The secret 'sex life' of bacteria: Study challenges old ideas about how species are formed

Researchers at the Georgia Institute of Technology have found that bacteria not only create species, but also maintain them in a unique process reminiscent of sexual reproduction.

Image: Selenibacter rover cells (in green) under a microscope. Other colors represent different organisms in the salt. (Credit: Tomeu Viver)
Image: Selenibacter rover cells (in green) under a microscope. Other colors represent different organisms in the salt. (Credit: Tomeu Viver)

When Costas Constantinidis demonstrated that many microbes—like plants and animals—are organized into species, he overturned a long-held scientific belief. Until then, many scientists believed that bacteria, due to their unique mechanisms of genetic exchange and the sheer size of their global populations, did not—and could not—form separate species.

New research by Konstantinidis and colleagues casts further doubt on this assumption, suggesting that not only do bacteria create species, but they also maintain the cohesion of their species in a process similar to "sexual" reproduction.

“The next question that occupied us was how individual microbes of the same species manage to maintain their cohesion. In other words, how do bacteria remain similar to each other?” noted Constantinidis, a professor in the School of Civil and Environmental Engineering at Georgia Tech.

It is now widely believed that bacteria and other microbes evolve primarily by binary fission—a form of asexual reproduction—while also undergoing rare genetic exchange. Using a novel bioinformatic method for identifying gene transfer, and aided by a novel genome database, Constantinidis and an international team of researchers examined how microbial species evolve and maintain themselves. Their findings revealed that bacteria create and maintain species in a more “sexual” way than previously thought.

The study was published in the journal Nature Communications.

To investigate how microbial species maintain their unique identities, the team analyzed the complete genomes of microbes from two natural populations. The researchers sequenced and analyzed more than 100 strains of Salinibacter ruber, a salt-loving bacterium, collected from solar salt pans in Spain. They then examined a previously published set of Escherichia coli (E. coli) genomes collected from animal farms in the UK.

The researchers compared the genomes of closely related microbes to examine how genes are passed on. They found that a process called “homologous recombination” plays a key role in keeping bacterial species together. Homologous recombination is a process in which microbes exchange DNA with each other, incorporating the new DNA into their genomes by replacing similar DNA from their own. The researchers observed that recombination occurs frequently and randomly throughout the entire genome of microorganisms, not just in specific regions.

"While this process is fundamentally different from sexual reproduction in animals, plants, fungi and non-bacterial organisms, where DNA is exchanged during cell division, the result in terms of species cohesion is very similar," Konstantinidis explained. "This constant exchange of genetic material acts as a cohesive force, maintaining similarity between members of the same species."

In addition, it has been found that members of the same species tend to exchange DNA with each other more than with members of other species, which helps maintain clear species boundaries.

"This work addresses a major, long-standing problem in microbiology that is relevant to many research areas," said Constantinidis. "It touches on questions of species definition, as well as the underlying mechanisms for maintaining species cohesion."

The research has broad implications across a range of fields, from environmental and evolutionary sciences to medicine and public health. The insights gained from the research contribute to the identification, modeling, and regulation of organisms of clinical or environmental importance. The methodology developed in the research also provides a molecular toolbox for future epidemiological and microbial studies.

Note: The study was made possible through collaborations with Ramon Rossello-Moore of the IMEDEA Institute in Mallorca, Spain, and Rudolf Ammann of the Max Planck Institute for Marine Microbiology in Germany. Both researchers contributed data from natural bacterial populations as well as data analysis and interpretation.

To the scientific article in Nature

More of the topic in Hayadan: (Beresheet is the Hebrew name for the book of Genesis)

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