Cultured meat: every village its own factory?

Rising global demand for meat will result in increased environmental pollution, energy consumption, and animal suffering. Cultured meat, produced in an animal-cell cultivation process, is a technically feasible alternative lacking these disadvantages, provided that an animal-component-free growth medium can be developed. Small-scale production looks particularly promising, not only technologically but also for societal acceptance. Economic feasibility, however, emerges as the real obstacle.

Deceleration-stats save much time during phototrophic culture optimization.

In case of phototrophic cultures, photobioreactor costs contribute significantly to the total operating costs. Therefore one of the most important parameters to be determined is the maximum biomass production rate, if biomass or a biomass associated product is the desired product. This is traditionally determined in time consuming series of chemostat cultivations. The goal of this work is to assess the experimental time that can be saved by applying the deceleration stat (D-stat) technique to assess the maximum biomass production rate of a phototrophic cultivation system, instead of a series of chemostat cultures. A mathematical model developed by Geider and co-workers was adapted in order to describe the rate of photosynthesis as a function of the local light intensity. This is essential for the accurate description of biomass productivity in phototrophic cultures. The presented simulations demonstrate that D-stat experiments executed in the absence of pseudo steady-state (i.e., the arbitrary situation that the observed specific growth rate deviates <5% from the dilution rate) can still be used to accurately determine the maximum biomass productivity of the system. Moreover, this approach saves up to 94% of the time required to perform a series of chemostat experiments that has the same accuracy. In case more information on the properties of the system is required, the reduction in experimental time is reduced but still significant.

Koji--where East meets West in fermentation.

Almost all biotechnological processes originate from traditional food fermentations, i.e. the many indigenous processes that can be found already in the written history of thousands of years ago. We still consume many of these fermented foods and beverages on a daily basis today. The evolution of these traditional processes, in particular since the 19th century, stimulated and influenced the development of modern biotechnological processes. In return, the development of modern biotechnology and related advanced techniques will no doubt improve the process, the product quality and the safety of our favourite fermented foods and beverages. In this article, we describe the relationship between these traditional food fermentations and modern biotechnology. Using Koji and its derived product soy sauce as examples, we address the mutual influences that will provide us with a better future concerning the quality, safety and nutritional effect of many fermented food products.

Modeling growth, lipid accumulation and lipid turnover in submerged batch cultures of Umbelopsis isabellina.

The production of lipids by oleaginous yeast and fungi becomes more important because these lipids can be used for biodiesel production. To understand the process of lipid production better, we developed a model for growth, lipid production and lipid turnover in submerged batch fermentation. This model describes three subsequent phases: exponential growth when both a C-source and an N-source are available, carbohydrate and lipid production when the N-source is exhausted and turnover of accumulated lipids when the C-source is exhausted. The model was validated with submerged batch cultures of the fungus Umbelopsis isabellina (formerly known as Mortierella isabellina) with two different initial C/N-ratios. Comparison with chemostat cultures with the same strain showed a significant difference in lipid production: in batch cultures, the initial specific lipid production rate was almost four times higher than in chemostat cultures but it decreased exponentially in time, while the maximum specific lipid production rate in chemostat cultures was independent of residence time. This indicates that different mechanisms for lipid production are active in batch and chemostat cultures. The model could also describe data for submerged batch cultures from literature well.

Modeling lipid accumulation in oleaginous fungi in chemostat cultures: I. Development and validation of a chemostat model for Umbelopsis isabellina.

Lipid-accumulating fungi may be able to produce biodiesel precursors from agricultural wastes. As a first step in understanding and evaluating their potential, a mathematical model was developed to describe growth, lipid accumulation and substrate consumption of the oleaginous fungus Umbelopsis isabellina (also known as Mortierella isabellina) in submerged chemostat cultures. Key points of the model are: (1) if the C-source supply rate is limited, maintenance has a higher priority than growth, which has a higher priority than lipid production; (2) the maximum specific lipid production rate of the fungus is independent of the actual specific growth rate. Model parameters were obtained from chemostat cultures of U. isabellina grown on mineral media with glucose and NH(4) (+). The model describes the results of chemostat cultures well for D > 0.04 h(-1), but it has not been validated for lower dilution rates because of practical problems with the filamentous fungus. Further validation using literature data for oleaginous yeasts is described in part II of this paper. Our model shows that not only the C/N-ratio of the feed, but also the dilution rate highly influences the lipid yield in chemostat cultures.

Modeling lipid accumulation in oleaginous fungi in chemostat cultures. II: Validation of the chemostat model using yeast culture data from literature.

