The concept of a core microbiome has become central to modern plant science. Just as humans carry consistent communities of gut bacteria that shape health, plants host recurring assemblages of microbes in the soil immediately surrounding their roots, on the root surface itself, and inside their tissues. These communities are not random collections; they are selected by the host and by environmental filters. Yet for many unusual plants, especially those thriving in chemically extreme environments, the identity of these constant microbial partners remains unknown. That gap is precisely what the team, led by Zihua Zhang and Linxi Yuan of Xi’an Jiaotong-Liverpool University together with colleagues at the Guangxi Academy of Agricultural Sciences and the University of Liverpool, set out to close.

Their strategy was deliberately comprehensive. Rather than sampling a single site or a single growth stage, the researchers integrated three separate experiments: a field survey capturing the plant in its natural habitat and two pot experiments that allowed them to manipulate conditions, including the addition of selenium to the soil. Across all three, they characterized bacterial communities using amplicon sequencing of the 16S ribosomal RNA gene, the standard molecular fingerprinting method for bacteria, and then searched for taxa that appeared consistently across compartments, sites, and growth stages. The logic is straightforward: microbes that persist everywhere the plant grows, regardless of soil variation, are likely to matter functionally rather than being incidental passengers.

The search converged on two bacterial orders: Micrococcales and Rhizobiales. These two lineages formed the native core microbiome of C. hupingshanensis, present across the soil–plant continuum from bulk soil through the rhizosphere, the rhizoplane, and into internal plant tissues. The finding is notable because core microbiomes are often defined more narrowly, for example within roots alone or within a single site. Demonstrating a core that spans the whole continuum suggests a stable, co-evolved partnership between the hyperaccumulator and its bacterial entourage, one that survives transplantation into pots and the altered conditions of greenhouse cultivation.

Intriguingly, the two core orders showed distinct spatial preferences. Amplicon sequence variants belonging to Micrococcales became relatively more abundant in the rhizoplane, the thin layer of soil and microbial cells adhering directly to the root surface, where the plant and microbe are in the most intimate contact. Core variants from Rhizobiales, by contrast, peaked in the rhizosphere, the zone of soil influenced by root exudates. This compartmentalization hints at a division of labor: different microbial partners may occupy different niches along the root, potentially performing complementary functions related to nutrient transformation, stress alleviation, or the chemical processing of selenium before it crosses the root membrane.

Beyond taxonomy, the team examined the architecture of the microbial community as a network, identifying keystone taxa, the highly connected species whose removal would disproportionately destabilize the whole system. Within the subset of the native core microbiome, keystone roles were dominated by members of the phyla Proteobacteria and Firmicutes. The core taxa also made a noticeable contribution to microbial stability across different plant growth stages, meaning that as the plant matured and its root architecture and exudation patterns changed, the core community helped hold the broader ecosystem of root-associated microbes together. Stability of this kind is increasingly recognized as a hallmark of beneficial microbiomes, in both plants and animals.

The most provocative result, however, concerns selenium itself. The researchers found that core taxa in the rhizosphere were significantly associated with selenium concentrations in that soil compartment, suggesting a measurable relationship between the presence of these microbes and the chemistry that governs how much selenium is available for the plant to take up. Selenium in soils exists in multiple chemical forms, ranging from poorly soluble elemental particles to soluble selenate and selenite ions that plant roots can absorb via sulfur transporters. Microbes are known to interconvert these forms, oxidizing, reducing, or methylating selenium depending on the species involved. A rhizosphere community enriched in selenium-active bacteria could therefore shift the local speciation of the element in ways that favor hyperaccumulation.

Adding weight to this interpretation, the pot experiments showed that supplying soil with selenium significantly increased the diversity of the native core microbiome. In other words, the element that defines the plant’s ecological niche also appears to shape its microbial partnership, enriching the community precisely where selenium chemistry matters most. This feedback loop, in which the plant and its microbes jointly engineer a selenium-processing rhizosphere, offers a new mechanistic window into how hyperaccumulation might have evolved. Rather than being a purely plant-borne trait, selenium hyperconcentration in C. hupingshanensis may be a genuinely collaborative achievement, refined over evolutionary time in the seleniferous soils of Enshi and neighboring regions.

