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Environment and sustainability

Researchers vastly reduce the cost of cell experiments

The cost of experiments on cells in laboratories around the world can be vastly reduced based on a system researchers have developed for storing and working with cells during experiments. The system is one hundredth as large as today’s standard system and therefore costs much less to operate.

Chemostat?

Most people are not familiar with a chemostat: a tank used for culturing cells.

Researchers performing experiments on cells know exactly what a chemostat is, and they are also very aware of the high cost of using one.

The costs of such supplies as culture media and nutrients can rapidly escalate to many thousands of euros for comprehensive experiments.

However, the high costs of many experiments may be a thing of the past, because researchers from Denmark and Sweden have developed a new way of performing experiments on a much smaller scale. Smaller experiments make experiments cheaper and researchers can also set up much larger experiments simultaneously.

“We definitely often waste resources when carrying out experiments because we use these large tanks of 1–2 litres that are expensive to operate. We have therefore developed a protocol for much smaller chemostats that are easier to use, quicker and less expensive,” explains a researcher behind the development of the new system, Jens Nielsen, Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Lyngby and Chalmers University of Technology, Gothenburg, Sweden.

Jens Nielsen supervised PhD student David Bergenholm from Chalmers University of Technology, who has developed the system, and the two researchers have jointly published a protocol in Biotechnology and Bioengineering.

Chemostats are crucial in experiments with cells

Understanding why the smaller chemostats are useful requires exploring how researchers use chemostats.

A chemostat is a system with a tank in which cells can grow under controlled conditions. The cells can include algae, yeast cells, bacteria and cells from humans and animals.

The principle is very simple. Researchers grow cells, such as yeast cells, in a closed chemostat with a culture medium and continuously supply oxygen and nitrogen so that the cells can grow. Since the chemostat is closed, the experiment cannot be contaminated with bacteria or any other contaminant. Researchers also ensure that the temperature in the chemostat and the acidity of the culture medium are constant so that they do not affect the outcome of the experiments.

In Jens Nielsen’s own research, the researchers work with yeast cells, which they genetically engineer to make them produce such substances as jet fuel, ingredients for perfume and plastic.

The chemostats are available in many different sizes. For example, Novo Nordisk uses chemostats of several thousand litres to culture yeast cells to produce insulin, whereas most university laboratories perform experiments in relatively small chemostats of 1–2 litres.

Chemostats use many litres of expensive culture media

However, the problem with the 1- to 2-litre tanks is that researchers performing experiments typically remove 100 ml of culture medium from the chemostats every hour to analyse the processes taking place within them.

They then replace the extracted culture medium with new medium at the same rate.

Removing 100 ml every hour may not sound like much, but each experiment lasts up to 10 days per chemostat, so this totals 24 litres after 10 days. The purchase and use of several hundred litres of culture medium is a costly affair for researchers using 20 chemostats with different yeast cells.

“This was why we wanted to make much smaller chemostats for culturing cells so that the experiments could be less expensive and easier to perform,” explains Jens Nielsen.

Chemostats with only 10 ml of culture medium

In the new study, Jens Nielsen and his colleagues developed a protocol for chemostats containing only 10 ml of culture medium. The protocol implies that the mini-chemostats can do everything the large chemostats can do.

This means that researchers can also very precisely control the temperature and acidity of the growth medium and the level of the oxygen supply in the mini-chemostats, so that the cells have the optimum growth conditions.

In addition, the researchers developed a computer program to keep track of all the parameters during experiments.

“We definitely faced some technical challenges reducing the size of the chemostats so much, but we now have the opportunity to work with these mini-chemostats, and the test results completely match those from the experiments we are doing in much larger set-ups,” says Jens Nielsen.

Researchers almost exclusively use small chemostats now

Jens Nielsen’s own laboratory almost exclusively uses the small chemostats when the experiment warrant this.

This means that scientists can set up large experiments with many chemostats much faster and more easily and at a lower cost. A single researcher can also manage the experiments with the entire set-up on a small corner of a table instead of across a whole laboratory of large chemostats used in previous experiments.

David Bergenholm, together with his fellow student David Hansson, started D2 Biotech, a company that sells the system or parts of it based on their development work.

Jens Nielsen hopes and thinks that several of his colleagues around the world agree with the idea of performing experiments on a smaller scale and thus conserving their research budgets.

“We have developed this protocol as a kit every researcher can assemble and set up. I believe many researchers will adopt this idea. We use large chemostats when we need to culture many yeast cells, but we mainly use the mini-chemostats now. In an experiment in which we previously used a 24-litre chemostat, we now use 240 ml,” says Jens Nielsen.

Construction of mini-chemostats for high-throughput strain characterization” has been published in Biotechnology and Bioengineering. A main author is Jens Nielsen, Novo Nordisk Foundation Center for Biosustainability and Professor, Chalmers University of Technology, Gothenburg, Sweden.

Jens Nielsen
Professor
To achieve large‐scale, high‐throughput experiments for systems biology research of microorganisms, reliable data from robust cultivation systems are needed. Chemostats are such systems, ensuring reproducibility and quality by providing a stable, well‐controlled environment for the cells. However, many of the available chemostat systems require large amounts of media and are complex to set up and expensive to purchase and maintain. To address these concerns, we developed a mini‐chemostat (MC) system with 16 reactors, each at a working volume of 40 ml. Sensors measure dissolved oxygen in the reactor, while OD600 is measured in the outflow. We further developed a CO2and pH sensor array that can be plugged into the outflow of the reactors. The system was used to characterize yeast physiology at four metabolically different conditions: limitations of glucose, both aerobic and anaerobic, nitrogen, and ethanol.