The ISME Journal最新文献

{"title":"Sinking particles exporting diatoms and hacrobia predict the magnitude of oceanic POC flux.","authors":"Sasha J Kramer,Erin L Jones,Margaret L Estapa,Nicola L Paul,Tatiana A Rynearson,Alyson E Santoro,Sebastian Sudek,Colleen A Durkin","doi":"10.1093/ismejo/wraf105","DOIUrl":"https://doi.org/10.1093/ismejo/wraf105","url":null,"abstract":"Carbon flux to the deep sea can be dictated by surface ocean phytoplankton community composition, but translating surface ocean observations into quantitative predictions of carbon export requires additional consideration of the underlying ecosystem drivers. Here, we used genetic tracers of phytoplankton detected in surface seawater and within sinking particles collected in the mesopelagic ocean to identify mechanistic links between surface communities and carbon export in the North Pacific and North Atlantic Oceans. Phytoplankton 18S rRNA gene sequences were sampled over a one-month period in surface seawater and within bulk-collected and individually isolated sinking particles using mesopelagic sediment traps (100-500 m). Nearly all phytoplankton amplicon sequence variants exported from the surface were packaged in large (>300 μm) particles. Individually, each of these particles contained only a few distinct phytoplankton amplicon sequence variants, but collectively, large particles transported about half of the surface taxonomic diversity into the mesopelagic. The relative sequence abundances of the surface community detected within particles were quantitatively related to measured carbon fluxes: a linear model based on the relative sequence abundance of just two pigment-based phytoplankton taxa, diatoms and photosynthetic Hacrobia, was predictive of carbon flux magnitude. These two taxa were also enriched in the ecologically distinct particle classes that had the greatest influence on carbon export magnitude. As global, hyperspectral ocean color satellites begin to quantify these taxonomic groups in the surface ocean, the relationship of these taxa to carbon fluxes demonstrated here may help in developing more accurate algorithms to estimate global carbon export in the ocean.","PeriodicalId":516554,"journal":{"name":"The ISME Journal","volume":"237 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144122170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Legume-specific recruitment of rhizobia by hyphae of arbuscular mycorrhizal fungi.","authors":"Jiadong He,Judith Van Dingenen,Sofie Goormachtig,Maryline Calonne-Salmon,Stéphane Declerck","doi":"10.1093/ismejo/wraf100","DOIUrl":"https://doi.org/10.1093/ismejo/wraf100","url":null,"abstract":"The legume-rhizobia symbiosis possesses great potential for sustainable agriculture because of its ability to fix atmospheric nitrogen, reducing crop dependence on nitrogen fertilizers. Rhizobia recognize the host legume through flavonoids released by the roots. These signals are detected by bacteria typically over a few millimeters. Recent research has shown that arbuscular mycorrhizal fungi extend this recognition beyond 15 cm by transporting flavonoids along their hyphae. In soil, common mycorrhizal networks linking plants are formed by arbuscular mycorrhizal fungi. We hypothesized that such networks linking different legumes can transmit host-specific signals, guiding rhizobia to their appropriate hosts. Using in vitro and greenhouse microcosms, we linked Medicago truncatula and Glycine max via a common mycorrhizal network of Rhizophagus irregularis and inoculated GFP-labeled Sinorhizobium meliloti and mCherry-labeled Bradyrhizobium diazoefficiens on the hyphae. S. meliloti preferentially migrated towards M. truncatula, whereas B. diazoefficiens preferentially migrated towards G. max (155 ± 8 and 13 ± 3 nodules, respectively). This was confirmed in the greenhouse with a higher concentration of S. meliloti (2.1-2.5 × 105 CFU·g-1) near M. truncatula and a higher concentration of B. diazoefficiens (1.5-1.6 × 105 CFU·g-1) near G. max (71-82 and 15-18 nodules, respectively). Metabolomics revealed host-specific flavonoids in hyphal exudates: M. truncatula-connected hyphae released DL-liquiritigenin, naringenin, sakuranetin, and 3,7-dimethylquercetin, whereas G. max-connected hyphae released daidzin, 6\"-O-malonyldaidzin, irilone, and erylatissin A. These findings establish that common mycorrhizal networks constitute a \"navigation system\", using chemical signals to orient rhizobia towards their specific hosts, thereby improving nodulation with potential applications in agriculture.","PeriodicalId":516554,"journal":{"name":"The ISME Journal","volume":"71 