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The coral symbiont Candidatus Aquarickettsia is variably abundant in threatened Caribbean acroporids and transmitted horizontally

Baker, Lydia J. and Reich, Hannah G. and Kitchen, Sheila A. and Klinges, J. Grace and Koch, Hanna R. and Baums, Iliana B. and Muller, Erinn M. and Vega Thurber, Rebecca (2022) The coral symbiont Candidatus Aquarickettsia is variably abundant in threatened Caribbean acroporids and transmitted horizontally. ISME Journal, 16 (2). pp. 400-411. ISSN 1751-7362. doi:10.1038/s41396-021-01077-8.

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The symbiont “Candidatus Aquarickettsia rohweri” infects a diversity of aquatic hosts. In the threatened Caribbean coral, Acropora cervicornis, Aquarickettsia proliferates in response to increased nutrient exposure, resulting in suppressed growth and increased disease susceptibility and mortality of coral. This study evaluated the extent, as well as the ecology and evolution of Aquarickettsia infecting threatened corals, Ac. cervicornis, and Ac. palmata and their hybrid (“Ac. prolifera”). Aquarickettsia was found in all acroporids, with coral host and geographic location impacting the infection magnitude. Phylogenomic and genome-wide single-nucleotide variant analysis of Aquarickettsia found phylogenetic clustering by geographic region, not by coral taxon. Analysis of Aquarickettsia fixation indices suggests multiple sequential infections of the same coral colony are unlikely. Furthermore, relative to other Rickettsiales species, Aquarickettsia is undergoing positive selection, with Florida populations experiencing greater positive selection relative to other Caribbean locations. This may be due in part to Aquarickettsia proliferating in response to greater nutrient stress in Florida, as indicated by greater in situ replication rates in these corals. Aquarickettsia was not found to significantly codiversify with either the coral animal or the coral’s algal symbiont (Symbiodinium “fitti”). Quantitative PCR analysis showed that gametes, larvae, recruits, and juveniles from susceptible, captive-reared coral genets were not infected with Aquarickettsia. Thus, horizontal transmission of Aquarickettsia via coral mucocytes or an unidentified host is more likely. The prevalence of Aquarickettsia in Ac. cervicornis and its high abundance in the Florida coral population suggests that coral disease mitigation efforts focus on preventing early infection via horizontal transmission.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Baker, Lydia J.0000-0002-1453-421X
Reich, Hannah G.0000-0002-8622-8801
Kitchen, Sheila A.0000-0003-4402-8139
Klinges, J. Grace0000-0003-3172-133X
Baums, Iliana B.0000-0001-6463-7308
Muller, Erinn M.0000-0002-2695-2064
Additional Information:© The Author(s) 2021. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit Received 27 January 2021; Revised 28 June 2021; Accepted 22 July 2021; Published 06 August 2021. Thanks to Dr Tory A. Hendry for feedback on the methods employed to evaluate symbiont evolution, as well as to the volunteers and staff at Mote Marine Labs for their assistance with experiments leading to the qPCR analysis. This work was funded by an NSF Biological Oceanography grant to RVT and EMM (#1923836) and an NSF CAREER award to EMM (#1452538-OCE). Funding for the S. “fitti” genomes was provided by NSF-OCE-1537959 to IBB. Data availability: All sequences used are available in the SRA in PRJNA473816 and assembled A. rohweri genomes are accessible under PRJNA66646. Author Contributions: LJB conducted the research, analyzed and interpreted the data, and wrote the manuscript. EMM and RVT assisted in the conceptualization of the work, financially supported the project, and assisted in the writing and editing of the manuscript. HGR, SAK, JGK, HRK, and IBB provided data, analysis, and resources and assisted in the editing of the manuscript. The authors declare no competing interests.
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Subject Keywords:Phylogenetics; Population genetics
Issue or Number:2
Record Number:CaltechAUTHORS:20210129-095514933
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Official Citation:Baker, L.J., Reich, H.G., Kitchen, S.A. et al. The coral symbiont Candidatus Aquarickettsia is variably abundant in threatened Caribbean acroporids and transmitted horizontally. ISME J 16, 400–411 (2022).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107802
Deposited By: Tony Diaz
Deposited On:29 Jan 2021 18:16
Last Modified:25 Jan 2022 22:40

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