Role of hydrodynamic shear in the cultivation of animal, plant and microbial cells

Overexpression of TwSQS, TwSE, and TwOSC Regulates Celastrol Accumulation in Cambial Meristematic Cells and Dedifferentiated Cells

Squalene synthase (SQS), squalene epoxidase (SE), and oxidosqualene cyclase (OSC) are encoding enzymes in downstream biosynthetic pathway of triterpenoid in plants, but the relationship between three genes and celastrol accumulation in Tripterygium wilfordii still remains unknown. Gene transformation system in plant can be used for studying gene function rapidly. However, there is no report on the application of cambial meristematic cells (CMCs) and dedifferentiated cells (DDCs) in genetic transformation systems. Our aim was to study the effects of individual overexpression of TwSQS, TwSE, and TwOSC on terpenoid accumulation and biosynthetic pathway related gene expression through CMCs and DDCs systems. Overexpression vectors of TwSQS, TwSE, and TwOSC were constructed by Gateway technology and transferred into CMCs and DDCs by gene gun. After overexpression, the content of celastrol was significantly increased in CMCs compared with the control group. However, there was no significant increment of celastrol in DDCs. Meanwhile, the relative expression levels of TwSQS, TwSE, TwOSC, and terpenoid biosynthetic pathway related genes were detected. The relative expression levels of TwSQS, TwSE, and TwOSC were increased compared with the control group in both CMCs and DDCs, while the pathway-related genes displayed different expression trends. Therefore, it was verified in T. wilfordii CMCs that overexpression of TwSQS, TwSE, and TwOSC increased celastrol accumulation and had different effects on the expression of related genes in terpenoid biosynthetic pathway, laying a foundation for further elucidating the downstream biosynthetic pathway of celastrol through T. wilfordii CMCs system.

Cambial meristematic cell culture: a sustainable technology toward in vitro specialized metabolites production

Cambial meristematic cells (CMCs) culture has received a fair share of scientific and industrial attention among the trending topics of plant cell culture, especially their potential toward secondary metabolites production. However, the conventional plant cell culture is often not commercially feasible because of difficulties associated with culture dedifferentiated cells. Several reports have been published to culture CMCs and bypass the dedifferentiation process in plant cell culture. Numerous mitochondria, multiple vacuoles, genetic stability, self-renewal, higher biomass, and stable metabolites accumulation are the characteristics features of CMCs compared with dedifferentiated cells (DDCs) culture. The CMCs culture has a broader application to produce large-scale natural compounds for: pharmaceuticals, food, and cosmetic industries. Cutting-edge progress in plant cellular and molecular biology has allowed unprecedented insights into cambial stem cell culture and its fundamental processes. Therefore, regarding sustainability and natural compound production, cambial cell culture ranks among the most vital biotechnological interventions for industrial and economic perspectives. This review highlights the recent advances in plant stem cell culture and understands the cambial cells induction and culture mechanisms that affect the growth and natural compounds production.

Chemical stabilization of dispersed Escherichia coli for enhanced recovery with a handheld electroflotation system and detection by Loop-mediated Isothermal AMPlification

Constraints related to sample preparation are some of the primary obstacles to widespread deployment of molecular diagnostics for rapid detection of trace quantities (≤103 CFU/mL) of food-borne pathogens. In this research, we report a sample preparation method using a novel handheld electroflotation system to concentrate and recover dilute quantities (102-103 CFU/mL) of Escherichia coli (E. coli) 25922 in artificially contaminated samples for reliable, rapid detection by loop-mediated isothermal amplification (LAMP). To protect suspended cells from shear stresses at bubble surfaces, a non-ionic surfactant (Pluronic-F68) and flocculant (chitosan oligosaccharide) were used to aggregate cells and reduce their surface hydrophobicity. Effective conditions for recovery were determined through multifactorial experiments including various concentrations of Pluronic-F68 (0.001, 0.01, 0.1, 1 g L-1), chitosan oligosaccharide (0.01, 0.1, 1, 10 g L-1), bacteria (102, 103, 104 CFU/mL E. coli 25922), recovery times (10, 15 and 20 minutes), and degrees of turbulent gas flux ("high" and "low"). The automated electroflotation system was capable of concentrating effectively all of the bacteria from a large sample (380 mL 0.1 M potassium phosphate buffer containing 102 CFU/mL E. coli) into a 1 mL recovered fraction in less than 30 minutes. This enabled detection of bacterial contaminants within 2 hours of collecting the sample, without a specialized laboratory facility or traditional enrichment methods, with at least a 2-3 order of magnitude improvement in detection limit compared to direct assay with LAMP.

