Table 2.

Overview of the bacteria most commonly found within octocoral holobionts. Taxonomy of the bacteria and which octocorals they associate with and their potential function are listed

Phylum	Class	Order	Family	Genus	Octocoral host	Potential function	Ref.
Actinobacteria	Actinobacteria	Propionibacteriales	Propionibacteriaceae	Propionibacterium	Anthothela spp. Corallium rubrum Paramuricea spp.	Unknown  –Zooxanthellate corals: coral–Symbiodinium symbiosis	[20, 82, 93, 94, 121]
Bacteroidetes	Flavobacteriia	Flavobacteriales	Flavobacteriaceae	Aquimarina	Antillogorgia elisabethae Eunicella spp. Leptogorgia sarmentosa	Nutrient cycling  Nitrogen cycling (denitrification)  Carbon cycling (chitin degradation)  Sulfur cycling (sulphate reduction) Microbiome regulation	[20, 89, 101]
Chlamydiae	Chlamydiae	Chlamydiales	Simkaniaceae	Candidatus Fritschea	Eunicella spp. Leptogorgia sarmentosa	Unknown	[20, 76]
Parcubacteria	–	–	–	–	Corallium rubrum	Unknown	[20, 83]
Proteobacteria	Alphaproteobacteria	Rickettsiales	Rickettsiales incertae sedis	Candidatus Lariskella	Eunicella spp. Leptogorgia sarmentosa	Unknown	[20, 76]
	Gammaproteobacteria	Cellvibrionales	Spongiibacteraceae	BD1-7 clade	Corallium rubrum Eunicella spp. Leptogorgia sarmentosa	Unknown	[20, 76]
		Oceanospirillales	Hahellaceae	Endozoicomonas	Antillogorgia elisabethae Corallium rubrum Erythropodium caribaeorum Eunicella spp. Eunicea fusca Gorgonia ventalina Leptogorgia sarmentosa Lobophytum pauciflorum Paramuricea clavata Plexaura sp. Sarcophyton sp. Sinularia flexibilis	Nutrient acquisition  Nitrogen cycling  Carbon cycling  Sulfur cycling  Amino acid synthesis Microbiome regulation	[19, 20, 76, 77, 83, 89–93, 257]
			ME2	–	Corallium rubrum	Unknown	[20, 83]
		Vibrionales	Vibrionaceae	Vibrio	Corallium rubrum Eunicella sp.	Putative pathogen (V. shiloi) Food digestion (V. gigantis-related)	[19, 20, 77, 105, 113–115]
		Chromatiales	Granulosicoccaceae	Granulosicoccus	Eunicella spp. Leptogorgia sarmentosa	Unknown	[20, 76]
Spirochaetae	Spirochaetes	Spirochaetales	Spirochaetaceae	Borrelia	Corallium rubrum	Unknown	[20, 83]
				Spirochaeta	Anthothela spp. Corallium rubrum Lobophytum pauciflorum Muricea spp.	Unknown	[20, 83, 91, 103, 121]
			Leptospiraceae	Leptospira	Corallium rubrum	Unknown	[20, 83]
Tenericutes	Mollicutes	Mycoplasmatales	Mycoplasmataceae	Mycoplasma	Cryogorgia koolsae Eunicella spp. Leptogorgia sarmentosa Muricea spp. Pennatula phosphorea Plumarella superba Pseudoplexaura porosa Pteroeides spinosum	Unknown  Commensal feeding on captured prey	[19, 20, 102–106]
		Entomoplasmatales	Entomoplasmatales incertae sedis	Candidatus Hepatoplasma	Eunicella spp. Leptogorgia sarmentosa Muricea spp.	Unknown  –Potentially copepod prey symbionts	[20, 103]