Cell division at record speed

Researchers developed a new variant of the fast-growing bacterium Vibrio natriegens

Vibrio natriegens, the bacterium with the highest known division rate, distributes its genetic material over two chromosomes. Is this the reason for its rapid growth? The answer is no, according to researchers at the Max Planck Institute for Terrestrial Microbiology and the Zentrum SYNMIKRO at the Philipps University of Marburg, Germany. Using synthetic biology, they have developed a new strain with only one chromosome. It could simplify future research and applications and is just as fast.

Speed is an advantage - this is also true for cell proliferation. Here, the replication of the DNA is a step that determines the speed. Some bacteria have therefore developed tricks to speed up this process. In bacteria, chromosomes are usually copied in two directions from a single starting point (the origin of replication), at a copying rate of about 1000 DNA building blocks per second. Escherichia coli additionally overlaps its replication cycles. This saves more than half the time because daughter cells emerge with chromosomes that are already replicating. As a result, the bacterium achieves a doubling time of 20 minutes.

But one is even faster: Vibrio natriegens is the bacterium with the fastest known growth rate. It can duplicate in less than 10 minutes. This makes Vibrio natriegens interesting not only for biotechnological applications, but also as a model for basic research.

Bacterium with two chromosomes

The bacterium has some special characteristics. For example, it loves high salt concentrations and thrives in coastal areas. Unlike E. coli, Vibrio natriegens has split its genome into two chromosomes. It shares this characteristic with its relative, the human pathogen Vibrio cholerae, which is known to cause cholera and can also multiply rapidly - but Vibrio natriegens can multiply almost twice as fast. Is splitting the chromosome the trick that Vibrio species use to speed up doubling? Researchers had already investigated this question in Vibrio cholerae. There, the artificial fusion of the two chromosomes had indeed led to an increase in the doubling time.

The groups led by Daniel Schindler and Anke Becker use synthetic biology methods to study processes in microorganisms. By rearranging genes, they can study functions and processes in a targeted and controlled manner. “We wanted to know if the simultaneous replication of two chromosomes in Vibrio natriegens is the prerequisite for its speed,” says Lea Ramming, who investigated this question in her master’s thesis.

Reorganized chromosomes

Using molecular biology techniques, microscopy and extensive analysis, the researchers developed and characterized a new strain with only one chromosome. “We have reorganized the chromosome architecture of the bacterium so that all replication starts from a single origin,” says Daniel Stukenberg, shared co-first author with Lea Ramming, who worked on the project as part of his doctoral thesis.

Based on previous findings, the researchers expected a longer replication time. The surprising result: despite the fusion, the strain was just as fast as the natural V. natriegens strain. This suggests that the shared genome is not a prerequisite for rapid growth.

New model organism

The new strain can now be used as a starting point for biotechnological applications, but also as a model for basic research into the chromosome biology of fast-growing bacteria. In addition, V. natriegens could provide an alternative model system to Vibrio cholerae, currently the best-studied model organism for bipartite microbial genomes. Here, chromosome biology would be studied without the risk of infection.

Using synthetic biology and applied research methods, the researchers will be able to introduce an additional synthetic chromosome into the strain in future. “Another advantage could be that the organism needs to be cultivated in salt water. This means that seawater can be used as a medium, which would reduce the pressure on limited freshwater resources, especially in view of climate change. The use of V. natriegens in biotechnological production can therefore potentially make it more sustainable. In particular, the strain with the fused chromosomes could become an excellent expression platform in the future,” says Daniel Schindler.