Establishing Rules for Self-Adhesion and Aggregation of N-Glycan Sugars Using Virus Glycan Shields

The surfaces of cells and pathogens are covered with short polymers of sugars known as glycans. Complex N-glycans have a core of three mannose sugars with distal repeats of N-acetylglucosamine and galactose sugars terminating with sialic acid (SA). Long-range tough and short-range brittle self-adhesions were observed between SA and mannose residues, respectively, in ill-defined artificial monolayers. We investigated if and how these adhesions translate when the residues are presented in N-glycan architecture with SA at the surface and mannose at the core and with other glycan sugars. Two pseudotyped viruses with complex N-glycan shields were brought together in force spectroscopy (FS). At higher ramp rates, slime-like adhesions were observed between the shields, whereas Velcro-like adhesions were observed at lower rates. The higher approach rates compress the virus as a whole, and the self-adhesion between the surface SA is sampled. At the lower ramp rates, however, the complex glycan shield is penetrated and adhesion from the mannose core is accessed. The slime-like and Velcro-like adhesions were lost when SA and mannose were cleaved, respectively. While virus self-adhesion in forced contact was modulated by glycan penetrability, the self-aggregation of the freely diffusing virus was only determined by the surface sugar. Mannose-terminal viruses self-aggregated in solution, and SA-terminal ones required Ca2+ ions to self-aggregate. Viruses with galactose or N-acetylglucosamine surfaces did not self-aggregate, irrespective of whether or not a mannose core was present below the N-acetylglucosamine surface. Well-defined rules appear to govern the self-adhesion and -aggregation of N-glycosylated surfaces, regardless of whether the sugars are presented in an ill-defined monolayer, or N-glycan, or even polymer architecture.

Shaving and breaking bacterial chains with a viscous flow

Some food and ferment manufacturing steps such as spray-drying result in the application of viscous stresses to bacteria. This study explores how a viscous flow impacts both bacterial adhesion functionality and bacterial cell organization using a combined experimental and modeling approach. As a model organism we study Lactobacillus rhamnosus GG (LGG) "wild type" (WT), known to feature strong adhesive affinities towards beta-lactoglobulin thanks to pili produced by the bacteria on cell surfaces, along with three cell-surface mutant strains. Applying repeated flows with high shear-rates reduces bacterial adhesive abilities up to 20% for LGG WT. Bacterial chains are also broken by this process, into 2-cell chains at low industrial shear rates, and into single cells at very high shear rates. To rationalize the experimental observations we study numerically and analytically the Stokes equations describing viscous fluid flow around a chain of elastically connected spheroidal cell bodies. In this model setting we examine qualitatively the relationship between surface traction (force per unit area), a proxy for pili removal rate, and bacterial chain length (number of cells). Longer chains result in higher maximal surface tractions, particularly at the chain extremities, while inner cells enjoy a small protection from surface tractions due to hydrodynamic interactions with their neighbors. Chain rupture therefore may act as a mechanism to preserve surface adhesive functionality in bacteria.

A novel strategy to enhance terpenoids production using cambial meristematic cells of Tripterygium wilfordii Hook. f

BACKGROUND

Tripterygium wilfordii Hook. f. (T. wilfordii) is an important medicinal plant with anti-inflammatory, immunosuppressive and anti-tumor activities. The main bioactive ingredients are diterpenoids and triterpenoids, such as triptolide, triptophenolide and celastrol. However, the production of terpenoids from original plants, hairy roots and dedifferentiated cells (DDCs) are not satisfactory for clinical applications. To find a new way to further improve the production of terpenoids, we established a new culture system of cambial meristematic cells (CMCs) with stem cell-like properties, which had strong vigor and high efficiency to produce large amounts of terpenoids of T. wilfordii.

