1
|
Yu MK, Fogarty EC, Eren AM. Diverse plasmid systems and their ecology across human gut metagenomes revealed by PlasX and MobMess. Nat Microbiol 2024; 9:830-847. [PMID: 38443576 PMCID: PMC10914615 DOI: 10.1038/s41564-024-01610-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Accepted: 01/17/2024] [Indexed: 03/07/2024]
Abstract
Plasmids alter microbial evolution and lifestyles by mobilizing genes that often confer fitness in changing environments across clades. Yet our ecological and evolutionary understanding of naturally occurring plasmids is far from complete. Here we developed a machine-learning model, PlasX, which identified 68,350 non-redundant plasmids across human gut metagenomes and organized them into 1,169 evolutionarily cohesive 'plasmid systems' using our sequence containment-aware network-partitioning algorithm, MobMess. Individual plasmids were often country specific, yet most plasmid systems spanned across geographically distinct human populations. Cargo genes in plasmid systems included well-known determinants of fitness, such as antibiotic resistance, but also many others including enzymes involved in the biosynthesis of essential nutrients and modification of transfer RNAs, revealing a wide repertoire of likely fitness determinants in complex environments. Our study introduces computational tools to recognize and organize plasmids, and uncovers the ecological and evolutionary patterns of diverse plasmids in naturally occurring habitats through plasmid systems.
Collapse
Affiliation(s)
- Michael K Yu
- Toyota Technological Institute at Chicago, Chicago, IL, USA.
| | - Emily C Fogarty
- Department of Medicine, University of Chicago, Chicago, IL, USA
- Committee On Microbiology, University of Chicago, Chicago, IL, USA
| | - A Murat Eren
- Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA, USA.
- Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany.
- Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg, Germany.
- Helmholtz Institute for Functional Marine Biodiversity, Oldenburg, Germany.
- Marine 'Omics Group, Max Planck Institute for Marine Microbiology, Bremen, Germany.
| |
Collapse
|
2
|
Fogarty EC, Schechter MS, Lolans K, Sheahan ML, Veseli I, Moore RM, Kiefl E, Moody T, Rice PA, Yu MK, Mimee M, Chang EB, Ruscheweyh HJ, Sunagawa S, Mclellan SL, Willis AD, Comstock LE, Eren AM. A cryptic plasmid is among the most numerous genetic elements in the human gut. Cell 2024; 187:1206-1222.e16. [PMID: 38428395 DOI: 10.1016/j.cell.2024.01.039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Revised: 10/03/2023] [Accepted: 01/25/2024] [Indexed: 03/03/2024]
Abstract
Plasmids are extrachromosomal genetic elements that often encode fitness-enhancing features. However, many bacteria carry "cryptic" plasmids that do not confer clear beneficial functions. We identified one such cryptic plasmid, pBI143, which is ubiquitous across industrialized gut microbiomes and is 14 times as numerous as crAssphage, currently established as the most abundant extrachromosomal genetic element in the human gut. The majority of mutations in pBI143 accumulate in specific positions across thousands of metagenomes, indicating strong purifying selection. pBI143 is monoclonal in most individuals, likely due to the priority effect of the version first acquired, often from one's mother. pBI143 can transfer between Bacteroidales, and although it does not appear to impact bacterial host fitness in vivo, it can transiently acquire additional genetic content. We identified important practical applications of pBI143, including its use in identifying human fecal contamination and its potential as an alternative approach to track human colonic inflammatory states.
