Shear sensitivity of plant cells in suspensions present and future

Rheological Droplet Interface Bilayers (rheo-DIBs): Probing the Unstirred Water Layer Effect on Membrane Permeability via Spinning Disk Induced Shear Stress

A new rheological droplet interface bilayer (rheo-DIB) device is presented as a tool to apply shear stress on biological lipid membranes. Despite their exciting potential for affecting high-throughput membrane translocation studies, permeability assays conducted using DIBs have neglected the effect of the unstirred water layer (UWL). However as demonstrated in this study, neglecting this phenomenon can cause significant underestimates in membrane permeability measurements which in turn limits their ability to predict key processes such as drug translocation rates across lipid membranes. With the use of the rheo-DIB chip, the effective bilayer permeability can be modulated by applying shear stress to the droplet interfaces, inducing flow parallel to the DIB membranes. By analysing the relation between the effective membrane permeability and the applied stress, both the intrinsic membrane permeability and UWL thickness can be determined for the first time using this model membrane approach, thereby unlocking the potential of DIBs for undertaking diffusion assays. The results are also validated with numerical simulations.

The potential of Physcomitrella patens as a platform for the production of plant-based vaccines

The moss Physcomitrella patens has a number of advantages for the production of biopharmaceuticals, including: i) availability of standardized conditions for cultivation in bioreactors; ii) not being part of the food chain; iii) high biosafety; iv) availability of highly efficient transformation methods; v) a haploid, fully sequenced genome providing genetic stability and uniform expression; vi) efficient gene targeting at the nuclear level allows for the generation of mutants with specific post-translational modifications (e.g., glycosylation patterns); and vii) oral formulations are a viable approach as no toxic effects are attributed to ingestion of this moss. In the light of this panorama, this opinion paper analyzes the possibilities of using P. patens for the production of oral vaccines and presents some specific cases where its use may represent significant progress in the field of plant-based vaccine development. The advantages represented by putative adjuvant effects of endogenous secondary metabolites and producing specific glycosylation patterns are highlighted.

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.

Bioreactor systems for in vitro production of foreign proteins using plant cell cultures

Plant cells have been demonstrated to be an attractive heterologous expression host (using whole plants and in vitro plant cell cultures) for foreign protein production in the past 20years. In recent years in vitro liquid cultures of plant cells in a fully contained bioreactor have become promising alternatives to traditional microbial fermentation and mammalian cell cultures as a foreign protein expression platform, due to the unique features of plant cells as a production host including product safety, cost-effective biomanufacturing, and the capacity for complex protein post-translational modifications. Heterologous proteins such as therapeutics, antibodies, vaccines and enzymes for pharmaceutical and industrial applications have been successfully expressed in plant cell culture-based bioreactor systems including suspended dedifferentiated plant cells, moss, and hairy roots, etc. In this article, the current status and emerging trends of plant cell culture for in vitro production of foreign proteins will be discussed with emphasis on the technological progress that has been made in plant cell culture bioreactor systems.

Excess turbulence as a cause of turbohypobiosis in cultivation of microorganisms

The present review describes the influence of different types of mixing systems under excess turbulence conditions on microorganisms. Turbohypobiosis phenomena were described by applying a method for measurement of the kinetic energy of flow fluctuations based on the piezoeffect. It can be assumed that the shear stress effect (the state of turbohypobiosis) plays a role mainly when alternative mechanisms in cells cannot ensure a normal physiological state under stress conditions. Practically any system (inner construction of a bioreactor, culture and cultivation conditions, including mixing) requires its own optimisation to achieve the final goal, namely, the maximum product and/or biomass yields from substrate (YP/S or/and YX/S), respectively. Data on the biotechnological performance of cultivation as well as power input, kinetic energy (e) of flow fluctuations, air consumption rate, rotational speed, tip speed, etc. do not correlate directly if the mixing systems (impellers-baffles) are dissimilar. Even the widely used specific power consumption cannot be relied upon for scaling up the cultivation performance using dissimilar mixing systems. A biochemical explanation for substrate and product transport via cell walls, carbon pathways, energy generation and utilisation, etc. furnishes insight into cellular interactions with turbulence of different origin for different types of microorganisms (single cells, mycelia forming cells, etc.).

Biotechnological significance of toxic marine dinoflagellates

Dinoflagellates are microalgae that are associated with the production of many marine toxins. These toxins poison fish, other wildlife and humans. Dinoflagellate-associated human poisonings include paralytic shellfish poisoning, diarrhetic shellfish poisoning, neurotoxic shellfish poisoning, and ciguatera fish poisoning. Dinoflagellate toxins and bioactives are of increasing interest because of their commercial impact, influence on safety of seafood, and potential medical and other applications. This review discusses biotechnological methods of identifying toxic dinoflagellates and detecting their toxins. Potential applications of the toxins are discussed. A lack of sufficient quantities of toxins for investigational purposes remains a significant limitation. Producing quantities of dinoflagellate bioactives requires an ability to mass culture them. Considerations relating to bioreactor culture of generally fragile and slow-growing dinoflagellates are discussed. Production and processing of dinoflagellates to extract bioactives, require attention to biosafety considerations as outlined in this review.