RESULTS

CMCs of T. wilfordii were isolated and cultured for the first time. CMCs were characterized consistent with stem cell identities based on their physiological and molecular analysis, including morphology of CMCs, hypersensitivity to zeocin, thin cell wall and orthogonal partial least square-discriminant analysis, combination of transcriptional data analysis. After induction with methyl jasmonate (MJ), the maximal production of triptolide, celastrol and triptophenolide in CMCs was 312%, 400% and 327% higher than that of control group, respectively. As for medium, MJ-induced CMCs secreted 231% triptolide and 130% triptophenolide at the maximum level into medium higher than that of control group. Maximal celastrol production of induced CMCs medium was 48% lower than that of control group. Long-term induction significantly enhanced the production of terpenoids both in cells and medium. The reason for increasing the yield of terpenoids was that expression levels of 1-deoxy-d-xylulose-5-phosphate synthase (DXS), 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR) and hydroxymethylglutaryl-CoA synthase (HMGS) were upregulated in CMCs after induction.

CONCLUSIONS

For the first time, CMCs of T. wilfordii were isolated, cultured, characterized and applied. Considering the significant enrichment of terpenoids in CMCs of T. wilfordii, CMCs could provide an efficient and controllable platform for sustainable production of terpenoids, which can be a better choice than DDCs.

Hydrodynamic performance of a single-use aerated stirred bioreactor in animal cell culture: applications of tomography, dynamic gas disengagement (DGD), and CFD

The hydrodynamics of gas-liquid two-phase flow in a single-use bioreactor were investigated in detail both experimentally and numerically. Electrical resistance tomography (ERT) and dynamic gas disengagement (DGD) combined with computational fluid dynamics (CFD) were employed to assess the effect of the volumetric gas flow rate and impeller speed on the gas-liquid flow field, local and global gas holdup values, and Sauter mean bubble diameter. From the results obtained from DGD coupled with ERT, the bubble sizes were determined. The experimental data indicated that the total gas holdup values increased with increasing both the rotational speed of impeller and volumetric gas flow rate. Moreover, the analysis of the flow field generated inside the aerated stirred bioreactor was conducted using CFD results. Overall, a more uniform distribution of the gas holdup was obtained at impeller speeds ≥ 100 rpm for volumetric gas flow rates ≥ 1.6 × 10^-5 m³/s.

Application of CFD in Bioprocessing: Separation of mammalian cells using disc stack centrifuge during production of biotherapeutics

Centrifugation continues to be one of the most commonly used unit operations for achieving efficient harvest of the product from the mammalian cell culture broth during production of therapeutic monoclonal antibodies (mAbs). Since the mammalian cells are known to be shear sensitive, optimal performance of the centrifuge requires a balance between productivity and shear. In this study, Computational Fluid Dynamics (CFD) has been successfully used as a tool to facilitate efficient optimization. Multiphase Eulerian-Eulerian model coupled with Gidaspow drag model along with Eulerian-Eulerian k-ε mixture turbulence model have been used to quantify the complex hydrodynamics of the centrifuge and thus evaluate the turbulent stresses generated by the centrifugal forces. An empirical model has been developed by statistical analysis of experimentally observed cell lysis data as a function of turbulent stresses. An operating window that offers the optimal balance between high productivity, high separation efficiency, and low cell damage has been identified by use of CFD modeling.

Focused Review: Cytotoxic and Antioxidant Potentials of Mangrove-Derived Streptomyces

Human life expectancy is rapidly increasing with an associated increasing burden of chronic diseases, such as neurodegenerative diseases and cancer. However, there is limited progress in finding effective treatment for these conditions. For this reason, members of the genus Streptomyces have been explored extensively over the past decades as these filamentous bacteria are highly efficient in producing bioactive compounds with human health benefits. Being ubiquitous in nature, streptomycetes can be found in both terrestrial and marine environments. Previously, two Streptomyces strains (MUSC 137T and MUM 256) isolated from mangrove sediments in Peninsular Malaysia demonstrated potent antioxidant and cytotoxic activities against several human cancer cell lines on bioactivity screening. These results illustrate the importance of streptomycetes from underexplored regions aside from the terrestrial ecosystem. Here we provide the insights and significance of Streptomyces species in the search of anticancer and/or chemopreventive agents and highlight the impact of next generation sequencing on drug discovery from the Streptomyces arsenal.