The implications extend well beyond one unusual mustard. Selenium is an essential micronutrient for humans, with an estimated one in seven people worldwide consuming less than adequate amounts, yet the margin between deficiency and toxicity is narrow. Understanding how hyperaccumulator plants and their core microbes mobilize, transform, and concentrate selenium could inform biofortification strategies, in which crops are engineered or managed to accumulate nutritional selenium in edible tissues. It could also aid phytoremediation, the use of plants to clean selenium-contaminated soils from mining and agricultural runoff, where microbial partners that enhance uptake or volatilize the element into harmless forms would be valuable allies. Previous work on other hyperaccumulators, including cadmium-accumulating Noccaea caerulescens and arsenic-tolerant Pteris vittata, has similarly revealed core endophytic communities with metal-processing capabilities, suggesting a general principle waiting to be exploited.

The study also carries a methodological message for microbiome science. By defining the core across three experiments, multiple compartments, and successive growth stages, the researchers filtered out the noise that plagues single-site surveys, where transient microbes often masquerade as important players. The identification of Proteobacteria and Firmicutes as keystone phyla, and of Micrococcales and Rhizobiales as the taxonomic backbone, provides concrete targets for the next phase of research: isolating these organisms, reconstructing synthetic communities, and testing directly whether they enhance selenium uptake under controlled conditions. If those experiments succeed, the invisible partners of a Chinese cliff-dwelling cress could become tools for building more nutritious crops and cleaner soils, a reminder that some of a plant’s most remarkable abilities are shared with the microscopic life it carries.

Subject of Research: The native core microbiome of the selenium hyperaccumulator Cardamine hupingshanensis across the soil–plant continuum

Article Title: A native core microbiome across the soil–plant continuum of the selenium hyperaccumulator Cardamine hupingshanensis

Article References: Zhang, Z., Yuan, L., Zhang, L., Liao, Q., Xing, Y., Pan, L., Liu, Y., & Paterson, S. (2026). A native core microbiome across the soil–plant continuum of the selenium hyperaccumulator Cardamine hupingshanensis. Plant and Soil. https://doi.org/10.1007/s11104-026-09174-3

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09174-3

Keywords: selenium hyperaccumulator, core microbiome, Cardamine hupingshanensis, rhizosphere, rhizoplane, Micrococcales, Rhizobiales, Proteobacteria, Firmicutes, keystone taxa, plant–soil interactions, phytoremediation

The core microbiome concept rests on a simple intuition. Within any habitat type, whether a host species, a soil ecosystem, or an ocean region, some members of the microbial community appear again and again across samples, while others come and go. The recurring members are presumed to matter most: they may perform essential functions for the host, stabilize community dynamics, or define the characteristic identity of that environment. In practice, researchers have typically identified the core by counting how often particular taxa occur across samples and keeping those that pass a predefined threshold of presence or abundance. Over the past decade, a rich toolbox of occurrence-based and abundance-based measures has grown around this idea, allowing scientists to quantify which microbes constitute the stable backbone of everything from human guts to coral reefs.

What has been missing, the Clemson authors argue, is evolution. Most existing core microbiome measures treat taxa as isolated labels, blind to the branching history that connects them. That blindness creates two well-known problems. The first is inconsistency across taxonomic rank: a microbe that appears in ninety percent of samples at the species level may be split into several lineages that each fail the threshold, or lumped into a genus that trivially passes it, so conclusions flip depending on whether the analyst works with operational taxonomic units, species, genera, or families. The second is sensitivity to strain variation: closely related strains within a single species can differ enormously in their presence across samples, causing non-phylogenetic measures to register dramatic turnover where, evolutionarily speaking, almost nothing has changed.

