Detection of growth rate-dependent product formation in miniaturized parallel fed-batch cultivations

Black glucose-releasing silicon elastomer rings for fed-batch operation allow measurement of the oxygen transfer rate from the top and optical signals from the bottom for each well of a microtiter plate

BACKGROUND

In industrial microbial biotechnology, fed-batch processes are frequently used to avoid undesirable biological phenomena, such as substrate inhibition or overflow metabolism. For targeted process development, fed-batch options for small scale and high throughput are needed. One commercially available fed-batch fermentation system is the FeedPlate^®, a microtiter plate (MTP) with a polymer-based controlled release system. Despite standardisation and easy incorporation into existing MTP handling systems, FeedPlates^® cannot be used with online monitoring systems that measure optically through the transparent bottom of the plate. One such system that is broadly used in biotechnological laboratories, is the commercial BioLector. To allow for BioLector measurements, while applying the polymer-based feeding technology, positioning of polymer rings instead of polymer disks at the bottom of the well has been proposed. This strategy has a drawback: measurement requires an adjustment of the software settings of the BioLector device. This adjustment modifies the measuring position relative to the wells, so that the light path is no longer blocked by the polymer ring, but, traverses through the inner hole of the ring. This study aimed at overcoming that obstacle and allowing for measurement of fed-batch cultivations using a commercial BioLector without adjustment of the relative measurement position within each well.

RESULTS

Different polymer ring heights, colours and positions in the wells were investigated for their influence on maximum oxygen transfer capacity, mixing time and scattered light measurement. Several configurations of black polymer rings were identified that allow measurement in an unmodified, commercial BioLector, comparable to wells without rings. Fed-batch experiments with black polymer rings with two model organisms, E. coli and H. polymorpha, were conducted. The identified ring configurations allowed for successful cultivations, measuring the oxygen transfer rate and dissolved oxygen tension, pH, scattered light and fluorescence. Using the obtained online data, glucose release rates of 0.36 to 0.44 mg/h could be determined. They are comparable to formerly published data of the polymer matrix.

CONCLUSION

The final ring configurations allow for measurements of microbial fed-batch cultivations using a commercial BioLector without requiring adjustments of the instrumental measurement setup. Different ring configurations achieve similar glucose release rates. Measurements from above and below the plate are possible and comparable to measurements of wells without polymer rings. This technology enables the generation of a comprehensive process understanding and target-oriented process development for industrial fed-batch processes.

High cell density culture of recombinant E. coli in the miniaturized bubble columns

Miniaturized bubble columns (MBCs) can provide mass transfer characteristics similar to stirred tank bioreactors. In this study, a new application was developed for MBCs to investigate the effect of feeding strategy and medium type on the fed-batch culture of recombinant E. coli. The results showed that the exponential feeding strategy and defined M9 medium were more suitable to achieve the high cell density culture (HCDC). The maximum obtained cell concentration in exponential feeding strategy in the defined medium without induction, was at OD₆₀₀ of 169, while glucose concentration was maintained under 2 g/L. To the best of our knowledge, this cell concentration cannot be achieved in lab or pilot scale bubble columns. At the end of the process, adverse effect of the metabolic burden due to induction and mass transfer limitations decreased the obtained final cell concentration to OD₆₀₀ of 116. Finally, a comparison of the results for fed-batch culture in the stirred tank bioreactor with those of the MBCs showed that their lower cell concentrations were due to the hydrodynamics limitations of MBCs. Yet, it was found that the MBCs are efficient tools in development of feeding strategies and evaluation of medium components for HCDC of recombinant E. coli.

Treatment with surfactants enables quantification of translational activity by O-propargyl-puromycin labelling in yeast

Background

Translation is an important point of regulation in protein synthesis. However, there is a limited number of methods available to measure global translation activity in yeast. Recently, O-propargyl-puromycin (OPP) labelling has been established for mammalian cells, but unmodified yeasts are unsusceptible to puromycin.

