The research, led by Erzsébet Baka and András Táncsics of the Hungarian University of Agriculture and Life Sciences in Gödöllő, together with colleagues from several departments at the same institution, set out to answer a deceptively simple question: when microbial communities that degrade petroleum hydrocarbons assemble, does it matter more where the microbes came from or what conditions they face? Ecologists have long debated the relative roles of these two forces. On one side stands environmental origin, the legacy of a site’s history, which shapes the baseline pool of species available to do the work. On the other side stands environmental selection, the abiotic conditions such as oxygen tension, temperature, and nutrient supply that favor some species over others. Disentangling their contributions is one of the central tasks of modern microbial ecology.

To separate these effects cleanly, the team designed an elegant experiment. They established parallel enrichment cultures from two sharply contrasting environments. The first was groundwater from a hydrocarbon-contaminated field site, a habitat unmistakably shaped by human activity, where decades of pollution have presumably selected for hydrocarbon-tolerant lineages. The second was formation water drawn from a crude oil well, a sample representing a natural petroleum system in which microbes have coexisted with hydrocarbons over geological timescales. From each source, the researchers grew microbial communities under two oxygen regimes: fully aerobic conditions with dissolved oxygen concentrations of 7 to 8 milligrams per liter, and microaerobic conditions with roughly 0.5 milligrams per liter, a level that mimics the oxygen-starved interiors of contaminated aquifers and deep reservoirs.

This two-by-two design, two origins crossed with two oxygen levels, allowed the team to track how community composition responded to each factor independently and in combination. Community dynamics were followed using 16S rRNA gene amplicon sequencing, the workhorse technique of microbial community profiling, which reads a conserved genetic marker to identify which bacterial taxa are present and in what proportions. The researchers analyzed their sequencing data at both the phylum level, which captures broad evolutionary lineages, and the genus level, which resolves finer ecological distinctions. Statistical rigor came from two complementary tools: permutational multivariate analysis of variance, known as PERMANOVA, which tests whether groups of samples differ significantly in composition, and distance-based redundancy analysis, or db-RDA, which relates community variation to specific environmental variables.

The results were strikingly clear. Both factors left a significant imprint on community composition, but they did so in different ways and to different degrees. Environmental origin explained the larger share of the variance, with an R-squared value of 0.44 and a p-value of 0.002, meaning that nearly half of the variation in community composition could be attributed simply to where the microbes had come from. Oxygen availability also mattered significantly, accounting for an R-squared of 0.26 with a p-value of 0.006. In plain terms, the historical identity of the source environment set the broad contours of the community, while oxygen availability sculpted the finer details, and both effects were statistically robust rather than artifacts of sampling noise.

Yet the more intriguing story emerged when the researchers looked at which specific organisms thrived under each regime. Oxygen availability, though it explained less total variance than origin, acted as a remarkably consistent ecological filter. Regardless of whether the starting community came from a contaminated aquifer or a natural oil well, the same redox-specific functional consortia appeared under the same oxygen conditions. This reproducibility suggests that oxygen tension exerts a kind of universal selective pressure on hydrocarbon degraders, one strong enough to override the idiosyncrasies of each site’s species pool. It is a vivid demonstration of what ecologists mean by an environmental filter: a condition that screens the available species and permits only those with the right traits to pass through and flourish.

At the phylum level, the aerobic filter favored the Actinomycetota, a group of bacteria renowned for their metabolic versatility and their capacity to attack recalcitrant organic compounds. Within this phylum, the genus Dietzia emerged as a key aerobic player, proliferating under oxygen-rich conditions and being consistently suppressed when oxygen became scarce. Dietzia species have attracted attention in bioremediation research for their ability to degrade alkanes and other petroleum constituents, and the new data confirm that their ecological niche is tightly bound to oxygen availability. For bioremediation practitioners, this is a useful signpost: if a treatment strategy involves stimulating degradation in an oxygenated zone, Actinomycetota and particularly Dietzia are the lineages most likely to respond.

The microaerobic picture was different in instructive ways. Pseudomonas, one of the most intensively studied genera in hydrocarbon biodegradation, maintained a strong presence under both oxygen regimes, underscoring its metabolic flexibility and its capacity to function across a range of redox conditions. Acinetobacter, by contrast, was largely restricted to the oxygen-limited enrichments, where it rose to become a major genus. This pattern highlights Acinetobacter’s ecological role as a hydrocarbon degrader specifically in oxygen-limited systems, a niche that has often been overshadowed by the genus’s better-known aerobic relatives. In the low-oxygen interiors of contaminated plumes and deep reservoirs, where oxygen diffusion is slow and consumption by other microbes is fast, Acinetobacter may be one of the unsung workhorses of natural attenuation.