Plant cell culture strategies for the production of natural products

Plants have evolved a vast chemical cornucopia to support their sessile lifestyles. Man has exploited this natural resource since Neolithic times and currently plant-derived chemicals are exploited for a myriad of applications. However, plant sources of most high-value natural products (NPs) are not domesticated and therefore their production cannot be undertaken on an agricultural scale. Further, these plant species are often slow growing, their populations limiting, the concentration of the target molecule highly variable and routinely present at extremely low concentrations. Plant cell and organ culture constitutes a sustainable, controllable and environmentally friendly tool for the industrial production of plant NPs. Further, advances in cell line selection, biotransformation, product secretion, cell permeabilisation, extraction and scale-up, among others, are driving increases in plant NP yields. However, there remain significant obstacles to the commercial synthesis of high-value chemicals from these sources. The relatively recent isolation, culturing and characterisation of cambial meristematic cells (CMCs), provides an emerging platform to circumvent many of these potential difficulties. [BMB Reports 2016; 49(3): 149-158]

Pneumatic hydrodynamics influence transplastomic protein yields and biological responses during in vitro shoot regeneration of Nicotiana tabacum callus: Implications for bioprocess routes to plant-made biopharmaceuticals

Transplastomic plants are capable of high-yield production of recombinant biopharmaceutical proteins. Plant tissue culture combines advantages of agricultural cultivation with the bioprocess consistency associated with suspension culture. Overexpression of recombinant proteins through regeneration of transplastomic Nicotiana tabacum shoots from callus tissue in RITA^® temporary immersion bioreactors has been previously demonstrated. In this study we investigated the hydrodynamics of periodic pneumatic suspension of liquid medium during temporary immersion culture (4 min aeration every 8 h), and the impact on biological responses and transplastomic expression of fragment C of tetanus toxin (TetC). Biomass was grown under a range of aeration rates for 3, 20 and 40-day durations. Growth, mitochondrial activity (a viability indicator) and TetC protein yields were correlated against the hydrodynamic parameters, shear rate and energy dissipation rate (per kg of medium). A critical aeration rate of 440 ml min^-1 was identified, corresponding to a shear rate of 96.7 s^-1, pneumatic power input of 8.8 mW kg^-1 and initial 20-day pneumatic energy dissipation of 127 J kg^-1, at which significant reductions in biomass accumulation and mitochondrial activity were observed. There was an exponential decline in TetC yields with increasing aeration rates at 40 days, across the entire range of conditions tested. These observations have important implications for the optimisation and scale-up of transplastomic plant tissue culture bioprocesses for biopharmaceutical production.

Equipment characterization to mitigate risks during transfers of cell culture manufacturing processes

The production of monoclonal antibodies by mammalian cell culture in bioreactors up to 25,000 L is state of the art technology in the biotech industry. During the lifecycle of a product, several scale up activities and technology transfers are typically executed to enable the supply chain strategy of a global pharmaceutical company. Given the sensitivity of mammalian cells to physicochemical culture conditions, process and equipment knowledge are critical to avoid impacts on timelines, product quantity and quality. Especially, the fluid dynamics of large scale bioreactors versus small scale models need to be described, and similarity demonstrated, in light of the Quality by Design approach promoted by the FDA. This approach comprises an associated design space which is established during process characterization and validation in bench scale bioreactors. Therefore the establishment of predictive models and simulation tools for major operating conditions of stirred vessels (mixing, mass transfer, and shear force.), based on fundamental engineering principles, have experienced a renaissance in the recent years. This work illustrates the systematic characterization of a large variety of bioreactor designs deployed in a global manufacturing network ranging from small bench scale equipment to large scale production equipment (25,000 L). Several traditional methods to determine power input, mixing, mass transfer and shear force have been used to create a data base and identify differences for various impeller types and configurations in operating ranges typically applied in cell culture processes at manufacturing scale. In addition, extrapolation of different empirical models, e.g. Cooke et al. (Paper presented at the proceedings of the 2nd international conference of bioreactor fluid dynamics, Cranfield, UK, 1988), have been assessed for their validity in these operational ranges. Results for selected designs are shown and serve as examples of structured characterization to enable fast and agile process transfers, scale up and troubleshooting.