A model that predicts cell growth, lipid accumulation and substrate consumption of oleaginous fungi in chemostat cultures (Meeuwse et al. in Bioproc Biosyst Eng. doi: 10.1007/s00449-011-0545-8 , 2011) was validated using 12 published data sets for chemostat cultures of oleaginous yeasts and one published data set for a poly-hydroxyalkanoate accumulating bacterial species. The model could describe all data sets well with only minor modifications that do not affect the key assumptions, i.e. (1) oleaginous yeasts and fungi give the highest priority to C-source utilization for maintenance, second priority to growth and third priority to lipid accumulation, and (2) oleaginous yeasts and fungi have a growth rate independent maximum specific lipid production rate. The analysis of all data showed that the maximum specific lipid production rate is in most cases very close to the specific production rate of membrane and other functional lipids for cells growing at their maximum specific growth rate. The limiting factor suggested by Ykema et al. (in Biotechnol Bioeng 34:1268-1276, 1989), i.e. the maximum glucose uptake rate, did not give good predictions of the maximum lipid production rate.

Accommodating the difference in students' prior knowledge of cell growth kinetics

This paper describes the development and benefits of an adaptive digital module on cell growth to tackle the problem of educating a heterogeneous group of students at the beginning of an undergraduate course on process engineering. Aim of the digital module is to provide students with the minimal level of knowledge on cell growth kinetics they need to comprehend the content knowledge of the subsequent lectures and pass the exam. The module was organised to offer the subject matter in a differentiated manner, so that students could follow different learning paths. Two student groups were investigated, one consisting of students who had received their prior education abroad and one of students that had not. Exam scores, questionnaires, and logged user data of the two student groups were analysed to discover whether the digital module had the intended effect. The results indicate that students did indeed follow different learning paths. Also, the differences in exam scores between the two student groups that was present before the introduction of the digital module was found to have decreased afterwards. In general, students appreciated the use of the material regardless of their prior education. We therefore conclude that the use of adaptive digital learning material is a possible way to solve the problem of differences in prior education of students entering a course.

ß-Lactam and glycopeptide antibiotics: first and last line of defense?

Most infections are caused by bacteria, many of which are ever-evolving and resistant to nearly all available antibiotics. ß-Lactams and glycopeptides are used to combat these infections by inhibiting bacterial cell-wall synthesis. This mechanism remains an interesting target in the search for new antibiotics in light of failed genomic approaches and the limited input of major pharmaceutical companies. Several strategies have enriched the pipeline of bacterial cell-wall inhibitors; examples include combining screening strategies with lesser-explored microbial diversity, or reinventing known scaffolds based on structure-function relationships. Drugs developed using novel strategies will contribute to the arsenal in fight against the continued emergence of bacterial resistance.

Maximum photosynthetic yield of green microalgae in photobioreactors.

The biomass yield on light energy of Dunaliella tertiolecta and Chlorella sorokiniana was investigated in a 1.25- and 2.15-cm light path panel photobioreactor at constant ingoing photon flux density (930 µmol photons m⁻² s⁻¹). At the optimal combination of biomass density and dilution rate, equal biomass yields on light energy were observed for both light paths for both microalgae. The observed biomass yield on light energy appeared to be based on a constant intrinsic biomass yield and a constant maintenance energy requirement per gram biomass. Using the model of Pirt (New Phytol 102:3-37, 1986), a biomass yield on light energy of 0.78 and 0.75 g mol photons⁻¹ and a maintenance requirement of 0.0133 and 0.0068 mol photons g⁻¹ h⁻¹ were found for D. tertiolecta and C. sorokiniana, respectively. The observed yield decreases steeply at low light supply rates, and according to this model, this is related to the increase of the amount of useable light energy diverted to biomass maintenance. With this study, we demonstrated that the observed biomass yield on light in short light path bioreactors at high biomass densities decreases because maintenance requirements are relatively high at these conditions. All our experimental data for the two strains tested could be described by the physiological models of Pirt (New Phytol 102:3-37, 1986). Consequently, for the design of a photobioreactor, we should maintain a relatively high specific light supply rate. A process with high biomass densities and high yields at high light intensities can only be obtained in short light path photobioreactors.

Expression of phosphofructokinase in Neisseria meningitidis.

