ORIGINAL RESEARCH article
Front. Protistol.
Sec. Symbiotic and Parasitic Protists
Volume 3 - 2025 | doi: 10.3389/frpro.2025.1663791
This article is part of the Research TopicExploring Protist-Prokaryote Symbioses: Diversity, Roles, and Molecular InteractionsView all articles
Integrative taxonomy, whole organelle genomes and endosymbiosis in Rhopalodia sterrenburgii Krammer
Provisionally accepted
Aimee Caye G. Chang1,2*
Mailor W. W. Amaral2
Kyle Keepers2
Megan Greenwood2
Jingchun Li2
Sarah E. Hamsher3
Scott R. Miller4
John Patrick Kociolek2*- 1University of Santo Tomas, Manila, Philippines
- 2University of Colorado Boulder, Boulder, United States
- 3Grand Valley State University - Robert C Pew Grand Rapids Campus, Grand Rapids, United States
- 4University of Montana, Missoula, United States
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Despite their ecological significance and unique endosymbiotic capabilities, diatoms in the genus Rhopalodia remain poorly represented in genomic databases, particularly with respect to the availability of complete genomes from multiple organellar compartments. This study addresses that gap by presenting, for the first time, the complete chloroplast (133,086 bp), mitochondrial (36,786 bp), and spheroid body (3,024,495 bp) genomes of Rhopalodia sterrenburgii, a nitrogen-fixing diatom with a cyanobacterial endosymbiont. Phylogenetic reconstruction based on five genes from different cellular compartments (18S, 28S, rbcL, psbC, cob) placed R. sterrenburgii as a basal lineage relative to R. gibba (Rhopalodia sensu lato) and the Epithemia sensu stricto species E. argus, E. turgida, and E. sorex, providing new insights into evolutionary relationships within Rhopalodiales. Additionally, pathway analysis revealed the progressive loss of genes involved in vitamin B12 and chlorophyll a biosynthesis in more recently diverged Rhopalodia and Epithemia lineages. Our findings support a pattern of genome reduction in symbiotic diazotrophic diatoms, potentially driven by coevolution with their endosymbionts, and an increasing reliance on integrated metabolic functions between the host and the endosymbiont.
Keywords: Diatoms, Symbiosis, plastomes, Mitogenomes, spheroid body, morphology
Received: 10 Jul 2025; Accepted: 07 Oct 2025.
Copyright: © 2025 Chang, Amaral, Keepers, Greenwood, Li, Hamsher, Miller and Kociolek. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Aimee Caye G. Chang, aimee.caye.chang@gmail.com
John Patrick Kociolek, patrick.kociolek@colorado.edu
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