Culturing microorganisms in the laboratory is an essential practice in microbiology that cannot be overlooked. This vital method typically involves growing these tiny organisms in a liquid medium rich in nutrients, making the process both straightforward and effective.
For aerobic microorganisms, oxygen is crucial for their growth; however, since oxygen doesn’t dissolve easily in liquid media, scientists must aerate it forcibly, often through shaking.
To optimize this aeration in traditional “shake” cultures, several innovative techniques have emerged, including the use of “baffled” shake flasks, which have specially designed indentations to enhance oxygen transfer, and the introduction of air bubbles in bioreactors. Unfortunately, these conventional shake cultures present a significant drawback: they impose physical shear stress on microorganisms, potentially affecting their growth and viability.
Now, a new study by a team of researchers from Kindai University in Japan, led by Professor Motomu Akita and Dr. Kenji Ito, have revealed an innovative method for “static” bacterial culturing in liquid mediums. They employed a polymer known as TPX, which has a high permeability to small gases, including oxygen. A bag made from TPX film was filled with a small volume of liquid medium, inoculated with bacteria, and placed on a flat surface to form a thin layer of medium suitable for culturing.
Through this technique, the researchers were able to culture Escherichia coli, which exhibited growth comparable to that in liquid shake cultures within the film bag.
To assess whether this method provided adequate oxygen levels, the team also cultivated Komagataella phaffi, a microorganism with a high oxygen demand for growth. They found that the growth rate of K. phaffi in the film bag was slightly lower than that observed in traditional shake cultures.
Utilizing a film bag presents significant advantages when compared to traditional culturing methods.
“Our method enables easy observation of biological phenomena that were previously unobservable,” explains Prof. Akita. “Until now, microorganisms have not been cultured in liquid conditions where sufficient oxygen was supplied, and physical stress was absent.”
This technique now grants researchers the chance to closely investigate the behavior of microorganisms when they aren’t exposed to shear stress.
One visible outcome of this is the development of “biofilms,” which are gel-like layers formed as microorganisms cling to a surface. Typically, biofilms cannot develop in liquid cultures that experience shaking. However, a recent study revealed that static culturing of Bacillus species led to biofilm formation at the bottom of the film bag.
“The possibilities for this new culturing method are enormous. For starters, reducing the space, energy, and resources needed to culture bacteria could promote more sustainable research activities,” says Prof. Akita. “This means experiments could be conducted even in limited physical spaces or when culturing equipment is constrained.”
This innovative technique offers exciting opportunities across various sectors, including science, medicine, and education. Its applications extend to healthcare, food production, and even space exploration, allowing for experiments in challenging environments like polar regions and space stations.
Additionally, it streamlines operations in budget-limited laboratories, enhances efficiency in medical settings, and simplifies educational experiments. By adopting this method, we could transform microbiological research and promote sustainability in numerous fields.
Journal reference:
- Kotaro Matsumoto, Kazuya Higashi, Yuki Naka, Kenji Ito & Motomu Akita. A liquid static culture using a gas-permeable film bag contributes to microbiology. Scientific Reports, 2024; DOI: 10.1038/s41598-024-74954-9