Neisseria meningitidis serogroup B is a pathogen that can infect diverse sites within the human host. According to the N. meningitidis genomic information and experimental observations, glucose can be completely catabolized through the Entner-Doudoroff pathway and the pentose phosphate pathway. The Embden-Meyerhof-Parnas pathway is not functional, because the gene for phosphofructokinase (PFK) is not present. The phylogenetic distribution of PFK indicates that in most obligate aerobic organisms, PFK is lacking. We conclude that this is because of the limited contribution of PFK to the energy supply in aerobically grown organisms in comparison with the energy generated through oxidative phosphorylation. Under anaerobic or microaerobic conditions, the available energy is limiting, and PFK provides an advantage, which explains the presence of PFK in many (facultatively) anaerobic organisms. In accordance with this, in silico flux balance analysis predicted an increase of biomass yield as a result of PFK expression. However, analysis of a genetically engineered N. meningitidis strain that expressed a heterologous PFK showed that the yield of biomass on substrate decreased in comparison with a pfkA-deficient control strain, which was associated mainly with an increase in CO(2) production, whereas production of by-products was similar in the two strains. This might explain why the pfkA gene has not been obtained by horizontal gene transfer, since it is initially unfavourable for biomass yield. No large effects related to heterologous expression of pfkA were observed in the transcriptome. Although our results suggest that introduction of PFK does not contribute to a more efficient strain in terms of biomass yield, achievement of a robust, optimal metabolic network that enables a higher growth rate or a higher biomass yield might be possible after adaptive evolution of the strain, which remains to be investigated.

Exploration of the hydrogen producing potential of Rhodobacter capsulatus chemostat cultures: The application of deceleration-stat and gradient-stat methodology.

In this work, the dependency of the volumetric hydrogen production rate of ammonium-limited Rhodobacter capsulatus chemostat cultures on their imposed biomass concentration and dilution rate was investigated. A deceleration-stat experiment was performed by lowering the dilution rate from 1.0 d(-1) to zero aimed at a constant biomass concentration of 4.0 g L(-1) at constant incident light intensity. The results displayed a maximal volumetric hydrogen production rate of 0.6 mmol m(-3) s(-1), well below model predictions. Possibly the high cell density limited the average light availability, resulting in a sub-optimal specific hydrogen production rate. To investigate this hypothesis, a gradient-stat experiment was conducted at constant dilution rate of 0.4 d(-1) at constant incident light intensity. The biomass concentration was increased from 0.7 to 4.0 g L(-1) by increasing the influent ammonium concentration. Up to a biomass concentration of 1.5 g L(-1), the volumetric hydrogen production rate of the system increased according to model predictions, after which it started to decline. The results obtained provide strong evidence that the observed decline in volumetric hydrogen production rate at higher biomass concentrations was at least partly caused by a decrease in light availability.

Gene-expression-based quality scores indicate optimal harvest point in Bordetella pertussis cultivation for vaccine production.

The evolution of vaccine product quality during batch cultivation of Bordetella pertussis, the causative agent of whooping cough, was investigated with the goal to determine the optimal harvest point. The process was explored by measuring mRNA expression at frequent intervals during cultivation. The genes that are involved in virulence are already known for this product and changes in their expression levels are proposed to be indicative for product quality. A quantitative product quality score is calculated based on the expression levels of these virulence genes, which allows comparison of expected product quality between culture samples. Product quality scores were maximal throughout the logarithmic growth phase, but dropped significantly at the start of the stationary phase. This showed that the decreasing lactate and glutamate concentrations towards the end of the batch are critical for product quality. On-line measurement of these nutrients allows the cultivation process to be harvested at the optimal harvest point, increasing process robustness and consistency.

Quantification and characterization of enzymatically produced hyaluronan with fluorophore-assisted carbohydrate electrophoresis.

Hyaluronan (HA) is a polysaccharide with high-potential medical applications, depending on the chain length and the chain length distribution. Special interest goes to homogeneous HA oligosaccharides, which can be enzymatically produced using Pasteurella multocida hyaluronan synthase (PmHAS). We have developed a sensitive, simple, and fast method, based on fluorophore-assisted carbohydrate electrophoresis (FACE), for characterization and quantification of polymerization products. A chromatographic pure fluorescent template was synthesized from HA tetrasaccharide (HA4) and 2-aminobenzoic acid. HA4-fluor and HA4 were used as template for PmHAS-mediated polymerization of nucleotide sugars. All products, fluorescent and nonfluorescent, were analyzed with gel electrophoresis and quantified using lane densitometry. Comparison of HA4- and HA4-fluor-derived polymers showed that the fluorophore did not negatively influence the PmHAS-mediated polymerization. Only even-numbered oligosaccharide products were observed using HA4-fluor or HA4 as template. The fluorophore intensity was linearly related to its concentration, and the limit of detection was determined to be 7.4pmol per product band. With this assay, we can now differentiate oligosaccharides of size range DP2 (degree of polymerization 2) to approximately DP400, monitor the progress of polymerization reactions, and measure subtle differences in polymerization rate. Quantifying polymerization products enables us to study the influence of experimental conditions on HA synthesis.

