Housekeeping Gene cpn60 Emerges as a Powerful Marker for Profiling Living Microbial Communities

For all the transformative power of high-throughput DNA sequencing in microbiome science, one stubborn problem has persisted at the heart of the field: sequencing reads cannot, on their own, tell researchers which microbes in a sample are alive and active, and which are merely the lingering genetic debris of organisms that have already died. A new study published in the journal Microbiome by a team led by Ya Wang and Curtis Huttenhower of the Harvard T.H. Chan School of Public Health and the Broad Institute of MIT and Harvard now offers a compelling solution built around a single, well-chosen gene. The researchers demonstrate that cpn60, a universal housekeeping gene encoding the chaperonin 60 protein, can serve double duty as both a taxonomic marker for mapping microbial community composition and a functional readout of which community members are transcriptionally active and therefore likely viable.

The significance of this advance lies in the fundamental biology of microbiomes. The functions that a microbial community performs in its host or environment, from fermenting dietary fiber in the human gut to cycling nutrients in forest soil, are driven overwhelmingly by living, metabolically active cells rather than by dormant or dead organisms. Standard amplicon sequencing of the 16S rRNA gene, the workhorse method of microbial ecology for two decades, captures DNA from living and dead cells alike, because extracellular DNA can persist in many environments long after cell death. This means that a 16S profile may substantially overestimate the abundance of organisms that contribute nothing to community function. Transcript-based approaches have long been proposed as a way around this limitation, but the idea had not been systematically evaluated across complex, multi-species communities until now.

Wang and colleagues approached the problem by comparing how well different sequencing targets reflected the composition and activity of microbial communities. Their central finding is that community-wide transcription and, more specifically, the activity of the cpn60 gene can effectively quantify community composition while simultaneously identifying its viable members. When the team generated targeted amplicon libraries for cpn60, they found that protein-coding RNA activity captured the differential structure of the active community more faithfully than the conventional 16S rRNA amplicon did. In practical terms, this means that a researcher sequencing cpn60 transcripts from a stool or soil sample obtains a picture of the community that is weighted toward the organisms actually doing work in that sample, rather than a picture blurred by the genetic ghosts of dead cells.

A major barrier to adopting any new marker gene at scale is the availability of a comprehensive reference database against which sequencing reads can be classified. The existing cpnDB database, long the standard resource for chaperonin 60 sequences, was too limited for broad community profiling. To overcome this, the team constructed an expanded database that integrates diverse cpn60 protein and nucleotide sequences, substantially extending cpnDB’s coverage. This expanded reference resource is a critical piece of infrastructure, because the utility of a marker gene depends not only on its biological properties but also on the computational ability to assign reads from complex samples to the correct taxa. With the enlarged database in place, cpn60 amplicon profiling becomes a scalable, cost-effective alternative to full shotgun metagenomics for many applications.

The strength of the new marker was validated against one of the most thoroughly characterized datasets in human microbiome research. Using data from the Human Microbiome Project II, the researchers showed that taxonomy inferred from cpn60 protein sequences agreed strongly with taxonomic profiles derived from shotgun metagenomic sequencing, the current gold standard for community characterization. This agreement is notable because shotgun metagenomics sequences all genes in a sample and is considerably more expensive and computationally demanding than targeted amplicon sequencing. A single-locus approach that approaches the accuracy of whole-community shotgun profiling, while adding information that shotgun DNA sequencing alone cannot provide, represents a meaningful shift in the cost-benefit calculus of microbiome study design.

Beyond composition, the study delivers evidence that cpn60 transcript abundance tracks microbial growth and viability. The team compared cpn60 transcript levels with bacterial growth rates estimated by the bPTR method, a peak-to-trough ratio approach that infers replication rates from the coverage pattern of bacterial genomes, in which actively replicating populations show characteristic peaks near the origin of replication. The positive correlation between cpn60 transcript abundance and bPTR-estimated growth rates indicates that cpn60 RNA serves as a marker of microbial transcriptional activity and, by extension, viability. This gives researchers a practical way to distinguish the growing, functional core of a community from its inactive passengers without requiring the deeper sequencing and analysis that growth-rate estimation from metagenomic coverage demands.

