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Ratcliffe S, Meyer EM, Walker CE, Knight M, McNair HM, Matson PG, Iglesias-Rodriguez D, Brzezinski M, Langer G, Sadekov A, Greaves M, Brownlee C, Curnow P, Taylor AR, Wheeler GL. Characterization of the molecular mechanisms of silicon uptake in coccolithophores. Environ Microbiol 2023; 25:315-330. [PMID: 36397254 PMCID: PMC10098502 DOI: 10.1111/1462-2920.16280] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2022] [Accepted: 11/05/2022] [Indexed: 11/19/2022]
Abstract
Coccolithophores are an important group of calcifying marine phytoplankton. Although coccolithophores are not silicified, some species exhibit a requirement for Si in the calcification process. These species also possess a novel protein (SITL) that resembles the SIT family of Si transporters found in diatoms. However, the nature of Si transport in coccolithophores is not yet known, making it difficult to determine the wider role of Si in coccolithophore biology. Here, we show that coccolithophore SITLs act as Na+ -coupled Si transporters when expressed in heterologous systems and exhibit similar characteristics to diatom SITs. We find that CbSITL from Coccolithus braarudii is transcriptionally regulated by Si availability and is expressed in environmental coccolithophore populations. However, the Si requirement of C. braarudii and other coccolithophores is very low, with transport rates of exogenous Si below the level of detection in sensitive assays of Si transport. As coccoliths contain only low levels of Si, we propose that Si acts to support the calcification process, rather than forming a structural component of the coccolith itself. Si is therefore acting as a micronutrient in coccolithophores and natural populations are only likely to experience Si limitation in circumstances where dissolved silicon (DSi) is depleted to extreme levels.
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Affiliation(s)
| | - Erin M Meyer
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina, USA
| | - Charlotte E Walker
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth, UK
| | - Michael Knight
- School of Ocean and Earth Science, University of Southampton, Southampton, UK
| | - Heather M McNair
- Department of Ecology Evolution and Marine Biology and the Marine Science Institute, University of California, Santa Barbara, California, USA
- Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA
| | - Paul G Matson
- Department of Ecology Evolution and Marine Biology and the Marine Science Institute, University of California, Santa Barbara, California, USA
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Debora Iglesias-Rodriguez
- Department of Ecology Evolution and Marine Biology and the Marine Science Institute, University of California, Santa Barbara, California, USA
| | - Mark Brzezinski
- Department of Ecology Evolution and Marine Biology and the Marine Science Institute, University of California, Santa Barbara, California, USA
- Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Gerald Langer
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth, UK
| | - Aleksey Sadekov
- ARC Centre of Excellence for Coral Reef Studies, Ocean Graduate School, University of Western Australia, Crawley, Western Australia, Australia
| | - Mervyn Greaves
- The Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | - Colin Brownlee
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth, UK
| | - Paul Curnow
- School of Biochemistry, University of Bristol, Bristol, UK
| | - Alison R Taylor
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina, USA
| | - Glen L Wheeler
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth, UK
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Maniscalco MA, Brzezinski MA, Lampe RH, Cohen NR, McNair HM, Ellis KA, Brown M, Till CP, Twining BS, Bruland KW, Marchetti A, Thamatrakoln K. Diminished carbon and nitrate assimilation drive changes in diatom elemental stoichiometry independent of silicification in an iron-limited assemblage. ISME COMMUNICATIONS 2022; 2:57. [PMID: 37938259 PMCID: PMC9723790 DOI: 10.1038/s43705-022-00136-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2021] [Revised: 05/12/2022] [Accepted: 06/09/2022] [Indexed: 06/17/2023]
Abstract
In the California Current Ecosystem, upwelled water low in dissolved iron (Fe) can limit phytoplankton growth, altering the elemental stoichiometry of the particulate matter and dissolved macronutrients. Iron-limited diatoms can increase biogenic silica (bSi) content >2-fold relative to that of particulate organic carbon (C) and nitrogen (N), which has implications for carbon export efficiency given the ballasted nature of the silica-based diatom cell wall. Understanding the molecular and physiological drivers of this altered cellular stoichiometry would foster a predictive understanding of how low Fe affects diatom carbon export. In an artificial upwelling experiment, water from 96 m depth was incubated shipboard and left untreated or amended with dissolved Fe or the Fe-binding siderophore desferrioxamine-B (+DFB) to induce Fe-limitation. After 120 h, diatoms dominated the communities in all treatments and displayed hallmark signatures of Fe-limitation in the +DFB treatment, including elevated particulate Si:C and Si:N ratios. Single-cell, taxon-resolved measurements revealed no increase in bSi content during Fe-limitation despite higher transcript abundance of silicon transporters and silicanin-1. Based on these findings we posit that the observed increase in bSi relative to C and N was primarily due to reductions in C fixation and N assimilation, driven by lower transcript expression of key Fe-dependent genes.
