Table 1.

Chromosome copy number of archaeal species and the distribution of archaeal histones

Phylum Order Species	Doubling time (h)	Genome copy number		Ploidy	Histones	Reference
		Exp. phase	Stat. phase
Euryarchaeota
Halobacteriales
Halobacterium cutirubrum	6.7	10.6		Polyploid	Yesa	Chant et al. (1986)
Halobacterium cutirubrum	13.3	6.3		Polyploid	Yesa	Chant et al. (1986)
Halobacterium salinarum	4	25	1	Polyploid	Yes	Breuert et al. (2006)
Halobacterium salinarum	8	25	15	Polyploid	Yes	Breuert et al. (2006)
Haloferax volcanii	4	17	10	Polyploid	Yes	Breuert et al. (2006)
Haloferax mediterranei		30–55	20–30	Polyploid	Yes	Liu et al. (2013)
Methanosarcinales
Methanosarcina acetivorans	6	18	16	Polyploid	Yes	Hildenbrand et al. (2011)
Methanosarcina acetivorans	49	3	5	Polyploid	Yes	Hildenbrand et al. (2011)
Methanobacteriales
Methanothermobacter  thermautotrophicus		2	1–2	Diploidb	Yes	Majerník et al. (2005)
Methanomicrobiales
Methanoculleus marisnigri					Yes
Thermococcales
Thermococcus kodakarensis	1.25	19.4	7.5	Polyploid	Yes	This study
Pyrococcus furiosus		Multiple			Yes	Malandrin et al. (1999)
Pyrococcus abyssi		Multiple			Yes	Marie et al. (1996)
Methanococcales
Methanocaldococcus jannaschii	0.5	10–15	1–5	Polyploid	Yes	Malandrin et al. (1999)
Methanococcus maripaludis	2	55	30	Polyploid	Yes	Hildenbrand et al. (2011)
Thermoplasmatales
Thermoplasma acidophilum					Noc
Thermoplasma volcanium					Noc
Ferroplasma acidarmanus					Noc
Archaeoglobales
Archaeoglobus fulgidus		Multiple			Yes	Malandrin et al. (1999)
Methanopyrales
Methanopyrus kandleri					Yes
Methanocellales
Methanocella paludicola					Yes
Crenarchaeota
Acidilobales
Acidianus hospitalis		1–2	2	Monoploid	No	Lundgren et al. (2008)
Desulfurococcales
Aeropyrum pernix	3.3	1–2	2	Monoploid	No	Lundgren et al. (2008)
Fervidicoccales
Fervidicoccus fontis					No
Sulfolobales
Sulfolobus acidocaldarius	3.5	1–2	2	Monoploid	No	Bernander and Poplawski (1997)
Sulfolobus tokodaii	8	1–2	2	Monoploid	No	Lundgren et al. (2008)
Sulfolobus solfataricus	7	1–2	2	Monoploid	No	Bernander and Poplawski (1997)
Thermoproteales
Pyrobaculum aerophilum		1–2	2	Monoploid	No	Lundgren et al. (2008)
Pyrobaculum calidifontis	3.4	1–2	2	Monoploid	No	Lundgren et al. (2008)
Thermofilum pendens					Yes
Caldivirga maquilingensis					Yes
Vulcanisaeta distributa					Yes
Thaumarchaeota
Cenarchaeales
Cenarchaeum symbiosum					Yes
Nitrosopumilales
Nitrosopumilus maritimus					Yes
Nitrososphaerales
Nitrososphaera viennensis					Yes
Korarchaeota
Candidatus Korarchaeum cryptofilum					Yes
Nanoarchaeota
Nanoarchaeum equitans					Yes

The table gives an overview of all studies in which chromosome copy numbers of archaeal species have been determined. The table was adapted from a table presented by Hillenbrand et al. (2011), by including chromosome copy numbers of several additional species, grouping the results per order and including an extra column showing the presence or absence of archaeal histone homologs. The organisms that were not present in the histone database were additionally checked by BLAST for histone homologs. For the orders for which no ploidy level data is available, representative species, whose genome is available and could be screened for the presence of archaeal histone homologs, were randomly picked

^aThe species Halobacterium salinarum, Halobacterium halobium, and Halobacterium cutirubrum are so similar that they should be regarded as strains of one species named Halobacterium salinarum. H. cutirubrum is therefore, as such, not present in the histone database (Ventosa and Oren 1996)

^bThe cells grow in filaments; the numbers given are genome copies per cell, not per filament

^cThe thermoplasmatales do not encode archaeal histones, however, they do encode homologs of HU-proteins (bacterial histone-like proteins)