Collapse
Affiliation(s)
- Emily C Fogarty
- Committee on Microbiology, University of Chicago, Chicago, IL 60637, USA; Duchossois Family Institute, University of Chicago, Chicago, IL 60637, USA; Department of Medicine, University of Chicago, Chicago, IL 60637, USA.
| | - Matthew S Schechter
- Committee on Microbiology, University of Chicago, Chicago, IL 60637, USA; Duchossois Family Institute, University of Chicago, Chicago, IL 60637, USA; Department of Medicine, University of Chicago, Chicago, IL 60637, USA
| | - Karen Lolans
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA
| | - Madeline L Sheahan
- Duchossois Family Institute, University of Chicago, Chicago, IL 60637, USA; Department of Microbiology, University of Chicago, Chicago, IL 60637, USA
| | - Iva Veseli
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA; Graduate Program in Biophysical Sciences, University of Chicago, Chicago, IL 60637, USA
| | - Ryan M Moore
- Center for Bioinformatics and Computational Biology, University of Delaware, Newark, DE, USA
| | - Evan Kiefl
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA; Graduate Program in Biophysical Sciences, University of Chicago, Chicago, IL 60637, USA
| | - Thomas Moody
- Department of Systems Biology, Columbia University, New York, NY 10032, USA
| | - Phoebe A Rice
- Committee on Microbiology, University of Chicago, Chicago, IL 60637, USA; Department of Biochemistry, University of Chicago, Chicago, IL 60637, USA
| | - Michael K Yu
- Toyota Technological Institute at Chicago, Chicago, IL 60637, USA
| | - Mark Mimee
- Committee on Microbiology, University of Chicago, Chicago, IL 60637, USA; Department of Microbiology, University of Chicago, Chicago, IL 60637, USA; Pritzker School of Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA
| | - Eugene B Chang
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA
| | - Hans-Joachim Ruscheweyh
- Department of Biology, Institute of Microbiology and Swiss Institute of Bioinformatics, ETH Zurich, Zurich 8093, Switzerland
| | - Shinichi Sunagawa
- Department of Biology, Institute of Microbiology and Swiss Institute of Bioinformatics, ETH Zurich, Zurich 8093, Switzerland
| | - Sandra L Mclellan
- School of Freshwater Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53204, USA
| | - Amy D Willis
- Department of Biostatistics, University of Washington, Seattle, WA 98195, USA
| | - Laurie E Comstock
- Committee on Microbiology, University of Chicago, Chicago, IL 60637, USA; Duchossois Family Institute, University of Chicago, Chicago, IL 60637, USA; Department of Microbiology, University of Chicago, Chicago, IL 60637, USA.
| | - A Murat Eren
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA; Marine Biological Laboratory, Woods Hole, MA 02543, USA; Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, 27570 Bremerhaven, Germany; Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, 26129 Oldenburg, Germany; Max Planck Institute for Marine Microbiology, 28359 Bremen, Germany; Helmholtz Institute for Functional Marine Biodiversity, 26129 Oldenburg, Germany.
| |
Collapse
|
3
|
Veseli I, Chen YT, Schechter MS, Vanni C, Fogarty EC, Watson AR, Jabri B, Blekhman R, Willis AD, Yu MK, Fernàndez-Guerra A, Füssel J, Eren AM. Microbes with higher metabolic independence are enriched in human gut microbiomes under stress. bioRxiv 2023:2023.05.10.540289. [PMID: 37293035 PMCID: PMC10245760 DOI: 10.1101/2023.05.10.540289] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
A wide variety of human diseases are associated with loss of microbial diversity in the human gut, inspiring a great interest in the diagnostic or therapeutic potential of the microbiota. However, the ecological forces that drive diversity reduction in disease states remain unclear, rendering it difficult to ascertain the role of the microbiota in disease emergence or severity. One hypothesis to explain this phenomenon is that microbial diversity is diminished as disease states select for microbial populations that are more fit to survive environmental stress caused by inflammation or other host factors. Here, we tested this hypothesis on a large scale, by developing a software framework to quantify the enrichment of microbial metabolisms in complex metagenomes as a function of microbial diversity. We applied this framework to over 400 gut metagenomes from individuals who are healthy or diagnosed with inflammatory bowel disease (IBD). We found that high metabolic independence (HMI) is a distinguishing characteristic of microbial communities associated with individuals diagnosed with IBD. A classifier we trained using the normalized copy numbers of 33 HMI-associated metabolic modules not only distinguished states of health versus IBD, but also tracked the recovery of the gut microbiome following antibiotic treatment, suggesting that HMI is a hallmark of microbial communities in stressed gut environments.