Taken together, the study paints a two-layered model of community assembly in petroleum-impacted ecosystems. Environmental origin determines the baseline diversity and the species-level composition of the potential degrader pool, reflecting each site’s unique geological and anthropogenic history. Oxygen availability then acts on that pool as a selective sieve, assembling functionally coherent consortia whose membership is predictable from redox conditions alone, regardless of where the microbes started. The two filters are not redundant but complementary: one supplies the cast of characters, the other decides which of them takes the stage. This interplay helps explain why bioremediation outcomes can differ so dramatically between sites with similar contamination but different histories, and why manipulating oxygen, for example through bioventing or air sparging, produces such consistent shifts in degrader community structure.

The practical implications extend beyond remediation. Natural petroleum systems host microbial communities that have adapted to hydrocarbons over millions of years, and understanding how these communities respond to changing oxygen conditions could inform strategies for enhanced oil recovery, reservoir management, and the assessment of biodegradation in subsurface environments. For contaminated aquifers, where oxygen is often the limiting factor for natural attenuation, the study’s identification of redox-specific degrader consortia offers a framework for predicting which organisms will respond to oxygen amendment and which will persist in the anoxic fringes of a plume. The work, funded by the National Research, Development and Innovation Office of Hungary through grant K146358, demonstrates that the assembly of hydrocarbon-degrading communities is neither purely a matter of history nor purely a matter of environment, but a governed interplay of both, and that redox control deserves a central place in our models of petroleum-impacted ecosystems.

Subject of Research: Ecological filtering of aerobic hydrocarbon-degrading microbial communities by oxygen availability and environmental origin

Article Title: Oxygen Availability and Environmental Origin as dual Ecological Filters Shaping Aerobic Hydrocarbon-degrading Enrichment Microbial Communities

Article References: Baka, E., Ábrahám, R., Bajzák, E., Pápai, M., Kobolák, J., Szabó, G., Kriszt, B., & Táncsics, A. (2026). Oxygen Availability and Environmental Origin as dual Ecological Filters Shaping Aerobic Hydrocarbon-degrading Enrichment Microbial Communities. Microbial Ecology. https://doi.org/10.1007/s00248-026-02909-w

Image Credits: AI Generated

DOI: 10.1007/s00248-026-02909-w

Keywords: hydrocarbon biodegradation, microbial ecology, oxygen availability, microaerobic enrichment, Actinomycetota, Dietzia, Pseudomonas, Acinetobacter, bioremediation, petroleum contamination, 16S rRNA sequencing, community assembly

The team’s central concept is what they call microbiome re-domestication, an extension of the earlier microbiome rewilding hypothesis. Rewilding proposes simply reintroducing wild microbial diversity to crops; re-domestication goes further, using host genetic variation from wild relatives to restore the plant-microbe interactions that were counterselected during domestication and breeding. Modern rice varieties were largely bred for above-ground traits under high fertilizer inputs, which means the below-ground microbial partnerships adapted to low-nutrient environments were never part of the selection criteria. The researchers hypothesized that if host genes governing microbiome recruitment could be identified and reintroduced, the beneficial functions those microbes provide, particularly nitrogen acquisition, could be recovered in elite cultivars without sacrificing their agronomic quality.

To test this, the researchers built two recombinant inbred line (RIL) populations, each of 100 lines, by crossing cultivated rice varieties, the japonica cultivar Longgeng 31 and the indica cultivar Huanghuazhan, with Chinese Dongxiang common wild rice, Oryza rufipogon, the northernmost naturally distributed wild rice germplasm in China and a genotype carrying cold and nutrient-deficiency resistance loci. Field experiments were conducted at the National Agricultural Station in Liaoheyuan, Jilin Province, on temperate black soil. Using 16S rRNA amplicon sequencing of 424 samples, including bulk soil, parental rhizospheres and both RIL populations, the team first defined the core rhizobacterial community specific to the paternal wild rice, excluding taxa shared with the cultivated parents. That analysis yielded 45 core amplicon sequence variants in the japonica cross and 48 in the indica cross, of which 20 were shared between the two populations.

