Integrin α\u3csub\u3ev\u3c/sub\u3eβ\u3csub\u3e8\u3c/sub\u3e Adopts a High Affinity State for Soluble Ligands Under Physiological Conditions

© 2016 Wiley Periodicals, Inc. It has been proposed that integrins adopt a low affinity conformation under physiological conditions. Integrin can either be activated through cytoplasm or by binding of cations such as Mn2+ to the head domain. The cytoplasmic activation pathway, that is, inside-out signaling has been regarded as the physiological pathway for integrin activation. Integrin β8 is important for neuron vascular development. However, due to the highly divergent cytoplasmic domain, this integrin probably does not rely on inside-out signaling for affinity regulation. We therefore hypothesized that the β8 integrin uniquely assumes a constitutively high affinity state under physiological conditions. We discovered that β8 indeed exhibited high binding to soluble vitronectin in the presence of Ca2+ and the ligand binding could not be further enhanced by addition of Mn2+. The lower ectodomain stalk of the integrin, which is comprised by the integrin epidermal growth factor-like (I-EGF) domains and βTD domain, is critical for this high affinity conformation. In addition, we found that unlike other integrins, Mg2+ at low concentration inhibited β8 ligand binding. Mutagenesis studies indicated that β8 integrin possesses a unique cation binding site which might contribute to the ligand binding affinity. Our study showed that both the β8 lower ectodomain stalk and the head domain play an important role in its high affinity state under physiological conditions. J. Cell. Biochem. 118: 2044–2052, 2017. © 2016 Wiley Periodicals, Inc

Airlift Column Photobioreactors for Porphyridium Sp. Culturing: Part II. Verification of Dynamic Growth Rate Model for Reactor Performance Evaluation

Dynamic Growth Rate Model Has Been Developed to Quantify the Impact of Hydrodynamics on the Growth of Photosynthetic Microorganisms and to Predict the Photobioreactor Performance. Rigorous Verification of Such Reactor Models, However, is Rare in the Literature. in This Part of Work, Verification of a Dynamic Growth Rate Model Developed in Luo and Al-Dahhan (2004) [Biotech Bioeng 85(4): 382-393.] Was Attempted using the Experimental Results Reported in Part I of This Work and Results from Literature. the Irradiance Distribution Inside the Studied Reactor Was Also Measured at Different Optical Densities and Successfully Correlated by the Lambert-Beer Law. When Reliable Hydrodynamic Data Were Used, the Dynamic Growth Rate Model Successfully Predicted the Algae\u27s Growth Rate Obtained in the Experiments in Both Low and High Irradiance Regime Indicating the Robustness of This Model. the Simulation Results Also Indicate the Hydrodynamics is Significantly Different between the Real Algae Culturing System and an Air-Water System that Signifies the Importance in using Reliable Data Input for the Growth Rate Model. © 2011 Wiley Periodicals, Inc

Local Gas Holdup in a Draft Tube Airlift Bioreactor

Airlift Column Bioreactors Are Gas-Liquid Contact Devices Characterized by a Rising Channel and a Down Flow Channel Due to Gas Holdup Differences in These Two Channels. Local Gas Holdup Distribution Strongly Affects the overall Gas-Liquid Flow Dynamics in Airlift Columns. in This Work, Local Gas Holdup Distributions in a Draft Tube Airlift Column Covering Both Bubbly Flow and Churn-Turbulent Flow Regimes Have Been Studied using Computed Tomography (CT) Technique as Well as Conventional Techniques. the Radial and Axial Evolutions of the Gas Holdup Distribution Will Be Discussed, Together with the Effects of Superficial Gas Velocity and Geometry Parameters. the Obtained Gas Holdup Results Will Also Be Used to Verify Various Empirical and Semi-Empirical Correlations in the Literature. Moreover, the Obtained Gas Holdup Information, Combined with Liquid Flow Dynamic Information Reported in Luo and Al-Dahhan (2008a, B), Forms a Benchmark Database for the Design and Scale-Up of Airlift Column Bioreactors and for Computational Fluid Dynamic (CFD) Modeling Validations. © 2010 Elsevier Ltd. All Rights Reserved

Airlift Column Photobioreactors for Porphyridium Sp. Culturing: Part I. Effects of Hydrodynamics and Reactor Geometry

Photosynthetic Microorganisms Have Been Attracting World Attention for their Great Potential as Renewable Energy Sources in Recent Years. Cost Effective Production in Large Scale, However, remains a Major Challenge to overcome. It is Known to the Field that Turbulence Could Help Improving the Performance of Photobioreactors Due to the So-Called Flashing Light Effects. Better Understanding of the Multiphase Fluid Dynamics and the Irradiance Distribution Inside the Reactor that Cause the Flashing Light Effects, as Well as Quantifying their Impacts on the Reactor Performance, Thus, Are Crucial for Successful Design and Scale-Up of Photobioreactors. in This Study, a Species of Red Marine Microalgae, Porphyridium Sp., Was Grown in Three Airlift Column Photobioreactors (I.e., Draft Tube Column, Bubble Column, and Split Column). the Physical Properties of the Culture Medium, the Local Fluid Dynamics and the Photobioreactor Performances Were Investigated and Are Reported in This Part of the Manuscript. Results Indicate that the Presence of Microalgae Considerably Affected the Local Multiphase Flow Dynamics in the Studied Draft Tube Column. Results Also Show that the Split Column Reactor Works Slightly Better Than the Draft Tube and the Bubble Columns Due to the Spiral Flow Pattern Inside the Reactor. © 2011 Wiley Periodicals, Inc