Collapse
Affiliation(s)
- Iva Veseli
- Biophysical Sciences Program, The University of Chicago, Chicago, IL 60637, USA
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
| | - Yiqun T. Chen
- Data Science Institute and Department of Biomedical Data Science, Stanford University, Stanford, CA, 94305, USA
| | - Matthew S. Schechter
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
- Committee on Microbiology, The University of Chicago, Chicago, IL 60637, USA
| | - Chiara Vanni
- MARUM Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
| | - Emily C. Fogarty
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
- Committee on Microbiology, The University of Chicago, Chicago, IL 60637, USA
| | - Andrea R. Watson
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
- Committee on Microbiology, The University of Chicago, Chicago, IL 60637, USA
| | - Bana Jabri
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
| | - Ran Blekhman
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
| | - Amy D. Willis
- Department of Biostatistics, University of Washington, Seattle, WA, 98195, USA
| | - Michael K. Yu
- Toyota Technological Institute at Chicago, Chicago, IL 60605, USA
| | - Antonio Fernàndez-Guerra
- Lundbeck Foundation GeoGenetics Centre, GLOBE Institute, University of Copenhagen, Copenhagen, Denmark
| | - Jessika Füssel
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
- Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg, Germany
| | - A. Murat Eren
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
- Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg, Germany
- Marine ‘Omics Bridging Group, Max Planck Institute for Marine Microbiology, 28359 Bremen, Germany
- Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
- Helmholtz Institute for Functional Marine Biodiversity, 26129, Oldenburg, Germany
| |
Collapse
|
4
|
Fogarty EC, Schechter MS, Lolans K, Sheahan ML, Veseli I, Moore R, Kiefl E, Moody T, Rice PA, Yu MK, Mimee M, Chang EB, Mclellan SL, Willis AD, Comstock LE, Eren AM. A highly conserved and globally prevalent cryptic plasmid is among the most numerous mobile genetic elements in the human gut. bioRxiv 2023:2023.03.25.534219. [PMID: 36993556 PMCID: PMC10055365 DOI: 10.1101/2023.03.25.534219] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 04/13/2023]
Abstract
Plasmids are extrachromosomal genetic elements that often encode fitness enhancing features. However, many bacteria carry 'cryptic' plasmids that do not confer clear beneficial functions. We identified one such cryptic plasmid, pBI143, which is ubiquitous across industrialized gut microbiomes, and is 14 times as numerous as crAssphage, currently established as the most abundant genetic element in the human gut. The majority of mutations in pBI143 accumulate in specific positions across thousands of metagenomes, indicating strong purifying selection. pBI143 is monoclonal in most individuals, likely due to the priority effect of the version first acquired, often from one's mother. pBI143 can transfer between Bacteroidales and although it does not appear to impact bacterial host fitness in vivo, can transiently acquire additional genetic content. We identified important practical applications of pBI143, including its use in identifying human fecal contamination and its potential as an inexpensive alternative for detecting human colonic inflammatory states.