Evaluation of a critical process parameter: oxygen limitation during cultivation has a fully reversible effect on gene expression of Bordetella pertussis.

Modern (bio)pharmaceutical process development requires thorough investigation of all process parameters that are critical to product quality. The impact of a disturbance of such a parameter during processing needs to be known so that a rational decision can be made about the release of the product. In cultivation processes the dissolved oxygen (DO) concentration is generally accepted as being a critical parameter. In this article the impact of a 90 min period of oxygen limitation during the cultivation of the strictly aerobic Bordetella pertussis bacterium is investigated. The cultivation is the most important process step for the manufacturing of a vaccine against whooping cough disease. Samples were taken immediately before and after oxygen limitation and at the end of cultivation of four oxygen limited and three control cultivations. DNA microarray analysis of the full transcriptome of the B. pertussis bacterium revealed that a 90 min period of oxygen limitation has a substantial effect on overall gene expression patterns. In total 104 genes were identified as a significant hit at any of the sample points, of which 58 were directly related to oxygen limitation. The other genes were mainly affected towards the end of cultivation. Of all genes involved in oxygen limitation none were identified to show a significant difference between the oxygen limited and control cultivations at the end of the batch. This indicates a fully reversible effect of oxygen limitation on gene expression. This finding has implications for the risk assessment of dissolved oxygen concentration as a critical process parameter.

Modeling Neisseria meningitidis B metabolism at different specific growth rates.

Neisseria meningitidis is a human pathogen that can infect diverse sites within the human host. The major diseases caused by N. meningitidis are responsible for death and disability, especially in young infants. At the Netherlands Vaccine Institute (NVI) a vaccine against serogroup B organisms is currently being developed. This study describes the influence of the growth rate of N. meningitidis on its macro-molecular composition and its metabolic activity and was determined in chemostat cultures. In the applied range of growth rates, no significant changes in RNA content and protein content with growth rate were observed in N. meningitidis. The DNA content in N. meningitidis was somewhat higher at the highest applied growth rate. The phospholipid and lipopolysaccharide content in N. meningitidis changed with growth rate but no specific trends were observed. The cellular fatty acid composition and the amino acid composition did not change significantly with growth rate. Additionally, it was found that the PorA content in outer membrane vesicles was significantly lower at the highest growth rate. The metabolic fluxes at various growth rates were calculated using flux balance analysis. Errors in fluxes were calculated using Monte Carlo Simulation and the reliability of the calculated flux distribution could be indicated, which has not been reported for this type of analysis. The yield of biomass on substrate (Y(x/s)) and the maintenance coefficient (m(s)) were determined as 0.44 (+/-0.04) g g(-1) and 0.04 (+/-0.02) g g(-1) h(-1), respectively. The growth associated energy requirement (Y(x/ATP)) and the non-growth associated ATP requirement for maintenance (m(ATP)) were estimated as 0.13 (+/-0.04) mol mol(-1) and 0.43 (+/-0.14) mol mol(-1) h(-1), respectively. It was found that the split ratio between the Entner-Doudoroff and the pentose phosphate pathway, the sole glucose utilizing pathways in N. meningitidis, had a minor effect on ATP formation rate but a major effect on the fluxes going through for instance the citric-acid cycle. For this reason, we presented flux ranges for underdetermined parts of metabolic network rather than presenting single flux values, which is more commonly done in literature.

Novel applications for microbial transglutaminase beyond food processing.

Transglutaminase (EC 2.3.2.13) initially attracted interest because of its ability to reconstitute small pieces of meat into a 'steak'. The extremely high cost of transglutaminase of animal origin has hampered its wider application and has initiated efforts to find an enzyme of microbial origin. Since the early 1990s, many microbial transglutaminase-producing strains have been found, and production processes have been optimized. This has resulted in a rapidly increasing number of applications of transglutaminase in the food sector. However, applications of microbial transglutaminase in other sectors have been explored to a much lesser extent. Here, we will present the wider potential of transglutaminases and discuss recent efforts that could contribute to the realization of their potential.

Design process of an area-efficient photobioreactor.

