Caterpillar-like bacteria have evolved to survive in the mouth

Presumably to survive in the oral cavity, bacteria have evolved to divide along their longitudinal axis without separating from each other. A research team led jointly by environmental cell biologist Silvia Bulgheresi of the University of Vienna and microbial geneticist Frédéric Verrier of the National Institute for Scientific Research (INRS) has just published their new insights in Nature Communications. In their work, they describe the way these caterpillar-like bacteria split and their evolution from a rod-like ancestor. They propose to establish oral Neisseriaceae bacteria as new model organisms that could help identify new antimicrobial targets.

Although our mouth contains over 700 species of bacteria, and therefore its microbiota is as diverse as that of our gut, not much is known about how oral bacteria grow and divide. The mouth is a difficult place for bacteria to live. The epithelial cells lining the inner surface of the oral cavity are constantly being shed, and together with the salivary flow, the organisms that inhabit this surface will struggle for attachment. Perhaps to better stick to our mouths, bacteria from the Neisseriaceae family have developed a new way to reproduce. While typical rods split transversely and then separate from each other, some commensal Neisseriaceae that live in our mouths, however, attach to the substrate with their tips and split longitudinally—along their long axis. In addition, after cell division is complete, they remain attached to each other, forming caterpillar-like threads. Some cells in the resulting filament also take on different shapes, presumably to perform specific functions for the benefit of the entire filament. The researchers explain: “Multicellularity makes cooperation between cells possible, for example in the form of division of labor, and may therefore help bacteria survive nutritional stress.”

The team of researchers first used electron microscopy to examine the shape of the bacterial cell in the family Neisseriaceae, which includes the two standard cell shapes (rod and coccus) in addition to caterpillar-like filaments. By comparing their cell shapes and genomes across the Neisseriaceae family, they could conclude that multicellular, longitudinally dividing bacteria evolved from rod-shaped, transversely dividing bacteria. In addition, they could determine which genes are likely responsible for the unusual breeding strategy. They then used fluorescent labeling techniques to visualize the progression of cell growth in the multicellular bacteria and finally compared their genetic makeup to the “classical”, rod-shaped species. Finally, they tried to recreate this evolution by introducing the genetic changes into the rod-shaped Neisseriaceae. Although they could not force rod-shaped bacteria to become multicellular, the genetic manipulation resulted in longer and thinner cells. “We speculate that in the course of evolution, by redesigning the processes of elongation and division, the shape of the cell changed, perhaps to better thrive in the oral cavity,” Frédéric Veyrier (INRS).

“In addition to helping us understand how cellular form evolved, multicellular Neisseriaceae can be useful for studying how bacteria learned to live attached to the surface of animals, the only place they have been found so far.” Half of us carry them in our mouths, by the way,” explains Silvia Bulgeresi from the Department of Functional and Evolutionary Ecology at the University of Vienna. However, Philipp Weber of the University of Vienna, a PhD student in Bulgeresi’s team who also worked on study, emphasizes that “expanding the field of cell biology to additional morphologies and symbiotic species is also critical to increasing the pool of protein targets (eg, antibiotic targets) for biopharmaceutical applications.” Sami Nyongesa, a PhD student in Veyrier’s team at INRS, adds: “An evolutionary approach such as the one taken here for the Neisseriaceae can shed light on new, unanticipated protein targets.”

Reference: Nyongesa S, Weber PM, Bernet ES, et al. Evolution of longitudinal division in multicellular bacteria of the family Neisseriaceae. Nat Common. 2022;13(1):4853. doi:10.1038/s41467-022-32260-w

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