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144103753","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Distinct iron acquisition strategies in oceanic and coastal variants of the mixotrophic dinoflagellate Karlodinium.","authors":"Se Hyeon Jang,YuanYu Lin,Adrian Marchetti","doi":"10.1093/ismejo/wraf099","DOIUrl":"https://doi.org/10.1093/ismejo/wraf099","url":null,"abstract":"The availability of the micronutrient iron is important in regulating phytoplankton growth across much of the world's oceans, particularly in the high-nutrient, low-chlorophyll regions. Compared to known mechanisms of iron acquisition and conservation in autotrophic protists (e.g., diatoms), those of dinoflagellates remain unclear, despite their frequent presence in offshore iron-limited waters. Here, we investigate the strategies of an ecologically important mixotrophic dinoflagellate to coping with low iron conditions. Coupled gene expression and physiological responses as a function of iron availability were examined in oceanic and coastal strains of the dinoflagellate Karlodinium. Under iron-replete conditions, grazing was only detected in coastal variants, resulting in faster growth rates compared to when grown autotrophically. Under iron-limited conditions, all isolates exhibited slower growth rates, reduced photosynthetic efficiencies, and lower cellular iron quotas than in iron-replete conditions. However, oceanic isolates exhibited higher relative growth rates compared to coastal isolates under similar low iron concentrations, suggesting they are better adapted to coping under iron limitation. Yet the oceanic isolates did not exhibit the ability to appreciably reduce cell volume or increase iron-use efficiencies compared to the coastal isolates to cope with iron limitation, as often observed in oceanic diatoms. Rather, molecular pathway analysis and corresponding gene expression patterns suggest oceanic Karlodiniumutilizes a high-affinity iron uptake system when iron is low. Our findings reveal cellular mechanisms by which dinoflagellates have adapted to low iron conditions, further shedding light on how they potentially survive in variable iron regions of the world's ocean.","PeriodicalId":516554,"journal":{"name":"The ISME Journal","volume":"13 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144103533","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dynamics of diazotroph particle colonization in the Arctic Ocean.","authors":"Arthur Coët,Cécile Carpaneto Bastos,Mathias Lechelon,Ruth Hawley,Oliver Flanagan,Maeve C Lohan,Pierre Ronceray,Joanne E Hopkins,Claire Mahaffey,Mar Benavides","doi":"10.1093/ismejo/wraf098","DOIUrl":"https://doi.org/10.1093/ismejo/wraf098","url":null,"abstract":"Global warming is causing sea ice retreat and intensifying algal blooms in the Arctic Ocean, in turn increasing nitrogen limitation in surface waters. Dinitrogen fixation by diazotrophic microorganisms, usually favored in low reactive nitrogen systems, may become an increasingly important source of nitrogen in the Arctic. Previous studies have shown that non-cyanobacterial diazotrophs are dominant in the Arctic Ocean. Lacking a photosynthetic apparatus, non-cyanobacterial diazotrophs may utilize organic particles as carbon- and energy-rich niches. However, cyanobacterial diazotrophs may also form particles by aggregation. To further understand diazotroph-particle associations, here we study the chemotactic behavior and colonization dynamics of diazotrophs on model organic particles using a modified chemotaxis assay. Artificial organic particles (agarose, alginate) were incubated with surface seawater communities from four contrasted stations in the Barents Sea, and their DNA was sequenced targeting nifHand 16S rRNA genes after 2, 36, and 72 h of incubation. Our results show that diazotroph groups have selective colonization behaviors, with Gammaproteobacteriamembers preferentially colonizing alginate particles derived from brown algae, a form of organic matter becoming more common in the Arctic as it warms up. We also observe niche partitioning among microbial groups, with diazotrophs colonizing nitrogen-poor, carbon-rich particles earlier than non-diazotrophic prokaryotes. As Arctic warming proceeds, increased algal blooms may expand the niches for particle-associated diazotrophs, whose dinitrogen fixation supports phytoplankton growth and primary productivity.","PeriodicalId":516554,"journal":{"name":"The ISME Journal","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144103527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Independently evolved extracellular electron transfer pathways in ecologically diverse