This article describes the design process of the Green Solar Collector (GSC), an area-efficient photobioreactor for the outdoor cultivation of microalgae. The overall goal has been to design a system in which all incident sunlight on the area covered by the reactor is delivered to the algae at such intensities that the light energy can be efficiently used for biomass formation. A statement of goals is formulated and constraints are specified to which the GSC needs to comply. Specifications are generated for a prototype which form and function achieve the stated goals and satisfy the specified constraints. This results in a design in which sunlight is captured into vertical plastic light guides. Sunlight reflects internally in the guide and eventually scatters out of the light guide into flat-panel photobioreactor compartments. Sunlight is focused on top of the light guides by dual-axis positioning of linear Fresnel lenses. The shape and material of the light guide is such that light is maintained in the guides when surrounded by air. The bottom part of a light guide is sandblasted to obtain a more uniform distribution of light inside the bioreactor compartment and is triangular shaped to ensure the efflux of all light out of the guide. Dimensions of the guide are such that light enters the flat-panel photobioreactor compartment at intensities that can be efficiently used by the biomass present. The integration of light capturing, transportation, distribution and usage is such that high biomass productivities per area can be achieved.

Improving the cellular pertussis vaccine: increased potency and consistency.

Although Europe, Canada and the US have switched from cellular to acellular pertussis vaccines, most developing countries will continue to use the more cost effective cellular vaccine. Consistency of production however is the typical problem inherent to cellular vaccines. Optimising the production process of cellular pertussis bulk suspensions using product potency as a measure is not possible, since the mandatory animal test to measure potency has little discriminatory power. To circumvent this problem, this study focussed on measuring process parameters related to consistency and potency instead, even though the extent of those relationships could not be quantified. Critical evaluation and modification of individual process steps lead to 2 optimised production processes, NVP-96 and NVP-THIJS. These were compared to the original NVP production process in terms of antigen and biomass content, potency, toxicity and immunogenicity in mice. The batch to batch variation for both optimised products was clearly less than the original product for all parameters tested. The biomass content of the NVP-THIJS product was 15% lower than that of the NVP-96 product, while the immunogenicity in mice was twofold to threefold higher. The stability of the NVP-THIJS product remained higher than the NVP-96 product over a period of 2 years, while the decline of the potency of both suspensions was comparable.

Modeling Neisseria meningitidis metabolism: from genome to metabolic fluxes.

BACKGROUND: Neisseria meningitidis is a human pathogen that can infect diverse sites within the human host. The major diseases caused by N. meningitidis are responsible for death and disability, especially in young infants. In general, most of the recent work on N. meningitidis focuses on potential antigens and their functions, immunogenicity, and pathogenicity mechanisms. Very little work has been carried out on Neisseria primary metabolism over the past 25 years. RESULTS: Using the genomic database of N. meningitidis serogroup B together with biochemical and physiological information in the literature we constructed a genome-scale flux model for the primary metabolism of N. meningitidis. The validity of a simplified metabolic network derived from the genome-scale metabolic network was checked using flux-balance analysis in chemostat cultures. Several useful predictions were obtained from in silico experiments, including substrate preference. A minimal medium for growth of N. meningitidis was designed and tested successfully in batch and chemostat cultures. CONCLUSION: The verified metabolic model describes the primary metabolism of N. meningitidis in a chemostat in steady state. The genome-scale model is valuable because it offers a framework to study N. meningitidis metabolism as a whole, or certain aspects of it, and it can also be used for the purpose of vaccine process development (for example, the design of growth media). The flux distribution of the main metabolic pathways (that is, the pentose phosphate pathway and the Entner-Douderoff pathway) indicates that the major part of pyruvate (69%) is synthesized through the ED-cleavage, a finding that is in good agreement with literature.

Scale-up for bulk production of vaccine against meningococcal disease.

At the Netherlands Vaccine Institute (NVI) a vaccine against Neisseria meningitidis serogroup B organisms based on different porA subtypes contained in outer membrane vesicles (OMVs) is in advanced stage of development and will be evaluated in clinical trial studies in the near future. In order to meet the expected demand for product, the current biopharmaceutical production process is being scaled-up. This study describes the scale-up approach for the upstream process and the resulting bioreactor design and operation strategy leading towards a feasible solution for bulk production of a vaccine against meningococcal disease. The technically realized 1.2 m(3) bioreactor, equipped with a turbine impeller for gas dispersion, was complemented with an upward pumping impeller and a rotary plate foam breaker to contain foam inside the bioreactor. Aeration and ventilation in the culture broth were controlled by increasing the stirrer speed and gas flow rate simultaneously at increasing oxygen demand. The scale-up was successful and comparable growth curves and nutrient consumption profiles were reached on 0.06 and 1.2 m(3).