Heterologous Cell Fusion: New Mechanism for Gene Transfer Offers New Insights Into Microbial Evolution

Exploring the natural multispecies microbiomes and synthetic microbial cocultures has attracted renewed interest due to their potential application in medicine, biotechnology, and ecology. In a recent study, a team of experts has shown a new mechanism for gene transfer between two bacterial species.

Prokaryotic Evolution in Bacteria

Eukaryotic organisms undergo evolution when mutations are passed down from parent to offspring in a process known as vertical gene transfer. For prokaryotes, it happens through horizontal gene transfer where genetic information is shared directly between bacteria.

In mutation-driven evolution, an individual cell undergoes random mutagenesis. Horizontal gene transfer allows individual organisms, and even entire species, to gain new genes quickly. This can even include potentially dangerous ones such as those that confer antibiotic resistance.

New DNA Transfer Mechanism

At the University of Delaware, a group of researchers led by doctoral alumnus Kamil Charubin and doctoral candidate John Hill discovered a new mechanism by which horizontal gene transfer can occur in bacteria. They explore the evolution and survival strategies for complex microbiomes.The findings in their study is reported in the paper "DNA transfer between two different species mediated by heterologous cell fusion in Clostridium coculture."

This study began after Charubin observed that two species of bacteria, Clostridium acetobutylicum and Clostridium Ijungdahlii, exchange metabolites, nutrients, and other cellular materials at high rates when they were in close proximity to one another. It was found that the cells use a mechanism called heterologous cell fusion as a mode of transferring materials.

The transfer did not just include a few proteins, but it actually encompasses most of the materials in the cytoplasm. Because of this, Charubin wanted to see if bacteria can also transfer genetic information, including plasmids, using the same mechanism.

To determine if gene transfer also occurs when the bacterial cells were in close contact, Hill tracked the movement of the bacteria's genome and plasmids. Selective subculturing techniques were also used which involve isolation of C. acetobutylicum cells after taking up plasmids from C. Ijungdahlii. Afterwards, the gene transfer was confirmed using PacBio Single-Molecule Real Time (SMRT) sequencing data.

It was revealed that the two species of Clostridium can indeed share genetic information through heterologous cell fusion, a mechanism which has not been previously observed before. The resulting hybrid cells were also discovered to contain large amounts of genomic DNA from both organisms.

It has been known that microbial life has evolved in naturally occurring communities. Large number of interspecies interactions, including gene exchange, could reveal another aspect of microbial evolution. This implies that microbes are not evolving independently from one another. Instead, a multiplicity of evolutionary trajectories exists within local environments which are motivated by different external factors like HGT.

The researchers believe that the result of their study provides new insights into the processes and drivers of bacterial evolution. According to Professor Eleftherios Papoutsakis, this study can also have implications on other fields, especially in studying the way bacteria demonstrate traits like antibiotic resistance. Since there is a lot more complexity and interaction between microbes in natural microbiomes, like in the environment or human gut, the newly-discovered mechanism for horizontal gene transfer can have important physiological and medical implications.