The critical question was whether these wild-derived bacteria would persist in hybrid progeny carrying mostly cultivated genomes. They did. Gaiella, for example, was detected in 88.5 percent of the japonica RIL accessions and 96.6 percent of the indica accessions, while Acinetobacter, Paenarthrobacter and Duganella reached 60.5, 64.6 and 80 percent respectively in the japonica population. Partial Mantel tests then linked the abundance of these core taxa to plant phenotypes: in the japonica population, ground diameter and total nitrogen content correlated significantly with the core community, while in the indica population, root biomass, chlorophyll and spike length did. This established that the inherited microbiome was not merely present but functionally associated with nitrogen-related traits.

Quantitative trait locus mapping, performed with the R package R/qtl2 on genotypic and phenotypic data from the same individual plants, identified 31 QTL peaks associated with the abundance of 17 core bacterial taxa. Notably, positive effects tended to associate with wild-rice alleles, and Acinetobacter and Vogesella were consistently wild-allele enriched. The chromosomal locations differed between populations, with Acinetobacter linked to chromosome 4 in the japonica cross but chromosome 2 in the indica cross, yet the overall message was consistent: specific host loci influence the abundance of specific bacterial taxa. Because rice typically uses only about 30 to 40 percent of applied nitrogen, the team focused on nitrogen-cycling functions, using FAPROTAX to infer ecological roles. Seven core taxa, including Acinetobacter, Novosphingobium, Sideroxydans, Streptomyces, Pantoea, Bacillus and Pseudomonas, were predicted nitrogen fixers, and one QTL overlapped the known nitrogen-use-efficiency gene OsAMT1;3, an ammonium transporter.

The most striking finding came when the researchers overlapped their microbiome QTLs with rice domestication loci. They sequenced whole genomes of 382 accessions, 117 wild and 265 cultivated, and calculated the ratio of nucleotide diversity between wild and cultivated rice across the genome, identifying 21 domestication loci. Two strong selective sweeps coincided with QTLs for Acinetobacter and Pantoea, meaning the very genomic regions controlling recruitment of these beneficial bacteria bear the fingerprints of human selection. In other words, as ancient farmers selected rice for non-shattering seeds and other traits, they inadvertently selected against the alleles that recruited nitrogen-fixing microbes. The Acinetobacter locus showed the strongest additive effect, the greatest phenotypic variance explained and the most pronounced selective sweep, making it the obvious candidate for functional dissection.

Transcriptomics then pinpointed the gene. The researchers grew wild rice in sterilized soil, non-sterilized soil and sterilized soil inoculated with a synthetic community of nine Acinetobacter strains isolated from wild-rice rhizosphere, including strains related to A. baumannii, A. halotolerans and A. sichuanensis. KEGG pathway analysis revealed that nitrogen metabolism was the only pathway significantly enriched in both comparisons. Within a 0.64 megabase region on chromosome 4 associated with Acinetobacter, only one gene met the stringent criteria of upregulation in both treatments, a log2 fold change above 2 and above-average transcript abundance: OsRLK (Os04g0659300), a receptor-like kinase found predominantly in wild rice. Receptor-like kinases are cell-surface proteins that mediate signaling between plants and their environment, and related DUF26/CRK kinases have been implicated in symbiotic nitrogen fixation in legumes, making OsRLK a biologically plausible candidate for sensing or recruiting beneficial bacteria.

Functional validation followed. The team cloned the wild-rice OsRLK into an overexpression vector under a maize ubiquitin promoter and generated CRISPR/Cas9 knockout mutants, then inoculated all lines with the Acinetobacter synthetic community in pot experiments. The results were decisive: total nitrogen content and dry biomass were significantly higher in SynCom-inoculated wild rice and OsRLK-overexpressing lines, but no differences appeared with a heat-killed SynCom or without inoculation, proving the effect depends on living bacteria. After 30 days, Acinetobacter abundance, nifH gene abundance, a key marker of nitrogen fixation, and nitrogenase protein levels ranked OsRLK-1 and wild rice highest, followed by OsRLK-2, then wild type, with knockout mutants lowest. Crucially, field trials showed that OsRLK overexpression lines significantly increased effective panicle number, seed-setting rate, thousand-grain weight and grain yield per plant, demonstrating that the microbiome effect translates into real agronomic performance.

