{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T06:07:44Z","timestamp":1788934064823,"version":"build-2803163510"},"reference-count":85,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T00:00:00Z","timestamp":1788912000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100009985","name":"Instituto Chico Mendes de Conserva\u00e7\u00e3o da Biodiversidade","doi-asserted-by":"publisher","id":[{"id":"10.13039\/501100009985","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Microbiol."],"abstract":"<jats:p>Karst aquifers represent dynamic subsurface environments where hydrological fluctuations and redox variability can strongly influence groundwater microbiomes and associated biogeochemical processes. However, microbial sulfur cycling in sulfate-rich karst aquifers remains poorly understood, particularly from a genome-resolved perspective that links hydrochemical gradients to microbial metabolic potential. Here, we investigated how hydrochemical heterogeneity and contrasting hydrological conditions relate to microbial community composition and sulfur-cycling potential in the Irec\u00ea Basin karst aquifer (Salitre Formation, northeastern Brazil), a sulfur-rich non-hydrothermal karst system. Hydrochemical analyses, 16S rRNA gene sequencing, and genome-resolved metagenomics were integrated to characterize groundwater microbial communities and evaluate relationships between hydrochemical variability and sulfur-related metabolic potential. Samples displayed significant hydrochemical heterogeneity, including remarkable variation in oxidation\u2013reduction potential, dissolved oxygen, sulfate concentrations, and dissolved sulfide accumulation. Amplicon sequencing of 10 samples generated more than 10,000 high-quality reads each and revealed substantial variation in community composition among groundwater samples, with substantial differences among environments and contrasting hydrological conditions, highlighting pronounced spatial and habitat-level heterogeneity. A total of 185 dereplicated medium- and high-quality metagenome-assembled genomes (MAGs) were recovered from three samples, many representing potentially novel microbial lineages. M00596-associated sulfur-transformation modules were detected in MAGs from all three metagenomic samples, whereas complete SOX modules were restricted to the comparatively more oxidizing groundwaters. Several MAGs contained both M00596 and SOX modules, indicating the potential for multiple sulfur-transformation pathways within the same genomes. Overall, these findings indicate that sulfur cycling represents a central component of groundwater biogeochemistry in this sulfate-rich karst aquifer and that hydrochemical heterogeneity is associated with variation in microbial community structure and sulfur-cycling metabolic potential. Together, the combination of sulfur-rich carbonate lithologies, heterogeneous redox conditions, and diverse sulfur-cycling microbial populations highlights the potential importance of sulfur transformations in the ecological and biogeochemical functioning of the Irec\u00ea Basin karst aquifer, with possible implications for local geochemical processes.<\/jats:p>","DOI":"10.3389\/fmicb.2026.1883366","type":"journal-article","created":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T06:00:20Z","timestamp":1788933620000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Groundwater microbial community structure under contrasting hydrological conditions in a sulfate-rich karst aquifer"],"prefix":"10.3389","volume":"17","author":[{"given":"Renato","family":"Romano","sequence":"first","affiliation":[{"name":"Oceanographic Institute, University of S\u00e3o Paulo","place":["S\u00e3o Paulo, Brazil"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tom","family":"Morita","sequence":"additional","affiliation":[{"name":"Geosciences Institute, University of S\u00e3o Paulo","place":["S\u00e3o Paulo, Brazil"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Francielli","family":"Peres","sequence":"additional","affiliation":[{"name":"Oceanographic Institute, University of S\u00e3o Paulo","place":["S\u00e3o Paulo, Brazil"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rebeca","family":"Liz\u00e1rraga","sequence":"additional","affiliation":[{"name":"Oceanographic Institute, University of S\u00e3o Paulo","place":["S\u00e3o Paulo, Brazil"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lucas","family":"Padoan","sequence":"additional","affiliation":[{"name":"Geosciences Institute, University of S\u00e3o Paulo","place":["S\u00e3o Paulo, Brazil"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Maria","family":"Nascimento","sequence":"additional","affiliation":[{"name":"Oceanographic Institute, University of S\u00e3o Paulo","place":["S\u00e3o Paulo, Brazil"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Livia","family":"Rocha","sequence":"additional","affiliation":[{"name":"Geosciences Institute, University of S\u00e3o Paulo","place":["S\u00e3o Paulo, Brazil"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Amanda","family":"Bendia","sequence":"additional","affiliation":[{"name":"Oceanographic Institute, University of S\u00e3o Paulo","place":["S\u00e3o Paulo, Brazil"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ivo","family":"Karmann","sequence":"additional","affiliation":[{"name":"Geosciences Institute, University of S\u00e3o Paulo","place":["S\u00e3o Paulo, Brazil"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Vivian","family":"Pellizari","sequence":"additional","affiliation":[{"name":"Oceanographic Institute, University of S\u00e3o Paulo","place":["S\u00e3o Paulo, Brazil"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,9,9]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"1144","DOI":"10.1038\/nmeth.3103","article-title":"Binning metagenomic contigs by coverage and composition.","volume":"11","author":"Alneberg","year":"2014","journal-title":"Nat. 