TM7x, a strain of Saccharibacteria, is an ultra-small bacterium that lives in the human mouth. As an episymbiont, it depends on its host microbe, Schaalia odontolytica, for essential nutrients, making it highly specialized and seemingly incapable of surviving on its own.
Scientists at the ADA Forsyth Institute first cultured this ultra-small, episymbiotic bacterial type Saccharibacteria about a decade ago. Despite its discovery, the mechanisms that allow it to survive independently in the oral microbiome remained a mystery.
A new study from the lab of ADA Forsyth Professor Xuesong He, D.D.S., Ph.D. sheds light on these mechanisms.
The paper, published in The ISME Journal, describes the survival strategies of TM7x, a strain of Nanosynbacter lyticus within the Saccharibacteria phylum. TM7x, researchers found, encodes two pathways for generating the basic energy currency for nearly all cells, adenosine triphosphate (ATP): glycolysis and an arginine deiminase system (ADS). These findings help explain how TM7x endures transient host-free states during horizontal transmission in the oral microbiome.
“We found that TM7x is actually a lot more capable than we expected,” Dr. He said. “Using targeted mutagenesis, Raman spectroscopy, and fluorescent imaging, we can now pinpoint key aspects of TM7x’s biology and better understand its role in the oral microbiome.”
The small genome of Saccharibacteria shows its metabolic capabilities are limited. Scientists previously wondered how this episymbiont persists during the host-free stage of its life cycle.
“We’re learning that TM7x is able to persist, remain metabolically active, and generate energy on its own before it finds a new host,” said lead author Nusrat Nahar, Ph.D., a postdoctoral researcher at ADA Forsyth.”
ADA Forsyth Scientists in the He Lab and Bor Lab continue to develop a stronger understanding of Saccharibacteria, with potential for developing strategies for control of periodontitis. They have recently elucidated more information on Saccharibacteria’s host attachment and motility and aspects of its interaction with human cells.
Contributors to the study, based at ADA Forsyth unless otherwise noted, include lead author Dr. Nahar, Pu-Ting Dong, Jing Tian (Peking University), Alex Grossman, Erik L. Hendrickson (University of Washington), Kristopher Kerns (University of Washington), Prof. Mary Ellen Davey, Prof. Batbileg Bor, Jeffrey McLean (University of Washington), and Dr. He.