Haplotype analysis across 105 rice accessions revealed why the gene had been lost. OsRLK coding sequences fall into three haplotypes, with the wild-rice HAP1 variant carrying 18 amino acid differences from the cultivated HAP2 variant, and Acinetobacter abundance was significantly higher in HAP1 accessions. Intriguingly, the major domestication gene Sh4, which controls seed shattering, lies only about 2 centimorgans from OsRLK, raising the possibility that beneficial OsRLK alleles were dragged to low frequency by linkage with Sh4 during selection for non-shattering rice. Because that distance is resolvable by recombination, the authors suggest that marker-assisted selection or genome editing could introgress the wild allele into elite cultivars while minimizing linkage drag, though they caution that practical deployment requires further validation and that trade-offs, including immune regulation, remain possible.

The broader significance of this work lies in reframing how we think about crop improvement. Rather than treating the microbiome as an external input to be engineered separately, the study shows that microbiome composition is itself a heritable, genetically tractable trait, shaped by domestication and recoverable through breeding. By connecting host loci to functionally validated core microbiota and to nitrogen-use efficiency under real field conditions, the researchers move beyond the correlation-based studies previously reported for maize, foxtail millet, tomato, barley and wheat. If the microbiome re-domestication framework can be extended to other crops and other nutrients, the era of breeding plants not just for what they are, but for the microbial partners they attract, may have quietly begun in the flooded paddies of northeastern China.

Subject of Research: Genetic recovery of beneficial rhizosphere microbiota from wild rice to improve nitrogen-use efficiency in cultivated rice

Article Title: Wild rice locus enables microbiome re-domestication for enhanced nitrogen-use efficiency

Article References: Chang, J., Wang, D., Yao, Z., Pang, Y., Zhang, H., Wang, C., Xie, Y., Sun, Y., Zhang, J., Li, W., Liang, A., Li, X., Chen, D., Chen, H., Chen, X., Wang, E., Tran, L.-S. P., Wang, J., Raaijmakers, J. M., … Kuramae, E. E. (2026). Wild rice locus enables microbiome re-domestication for enhanced nitrogen-use efficiency. Nature Microbiology. https://doi.org/10.1038/s41564-026-02498-x

Image Credits: AI Generated

DOI: 10.1038/s41564-026-02498-x

Keywords: rice, microbiome, nitrogen-use efficiency, Oryza rufipogon, domestication, QTL mapping, receptor-like kinase, Acinetobacter, nitrogen fixation, plant-microbe interactions, synthetic community, crop breeding

The research team set out to answer a deceptively simple question: how does temperature affect the abundance and composition of antibiotic resistance genes in activated sludge systems, when everything else is held constant? This question matters because real-world treatment plants experience seasonal swings, and previous field studies have struggled to disentangle the effects of temperature from the effects of changing influent composition. Winter brings not only colder basins but also different patterns of water use, different chemical loads, and different microbial communities arriving at the plant. To isolate temperature as a single variable, the researchers designed an elegant controlled experiment conducted directly at an urban wastewater treatment plant in Portugal, ensuring that the wastewater feeding their experimental systems reflected genuine, real-world conditions rather than synthetic laboratory mixtures.

Two laboratory-scale conventional activated sludge systems were operated side by side for 147 days under identical conditions, with one crucial exception. The control system was maintained at approximately 20 degrees Celsius, a temperature representative of moderate operating conditions, while the test system was run sequentially at 10, 5, 15, and 28 degrees Celsius. This sequential design allowed the researchers to observe how the same microbial community responded as the thermal regime shifted up and down over time. Throughout the experiment, the team sampled the feed, which consisted of primary effluent from the host treatment plant, as well as the treated effluent and the sludge from each system. These samples were analyzed for physicochemical parameters, fecal indicator bacteria, the abundance of specific antibiotic resistance genes, and the composition of the bacterial communities using molecular profiling techniques.

The results revealed a striking interplay between what enters the plant and what happens inside it. The patterns of antibiotic resistance genes in the treated effluent were clearly influenced by the composition of the incoming feed, confirming that influent characteristics drive much of the resistance dynamics in activated sludge systems. However, temperature exerted an additional, independent influence on top of this influent-driven variability. The most dramatic effect emerged when the test system was operated at 5 degrees Celsius. Under this cold regime, the abundance of intI1, a gene widely used as a proxy for anthropogenic antibiotic resistance pollution and a marker of mobile genetic elements, dropped significantly compared with the control system held at 20 degrees Celsius.