Desulfobacterota","authors":"Dario R Shaw, Krishna P Katuri, Veerraghavulu Sapireddy, Olga Douvropoulou, Jeffrey A Gralnick, Pascal E Saikaly","doi":"10.1093/ismejo/wraf097","DOIUrl":"https://doi.org/10.1093/ismejo/wraf097","url":null,"abstract":"Extracellular electron transfer plays a role in the biogeochemical cycling of carbon, metals, sulfur, and nitrogen, and has wide-ranging biotechnological applications. The metal-reducing (Mtr), outer-membrane cytochrome (Omc), and porin-cytochrome (Pcc) pathways facilitate electron transfer to insoluble electron acceptors via trans-outer membrane cytochrome complexes. Although these pathways perform a similar function, they are phylogenetically unrelated, indicating independent evolutionary origins. Here, we report an extracellular electron transfer mechanism in which the high-current producing bacterium Desulfuromonas acetexigens differentially co-expresses, at transcript and protein levels, the porin-cytochrome, outer-membrane cytochrome, and metal-reducing pathways, along with high-molecular-weight cytochromes containing a large number of hemes (up to 86 heme-binding motifs), under extracellular electron transfer growth conditions (i.e., electrode under set potential or naturally occurring iron oxide minerals as the electron acceptor). Additionally, we identified over 40 Desulfobacterota species from diverse ecological environments that encode the outer-membrane cytochrome and metal-reducing pathways, with the majority also expressing the porin-cytochrome pathway. The newly identified metal-reducing proteins in Desulfobacterota form a major lineage, greatly expanding the known diversity of these proteins. To our knowledge, mtrCAB genes have not been reported in the Desulfobacterota phylum (formerly classified as Deltaproteobacteria), nor has any electroactive organism been shown to express these phylogenetically distant pathways simultaneously. These findings have ecological implications, challenging the belief that certain extracellular electron transfer pathways are exclusive to specific taxa, and suggesting that these pathways are more widespread than previously thought. Additionally, this reveals a previously unrecognized versatility in microbial electron transfer mechanisms that can be exploited in biotechnological applications.","PeriodicalId":516554,"journal":{"name":"The ISME Journal","volume":"127 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatially structured bacterial interactions alter algal carbon flow to bacteria","authors":"Hyungseok Kim, Vanessa L Brisson, John R Casey, Courtney Swink, Kristina A Rolison, Nathaniel McCall, Amber N Golini, Trent R Northen, Dušan Veličković, Peter K Weber, Cullen R Buie, Xavier Mayali, Rhona K Stuart","doi":"10.1093/ismejo/wraf096","DOIUrl":"https://doi.org/10.1093/ismejo/wraf096","url":null,"abstract":"Phytoplankton account for nearly half of global photosynthetic carbon fixation, and the fate of that carbon is regulated in large part by microbial food web processing. We currently lack a mechanistic understanding of how interactions among heterotrophic bacteria impact the fate of photosynthetically fixed carbon. Here, we used a set of bacterial isolates capable of growing on exudates from the diatom Phaeodactylum tricornutum to investigate how bacteria-bacteria interactions affect the balance between exudate remineralization and incorporation into biomass. With exometabolomics and genome-scale metabolic modeling, we estimated the degree of resource competition between bacterial pairs. In a sequential spent media experiment, we found that pairwise interactions were more beneficial than predicted based on resource competition alone, and 30% exhibited facilitative interactions. To link this to carbon fate, we used single-cell isotope tracing in a custom cultivation system to compare the impact of different “primary” bacterial strains in close proximity to live P. tricornutum on a distal “secondary” strain. We found that a primary strain with a high degree of competition decreased secondary strain carbon drawdown by 51% at the single-cell level, providing a quantitative metric for the “cost” of competition on algal carbon fate. Additionally, a primary strain classified as facilitative based on sequential interactions increased total algal-derived carbon assimilation by 7.6 times, integrated over all members, compared to the competitive primary strain. Our findings suggest that the degree of interaction between bacteria along a spectrum from competitive to facilitative is directly linked to algal carbon drawdown.","PeriodicalId":516554,"journal":{"name":"The ISME Journal","volume":"21 