Collapse
Affiliation(s)
- Emily C Fogarty
- Committee on Microbiology, University of Chicago, Chicago, IL 60637, USA
- Duchossois Family Institute, University of Chicago, Chicago, IL 60637, USA
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA
| | - Matthew S Schechter
- Committee on Microbiology, University of Chicago, Chicago, IL 60637, USA
- Duchossois Family Institute, University of Chicago, Chicago, IL 60637, USA
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA
| | - Karen Lolans
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA
| | - Madeline L. Sheahan
- Duchossois Family Institute, University of Chicago, Chicago, IL 60637, USA
- Department of Microbiology, University of Chicago, Chicago, IL, 60637, USA
| | - Iva Veseli
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA
- Graduate Program in Biophysical Sciences, University of Chicago, Chicago, IL 60637, USA
| | - Ryan Moore
- Center for Bioinformatics and Computational Biology, University of Delaware, Newark, DE, USA
| | - Evan Kiefl
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA
- Graduate Program in Biophysical Sciences, University of Chicago, Chicago, IL 60637, USA
| | - Thomas Moody
- Department of Systems Biology, Columbia University, New York, NY, 10032 USA
| | - Phoebe A Rice
- Committee on Microbiology, University of Chicago, Chicago, IL 60637, USA
- Department of Biochemistry, University of Chicago, Chicago, IL, 60637, USA
| | | | - Mark Mimee
- Committee on Microbiology, University of Chicago, Chicago, IL 60637, USA
- Department of Microbiology, University of Chicago, Chicago, IL, 60637, USA
- Pritzker School of Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA
| | - Eugene B Chang
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA
| | - Sandra L Mclellan
- School of Freshwater Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI, 53204, USA
| | - Amy D Willis
- Department of Biostatistics, University of Washington, Seattle, WA, 98195, USA
| | - Laurie E Comstock
- Duchossois Family Institute, University of Chicago, Chicago, IL 60637, USA
- Department of Microbiology, University of Chicago, Chicago, IL, 60637, USA
| | - A Murat Eren
- Marine Biological Laboratory, Woods Hole, MA, 02543, USA
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, 27570 Bremerhaven, Germany
- Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, 26129 Oldenburg, Germany
- Helmholtz Institute for Functional Marine Biodiversity, 26129 Oldenburg, Germany
| |
Collapse
|
5
|
Runde J, Veseli I, Fogarty EC, Watson AR, Clayssen Q, Yosef M, Shaiber A, Verma R, Quince C, Gerasimidis K, Rubin DT, Eren AM. Transient Suppression of Bacterial Populations Associated with Gut Health is Critical in Success of Exclusive Enteral Nutrition for Children with Crohn's Disease. J Crohns Colitis 2023:7080705. [PMID: 36934439 DOI: 10.1093/ecco-jcc/jjad031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2022] [Indexed: 03/20/2023]
Abstract
BACKGROUND AND AIMS Exclusive enteral nutrition [EEN] is a dietary intervention to induce clinical remission in children with active luminal Crohn's disease [CD]. While changes in the gut microbial communities have been implicated in achieving this remission, a precise understanding of the role of microbial ecology in the restoration of gut homeostasis is lacking. METHODS Here we reconstructed genomes from the gut metagenomes of 12 paediatric subjects who were sampled before, during and after EEN. We then classified each microbial population into distinct 'phenotypes' or patterns of response based on changes in their relative abundances throughout the therapy on a per-individual basis. RESULTS Our data show that children achieving clinical remission during therapy were enriched with microbial populations that were either suppressed or that demonstrated a transient bloom as a function of EEN. In contrast, this ecosystem-level response was not observed in cases of EEN failure. Further analysis revealed that populations that were suppressed during EEN were significantly more prevalent in healthy children and adults across the globe compared with those that bloomed ephemerally during the therapy. CONCLUSIONS These observations taken together suggest that successful outcomes of EEN are marked by a temporary emergence of microbial populations that are rare in healthy individuals, and a concomitant reduction in microbes that are commonly associated with gut homeostasis. Our work is a first attempt to highlight individual-specific, complex environmental factors that influence microbial response in EEN. This model offers a novel, alternative viewpoint to traditional taxonomic strategies used to characterize associations with health and disease states.
