TY - JOUR

T1 - Symbiont replacement between bacteria of different classes reveals additional layers of complexity in the evolution of symbiosis in the ciliate Euplotes

AU - Boscaro, Vittorio

AU - Fokin, Sergei I.

AU - Petroni, Giulio

AU - Verni, Franco

AU - Keeling, Patrick J.

AU - Vannini, Claudia

PY - 2018/2/1

Y1 - 2018/2/1

N2 - Symbiosis is a diverse and complex phenomenon requiring diverse model systems. The obligate relationship between a monophyletic group of Euplotes species (“clade B”) and the betaproteobacteria Polynucleobacter and “Candidatus Protistobacter” is among the best-studied in ciliates, and provides a framework to investigate symbiont replacements. Several other Euplotes-bacteria relationships exist but are less understood, such as the co-dependent symbiosis between Euplotes magnicirratus (which belongs to “clade A”) and the alphaproteobacterium “Candidatus Devosia euplotis”. Here we describe a new Devosia inhabiting the cytoplasm of a strain of Euplotes harpa, a clade B species that usually depends on Polynucleobacter for survival. The novel bacterial species, “Candidatus Devosia symbiotica”, is closely related to the symbiont of E. magnicirratus, casting a different light on the history of bacteria colonizing ciliates of this genus. The two Devosia species may have become symbionts independently or as the result of a symbiont exchange between hosts, in either case replacing a previous essential bacterium in E. harpa. Alternatively, both may be remnants of an ancient symbiotic relationship between Euplotes and Devosia, in which case Polynucleobacter and “Ca. Protistobacter” are recent invaders. Either way, symbiont replacement between bacteria belonging to different classes must be evoked to explain this fascinating system.

AB - Symbiosis is a diverse and complex phenomenon requiring diverse model systems. The obligate relationship between a monophyletic group of Euplotes species (“clade B”) and the betaproteobacteria Polynucleobacter and “Candidatus Protistobacter” is among the best-studied in ciliates, and provides a framework to investigate symbiont replacements. Several other Euplotes-bacteria relationships exist but are less understood, such as the co-dependent symbiosis between Euplotes magnicirratus (which belongs to “clade A”) and the alphaproteobacterium “Candidatus Devosia euplotis”. Here we describe a new Devosia inhabiting the cytoplasm of a strain of Euplotes harpa, a clade B species that usually depends on Polynucleobacter for survival. The novel bacterial species, “Candidatus Devosia symbiotica”, is closely related to the symbiont of E. magnicirratus, casting a different light on the history of bacteria colonizing ciliates of this genus. The two Devosia species may have become symbionts independently or as the result of a symbiont exchange between hosts, in either case replacing a previous essential bacterium in E. harpa. Alternatively, both may be remnants of an ancient symbiotic relationship between Euplotes and Devosia, in which case Polynucleobacter and “Ca. Protistobacter” are recent invaders. Either way, symbiont replacement between bacteria belonging to different classes must be evoked to explain this fascinating system.

KW - fluorescence in situ hybridization

KW - phylogeny

KW - SSU rRNA gene

KW - Symbiosis

KW - transmission electron microscopy.

KW - Biological Evolution

KW - Hyphomicrobiaceae/genetics

KW - Ciliophora/classification

KW - Cytoplasm/microbiology

KW - Phylogeny

KW - ENDOSYMBIONTS

KW - SPIROTRICHEA

KW - CANDIDATUS DEVOSIA EUPLOTIS

KW - GENOME REDUCTION

KW - EMENDED DESCRIPTION

KW - SP NOV.

KW - MAGNICIRRATUS CILIOPHORA

KW - HYPOTRICHIA

KW - AEDICULATUS

KW - transmission electron microscopy

KW - POLYNUCLEOBACTER-NECESSARIUS

UR - http://www.scopus.com/inward/record.url?scp=85041626721&partnerID=8YFLogxK

U2 - 10.1016/j.protis.2017.12.003

DO - 10.1016/j.protis.2017.12.003

M3 - Article

C2 - 29414319

AN - SCOPUS:85041626721

VL - 169

SP - 43

EP - 52

JO - Protist

JF - Protist

SN - 1434-4610

IS - 1

ER -