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083198","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Holocene and contemporary marine dinoflagellate community patterns predict expansion of generalist dinoflagellate blooms in warming oceans","authors":"Lemian Liu, Siqi Zhu, Yifan Gu, Shuqin Tao, Bernd Krock, Changyou Wang, Xinguo Shi, Qi Yan, Xiusong Pan, Jianfeng Chen, Senjie Lin, Zhaohe Luo","doi":"10.1093/ismejo/wraf095","DOIUrl":"https://doi.org/10.1093/ismejo/wraf095","url":null,"abstract":"Existing data and models suggest increasing prominence of dinoflagellates and their blooms in future warmer ocean but supporting long-term data are sparse. Here, we used 18S rRNA gene sequencing to investigate sedimentary ancient dinoflagellate communities in northern South China Sea and compared them with contemporary dinoflagellate data from global oceans (TARA Oceans data) and 40 years of dinoflagellate bloom records in China. We found a continuous warming (by ~4.3°C in mean annual sea surface temperature) from 12 to 4.3 kiloyears before present (kyr BP), which caused an initial increase in the relative abundance and diversity of dinoflagellates, followed by a decrease reaching the lowest value, probably due to thermal stress. However, dinoflagellates flourished again after 4.3 kyr BP, coinciding with a rapid increase in human activities. Further analyses indicated that warming and environmental changes during the Holocene favored dinoflagellate generalists over specialists. These generalists have also been abundant throughout contemporary low- and mid-latitude regions, whereas specialists were more abundant at higher latitudes. The predominant generalist genera Noctiluca, Gymnodinium, and Prorocentrum in core sediment corresponded to taxa responsible for most dinoflagellate blooms in the contemporary China Seas over the past 40 years. The success of generalists during warmer periods suggests that dinoflagellate blooms are likely to expand geographically rather than simply shift toward high latitudes under global warming. Moreover, the homogenization of dinoflagellate communities resulting from generalist expansion may significantly reduce the complexity of marine plankton interactions and compromise ecosystem services under global warming.","PeriodicalId":516554,"journal":{"name":"The ISME Journal","volume":"53 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143979954","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Natural and lab-derived microbiomes differentially shape stressor interaction patterns of Daphnia magna.","authors":"Shira Houwenhuyse,Lore Bulteel,Isabel Vanoverberghe,Anna Krzynowek,Marlies Van de Maele,Manon Coone,Silke Van den Wyngaert,Arne Sinnesael,Robby Stoks,Ellen Decaestecker","doi":"10.1093/ismejo/wrae249","DOIUrl":"https://doi.org/10.1093/ismejo/wrae249","url":null,"abstract":"Organisms are facing multiple, potentially interacting stressors in natural populations. The ability of populations coping with combined stressors depends on their tolerance to individual stressors and how stressors interact, which may not be correctly captured in controlled laboratory settings. One reason for this is that the microbial communities in laboratory settings often differ from the natural environment, which could result in different stressor responses and interaction patterns. In this study, we investigated the impact of single and combined exposure to a toxic cyanobacterium and an oomycete parasite on the performance of three Daphnia magna genotypes. Daphnia individuals were sterilized and subsequently exposed to a natural or a laboratory-derived microbial inoculum. Survival, reproduction and body size were monitored, and gut microbiomes were characterized. Our study confirmed that natural and laboratory microbial inocula and gut microbiomes are differently structured. An antagonistic interaction between the two biotic stressors was revealed with respect to survival when Daphnia, across all three genotypes, were exposed to the laboratory microbial inoculum, with a higher survival in the multiple stressor treatment than in the single stressor treatments. In contrast, no antagonistic interaction was detected in Daphnia exposed to a natural microbial inoculum, where the interaction effects were mainly host genotype-dependent. Our results provide the first causal evidence that host-stressor interaction patterns may be shaped by the gut microbiome and the uptake from certain strains from the environment. This raises concern that the many multiple stressor studies on lab-cultured animals with a differently structured microbiome may provide misleading