Collapse
Affiliation(s)
- Joseph Runde
- Department of Pediatrics, Lurie Children's Hospital of Chicago, Chicago, IL 60611, USA
| | - Iva Veseli
- Biophysical Sciences Program, The University of Chicago, Chicago, IL 60637, USA
| | - Emily C Fogarty
- Committee on Microbiology, The University of Chicago, Chicago, IL 60637, USA.,Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
| | - Andrea R Watson
- Committee on Microbiology, The University of Chicago, Chicago, IL 60637, USA.,Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
| | - Quentin Clayssen
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
| | - Mahmoud Yosef
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
| | - Alon Shaiber
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
| | - Ritu Verma
- Department of Pediatrics, The University of Chicago, Chicago, IL 60637, USA
| | | | | | - David T Rubin
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
| | - A Murat Eren
- Josephine Bay Paul Center, Marine Biological Laboratory, Woods Hole, MA 02543, USA.,Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, 26129, Oldenburg, Germany.,Alfred-Wegener-Institute for Marine and Polar Research, 27570 Bremerhaven, Germany.,Helmholtz Institute for Functional Marine Biodiversity, 26129 Oldenburg, Germany
| |
Collapse
|
6
|
Cotto I, Vilardi KJ, Huo L, Fogarty EC, Khunjar W, Wilson C, De Clippeleir H, Gilmore K, Bailey E, Lücker S, Pinto AJ. Low diversity and microdiversity of comammox bacteria in wastewater systems suggest specific adaptations within the Ca. Nitrospira nitrosa cluster. Water Res 2023; 229:119497. [PMID: 36563511 DOI: 10.1016/j.watres.2022.119497] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Revised: 12/12/2022] [Accepted: 12/13/2022] [Indexed: 06/17/2023]
Abstract
Studies have found Ca. Nitrospira nitrosa-like bacteria to be the principal or sole comammox bacteria in nitrogen removal systems for wastewater treatment. In contrast, multiple populations of strict ammonia and nitrite oxidizers co-exist in similar systems. This apparent lack of diversity is surprising and could impact the feasibility of leveraging comammox bacteria for nitrogen removal. We used full-length 16S rRNA gene sequencing and genome-resolved metagenomics to compare the species-level diversity of comammox bacteria with that of strict nitrifiers in full-scale wastewater treatment systems and assess whether this comparison is consistent or diverged at the strain-level. Full-length 16S rRNA gene sequencing indicated that Nitrosomonas-like bacteria exhibited higher species-level diversity in comparison with other nitrifying bacteria, while the strain-level diversity (also called microdiversity) of most Nitrospira-like bacteria were higher than Nitrosomonas-like bacteria with few exceptions (one Nitrospira lineage II population). Comammox bacterial metagenome assembled genomes (MAGs) were associated with Ca. Nitrospira nitrosa. The average amino acid identity between principal comammox bacterial MAGs (93% ± 3) across systems was significantly higher than that of the Nitrosomonas-like ammonia oxidizers (73% ± 8), the Nitrospira_A-like nitrite oxidizer (85% ± 4), and the Nitrospira_D-like nitrite oxidizer (83% ± 1). This demonstrated the low species-level diversity of comammox bacteria compared with strict nitrifiers and further suggests that the same comammox population was detected in all systems. Comammox bacteria (Nitrospira lineage II), Nitrosomonas and, Nitrospira_D (Nitrospira lineage II) MAGs were significantly less microdiverse than the Nitrospira_A (lineage I) MAGs. Interestingly, strain-resolved analysis also indicates that different nitrogen removal systems harbor different comammox bacterial strains within the Ca. Nitrospira nitrosa cluster. These results suggest that comammox bacteria associated with Ca. Nitrospira nitrosa have low species- and strain-level diversity in nitrogen removal systems and may thus harbor specific adaptations to the wastewater ecosystem.