Results

We could increase susceptibility by using a Komagataella phaffii strain with an impaired ergosterol pathway (erg6Δ), but translation measurements are restricted to this strain background, which displayed growth deficits. Using surfactants, specifically Imipramine, instead, proved to be more advantageous and circumvents previous restrictions. Imipramine-supplemented OPP-labelling with subsequent flow cytometry analysis, enabled us to distinguish actively translating cells from negative controls, and to clearly quantify differences in translation activities in different strains and growth conditions. Specifically, we investigated K. phaffii at different growth rates, verified that methanol feeding alters translation activity, and analysed global translation in strains with genetically modified stress response pathways.

Conclusions

We set up a simple protocol to measure global translation activity in yeast on a single cell basis. The use of surfactants poses a practical and non-invasive alternative to the commonly used ergosterol pathway impaired strains and thus impacts a wide range of applications where increased drug and dye uptake is needed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02185-3.

Kinetic study and optimization of recombinant human tumor necrosis factor-alpha (rhTNF-α) production in Escherichia coli

Tumor necrosis factor-alpha (TNF-α) is an inflammatory cytokine that plays a major role in immune regulation, homeostatic function, and cellular organization. The present study was undertaken to overproduce recombinant human TNF-α (rhTNF-α) in Escherichia coli (E.coli) in high cell density culture. The use of a codon-optimized gene and strong promoter-based (T7) expression system, choice of Terrific Broth (TB) as medium, and subsequent optimization of culture conditions in shake flasks resulted in production of 0.95 g/L insoluble rhTNF-α comprising upto 50% of total cellular protein (TCP) The protein yield further increased upto 1.26 g/L in 1 L TB medium batch culture in bioreactor with the controlled temperature, pH, and dissolved oxygen. In a series of chemostats operated at dilution rates of 0.2 h^-1, 0.3 h^-1, 0.4 h^-1 and 0.5 h^-1 the specific growth rate (μ) positively correlated with specific yield (Y_p/x) and a maximum yield of 164 mg/g DCW was obtained at μ = 0.4 h^-1 within 4 h post-induction. A fed-batch cultivation in TB with an exponential feeding profile (μ = ∼0.4 h^-1) of concentrated feed resulted in an accumulation of 5.5 g/L of rhTNF-α within 14 h of cultivation which accounted for ∼29% of TCP.

Polymer-based controlled-release fed-batch microtiter plate - diminishing the gap between early process development and production conditions

BACKGROUND

Fed-batch conditions are advantageous for industrial cultivations as they avoid unfavorable phenomena appearing in batch cultivations. Those are for example the formation of overflow metabolites, catabolite repression, oxygen limitation or inhibition due to elevated osmotic concentrations. For both, the early bioprocess development and the optimization of existing bioprocesses, small-scale reaction vessels are applied to ensure high throughput, low costs and prompt results. However, most conventional small-scale procedures work in batch operation mode, which stands in contrast to fed-batch conditions in large-scale bioprocesses. Extensive expenditure for installations and operation accompany almost all cultivation systems in the market allowing fed-batch conditions in small-scale. An alternative, more cost efficient enzymatic glucose release system is strongly influenced by environmental conditions. To overcome these issues, this study investigates a polymer-based fed-batch system for controlled substrate release in microtiter plates.

RESULTS

Immobilizing a solid silicone matrix with embedded glucose crystals at the bottom of each well of a microtiter plate is a suitable technique for implementing fed-batch conditions in microtiter plates. The results showed that the glucose release rate depends on the osmotic concentration, the pH and the temperature of the medium. Moreover, the applied nitrogen source proved to influence the glucose release rate. A new developed mathematical tool predicts the glucose release for various media conditions. The two model organisms E. coli and H. polymorpha were cultivated in the fed-batch microtiter plate to investigate the general applicability for microbial systems. Online monitoring of the oxygen transfer rate and offline analysis of substrate, product, biomass and pH confirmed that fed-batch conditions are comparable to large-scale cultivations. Furthermore, due to fed-batch conditions in microtiter plates, product formation could be enhanced by the factor 245 compared to batch cultivations.

