Axenic Culture of a Candidate Division TM7 Bacterium from the Human Oral Cavity and Biofilm Interactions with Other Oral Bacteria

Abstract

cThe diversity of bacterial species in the human oral cavity is well recognized, but a high proportion of them are presently uncultivable. Candidate division TM7 bacteria are almost always detected in metagenomic studies but have not yet been cultivated. In this paper, we identified candidate division TM7 bacterial phylotypes in mature plaque samples from around orthodontic bonds in subjects undergoing orthodontic treatment. Successive rounds of enrichment in laboratory media led to the isolation of a pure culture of one of these candidate division TM7 phylotypes. The bacteria formed filaments of 20 to 200 m in length within agar plate colonies and in monospecies biofilms on salivary pellicle and exhibited some unusual morphological characteristics by transmission electron microscopy, including a trilaminated cell surface layer and dense cytoplasmic deposits. Proteomic analyses of cell wall protein extracts identified abundant polypeptides predicted from the TM7 partial genomic sequence. Pleiomorphic phenotypes were observed when the candidate division TM7 bacterium was grown in dual-species biofilms with representatives of six different oral bacterial genera. The TM7 bacterium formed long filaments in dual-species biofilm communities with Actinomyces oris or Fusobacterium nucleatum. However, the TM7 isolate grew as short rods or cocci in dual-species biofilms with Porphyromonas gingivalis, Prevotella intermedia, Parvimonas micra, or Streptococcus gordonii, forming notably robust biofilms with the latter two species. The ability to cultivate TM7 axenically should majorly advance understanding of the physiology, genetics, and virulence properties of this novel candidate division oral bacterium.

Microbial Diversity in the Early In Vivo -Formed Dental Biofilm

“…It is obvious that the functional properties of these microorganisms in the oral biofilm environment are of high interest from the clinical and disease prevention perspectives. While one strategy would be to prevent growth conditions favoring detrimental bacteria, other pursuits will require a more detailed knowledge pertaining to the cultivation and cocultivation of all biofilm inhabitants (62)(63)(64)(65). Such insights will be helpful in designing target-specific approaches for the prevention of and/or intervention in diseases exhibiting an oral-biofilm-based etiology.…”

The Biofilm Community: Rebels with a Cause

“…Studies have shown that candidate division TM7 bacteria are detected in biofilm metagenome and this bacterium, when grown in dual species biofilm showed pleiomorphic phenotypes. The TM7 bacteria formed long filaments with A. oris or F. nucleatum but grew as short rod or cocci with P. gingivalis, P. intermedia, P. micra or S. gordonii [80]. Also, the TM7 bacteria were shown to be closely associated with A. oris, F. nucleatum, P. gingivalis, P. intermedia, P. micra and S. gordonii [80].…”

“…The TM7 bacteria formed long filaments with A. oris or F. nucleatum but grew as short rod or cocci with P. gingivalis, P. intermedia, P. micra or S. gordonii [80]. Also, the TM7 bacteria were shown to be closely associated with A. oris, F. nucleatum, P. gingivalis, P. intermedia, P. micra and S. gordonii [80]. The importance of F. alocis is noted as it is present in high abundance in the periodontal pocket, shows community synergism and is involved in oral biofilm formation with other important periodontopathic bacteria [81,70,82].…”

Cultivation of a human-associated TM7 phylotype reveals a reduced genome and epibiotic parasitic lifestyle

“…However, due to their seemingly recalcitrant nature toward cultivation, only one single TM7 phylotype has been reportedly cultivated, with no detailed genomic information (20). Thus, knowledge regarding TM7 genotypes and physiological properties, as well as their potential role in the pathogenesis of oral mucosal disease, is very limited.…”