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A.\n            \n          \n          Projeto Bacia de Irec\u00ea.\n          \n          1985"},{"key":"B14","doi-asserted-by":"publisher","first-page":"725","DOI":"10.1038\/nbt.3893","article-title":"Minimum Information about a Single Amplified Genome (MISAG) and a Metagenome-Assembled Genome (MIMAG) of bacteria and archaea.","volume":"35","author":"Bowers","year":"2017","journal-title":"Nat. Biotechnol."},{"key":"B15","doi-asserted-by":"publisher","first-page":"208","DOI":"10.1038\/nature14486","article-title":"Unusual biology across a group comprising more than 15% of domain Bacteria.","volume":"523","author":"Brown","year":"2015","journal-title":"Nature"},{"key":"B16","doi-asserted-by":"publisher","first-page":"581","DOI":"10.1038\/nmeth.3869","article-title":"DADA2: High-resolution sample inference from Illumina amplicon data.","volume":"13","author":"Callahan","year":"2016","journal-title":"Nat. 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C.\n            \n            \n              Pedreira\n              A. J.\n            \n          \n          Seabra: Folha SD.24-V-A, Estado da Bahia.\n          \n          1999"},{"key":"B25","doi-asserted-by":"publisher","first-page":"e025033","DOI":"10.20396\/td.v21i00.8680863","article-title":"Cole\u00e7\u00e3o did\u00e1tica das rochas carbon\u00e1ticas e carste no Estado da Bahia: um recurso para interpreta\u00e7\u00e3o da Geodiversidade.","volume":"21","author":"de Pereira","year":"2025","journal-title":"Terrae Didatica"},{"key":"B26","doi-asserted-by":"publisher","first-page":"593","DOI":"10.1007\/s12665-018-7769-8","article-title":"Evaluation of susceptibility for terrain collapse and subsidence in karst areas, municipality of Iraquara, Chapada Diamantina (BA), Brazil.","volume":"77","author":"de Queiroz Salles","year":"2018","journal-title":"Environ. Earth Sci."},{"key":"B27","unstructured":"de Souza\n              J. D.\n            \n            \n              de Melo\n              R. C.\n            \n            \n              Kosin\n              M.\n            \n          \n          Mapa geol\u00f3gico do estado da Bahia.\n          \n          2003"},{"key":"B28","doi-asserted-by":"publisher","first-page":"452","DOI":"10.1016\/j.geomorph.2015.10.019","article-title":"Sulfuric Acid Speleogenesis (SAS) close to the water table: Examples from southern France, Austria, and Sicily.","volume":"253","author":"De Waele","year":"2016","journal-title":"Geomorphology"},{"key":"B29","doi-asserted-by":"publisher","first-page":"104693","DOI":"10.1016\/j.earscirev.2024.104693","article-title":"Sulfuric acid caves of the world: A review.","volume":"250","author":"De Waele","year":"2024","journal-title":"Earth-Sci. 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G.\n            \n            \n              Friendly\n              M.\n            \n            \n              Kindt\n              R.\n            \n            \n              Legendre\n              P.\n            \n            \n              McGlinn\n              D.\n            \n          \n          vegan: Community Ecology Package.\n          \n          2020"},{"key":"B60","doi-asserted-by":"publisher","first-page":"2864","DOI":"10.1038\/ismej.2017.126","article-title":"dRep: A tool for fast and accurate genomic comparisons that enables improved genome recovery from metagenomes through de-replication.","volume":"11","author":"Olm","year":"2017","journal-title":"ISME J."},{"key":"B61","doi-asserted-by":"publisher","first-page":"1032","DOI":"10.1111\/mec.13536","article-title":"Application of multivariate statistical techniques in microbial ecology.","volume":"25","author":"Paliy","year":"2016","journal-title":"Mol. 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Microbiol."},{"key":"B64","doi-asserted-by":"publisher","first-page":"1043","DOI":"10.1101\/gr.186072.114","article-title":"CheckM: Assessing the quality of microbial genomes recovered from isolates, single cells, and metagenomes.","volume":"25","author":"Parks","year":"2015","journal-title":"Genome Res."},{"key":"B65","doi-asserted-by":"publisher","first-page":"328","DOI":"10.1038\/s41564-017-0098-y","article-title":"Differential depth distribution of microbial function and putative symbionts through sediment-hosted aquifers in the deep terrestrial subsurface.","volume":"3","author":"Probst","year":"2018","journal-title":"Nat. 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