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Affiliation(s)
- Michael A Maniscalco
- Marine Science Institute and The Department of Ecology Evolution and Marine Biology, University of California, Santa Barbara, CA, USA.
| | - Mark A Brzezinski
- Marine Science Institute and The Department of Ecology Evolution and Marine Biology, University of California, Santa Barbara, CA, USA
| | - Robert H Lampe
- Integrative Oceanography Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA
| | - Natalie R Cohen
- Skidaway Institute of Oceanography, University of Georgia, Savannah, GA, USA
| | - Heather M McNair
- University of Rhode Island, Graduate School of Oceanography, Narragansett, RI, USA
| | - Kelsey A Ellis
- Department of Earth, Marine and Environmental Sciences, University of North Carolina at Chapel Hill, Chapel Hill, USA
| | | | - Claire P Till
- Chemistry Department, California State Polytechnic University, Humboldt, Arcata, CA, USA
| | | | - Kenneth W Bruland
- Department of Ocean Sciences, University of California, Santa Cruz, CA, USA
| | - Adrian Marchetti
- Department of Earth, Marine and Environmental Sciences, University of North Carolina at Chapel Hill, Chapel Hill, USA
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McNair HM, Brzezinski MA, Krause JW. Diatom populations in an upwelling environment decrease silica content to avoid growth limitation. Environ Microbiol 2018; 20:4184-4193. [PMID: 30253028 DOI: 10.1111/1462-2920.14431] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Revised: 09/21/2018] [Accepted: 09/22/2018] [Indexed: 11/30/2022]
Abstract
A mix of adaptive strategies enable diatoms to sustain rapid growth in dynamic ocean regions, making diatoms one of the most productive primary producers in the world. We illustrate one such strategy off coastal California that facilitates continued, high, cell division rates despite silicic acid stress. Using a fluorescent dye to measure single-cell diatom silica production rates, silicification (silica per unit area) and growth rates we show diatoms decrease silicification and maintain growth rate when silicon concentration limits silica production rates. While this physiological response to silicon stress was similar across taxa, in situ silicic acid concentration limited silica production rates by varying degrees for taxa within the same community. Despite this variability among taxa, silicon stress did not alter the contribution of specific taxa to total community silica production or to community composition. Maintenance of division rate at the expense of frustule thickness decreases cell density which could affect regional biogeochemical cycles. The reduction in frustule silicification also creates an ecological tradeoff: thinner frustules increase susceptibility to predation but reducing Si quotas maximizes cell abundance for a given pulse of silicic acid, thereby favouring a larger eventual population size which facilitates diatom persistence in habitats with pulsed resource supplies.
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Affiliation(s)
- Heather M McNair
- Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, USA
| | - Mark A Brzezinski
- Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, USA.,Marine Science Institute, University of California Santa Barbara, Santa Barbara, CA, USA
| | - Jeffrey W Krause
- Dauphin Island Sea Lab, University of South Alabama, Mobile, AL, USA.,Department of Marine Sciences, University of South Alabama, Mobile, AL, USA
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