Local Characteristics of Hydrodynamics in Draft Tube Airlift Bioreactor

Airlift Column Reactors Have Been Widely Used in Bioprocesses. the Design, Scale-Up, and Performance Evaluation of Such Reactors All Require Extensive and Accurate Information About the Gas-Liquid Flow Dynamics, Particularly as Computational Fluid Dynamics (CFD) Has Become More Popular in the Last Decade. However, Due to the Limitation of Most Conventional Techniques for Gas-Liquid Flow Dynamics Measurement, Only Global Hydrodynamic Parameters (E.g., Cross-Sectionally Averaged Liquid Circulation Velocity, overall Gas Holdup, and overall Mass Transfer Rate) Have Been Extensively Studied. the Local Flow Characteristics (E.g., the Macro-Mixing and the Turbulence Intensity) Remain Unclear. in This Study, We Use the Computer Automated Radioactive Particle Tracking (CARPT) Technique to Investigate the Details of the Multiphase Flow Dynamics in a Draft Tube Airlift Bioreactor, Such as the Liquid Velocity Field, Turbulent Kinetic Energy Field, Distributions of Shear Stresses, Etc. the Flow Structures in the Whole Reactor, as Well as the Structure in Individual Regions, I.e., the Top, the Bottom, the Riser, and the Downcorner Are Also Characterized. We Found Significantly Large Turbulent Kinetic Energy in the Top and the Bottom Regions, with Spots of Very High Shear Stress, Which Were Also Found in the Vicinity of the Sparger. the Results Also Suggest that the Top and Bottom Clearances Have Significant Effects on the Flow Structures, Which May Have Substantial Effects on the Bioreactor Performance. © 2008 Elsevier Ltd. All Rights Reserved

Analyzing and Modeling of Photobioreactors by Combining First Principles of Physiology and Hydrodynamics

Mixing in Photobioreactors is Known to Enhance Biomass Productivity Considerably, and Flow Dynamics Play a Significant Role in the Reactor\u27s Performance, as They Determine the Mixing and the Cells\u27 Movement. in This Work We Focus on Analyzing the Effects of Mixing and Flow Dynamics on the Photobioreactor Performance. based on Hydrodynamic Findings from the CARPT(Computer Automated Radioactive Particle Tracking) Technique, a Possible Mechanism for the Interaction between the Mixing and the Physiology of Photosynthesis is Presented, and the Effects of Flow Dynamics on Light Availability and Light Intensity Fluctuation Are Discussed and Quantitatively Characterized. Furthermore, a Dynamic Modeling Approach is Developed for Photobioreactor Performance Evaluation, Which Integrates First Principles of Photosynthesis, Hydrodynamics, and Irradiance Distribution within the Reactor. the Results Demonstrate the Reliability and the Possible Applicability of This Approach to Commercially Interesting Microalgae/cyanobacteria Culture Systems. © 2004 Wiley Periodicals, Inc

Verification and Validation of CFD Simulations for Local Flow Dynamics in a Draft Tube Airlift Bioreactor

Airlift Reactors Have Been Recognized as One of the Promising Photobioreactors for Biomass/bio-Energy Production, Where Mixing Has Significant Impact on the Reactor Performance. in Recent Years, using CFD Simulations to Track Microorganism Cells and to Generate their Trajectories in the Reactor for Reactor Performance Evaluations Becomes More Common. However, there is a Lack of Systematic and Rigorous Verifications and Validations of the Reliability of CFD Models in Particle Tracking Against Experimental Measurements in the Open Literature, Which is Vital for the Faithful Application of CFD in Reactor Design and Scale-Ups. in This Work, We Attempt to Evaluate the Reliability of using CFD Simulations to Generate Trajectories of Microorganisms in a Draft Tube Column Photobioreactor. a Computationally Promising CFD Simulation Model based on CFX5.7 Was Validated Against a Benchmark Experimental Database Reported in Luo and Al-Dahhan (2008a, B, 2010). This Model Was Then Used to Generate Typical Trajectories of Microorganisms in the Studied Airlift Column, Which Was Further Validated Against Experimentally Measured Tracer Trajectories. the Results Indicated that the CFD Model Reasonably Predicted the Recirculation of the Microorganism Around the Draft Tube, however, over-Estimated the Cells\u27 Residence Time in the Wall Regions. Proper Treatment for the Wall Region Such as Griding and Wall Function is Needed to Better Capture the Movement of Microorganism Cells in Such Bioreactors. © 2010 Elsevier Ltd