Fermentation Conditions that Affect Clavulanic Acid Production in Streptomyces clavuligerus: A Systematic Review

The β-lactamase inhibitor, clavulanic acid is frequently used in combination with β-lactam antibiotics to treat a wide spectrum of infectious diseases. Clavulanic acid prevents drug resistance by pathogens against these β-lactam antibiotics by preventing the degradation of the β-lactam ring, thus ensuring eradication of these harmful microorganisms from the host. This systematic review provides an overview on the fermentation conditions that affect the production of clavulanic acid in the firstly described producer, Streptomyces clavuligerus. A thorough search was conducted using predefined terms in several electronic databases (PubMed, Medline, ScienceDirect, EBSCO), from database inception to June 30th 2015. Studies must involve wild-type Streptomyces clavuligerus, and full texts needed to be available. A total of 29 eligible articles were identified. Based on the literature, several factors were identified that could affect the production of clavulanic acid in S. clavuligerus. The addition of glycerol or other vegetable oils (e.g., olive oil, corn oil) could potentially affect clavulanic acid production. Furthermore, some amino acids such as arginine and ornithine, could serve as potential precursors to increase clavulanic acid yield. The comparison of different fermentation systems revealed that fed-batch fermentation yields higher amounts of clavulanic acid as compared to batch fermentation, probably due to the maintenance of substrates and constant monitoring of certain entities (such as pH, oxygen availability, etc.). Overall, these findings provide vital knowledge and insight that could assist media optimization and fermentation design for clavulanic acid production in S. clavuligerus.

Bubble pump: scalable strategy for in-plane liquid routing

We present an on-chip liquid routing technique intended for application in well-based microfluidic systems that require long-term active pumping at low to medium flowrates. Our technique requires only one fluidic feature layer, one pneumatic control line and does not rely on flexible membranes and mechanical or moving parts. The presented bubble pump is therefore compatible with both elastomeric and rigid substrate materials and the associated scalable manufacturing processes. Directed liquid flow was achieved in a microchannel by an in-series configuration of two previously described "bubble gates", i.e., by gas-bubble enabled miniature gate valves. Only one time-dependent pressure signal is required and initiates at the upstream (active) bubble gate a reciprocating bubble motion. Applied at the downstream (passive) gate a time-constant gas pressure level is applied. In its rest state, the passive gate remains closed and only temporarily opens while the liquid pressure rises due to the active gate's reciprocating bubble motion. We have designed, fabricated and consistently operated our bubble pump with a variety of working liquids for >72 hours. Flow rates of 0-5.5 μl min(-1), were obtained and depended on the selected geometric dimensions, working fluids and actuation frequencies. The maximum operational pressure was 2.9 kPa-9.1 kPa and depended on the interfacial tension of the working fluids. Attainable flow rates compared favorably with those of available micropumps. We achieved flow rate enhancements of 30-100% by operating two bubble pumps in tandem and demonstrated scalability of the concept in a multi-well format with 12 individually and uniformly perfused microchannels (variation in flow rate <7%). We envision the demonstrated concept to allow for the consistent on-chip delivery of a wide range of different liquids that may even include highly reactive or moisture sensitive solutions. The presented bubble pump may provide active flow control for analytical and point-of-care diagnostic devices, as well as for microfluidic cells culture and organ-on-chip platforms.

Cambial meristematic cells: a platform for the production of plant natural products

Plant cell culture constitutes a sustainable, controllable and environmentally friendly tool to produce natural products for the pharmaceutical, cosmetic and industrial biotechnology industries. However, there are significant obstacles to the commercial synthesis of high value chemicals from plant culture including low yields, performance instability, slow plant cell growth, industrial scale-up and downstream processing. Cambial meristematic cells constitute a platform to ameliorate many of these potential problems enabling the commercial production of high value chemicals.

The role of hydrodynamic conditions and pH on algal-rich water fouling of ultrafiltration

The aim of this paper was to study the membrane fouling phenomena by eutrophic water using Microcystis aeruginosa under various operational conditions (flux and air flow rate) and solution chemistry (pH). All the experiments were performed in a lab scale employing the polyvinyl chloride ultrafiltration membrane with nominal cut-off of 10 kDa. A slight fouling appeared at the flux not more than 10 L/m²/h, and the trend of trans-membrane pressure (TMP) development varied as a function of flux from linear to exponential with the increase of cell concentration. This paper also studied an important consideration of aeration in algal fouling: shear force. Besides alleviating membrane fouling, the shear produced by the bubbling should take responsible for the breakup of cells and the release of intracellular organic matters which caused the rate of the TMP increase closed to that without aeration. The optimum aeration intensity was observed to be 2.5 m³/m²/h in this experimental condition. As another important parameter considered in the study, the pH value of the raw water changed the physical and chemical reaction between the membrane and foulants or themselves. The results showed that the final TMP reduced with the pH increase due to the electro-static repulsion strengthening between the macromolecules which developed a looser gel. The most severe fouling was obtained at pH 5.0 near to the iso-electric point of algal solution, where electrostatic repulsion between algal cells was weakest. Furthermore, low pH value had a negative impact on cell integrity which gave rise to much more dissolved algogenic organic matter in the solution. It also played a part role on the membrane fouling.

