean force (PMF) calculations reveal that the constriction presents a barrier of height ca. 10 kT to the permeation of sodium ions, placing an upper bound on the closed channel conductance of 0.3 pS. Thus, a 3 A radius hydrophobic pore can form a functional barrier to the permeation of a 1 A radius Na+ ion. Using a united atom force field for the protein instead of an all atom one retains the qualitative features but results in differing conductances, showing that the PMF is sensitive to the detailed molecular interactions.Comment: Accepted by Physical Biology; includes a supplement and a supplementary mpeg movie can be found at http://sbcb.bioch.ox.ac.uk/oliver/download/Movies/watergate.mp