Bewick and Camper’s solution begins with a new object they call the core community phylogeny. Rather than selecting individual taxa that pass an occurrence threshold, the approach works directly on the evolutionary tree that describes the relationships among all microbes detected across a set of samples from a single habitat type. Branches of that tree are retained if they are present in multiple samples, in effect asking not whether a particular named species is shared, but whether a particular slice of evolutionary history is shared. The result is a pruned phylogeny whose branches represent the conserved evolutionary fabric of the community, the portion of the microbial tree of life that reliably shows up in that habitat, regardless of how individual strains or species shuffle beneath it.

From this core community phylogeny, the authors derive a family of phylogenetic metrics that mirror the classic questions microbiome ecologists already ask, but answer them in evolutionary currency. The first describes the phylogenetic diversity of a core microbiome within a single habitat type, capturing how much of the tree of life the conserved branches span. The second quantifies phylogenetic turnover between core microbiomes drawn from two different habitat types, measuring how much of the conserved evolutionary history is replaced when moving from one environment to another. The third measures shared phylogenetic diversity across core microbiomes from two or more habitat types, identifying the deep, evolutionarily conserved component that persists across otherwise distinct communities. Together, these measures extend the familiar logic of phylogenetic beta diversity into the specific context of core microbiome analysis.

The technical payoff is consistency. Because the metrics are computed on branches of a phylogeny rather than on labels at a chosen rank, their values remain stable whether the underlying community data are summarized at fine or coarse taxonomic resolution. When the same microbial community is described at the level of strains, species, or higher taxa, the core community phylogeny and its associated measures converge on the same answer, because the evolutionary information is preserved at every level. Likewise, strain-level variation, which can dominate and distort occurrence-based core definitions, is absorbed naturally into the tree: closely related strains contribute overlapping branches, so their idiosyncratic patterns of presence and absence no longer masquerade as wholesale community change. The authors report that, compared with non-phylogenetic metrics, their framework shows greater consistency across taxonomic rank and phylogenetic level, along with reduced sensitivity to strain variation.

That robustness matters far beyond statistical tidiness. Meta-analyses in microbiome science are frequently hampered by the fact that different studies process their sequencing data at different resolutions, making it hazardous to compare core microbiome findings across papers, hosts, or ecosystems. A framework that integrates seamlessly across taxonomic rank and phylogenetic level allows researchers to pool and compare results without first forcing every dataset into an identical labeling scheme. It also opens the door to genuinely novel biological questions. Instead of asking which named taxa form the core of a habitat, scientists can ask which lineages, and which evolutionary functions embedded in the tree, are conserved across hosts or environments, and how deep in the tree that conservation runs. A core defined by deep branches suggests ancient, possibly co-evolved associations; a core confined to shallow branches suggests recent ecological filtering of whatever lineages happen to be available locally.

The study did not emerge from simulations alone. The acknowledgements and supplementary materials reveal an empirical foundation built from fieldwork in New Mexico, where the authors, with support from National Science Foundation awards and Clemson University programs, assembled gut and skin microbiome samples from lizards, along with the read counts, taxonomy assignments, microbial phylogenies, and metadata that accompany them. Lizards, with their partitioned gut and skin habitats on the same individual animals, provide a natural test bed for contrasting core microbiomes across habitat types and for demonstrating how phylogenetic turnover and shared diversity behave when the same host carries distinct microbial communities in different body regions. A simplified worked example accompanying the paper walks readers through the construction of core community phylogenies and the calculation of the associated metrics step by step, lowering the barrier for laboratories that want to adopt the approach.

The implications ripple outward across applied microbiome research. In human health, core microbiome analyses inform debates about which microbes are essential partners rather than transient passengers, and inconsistent rank-dependent results have complicated efforts to define a healthy reference core. In agriculture, core definitions guide the design of synthetic microbial communities and probiotic formulations for crops and livestock, where strain-level variability among commercial inoculants has been a persistent headache. In conservation and ecosystem management, comparing cores across disturbed and intact habitats depends on measures that do not change their verdict when taxonomic pipelines change. A phylogenetically grounded core concept offers each of these fields a common, evolution-aware yardstick, one in which the currency is conserved branch length rather than mutable species lists.