Bioactives from microalgal dinoflagellates

Dinoflagellate microalgae are an important source of marine biotoxins. Bioactives from dinoflagellates are attracting increasing attention because of their impact on the safety of seafood and potential uses in biomedical, toxicological and pharmacological research. Here we review the potential applications of dinoflagellate toxins and the methods for producing them. Only sparing quantities of dinoflagellate toxins are generally available and this hinders bioactivity characterization and evaluation in possible applications. Approaches to production of increased quantities of dinoflagellate bioactives are discussed. Although many dinoflagellates are fragile and grow slowly, controlled culture in bioreactors appears to be generally suitable for producing many of the metabolites of interest.

CFD Simulation of Annular Centrifugal Extractors

Annular centrifugal extractors (ACE), also called annular centrifugal contactors offer several advantages over the other conventional process equipment such as low hold-up, high process throughput, low residence time, low solvent inventory and high turn down ratio. The equipment provides a very high value of mass transfer coefficient and interfacial area in the annular zone because of the high level of power consumption per unit volume and separation inside the rotor due to the high g of centrifugal field. For the development of rational and reliable design procedures, it is important to understand the flow patterns in the mixer and settler zones. Computational Fluid Dynamics (CFD) has played a major role in the constant evolution and improvements of this device. During the past thirty years, a large number of investigators have undertaken CFD simulations. All these publications have been carefully and critically analyzed and a coherent picture of the present status has been presented in this review paper. Initially, review of the single phase studies in the annular region has been presented, followed by the separator region. In continuation, the two-phase CFD simulations involving liquid-liquid and gas-liquid flow in the annular as well as separator regions have been reviewed. Suggestions have been made for the future work for bridging the existing knowledge gaps. In particular, emphasis has been given to the application of CFD simulations for the design of this equipment.

Growth dynamics and the proximate biochemical composition and fatty acid profile of the heterotrophically grown diatom Cyclotella cryptica

To investigate the nutritional value of the diatom Cyclotella cryptica as an alternative feed for aquaculture, its heterotrophic growth characteristics were studied. First, the proximate biochemical composition and fatty acid profiles were studied under a controlled heterotrophic growth condition. The approximate total ash, carbohydrate, lipid, and protein content were 245 mg g(-1) (dry weight), 360 mg g(-1), 165 mg g(-1) and 260 mg g(-1), respectively. Polyunsaturated fatty acids accounted for 24.5, 31.3, 45.1 and 17.3% of the total lipids in the phospholipid, sterol, free fatty acid and triglyceride classes. Secondly, the effect of aeration and agitation rates on the specific growth rate of C. cryptica under heterotrophic conditions was studied. The maximum specific growth rate was not significantly affected (P > 0.05) by the rate of agitation within the range of 100 to 160 rpm, but it was significantly affected (P > 0.05) by the rate of aeration. Optimal growth occurred when the aeration rate was within the range of 0.44 to 1.07 v/v/min. Viability measurements throughout the growth period showed that the C. cryptica cells remained viable in spite of the varied cultivation conditions. Hydrodynamic forces are an important parameter within biological systems, and optimisation is crucial for the successful scale-up of microalgal cultivation systems. Whilst the investigation was preliminary in nature, the information gained in this study will be useful for the continual development of an alternative and cost-effective feed for bivalve spat rations.