Even more importantly from a clinical standpoint, the cold treatment significantly reduced genes of direct medical relevance, including blaIMP, which confers resistance to carbapenem antibiotics, a last-resort class of drugs used against multidrug-resistant infections, and qnrS, which is associated with reduced susceptibility to fluoroquinolones. These are not obscure genetic markers; carbapenem resistance in particular represents one of the most alarming developments in infectious disease medicine. The observation that a simple operational parameter like temperature could measurably suppress these genes in treated effluent carries substantial implications for how treatment plants might be managed to limit the environmental dissemination of resistance.

To understand why cold temperatures had this effect, the researchers turned to the bacterial community composition data. The shifts in gene abundance were associated with changes in the microbial community itself, particularly a decrease in genera such as Acinetobacter and Escherichia-Shigella, both of which are considered potential hosts for antibiotic resistance genes and both of which include clinically significant pathogens. In other words, the cold did not simply disable the genes while leaving their carriers intact; it appears to have reduced the fitness of the key bacterial hosts that harbor and propagate these genes. When the host organisms decline, the genes they carry decline with them, offering a mechanistic explanation for the observed reductions in effluent ARG loads.

An equally important finding concerned where in the system these effects occurred. The researchers found no significant differences in antibiotic resistance gene abundance in the sludge fraction between the cold and control systems, indicating that temperature mainly influenced ARG persistence in the liquid phase. This distinction matters because the liquid effluent is what gets discharged into receiving rivers and coastal waters, while sludge is typically handled separately, often through anaerobic digestion and land application. The selective reduction of ARGs in the liquid phase suggests that low-temperature operation specifically curtails the release of resistance genes into the aquatic environment, which is one of the principal pathways by which resistance spreads from human settlements into natural ecosystems.

The temperature effect extended beyond resistance genes to the removal of fecal indicator organisms. Reductions of Escherichia coli, the standard marker of fecal contamination, were significantly greater at 5 degrees Celsius than at the control temperature, indicating that cold operation also enhanced the removal of this pathogen indicator from the effluent. This finding adds to the appeal of cold operation from a water quality perspective, although the researchers caution that the picture is not uniformly positive. Low temperature impaired nutrient removal, a critical function of activated sludge systems that protects receiving waters from eutrophication. Nitrifying bacteria and other nutrient-cycling microorganisms are notoriously sensitive to cold, and their slowed activity under low-temperature conditions translated into poorer nutrient removal performance.

Crucially, however, the overall effluent quality remained within discharge limits even during the cold-temperature runs, meaning that the trade-off between enhanced ARG suppression and reduced nutrient removal did not push the system out of regulatory compliance in this study. This balance is central to any practical consideration of the findings. Treatment plant operators cannot simply chill their reactors without consequence, but the study demonstrates that the penalty may be more manageable than feared, while the benefit, a significant reduction in clinically relevant resistance genes entering the environment, could be substantial. The authors frame temperature as an important operational driver of antibiotic resistance dissemination, a variable that deserves deliberate attention rather than passive acceptance.

The broader significance of this work lies in its contribution to the growing field of evidence-based wastewater management for antibiotic resistance control. As concerns mount over the role of treatment plants as conduits for resistance genes into rivers, irrigation systems, and drinking water sources, engineers and regulators are searching for interventions that are feasible within existing infrastructure. This study suggests that temperature, a parameter already monitored and in some contexts already manipulated, could be part of that toolkit, particularly in climates or seasons where colder operation is achievable. It also underscores a fundamental ecological principle: the fate of antibiotic resistance genes in engineered environments is governed not only by the genes themselves but by the fitness of the microbial communities that carry them. By shifting the thermal environment, operators can shift the competitive balance of those communities, and with it, the resistance burden flowing out of the plant and into the world downstream.

Subject of Research: Effect of temperature on antibiotic resistance gene dynamics in conventional activated sludge wastewater treatment

Article Title: Influent-driven antibiotic resistance dynamics are constrained by low temperatures in conventional activated sludge systems

Article References: Influent-driven antibiotic resistance dynamics are constrained by low temperatures in conventional activated sludge systems. (n.d.). https://doi.org/10.1007/s00253-026-14036-0

Image Credits: AI Generated

DOI: 10.1007/s00253-026-14036-0

Keywords: antibiotic resistance genes, wastewater treatment, activated sludge, temperature, intI1, blaIMP, qnrS, Escherichia coli, Acinetobacter, bacterial community, nutrient removal, environmental microbiology