TABLE 1.

Genomic and respiratory characteristics of selected Pyrobaculum species

Species	Genome size (Mbp), gene count, GC %	Oxygen tolerance	Terminal electron acceptors supporting growth	Terminal electron acceptors not supporting growth	Reference(s)
P. aerophilum	2.2, 2,706, 51	Facultative microaerobe	O2, NO3−, NO2−, As(V), Se(VI), Se(IV), S2O32−,a Fe(III)-citrate, FeOOH	S0, N2Ob	2, 20, 21, 29, 31, 65
P. arsenaticum	2.1, 2,408, 55	Strict anaerobe	S0, S2O32−, As(V), Se(VI), Fe(III)-citrate, FeOOH	O2, NO3−, Se(IV)	21, 29
P. calidifontis	2.0, 2,200, 57	Facultative aerobe	O2, NO3−, As(V),d Fe(III)-citrate, FeOOH	NO2−,c S0, S2O32−, SO32−, SO42−	6, 21
P. islandicum	1.8, 2,062, 50	Strict anaerobe	S0, S2O32−, SO32−, l-cystine, oxidized glutathione, As(V),a Fe(III)-citrate, FeOOH	dl-Lanthionine, fumarate, (CH3)2SO2, S4O62−, SO42−	21, 28, 31
T. neutrophilus	1.8, 2,053, 60	Strict anaerobe	S0		22

^aWeak growth, final densities of ≤10⁷ cells/ml.

^bP. aerophilum reduced NO₃⁻ and NO₂⁻ to N₂ during growth (2, 65) and N₂O reductase activity has been demonstrated in P. aerophilum cells (16), but N₂O provided as the sole electron acceptor did not support growth (65).

^cP. calidifontis reduced NO₃⁻ to N₂ during growth, but NO₂⁻ as the sole electron acceptor did not support growth (6).

^dSee Results and Discussion.