None of this means the era of taxon-based core microbiome analysis is over; named taxa remain indispensable for communication, culturing, and mechanistic follow-up, and phylogenetic measures complement rather than replace occurrence and abundance metrics. But the study marks a conceptual maturation for the field, aligning the core microbiome with the tree-thinking that already underpins much of ecology and evolutionary biology. As microbiome datasets continue to explode in size and diversity, tools that deliver stable answers across resolutions, and that translate the question of what is shared into the question of what evolutionary history is shared, are likely to spread quickly through the community. The core microbiome, long a moving target, may finally have a measure that holds still.

Subject of Research: Phylogenetic methods for measuring and comparing the core microbiome across habitat types

Article Title: Phylogenetic measures of the core microbiome

Article References: Bewick, S. A., & Camper, B. T. (2026). Phylogenetic measures of the core microbiome. Microbiome. https://doi.org/10.1186/s40168-026-02520-8

Image Credits: AI Generated

DOI: 10.1186/s40168-026-02520-8

Keywords: core microbiome, microbial ecology, phylogenetics, community phylogeny, phylogenetic diversity, beta diversity, taxonomic rank, strain variation, microbiome metrics, lizard microbiome, evolutionary conservation, Microbiome journal

The research, published in the journal Microbial Ecology, provides the first comprehensive overview of the mangrove microbiome across the highly biodiverse but chronically understudied habitats of Papua New Guinea. Led by Golam Rabbani and Benjamin J. Wainwright of the National University of Singapore, together with Ralph Mana and Ismael Kunning of the University of Papua New Guinea, the study surveyed the microbial communities associated with two widespread mangrove species, Avicennia alba and Sonneratia alba. By sampling across multiple sites and dissecting the trees into distinct compartments, the team set out to answer a fundamental question in microbial ecology: what forces structure the microscopic ecosystems living within a macroscopic one?

The answer, it turns out, is a layered interplay of factors operating at very different scales. The researchers found that the bacterial and fungal communities inhabiting these mangroves are shaped by three principal drivers: the specific section of the host plant in which the microbes reside, the geographic site where the trees grow, and the identity of the host species itself. This concept, known as host compartmentalization, reflects the fact that a mangrove tree is not a uniform habitat but a mosaic of radically different environments. The leaves exposed to hot, dry, saline air; the roots submerged in anoxic, sulfide-rich sediment; and the sediments themselves each host distinct microbial assemblages adapted to their particular conditions.

This spatial variability is precisely what makes mangroves such a compelling system for microbiome research. Intertidal plants experience some of the most variable environmental conditions of any ecosystem on the planet, with above-ground structures alternating between exposure at low tide and inundation at high tide, while below-ground tissues remain permanently submerged in sediments that are often oxygen-starved and chemically reducing. The microbes that colonize these different niches must cope with dramatically different challenges, from desiccation and ultraviolet radiation in the canopy to the absence of oxygen and the presence of toxic reduced compounds in the rhizosphere. Understanding which microbes live where, and why, is essential for grasping how mangrove trees manage to thrive under such punishing circumstances.

One of the study’s most significant findings is the identification of a shared core microbiome comprising 31 bacterial and fungal taxa common to both Avicennia alba and Sonneratia alba. The concept of a core microbiome is central to modern microbial ecology: it refers to the set of microbial taxa that are consistently associated with a particular host across individuals, populations, or environments, suggesting that these microbes play functional roles important enough to be maintained through host-microbe selection. The discovery that two species from different mangrove genera share a core set of microbial partners hints at deep evolutionary or functional conservation in the mangrove microbiome, and raises intriguing questions about what services these microbes provide to their hosts, whether nutrient acquisition, stress tolerance, or protection against pathogens.