One of the most intriguing applications demonstrated in the paper involves separating resident microbes from transient ones in the human gut. The gut harbors a stable, co-evolved community of resident species, but it also regularly receives visitors, including oral-typical organisms that are swallowed with saliva and pass through the digestive tract. Distinguishing true residents from these transients is important for interpreting disease associations, since a transient oral species detected in a gut sample may not play the same ecological or pathological role as an established colonizer. The researchers showed that cpn60-based activity measurements could distinguish resident gut microbes from potentially transient members, with oral species showing different transcriptional activity patterns in gut samples. This capability has particular relevance for conditions such as inflammatory bowel disease, where ectopic colonization by oral bacteria has been implicated in disease progression, and where the supplementary analyses in the paper examined correlations across Crohn’s disease, ulcerative colitis, and healthy controls.

Technically, the approach rests on well-established molecular biology. The cpn60 gene, also known as groEL, encodes the 60-kilodalton chaperonin subunit of the GroEL/GroES protein-folding complex, an essential housekeeping function present in essentially all bacteria and many archaea and eukaryotic microbes. Because the gene is universally distributed yet evolves at a rate that provides resolution at the species level in many groups, it has long been recognized as a promising taxonomic marker. The universal region of cpn60, the so-called UT region used for amplicon design, offers discriminatory power that in some comparisons exceeds that of the 16S V4 region, and the supplementary analyses in the study compared within- and between-phyla sequence identities for both markers. At the same time, because cpn60 is a protein-coding gene, its messenger RNA provides a direct window into cellular activity, something the ribosomal RNA operon structure of 16S does not offer in the same straightforward way.

The authors also addressed the practical question of how best to classify cpn60 amplicon reads, comparing the cpn60 RDP classifier, SINTAX with a full-length cpn60 database, and SINTAX with a database restricted to the UT region. All methods produced similar phylum-level profiles, and while the alternative classifiers left more reads unclassified at the kingdom level, they offered minimal additional taxonomic insight over the original cpnDB-based classification. This kind of methodological benchmarking matters for adoption, because it tells other laboratories which computational pipelines will reproduce the results. The study’s validation extended beyond the human body as well, with forest soil samples profiled to show that the framework generalizes across ecosystems, supporting the authors’ argument that the approach can be extended to other rationally selected genes in diverse environments.

Taken together, the study outlines a framework that integrates DNA and RNA sequences at a single locus to profile both what is present in a microbial community and what is actively functioning within it. For researchers studying environmental microbiomes, the ability to separate viable from nonviable organisms could sharpen interpretations of community dynamics in soils, waters, and built environments, where dead biomass can dominate DNA pools. For clinical microbiome research, the capacity to flag active residents versus transient passers-through could refine biomarker discovery, where spurious associations with dead or transient organisms have long muddied the literature. And because targeted amplicon sequencing remains far cheaper than shotgun metagenomics, the cpn60 approach lowers the barrier to including activity-aware profiling in large cohort studies. As the field moves from cataloging microbial communities toward understanding and eventually engineering them, tools that reveal not just who is present but who is at work are likely to become indispensable.

Subject of Research: Use of the cpn60 housekeeping gene as a dual marker for microbial community profiling and viability assessment

Article Title: Using the housekeeping gene cpn60 as a marker for microbial community profiling and viability assessment

Article References: Wang, Y., Thompson, K. N., Maharjan, S., Chen, M., Short, M. I., Nearing, J., Hartmann, E. M., Franzosa, E. A., & Huttenhower, C. (2026). Using the housekeeping gene cpn60 as a marker for microbial community profiling and viability assessment. Microbiome. https://doi.org/10.1186/s40168-026-02545-z

Image Credits: AI Generated

DOI: 10.1186/s40168-026-02545-z

Keywords: cpn60, microbiome, microbial viability, 16S rRNA, amplicon sequencing, metagenomics, chaperonin 60, Human Microbiome Project, bPTR, gut microbiota, transcriptional activity, cpnDB