New findings indicate that bacteria create distinct species and maintain their unity by frequently exchanging DNA through a process known as homologous recombination.
Kostas Konstantinidis challenged a long-standing scientific belief when he demonstrated that many microbes, much like plants and animals, are categorized into species. Previously, it was widely accepted that bacteria, because of their unique methods of genetic exchange and the enormous size of their worldwide populations, did not and could not form separate species.
Recent work by Konstantinidis and his team further contests this idea, showing that bacteria not only create species but also sustain these species in a way that is somewhat comparable to “sexual” reproduction.
“Our next question was how individual microbes within the same species preserve their unity. In simpler terms, how do bacteria remain alike?” explained Konstantinidis, who holds the position of Richard C. Tucker Professor at Georgia Tech’s School of Civil and Environmental Engineering.
It was previously believed that bacteria and other microbes mainly evolve through a process called binary fission, which is a form of asexual reproduction, while also engaging in occasional genetic exchanges. Utilizing an innovative bioinformatic approach to detect gene transfers and a new collection of whole genome data, Konstantinidis and a global team of researchers examined their theory on how species come into existence and are sustained. They discovered that bacteria evolve and establish species in a manner that is more “sexual” than had been previously recognized.
Their findings were published in Nature Communications.
To explore how microbial species keep their unique identities, the research team analyzed the complete DNA sequences of microbes from two natural populations. They gathered and sequenced over 100 strains of Salinibacter ruber (a microbe that thrives in salty environments) collected from solar salterns in Spain. They also analyzed already published Escherichia coli genomes obtained from livestock farms in the U.K. The researchers compared the genomes of closely related microbes to examine patterns of gene exchange.
They found that a process called “homologous recombination” is crucial for maintaining the integrity of microbial species. This process involves microbes swapping DNA and integrating this new genetic material into their own genomes by replacing similar sequences. The team observed that recombination happens frequently and randomly throughout the microbial genome, instead of being restricted to specific areas.
“This may fundamentally differ from sexual reproduction in animals, plants, fungi, and other non-bacterial organisms, where DNA exchange occurs during meiosis, yet the effect on species cohesion could be similar,” noted Konstantinidis. “This ongoing exchange of genetic material serves as a binding force, keeping organisms of the same species closely related.”
The researchers also noted that individuals from the same species are more inclined to exchange DNA among themselves compared to members from different species, which helps to define distinct species boundaries.
“This research addresses a significant, enduring challenge in microbiology that has implications for numerous fields,” stated Konstantinidis. “It revolves around how to define species and the fundamental mechanisms that contribute to species cohesion.”
This study holds relevance for various disciplines, including environmental science, evolutionary biology, medicine, and public health. It offers crucial insights for recognizing, modeling, and managing clinically or environmentally significant organisms. Additionally, the methodologies developed during this research serve as a molecular toolkit for upcoming studies related to epidemiology and micro-diversity.