Collapse
Affiliation(s)
- Irmarie Cotto
- Department of Civil and Environmental Engineering, Northeastern University, Boston, MA, United States
| | - Katherine J Vilardi
- Department of Civil and Environmental Engineering, Northeastern University, Boston, MA, United States
| | - Linxuan Huo
- School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, United States
| | - Emily C Fogarty
- Committee on Microbiology, The University of Chicago, Chicago, IL, United States
| | | | | | | | - Kevin Gilmore
- Department of Civil and Environmental Engineering, Bucknell University, Lewisburg, PA, United States
| | - Erika Bailey
- City of Raleigh Public Utilities, Raleigh, NC, United States
| | - Sebastian Lücker
- Department of Microbiology, RIBES, Radboud University, Nijmegen, the Netherlands
| | - Ameet J Pinto
- School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, United States.
| |
Collapse
|
7
|
Weigel BL, Miranda KK, Fogarty EC, Watson AR, Pfister CA. Functional Insights into the Kelp Microbiome from Metagenome-Assembled Genomes. mSystems 2022; 7:e0142221. [PMID: 35642511 PMCID: PMC9238374 DOI: 10.1128/msystems.01422-21] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Accepted: 05/13/2022] [Indexed: 11/20/2022] Open
Abstract
Eukaryotic organisms evolved in a microbial world and often have intimate associations with diverse bacterial groups. Kelp, brown macroalgae in the order Laminariales, play a vital role in coastal ecosystems, yet we know little about the functional role of the microbial symbionts that cover their photosynthetic surfaces. Here, we reconstructed 79 bacterial metagenome-assembled genomes (MAGs) from blades of the bull kelp, Nereocystis luetkeana, allowing us to determine their metabolic potential and functional roles. Despite the annual life history of bull kelp, nearly half of the bacterial MAGs were detected across multiple years. Diverse members of the kelp microbiome, spanning 6 bacterial phyla, contained genes for transporting and assimilating dissolved organic matter (DOM), which is secreted by kelp in large quantities and likely fuels the metabolism of these heterotrophic bacteria. Bacterial genomes also contained alginate lyase and biosynthesis genes, involved in polysaccharide degradation and biofilm formation, respectively. Kelp-associated bacterial genomes contained genes for dissimilatory nitrate reduction and urea hydrolysis, likely providing a reduced source of nitrogen to the host kelp. The genome of the most abundant member of the kelp microbiome and common macroalgal symbiont, Granulosicoccus, contained a full suite of genes for synthesizing cobalamin (vitamin B12), suggesting that kelp-associated bacteria have the potential to provide their host kelp with vitamins. Finally, kelp-associated Granulosicoccus contained genes that typify the aerobic anoxygenic phototrophic bacteria, including genes for bacteriochlorophyll synthesis and photosystem II reaction center proteins, making them the first known photoheterotrophic representatives of this genus. IMPORTANCE Kelp (brown algae in the order Laminariales) are foundational species that create essential habitat in temperate and arctic coastal marine ecosystems. These photosynthetic giants host millions of microbial taxa whose functions are relatively unknown, despite their potential importance for host-microbe interactions and nutrient cycling in kelp forest ecosystems. We reconstructed bacterial genomes from metagenomic samples collected from blades of the bull kelp, Nereocystis luetkeana, allowing us to determine the functional gene content of specific members of the kelp microbiome. These bacterial genomes spanned 6 phyla and 19 families and included common alga-associated microbial symbionts such as Granulosicoccus. Key functions encoded in kelp-associated bacterial genomes included dissolved organic matter assimilation, alginate metabolism, vitamin B12 biosynthesis, and nitrogen reduction from nitrate and urea to ammonium, potentially providing the host kelp with vitamins and reduced nitrogen.
Collapse
Affiliation(s)
- Brooke L. Weigel
- Committee on Evolutionary Biology, University of Chicago, Chicago, Illinois, USA
| | | | - Emily C. Fogarty
- Committee on Microbiology, University of Chicago, Chicago, Illinois, USA
- Department of Medicine, University of Chicago, Chicago, Illinois, USA
| | - Andrea R. Watson
- Committee on Microbiology, University of Chicago, Chicago, Illinois, USA
- Department of Medicine, University of Chicago, Chicago, Illinois, USA
| | - Catherine A. Pfister
- Department of Ecology & Evolution, University of Chicago, Chicago, Illinois, USA
| |
Collapse
|