Establishing Stable Binary Cultures of Symbiotic Saccharibacteria from the Oral Cavity
April 13th, 2021
4.5K views
We demonstrate a method for isolating difficult-to-grow members of the novel bacterial phylum, Saccharibacteria, by filtering dental plaque and co-culturing with host bacteria.
Overview
This article presents a detailed protocol for isolating and culturing Saccharibacteria, obligate parasitic bacteria from the Candidate Phyla Radiation (CPR), using co-culture with appropriate host bacteria. The method enables researchers to obtain binary cultures of Saccharibacteria and their hosts from dental plaque samples, facilitating further physiological and genomic studies of these previously uncultivable microbes.
Key Study Components
Area of Science
- Microbiology
- Bacterial symbiosis
- Microbial cultivation techniques
Background
- Many bacterial species, including those in the CPR, cannot be cultured using standard laboratory methods.
- Saccharibacteria are obligate parasites that require co-culture with specific host bacteria.
- The CPR represents a significant portion of Earth's microbial diversity.
- Studying these organisms in the lab is essential for understanding their physiology and ecological roles.
Purpose of Study
- To provide a reproducible protocol for isolating and culturing Saccharibacteria from dental plaque.
- To enable laboratories to establish their own binary co-cultures of Saccharibacteria and host bacteria.
- To facilitate future research on the physiology, genomics, and pathogenicity of Saccharibacteria.
Methods Used
- Collection of dental plaque samples using sterile instruments.
- Filtration of plaque suspensions through 0.2 μm filters to enrich for Saccharibacteria.
- Centrifugation to concentrate filtered cells.
- Co-culturing concentrated Saccharibacteria with host bacteria (e.g., Arachnia propionica) in suitable growth media.
- Serial passaging of binary cultures to establish stable infection.
- PCR-based confirmation of Saccharibacteria presence in cultures.
- Plating and colony screening to purify binary cultures and check for contamination.
Main Results
- The protocol successfully cultured over 30 isolates representing six Saccharibacteria species.
- Stable binary cultures can be established and maintained through serial passaging.
- PCR detection confirms the presence of Saccharibacteria, with a characteristic ~600 bp band.
- Colony morphology differences can help identify infected colonies for purification.
Conclusions
- This protocol enables routine isolation and maintenance of Saccharibacteria in the laboratory.
- The method is adaptable to other environments and host species, given appropriate host identification.
- Binary cultures can be used for genomic, transcriptomic, and pathogenicity studies.
Frequently Asked Questions
What are Saccharibacteria and why are they difficult to culture?
Saccharibacteria are obligate parasitic bacteria from the Candidate Phyla Radiation that require co-culture with specific host bacteria, making them challenging to culture using standard methods.
What is the main advantage of this protocol?
It allows researchers to isolate and maintain binary cultures of Saccharibacteria and their hosts from dental plaque, enabling laboratory studies of these previously uncultivable microbes.
How is the presence of Saccharibacteria confirmed in cultures?
PCR is used to detect Saccharibacteria, with a positive result indicated by a ~600 bp band on an agarose gel.
What host bacteria are used in this protocol?
Host bacteria such as Arachnia propionica are used, but the protocol can be adapted to other actinobacterial hosts if identified and isolated.
How can contamination in binary cultures be addressed?
Contaminated cultures can be purified by plating and picking infected colonies, which may have irregular shapes compared to uninfected colonies.
Can this protocol be applied to other environments or species?
Yes, with appropriate host identification, the protocol may be useful for isolating Saccharibacteria and other CPR species from various environments and hosts.
What downstream applications are possible with these binary cultures?
Binary cultures can be used for DNA/RNA extraction, genome sequencing, transcriptome analysis, and pathogenicity studies in animal models.
Executive Industry Relevance
Unlocking stable binary cultures of symbiotic Saccharibacteria addresses a critical barrier in microbiome-targeted drug discovery by enabling laboratory access to previously uncultivable microbial taxa. This capability enhances predictive confidence in early-stage target validation and supports mechanistic de-risking for microbiome-related therapeutic hypotheses. The protocol's reproducibility and adaptability position it as a foundational tool for expanding the diversity of disease-relevant microbial models in biopharma R&D portfolios.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables direct interrogation of symbiotic microbial interactions relevant to human health.
