Understanding how bacteria interact is critical to solving growing problems such as antibiotic resistance, in which infectious bacteria form defenses to thwart the medicines used to fight them. Like humans, bacteria live together in communities, sometimes lending a hand—or in the case of bacteria, a metabolite or two—to help their neighbors thrive. New data from a team of investigators at the University of Delaware (UD) describes how bacteria do more than just work together.

The current research study shows how bacterial cells from different species can combine into unique hybrid cells by fusing their cell walls and membranes and sharing cellular contents, including proteins and RNA, the molecules which regulate gene expression and control cell metabolism. In other words, the organisms exchange material and lose part of their own identity in the process.

Findings from the new study—published recently in mBio through an article titled “Interspecies Microbial Fusion and Large-Scale Exchange of Cytoplasmic Proteins and RNA in a Syntrophic Clostridium Coculture”—has the potential to shed light on unexplained phenomena affecting human health, energy research, biotechnology, and more.

The UD researchers were focused on the interactions between Clostridium ljungdahlii and C. acetobutylicum. These species of bacteria work together in a syntrophic system, producing metabolites that are mutually beneficial to each other’s survival. The scientists saw that C. ljungdahlii invades C. acetobutylicum. The two organisms combine cell walls and membranes and exchange proteins and RNA to form hybrid cells, some of which continue to divide and in fact, differentiate into the characteristic sporulation program.

“Transmission electron microscopy and electron tomography demonstrated cell wall and membrane fusions between the two organisms, whereby C. ljungdahlii appears to invade C. acetobutylicum pole to pole,” the authors wrote. “Correlative fluorescence transmission electron microscopy demonstrated the large-scale exchange of proteins. Flow cytometry analysis captured the extent and dynamic persistence of these interactions. Dividing hybrid cells were identified containing stained proteins from both organisms, thus demonstrating the persistence of cells with exchanged cellular components. Fluorescence microscopy and flow cytometry of one species with stained RNA and the other tagged with a fluorescent protein demonstrated extensive RNA exchange and identified hybrid cells, some of which continued to divide, while some were in an advanced C. acetobutylicum sporulation form. These data demonstrate that cell fusion enables large-scale cellular material exchange between the two organisms.”

“They mix their machinery to survive or do metabolism, and that’s kind of extraordinary because we always assumed that each and every organism has its own independent identity and machinery,” added senior stud investigator Eleftherios Papoutsakis, PhD, chair of the department of chemical engineering at UD.

Though this phenomenon of interspecies microbial fusion is only now being reported, it is likely ubiquitous in nature among many bacterial pairs. So why do bacteria bother to fuse together? The simple answer is likely because this process allows the microbes to share machinery that will increase their odds of survival.

For instance, some pathogenic bacteria may borrow proteins from other antibiotic-resistant bacteria in order to shore up their own resistance. Some bacteria might borrow machinery from others in order to evade detection by the immune system. This could also help to explain why some bacteria are difficult to culture or grow for study or medical diagnostic purposes. These difficult-to-culture bacteria might combine with or work with and depend on other microorganisms for their existence instead of growing and multiplying on their own.

The team’s findings may influence the understanding of the evolution of biology because once bacterial species share machinery, they can evolve together instead of only evolving on their own, said Papoutsakis.

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