Beyond the core, the researchers went a step further and pinpointed the specific taxa that drive the differences between communities. They identified 13 taxa from within the core microbiome that distinguish the environmental microbiome of the sediment from the microbiomes of the mangrove trees themselves, and 11 taxa that drive variation between different sections of the mangrove plants. These differentially abundant taxa are more than statistical curiosities; they represent a shortlist of candidate microbes that may be disproportionately important in mangrove biology. By narrowing the field from thousands of species to a handful of pivotal players, the study provides a concrete starting point for future experiments aimed at isolating these organisms, characterizing their functions, and testing their effects on host health and growth.

The biogeographical dimension of the findings is equally noteworthy. Papua New Guinea sits at the heart of the Coral Triangle, one of the most species-rich marine regions on Earth, yet its mangrove ecosystems have received far less scientific attention than those of neighboring countries. By documenting the microbial communities of these forests for the first time, the study fills a conspicuous gap in the global map of mangrove microbiomes. The finding that site, or geographic location, significantly shapes microbial community composition suggests that local environmental conditions, dispersal limitation, and historical factors all leave their imprint on which microbes are present, meaning that mangrove microbiomes cannot be assumed to be uniform across regions even when the host species are the same.

The practical implications of this work extend directly to one of the most urgent conservation challenges of our time: mangrove restoration. Billions of dollars have been invested in replanting mangroves worldwide, yet many restoration projects fail, often because seedlings are transplanted into sites without adequate consideration of the soil conditions, hydrology, and biological partnerships they need to establish. If the microbes identified in this study prove to be beneficial symbionts that help mangrove seedlings acquire nutrients, tolerate salinity, or resist disease, then incorporating them into restoration practice, for example through soil inoculation or nursery treatments, could meaningfully improve survival and growth rates. The authors explicitly frame their taxon lists as starting points for investigating potentially important microbial members within mangroves, contributing to improved restoration outcomes.

The study also underscores a broader shift in ecological thinking. For decades, ecologists studied plants largely as autonomous organisms responding to their physical and chemical environments. The microbiome revolution has revealed that plants are, in reality, holobionts, integrated assemblages of host and microbial life whose collective properties emerge from their interactions. Mangroves, with their extreme environments and outsized ecological importance, are an ideal frontier for this perspective. The microbial communities in mangrove sediments drive biogeochemical cycles, including the transformation of nitrogen, sulfur, and carbon, that determine whether these forests act as powerful carbon sinks or sources of greenhouse gases. The microbes associated with roots may facilitate the oxidation of the rhizosphere and the detoxification of sulfide, processes without which mangrove trees could not survive their anoxic soils.

As mangrove forests continue to decline under pressure from aquaculture, coastal development, pollution, and sea-level rise, studies like this one remind us that saving these ecosystems requires understanding them at every scale, from the satellite imagery that tracks deforestation down to the genes of the bacteria living within a single root. The first microbiome survey of Papua New Guinea’s mangroves is a milestone for a region where biodiversity is extraordinary and scientific baseline data are scarce. Its catalog of core and differentially abundant taxa offers researchers a roadmap for the next phase of inquiry: culturing the key microbes, deciphering their functions, and ultimately translating that knowledge into smarter, more effective strategies for restoring the world’s mangrove forests before it is too late.

Subject of Research: Mangrove microbiome structure and host-microbe interactions in Papua New Guinea

Article Title: Host Compartmentalization and Biogeography Shape the Bacterial and Fungal Communities of Papua New Guinea Mangroves

Article References: Rabbani, G., Mana, R., Kunning, I., & Wainwright, B. J. (2026). Host Compartmentalization and Biogeography Shape the Bacterial and Fungal Communities of Papua New Guinea Mangroves. Microbial Ecology. https://doi.org/10.1007/s00248-026-02874-4

Image Credits: AI Generated

DOI: 10.1007/s00248-026-02874-4

Keywords: mangrove microbiome, core microbiome, Papua New Guinea, Avicennia alba, Sonneratia alba, host compartmentalization, biogeography, bacteria, fungi, microbial ecology, mangrove restoration, Coral Triangle