CONCLUSIONS

The polymer-based fed-batch microtiter plate represents a sophisticated and cost efficient system to mimic typical industrial fed-batch conditions in small-scale. Thus, a more reliable strain screening and early process development can be performed. A systematical scale-down with low expenditure of work, time and money is possible.

Accelerated Bioprocess Development of Endopolygalacturonase-Production with Saccharomyces cerevisiae Using Multivariate Prediction in a 48 Mini-Bioreactor Automated Platform

Mini-bioreactor systems enabling automatized operation of numerous parallel cultivations are a promising alternative to accelerate and optimize bioprocess development allowing for sophisticated cultivation experiments in high throughput. These include fed-batch and continuous cultivations with multiple options of process control and sample analysis which deliver valuable screening tools for industrial production. However, the model-based methods needed to operate these robotic facilities efficiently considering the complexity of biological processes are missing. We present an automated experiment facility that integrates online data handling, visualization and treatment using multivariate analysis approaches to design and operate dynamical experimental campaigns in up to 48 mini-bioreactors (8⁻12 mL) in parallel. In this study, the characterization of Saccharomyces cerevisiae AH22 secreting recombinant endopolygalacturonase is performed, running and comparing 16 experimental conditions in triplicate. Data-driven multivariate methods were developed to allow for fast, automated decision making as well as online predictive data analysis regarding endopolygalacturonase production. Using dynamic process information, a cultivation with abnormal behavior could be detected by principal component analysis as well as two clusters of similarly behaving cultivations, later classified according to the feeding rate. By decision tree analysis, cultivation conditions leading to an optimal recombinant product formation could be identified automatically. The developed method is easily adaptable to different strains and cultivation strategies, and suitable for automatized process development reducing the experimental times and costs.

Application of Continuous Culture Methods to Recombinant Protein Production in Microorganisms

Depending on the environmental conditions, cells adapt their metabolism and specific growth rate. Rearrangements occur on many different levels such as macromolecular composition, gene and protein expression, morphology and metabolic flux patterns. As the interplay of these processes also determines the output of a recombinant protein producing system, having control over specific growth rate of the culture is advantageous. Continuous culture methods were developed to grow cells in a constant environment and have been used for decades to study basic microbial physiology in a controlled and reproducible manner. Our review summarizes the uses of continuous cultures in cell physiology studies and process development, with a focus on recombinant protein-producing microorganisms.

Rapid process synthesis supported by a unified modular software framework

Although known to be very powerful, the widespread application of model-based techniques is still significantly hampered in the area of bio-processes. Reasons for this situation can be found along the whole chain to set up and implement such approaches. In a time-consuming step, models are typically hand-crafted. Whether alternatives of better models exist to actually fulfill the final goals is undocumented, most often even unknown. In a next step, model-based process control methods are hand-coded in an error-prone procedure. For many of these methods given in the literature, only simulation studies are shown, leaving the interested reader with the unanswered question whether the implementation of a specific method in a real process is viable. As the potentially time-consuming implementation of such a method presents a risk for a rapid process development, promising candidates may be overlooked. To remediate this unsatisfactory situation, a combination of theoretical methods and information technology is proposed here. By an exemplarily realized software tool, it is shown how such an environment helps to promote model-based optimization, supervision, and control of bio-processes and allows for an inexpensive test of new ideas as well in real-life experiments. The contribution concentrates on an overview of a possible software architecture with respect to necessary methods and a meaningful information strategy, highlighting some of the more crucial building blocks. Experimental results exploiting parts of the proposed methods are given for a yeast strain synthesizing a product of industrial interest.