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

The research, led by Behnam Abooali, Behzad Satari and Mohammad Hossein Kianmehr, tackles a deceptively simple problem with an unusually demanding constraint. Composting has long been recognized as a way to convert raw bagasse into a stable, biologically active soil amendment: microbial consortia degrade cellulose, hemicellulose and lignin, enriching the material with humic substances and plant-available nutrients. Compost applied to fields improves water retention by 18 to 35 percent, sequesters 0.5 to 1.5 tonnes of carbon per hectare per year, and suppresses soil-borne pathogens through microbiome modulation. But compost is bulky and fluffy, with a bulk density of only 100 to 200 kilograms per cubic meter, which inflates transportation costs by 40 to 70 percent and makes mechanized field spreading a logistical headache. Densification through pelletization can raise that density four- to six-fold, yet conventional pellet mills run hot, often above 100 degrees Celsius, precisely the range at which the beneficial bacteria, fungi and actinomycetes that make compost valuable are killed outright.

The team’s solution is what they call cold pelletization: densification performed without external heating, with die temperatures verified by thermocouples to remain below 60 degrees Celsius throughout compression. That threshold matters because compost microorganisms typically perish above 60 degrees, while the material’s glass transition temperature, the point at which lignin begins to flow and act as a natural binder, sits much higher at 89.7 degrees Celsius, as measured by differential scanning calorimetry. In other words, the thermal route to binding is neither necessary nor desirable for this feedstock. The researchers believe this is the first systematic optimization of cold pelletization parameters for composted bagasse with explicit preservation of microbial viability, and their maximum recorded die temperature of 54 degrees Celsius stayed comfortably within the safe zone.

Getting there required navigating a minefield of trade-offs. The compost, produced by windrow composting of bagasse blended with cattle manure and urea to a carbon-to-nitrogen ratio of 25:1, was ground in a hammer mill fitted with 1, 2.5 and 4 millimeter screens. Grinding energy proved exquisitely sensitive to both moisture and screen size. At 8 percent moisture and 1400 rpm, energy consumption climbed from 11 kilojoules per kilogram with the 4 millimeter screen to 155 kilojoules per kilogram with the 1 millimeter screen, a fourteen-fold penalty. Push moisture to 16 percent and the smallest screen, and energy demand exploded to 750 kilojoules per kilogram. The culprit is plasticity: wet composted fibers deform rather than fracture, dissipating energy as heat instead of breaking cleanly. For industrial scaling, the authors conclude, coarser screens and pre-drying to 12 percent moisture or less are strongly preferred, with diminishing returns below 8 percent where dust and fire hazards emerge.

Composting itself changes the material in ways that complicate densification. Scanning electron microscopy revealed that composted fibers bear irregular surfaces, longitudinal cracks and open fiber bundles, the fingerprints of microbial attack, in stark contrast to the smooth, uniform surface of raw bagasse. X-ray diffraction showed the crystallinity index rising from 62 percent in raw bagasse to 75 percent in compost, evidence that amorphous hemicellulose and some lignin were selectively degraded while crystalline Cellulose I remained intact. Fourier transform infrared spectroscopy confirmed hemicellulose breakdown through a diminished peak near 1734 per centimeter and documented the consumption of glucose by microorganisms. These microstructural changes explain a counterintuitive result: unlike raw biomass, where fine particles pack efficiently, the mean particle size of compost had no significant effect on pellet density, because the degraded fiber geometry dominates packing behavior regardless of grind fineness.

Using response surface methodology with a Box-Behnken design of 17 runs, the team mapped how pressure, moisture and particle size jointly shape pellet quality. Pressure mattered most for density: raising compaction from 50 to 150 megapascals lifted pellet density from 0.89 to 1.08 grams per cubic centimeter, with the optimum of 1.09 grams per cubic centimeter achieved at 150 megapascals and 16.35 percent moisture. Fracture resistance told a different story, with moisture as the dominant factor. Increasing moisture from 8 to 20 percent raised fracture resistance from 14.65 to 27.095 kilograms, and the maximum fracture force of 37 kilograms, equivalent to 363 newtons, was recorded at 150 megapascals. That figure exceeds the 150 to 250 newtons typical of commercial organic fertilizer pellets, suggesting that moisture-activated natural binders, including residual proteins, lignin and starches, compensate for the cohesion lost with degraded hemicellulose.

Particle size delivered its own surprise. While mean particle size barely influenced density, coarser grinding with the 4 millimeter screen produced broader particle size distributions whose fine fractions filled the voids between larger particles, boosting mechanical interlocking and fracture resistance. Fracture force jumped from 14.65 kilograms at 1 millimeter to 26.60 kilograms at 4 millimeters under identical pressure and moisture. The effect was non-linear, remaining flat between 1 and 2.5 millimeters before rising sharply, a signature of distribution width rather than mean size. Compaction energy followed a similar nuance: at low pressure, coarser particles demanded more energy due to friction and poor packing, but at 150 megapascals the trend reversed, as larger particles fractured and rearranged more readily under extreme force.

The resulting pellets are positioned as a soil conditioner rather than a concentrated fertilizer. Chemical analysis showed 0.74 percent nitrogen, 30.66 percent organic carbon, a mature C:N ratio of 18:1 and a mildly alkaline pH of 8.68, making the pellets well suited to the acidic soils common in sugarcane regions, where they can raise pH and improve micronutrient availability. The nitrogen content falls below the 1 percent threshold of some commercial organic fertilizer standards, so the authors recommend blending with urea or other nitrogen sources for higher fertilizer value, an approach their earlier work showed can slow nitrogen release, with 80 percent released over 98 days in soil versus 61 percent in five days in water. Densifying the compost cuts bulk volume 4.6-fold, potentially lowering transport and storage costs by 60 to 80 percent, a gain that aligns squarely with circular bioeconomy goals and responsible consumption targets.

The authors are candid about the limits of their evidence. Microbial preservation was inferred from temperature control rather than measured directly, and they call for colony-forming unit counts, qPCR or phospholipid fatty acid profiling to confirm viability after pelleting. Chemical composition was characterized before pelletization, not after, and long-term storage stability under varying humidity remains untested, as hygroscopic pellets exposed to relative humidity above 70 percent may swell and lose strength. Field trials comparing pelletized and raw compost on crop yield, carbon sequestration and greenhouse gas emissions are the logical next step. Still, the demonstration that industrial-scale density and exceptional mechanical strength can be achieved cold, without sacrificing the living biology that makes compost worth spreading, marks a genuine advance for waste management in the Global South’s sugarcane belt, turning one of agriculture’s messiest byproducts into a standardized, shippable and biologically potent product.

Subject of Research: Cold pelletization of sugarcane bagasse compost for sustainable agricultural waste densification and soil amendment production

Article Title: Bagasse compost pelletization: Sustainable densification for agricultural waste management

Article References: Abooali, B., Satari, B., & Kianmehr, M. H. (2026). Bagasse compost pelletization: Sustainable densification for agricultural waste management. Cleaner Engineering and Technology, 34, Article 101316. https://doi.org/10.1016/j.clet.2026.101316

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101316

Keywords: sugarcane bagasse, compost pelletization, cold pelletization, agricultural waste management, soil conditioner, biomass densification, response surface methodology, microbial viability, cellulose crystallinity, circular economy, renewable resources, sustainable agriculture