results.","PeriodicalId":516554,"journal":{"name":"The ISME Journal","volume":"125 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143932780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Emergence and disruption of cooperativity in a denitrifying microbial community","authors":"Alex V Carr, Anne E Otwell, Kristopher A Hunt, Yan Chen, James Wilson, José P Faria, Filipe Liu, Janaka N Edirisinghe, Jacob J Valenzuela, Serdar Turkarslan, Lauren M Lui, Torben N Nielsen, Adam P Arkin, Christopher S Henry, Christopher J Petzold, David A Stahl, Nitin S Baliga","doi":"10.1093/ismejo/wraf093","DOIUrl":"https://doi.org/10.1093/ismejo/wraf093","url":null,"abstract":"Anthropogenic perturbations to the nitrogen cycle, primarily through use of synthetic fertilizers, is driving an unprecedented increase in the emission of nitrous oxide (N2O), a potent greenhouse gas and an ozone depleting substance, causing urgency in identifying the sources and sinks of N2O. Microbial denitrification is a primary contributor to biotic production of N2O in anoxic regions of soil, marine systems, and wastewater treatment facilities. Here, through comprehensive genome analysis, we show that pathway partitioning is a ubiquitous mechanism of complete denitrification within microbial communities. We have investigated mechanisms and consequences of process partitioning of denitrification through detailed physiological characterization and kinetic modeling of a synthetic community of Rhodanobacter thiooxydans FW510-R12 and Acidovorax sp. GW101-3H11. We have discovered that these two bacterial isolates, from a heavily nitrate (NO3−) contaminated superfund site, complete denitrification through the exchange of nitrite (NO2−) and nitric oxide (NO). The process partitioning of denitrification and other processes, including amino acid metabolism, contribute to increased cooperativity within this denitrifying community. We demonstrate that certain contexts, such as high NO3−, cause unbalanced growth of community members, due to differences in their substrate utilization kinetics. The altered growth characteristics of community members drives accumulation of toxic NO2−, which disrupts denitrification causing N2O off gassing.","PeriodicalId":516554,"journal":{"name":"The ISME Journal","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143932421","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Drug delivery dynamics dictate evolution of bacterial antibiotic responses","authors":"John C Crow, Hao Geng, Christopher J Geiger, Timothy J Sullivan, Shannon M Soucy, Daniel Schultz","doi":"10.1093/ismejo/wraf082","DOIUrl":"https://doi.org/10.1093/ismejo/wraf082","url":null,"abstract":"Microbes inhabit natural environments that are remarkably dynamic. Therefore, microbes harbor regulated genetic mechanisms to sense shifts in conditions and induce the appropriate responses. Recent studies suggest that the initial evolution of microbes occupying new niches favors mutations in regulatory pathways. However, it is not clear how this evolution is affected by how quickly conditions change (i.e. dynamics), or which mechanisms are commonly used to implement new regulation. Here, we perform experimental evolution on continuous cultures of E. coli carrying the tetracycline resistance tet operon to identify specific mutations that adapt drug responses to different dynamic regimens of drug administration. We find that cultures evolved under gradually increasing tetracycline concentrations show no mutations in the tet operon, but instead a predominance of fine-tuning mutations increasing the affinity of an alternative efflux pump AcrB to tetracycline. When cultures are instead periodically exposed to large drug doses, all populations evolved transposon insertions in repressor TetR, resulting in loss of regulation and constitutive expression of efflux pump TetA. We use a mathematical model of the dynamics of antibiotic responses to show that sudden exposure to large drug concentrations overwhelm regulated responses, which cannot induce resistance fast enough, resulting in selection for constitutive expression of resistance. These results help explain the frequent loss of regulation of antibiotic resistance by pathogens evolved in clinical environments. Our experiment supports the notion that initial evolution in new ecological niches proceeds largely through regulatory mutations and suggests that transposon insertions are a main mechanism driving this process.","PeriodicalId":516554,"journal":{"name":"The ISME Journal","volume":"126 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143932424","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}