Analysis of the influence of flame sterilization included in sampling operations on shake-flask cultures of microorganisms

A forced aeration system for microbial culture of multiple shaken vessels suppresses volatilization

Shake-flask culture, an aerobic submerged culture, has been used in various applications involving cell cultivation. However, it is not designed for forced aeration. Hence, this study aimed to develop a small-scale submerged shaking culture system enabling forced aeration into the medium. A forced aeration control system for multiple vessels allows shaking, suppresses volatilization, and is attachable externally to existing shaking tables. Using a specially developed plug, medium volatilization was reduced to less than 10%, even after 45 h of continuous aeration (~ 60 mL/min of dry air) in a 50 mL working volume. Escherichia coli IFO3301 cultivation with aeration was completed within a shorter period than that without aeration, with a 35% reduction in the time-to-reach maximum bacterial concentration (26.5 g-dry cell/L) and a 1.25-fold increase in maximum concentration. The maximum bacterial concentration achieved with aeration was identical to that obtained using the Erlenmeyer flask, with a 65% reduction in the time required to reach it.

Fluorine materials scavenge excess carbon dioxide and promote Escherichia coli growth

Fluorinated solvents have been used as oxygen carriers in closed microbial cultures to sustain aerobic conditions. However, the growth-promoting effects of fluorinated solvents remain unclear. Therefore, this study aimed to elucidate the mechanism by which fluorinated solvents promote microbial growth and to explore alternative materials that can be easily isolated after culture. Escherichia coli and HFE-7200, a fluorinated solvent, were used to explore factors other than oxygen released by fluorinated solvents that promote microbial growth. E. coli growth was promoted in gas-permeable cultures, and HFE-7200 alleviated medium acidification. Gas chromatography confirmed that HFE-7200 functioned as a scavenger of carbon dioxide produced by E. coli metabolism. Because fluorinated solvents can dissolve various gases, they could scavenge metabolically produced toxic gases from microbial cultures. Furthermore, using polytetrafluoroethylene, a solid fluorine material, results in enhanced bacterial growth. Such solid materials can be easily isolated and reused for microbial culture, suggesting their potential as valuable technologies in food production and biotechnology.

Control of carbon dioxide concentration in headspace of multiple flasks using both non-electric bellows pump and shaking incubator

Current methods of controlling gas in the headspace involve constant speed aeration and proportional-integral-differential (PID) controlled aeration using improved monitoring devices or gas cylinders. However, these approaches are restricted and inconvenient to use. In this study, we propose a method to control the CO₂ concentration in the headspace while maintaining the convenience of shake-flask culture. A combination of a non-electric bellows pump for shake-flask (NeBP-sf) and a CO₂ incubator was used to control the flask gas phase by shaking without additional external power. The CO₂ half-life, as an indicator of the ventilation ability of the system, was measured using a circulation direct monitoring and sampling system, and the NeBP-sf was optimised. The ventilation capacity varied depending on the shaking speed, and under optimal conditions, was 10 min compared with 45 min when only a breathable culture plug was used. In conventional microbial shaking culture, the CO₂ concentration in the flask gas phase remained higher than the 5% set-value with a maximum of 9%, resulting in a large concentration difference with the set point. Therefore, the ventilation capacity of the conventional shake-flask culture was insufficient for aerobic culture. Cultivation of Escherichia coli and Lactiplantibacillus plantarum using the system showed no significant difference between the set point and real point values. Thus, the system combined an NeBP-sf and a gas incubator built-in shaking table to achieve the reproducibility of gas control while maintaining a high level of convenience.

Starting a new recombinant protein production project in Escherichia coli

One of the goals in recombinant protein production in Escherichia coli is to maximize productivity. High volumetric and specific yields can be reached after careful selection of expression strains and optimization of cultivation parameters. In this chapter, we review the many tools available to make the most out of this versatile microbial cell factory. Useful guidelines and options for troubleshooting production are presented.

Analysis of porous breathable stopper and development of PID control for gas phase during shake-flask culture with microorganisms

We evaluated the ventilation ability of two types (plug-type and cap-type) of culture-stoppers having standard air permeability. The culture-stoppers were evaluated using the circulation direct monitoring and sampling system with CO₂ concentration in the gas phase of a shake-flask culture as an index. The half-lives of CO₂ in the headspace of the shake flask with the plug-type and cap-type stoppers were about 51.5 min and about 30.3 min, respectively. Based on these half-lives, we formulated a model equation to simulate the behaviour of CO₂ with different culture-stoppers. After validating the model equation by shake-flask culture with Saccharomyces cerevisiae, we investigated the effect of different ventilation abilities of the culture-stoppers on the growth of Pelomonas saccharophila and Escherichia coli: the sensitivity of the culture-stopper to the ventilation ability was dependent on the microorganism species. In the case of P. saccharophila, when the plug-type culture-stopper was combined with controlled CO₂ concentration (6%) in the flask, the maximum yield increased by twofold compared to that of the control. This study shows the importance of ventilation in headspace and conventional culture-stoppers during the shake-flask culture of microorganisms. The problems that may occur between the conventional shake-flask culture approach using a breathable culture-stopper and the next-generation shake-flask culture without a conventional culture-stopper were clarified from the evaluation of gas-permeable culture-stoppers. The importance of controlled gaseous phase in the headspace during shake-flask culture of the microorganisms was also elucidated. KEY POINTS: • Ventilation capacity of culture-stoppers was evaluated using the CO₂ half-life concentration. • Behaviour of microorganisms varies with the type of culture-stopper. • Developed a PID system for control of CO₂ in flask gas phase to enhance the shake-flask culture.