Cyanobacterial endobionts within a major marine, planktonic, calcifier (Globigerina bulloides, Foraminifera) revealed by 16S rRNA metabarcoding

Clare Bird*, Kate F. Darling, Ann D. Russell, Catherine V. Davis, Jennifer Fehrenbacher, Andrew Free, Michael Wyman, Bryne T. Ngwenya

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

We investigated the possibility of bacterial symbiosis in Globigerina bulloides, a palaeoceanographically important, planktonic foraminifer. This marine protist is commonly used in micropalaeontological investigations of climatically sensitive subpolar and temperate water masses as well as wind-driven upwelling regions of the world's oceans. G. bulloides is unusual because it lacks the protist algal symbionts that are often found in other spinose species. In addition, it has a large offset in its stable carbon and oxygen isotopic compositions compared to other planktonic foraminifer species, and also that predicted from seawater equilibrium. This is suggestive of novel differences in ecology and life history of G. bulloides, making it a good candidate for investigating the potential for bacterial symbiosis as a contributory factor influencing shell calcification. Such information is essential to evaluate fully the potential response of G. bulloides to ocean acidification and climate change. To investigate possible ecological interactions between G. bulloides and marine bacteria, 18S rRNA gene sequencing, fluorescence microscopy, 16S rRNA gene metabarcoding and transmission electron microscopy (TEM) were performed on individual specimens of G. bulloides (type IId) collected from two locations in the California Current. Intracellular DNA extracted from five G. bulloides specimens was subjected to 16S rRNA gene metabarcoding and, remarkably, 37–87 % of all 16S rRNA gene sequences recovered were assigned to operational taxonomic units (OTUs) from the picocyanobacterium Synechococcus. This finding was supported by TEM observations of intact Synechococcus cells in both the cytoplasm and vacuoles of G. bulloides. Their concentrations were up to 4 orders of magnitude greater inside the foraminifera than those reported for the California Current water column and approximately 5 % of the intracellular Synechococcus cells observed were undergoing cell division. This suggests that Synechococcus is an endobiont of G. bulloides type IId, which is the first report of a bacterial endobiont in the planktonic foraminifera. We consider the potential roles of Synechococcus and G. bulloides within the relationship and the need to determine how widespread the association is within the widely distributed G. bulloides morphospecies. The possible influence of Synechococcus respiration on G. bulloides shell geochemistry is also explored.
Original languageEnglish
Pages (from-to)901-920
Number of pages20
JournalBiogeosciences
Volume14
Issue number4
DOIs
Publication statusPublished - 28 Feb 2017

Keywords

  • SOUTHERN CALIFORNIA BIGHT
  • CARBON ISOTOPIC COMPOSITION
  • ORBULINA-UNIVERSA
  • NEOGLOBOQUADRINA-PACHYDERMA
  • GENETIC DIVERSITY
  • SURFACE WATERS
  • SARGASSO SEA
  • ARABIAN SEA
  • GLOBOROTALIA-TRUNCATULINOIDES
  • PALEOTEMPERATURE EQUATIONS

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