Effect of shear stress on intrinsic CHO culture state and glycosylation of recombinant tissue-type plasminogen activator protein

Shear stress in suspension culture was investigated as a possible manipulative parameter for the control of glycosylation of the recombinant tissue-type plasminogen activator protein (r-tPA) produced by recombinant Chinese hamster ovary (CHO) cell culture, grown in protein-free media. Resulting fractions of partially glycosylated, Type II, and fully glycosylated, Type I, r-tPA protein were monitored as a direct function of the shear characteristics of the culture environment. The shear-induced response of CHO culture to levels of low shear stress, where exponential growth was not obtained, and to higher levels of shear stress, which resulted in extensive cell death, were examined through manipulation of the bioreactor stirring velocity. Both apparent and intrinsic cell growth, metabolite consumption, byproduct and r-tPA production, and r-tPA glycosylation, from a variable site-occupancy standpoint, were monitored throughout. Kinetic analyses revealed a shear-stress-induced alteration of cellular homeostasis resulting in a nonlinear dependency of metabolic yield coefficients and an intrinsic cell lysis kinetic constant on shear stress. Damaging levels of shear stress were used to investigate the shear dependence of cell death and lysis, as well as the effects on the intrinsic growth rate of the culture. Kinetic models were also developed on the basis of the intrinsic state of the culture and compared to traditional models. Total r-tPA production was maximized under moderate shear conditions, as was the viable CHO cell density of the culture. However, Type II r-tPA production and the fraction of Type II glycoform production ratio was maximized under damaging levels of shear stress. Analyses of biomass production yield coefficients coupled with a plug-flow reactor model of glycan addition in the endoplasmic reticulum (ER) were used to propose an overall mechanism of decreased r-tPA protein site-occupancy glycosylation with increasing shear stress. Decreased residence time of r-tPA in the ER as a result of increased protein synthesis related to shear protection mechanisms is proposed to limit contact of site Asn184 with the membrane-bound oligosaccharyltransferase enzyme in the ER.

Biodegradation-based polymer surface erosion and surface renewal for foul-release at low ship speeds

Non-toxic foul-release provides an environmentally friendly and sustainable technical solution to control micro- and/or macrofouling on ships' hulls. Silicone-based coatings have been used for foul-release at high or moderate ship speeds (> 15 knots). To remove the fouling from slower ships (< 15 knots), the macrofoulers in particular, biodegradable polymers may be used to make the coating surface self-renewable. Synthesized by micro-organisms for carbon and energy storage under controlled conditions, polyhydroxyalkanoates (PHAs) are hydrophobic bipolymers that are gradually decomposed into CO2 and water in the environment. Because of their hydrophobic property and lack of hydrolysis in sterile aqueous solution, PHAs do not dissolve in water, but erode at the polymer surface (2-5 microns in depth) catalyzed exclusively by microbial enzymes (depolymerases) that are attached on the solid surface. The thin-layer surface erosion behaves like a self-renewable surface coating, which approaches a constant renewal rate at a relative hydraulic speed as low as 3 knots. A turbulence eddy model is used to describe the effect of energy consumption per mass of liquid on the turbulent shear stress and the surface renewal rate. Furthermore, the polymer biodegradation or surface renewal rate can be controlled within a broad range by blending the material with polymers such as poly (epsilon-caprolactone) (PCL). The biodegradation of binary blends of PHA/PCL of different compositions was quantitatively monitored by means of weight loss and Raman spectroscopy.

Role of hydrodynamic shear on activity and structure of proteins

Proteins are important products used in industry. They may be enzymes which catalyze different reactions or they may be required for their biological activities as hormones, growth factors or therapeutics. During production and recovery, proteins are subjected to fluid forces which arise due to operations such as stirring, pumping and centrifugation. The resulting hydrodynamic shear forces may cause damage to the large molecular weight proteins, resulting in denaturation and inactivation of the protein. This is a major concern as it affects the overall efficiency of protein recovery and final yield of the product. A considerable amount of research has been devoted to studying the effects of hydrodynamic shear stress on proteins, especially with respect to the enzymes. Enzymes are subjected to shear stresses during their production in fermentors, during isolation and purification steps in downstream operations and also during their use in enzyme reactors, especially if stirred reactors are employed to perform enzyme catalysed reactions. The present review discusses the effects of fluid shear stress on proteins including enzymes. A brief description on deactivation has been included in order to understand the effect of shear on the deactivation kinetics of proteins. The model systems used to subject proteins to shear and some unit operations during protein processing or use wherein they are exposed to shear stresses have also been presented. The significance of shear effects in designing bioprocesses involving shear sensitive biocatalysts as well as suggestions for future work have also been given.