Enhancement of shikonin production in single- and two-phase suspension cultures of Lithospermum erythrorhizon cells using low-energy ultrasound

This work demonstrates the use of low-energy ultrasound (US) to enhance secondary metabolite production in plant cell cultures. Suspension culture of Lithospermum erythrorhizon cells was exposed to low-power US (power density < or = 113.9 mW/cm(3)) for short periods (1-8 min). The US exposure significantly stimulated the shikonin biosynthesis of the cells, and at certain US doses, increased the volumetric shikonin yield by about 60%-70%. Meanwhile, the shikonin excreted from the cells was increased from 20% to 65%-70%, due partially to an increase in the cell membrane permeability by sonication. With combined use of US treatment and in situ product extraction by an organic solvent, or the two-phase culture, the volumetric shikonin yield was increased more than two- to threefold. Increasing in the number of US exposures during the culture process usually resulted in negative effects on shikonin yield but slight stimulation of shikonin excretion. US at relatively high energy levels caused slight cell growth depression (maximum 9% decrease in dry cell weight). Two key enzymes for the secondary metabolite biosynthesis of cells, phenylalanine ammonia lyase and p-hydroxybenzoic acid geranyltransferase, were found to be stimulated by the US. The US stimulation of secondary metabolite biosynthesis was attributed to the metabolic activity of cells activated by US, and more specifically, the defense responses of plant cells to the mechanical stress of US irradiation.

Effects of hydrodynamic and interfacial forces on plant cell suspension systems

Plant cells are perceived to be sensitive to the hydrodynamic environment in conventional bioreactors. Heightened sensitivity, relative to most bacterial cultures, is frequently attributed to larger plant cell sizes, extensive vacuolization and aggregation patterns. Early studies of shear sensitivity focused on cell lysis and/or loss of viability. More recently, an extensive array of sub-lethal responses has been identified. A fuller understanding of these sub-lytic effects may assist in the optimization of large-scale cultivation conditions. This paper reviews recent work on the hydrodynamic shear sensitivity of plant cell systems, under cultivation conditions and in purpose-built shearing devices. The relevance of different approaches to the characterization of the intensity of a given hydrodynamic environment is discussed. Indicators of cell response to hydrodynamic stress are evaluated. The potential significance of cellular defense mechanisms, observed in response to mechanical stimulants, is identified.

The engineering effects of fluids flow on freely suspended biological macro-materials and macromolecules

The manufacture of many biotechnologically important products requires consideration of the physical breakage and biochemical degradation pathways at all stages during processing, storage and transportation. The engineering flow environment in most items of bioprocess equipment has long been recognised as a key factor in determining these pathways and is the focus of the present review. Because of its industrial significance, the detrimental effects of the engineering flow environment on freely suspended bioparticles have been the subject of many scientific investigations over the past few decades. There is a general consensus of opinion that fluid shear and elongational stresses are the two main breakage pathways of relevance to processing of most biomaterials. An additional degradation pathway has also been identified involving significant losses of biological activity of macromolecules at gas-liquid, gas-solid and liquid-liquid interfaces. In such cases, the engineering flow field is shown to have a secondary role in determining the kinetics of inactivation. An equally important consideration in the optimisation of the relevant unit operations is the biomechanical integrity of the flow sensitive material. The biomechanical and biorheological parameters that determine the integrity of biomaterials are poorly defined, their evaluations present future research challenges and are of immediate engineering significance.

The effects of turbulent jet flows on plant cell suspension cultures

Cell suspensions of Morinda citrifolia were subjected to turbulent flow conditions in a submerged jet apparatus, to investigate their hydrodynamic shear susceptibility. The suspensions were exposed to repeated, pressure-driven passages through a submerged jet. Two nozzles, of 1 mm and 2 mm diameter, were employed. Average energy dissipation rates were in the range 10(3)-10(5) W/kg and cumulative energy dissipation in the range 10(5)-10(7) J/m3. System response to the imposed conditions was evaluated in terms of suspension viability (determined using a dye exclusion technique) and variations in both chain length distribution and maximum chain length. Viability loss was well-described by a first-order model, and a linear relationship was identified between the specific death rate constant and the average energy dissipation rate. This relationship was consistent with results obtained using the same suspension cultures in a turbulent capillary flow device. Morphological measurements indicated that exposure to the hydrodynamic environment generated in the jet resulted in a significant reduction in both the average and maximum chain lengths, and the reduction in the maximum chain length was identified as an appropriate measure of sustained damage. Analysis of both viability and chain length in terms of cumulative energy dissipated revealed good agreement with results reported by other authors for morphologically different plant cell systems. Copyright 1998 John Wiley & Sons, Inc.

Plant cell suspension cultures: some engineering considerations

Higher plants are the source of a vast array of biochemicals which are used as drugs, pesticides, flavourings and fragrances. For some of these compounds, plant cell culture can provide a potential production alternative to traditional cultivation methods or chemical synthesis routes. Many systems have been patented and the last 20 years have seen considerable industrial and academic interest in the development of large scale cultures to produce pharmaceutically active, high value substances. However, the industrial application of plant cell suspension cultures has, to date, been limited. Commercialisation has essentially been impeded by economic feasibility, arising from both biological and engineering considerations. This paper reviews the commercial development of the technology to date and focuses on the impact of specific engineering-related factors, in particular, the shear sensitivity of plant cell suspension cultures. Evidence of sensitivity to hydrodynamic shear in bioreactors has generally been attributed to the physical characteristics of the suspended cells. Recent studies indicate that shear sensitivity may not be as important, in some cases, as initially anticipated.