- Supports functional validation of microbial targets through controlled co-culture systems.
- Facilitates mechanistic de-risking by allowing manipulation and observation of obligate symbionts.
- Improves predictive confidence for microbiome-based therapeutic strategies.
Screening & Assay Development
- Provides standardized binary cultures for reproducible assay development.
- Enables quantitative PCR-based detection of symbiont presence for assay readouts.
- Supports scalability and platform reuse across multiple Saccharibacteria-host pairs.
- Prepares validated biological systems for downstream compound screening workflows.
Translational & Preclinical Research
- Expands access to disease-relevant microbial systems for translational biomarker discovery.
- Enables continuity from in vitro discovery to in vivo pathogenicity studies using animal models.
- Supports risk-adjusted advancement decisions by providing robust preclinical microbial models.
- Aligns with efforts to characterize the functional impact of the human microbiome on disease.
Pipeline & Workflow Integration
This protocol integrates into the discovery continuum from early hypothesis testing through preclinical model development, enabling iterative validation and mechanistic studies of symbiotic bacteria.
- Discovery Biology: Supports hypothesis testing and pathway clarification for symbiotic microbial interactions.
- Screening: Delivers reproducible, quantitative PCR outputs for assay standardization.
- Analytics: Provides molecular confirmation of symbiont presence, enabling comparative condition analysis.
- Translational Research: Bridges in vitro findings to in vivo models for biomarker and pathogenicity studies.
- Enterprise Reuse: Establishes a reusable platform for culturing diverse CPR species across projects.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence and reduces mechanistic ambiguity in microbiome research.
- Operational Value: Standardizes and scales the cultivation of previously uncultivable microbes.
- Strategic Value: Enables informed go/no-go decisions and reduces late-stage biological risk in microbiome programs.
- Portfolio Impact: Supports risk-adjusted prioritization and expansion of microbiome-targeted assets.
Implementation Considerations
- Requires expertise in microbiological co-culture and aseptic technique.
- Needs access to standard microbiology instrumentation and PCR analytical infrastructure.
- Demands rigorous cross-team standardization for reproducibility and contamination control.
- Adaptation to new host-microbe pairs may require empirical optimization.
- Contamination risk and host specificity are practical limitations that must be managed.
Biopharma FAQs
Why does null hypothesis testing matter for PCR-based infection confirmation?
Null hypothesis testing ensures that PCR detection of Saccharibacteria is statistically significant and not due to background or contamination, supporting robust target validation in binary cultures.
How does independent variable isolation fit the binary co-culture workflow?
Isolating variables such as host strain or environmental conditions allows teams to attribute observed symbiotic effects specifically to Saccharibacteria-host interactions, strengthening discovery-stage conclusions.
What do quantitative PCR measurements enable in binary culture assays?
Quantitative PCR provides objective confirmation of symbiont presence and abundance, enabling reproducible assay outputs and facilitating cross-condition comparisons in screening and validation workflows.
Why are replication requirements critical for cross-functional microbiome studies?
Replication ensures that binary culture establishment and PCR confirmation are reproducible across teams and experiments, supporting reliable data for collaborative R&D and portfolio decision-making.
What statistical analysis capabilities are required before implementing PCR-based detection?
Teams must apply statistical analysis to PCR results to distinguish true positives from background, set detection thresholds, and validate assay performance prior to broader implementation in discovery pipelines.
Chapters in this video
0:04
Introduction
1:11
Preparation Initiating Host Cultures and Sterilizing Equipment
1:55
Obtaining Sample of Oral Bacteria
2:30
Preparation of Filtrate from Oral Sample
3:28
Concentration of the Saccharibacteria Cells by Centrifugation
4:02
Infection of Host Cultures with Saccharibacteria-enriched Filtrate
4:47
Confirmation of Infection by PCR and Verification of Purity
5:36
Results: Confirmation of Infection and Purity of Binary Cultures of Symbiotic Saccharibacteria
6:54
Conclusion
