TABLE 1.

Comparison of metabolic features predicted in thiotrophic symbiont genomes^a

Feature	Host habitat and organism
	Hydrothermal vents and seeps			Shallow water sediment interstitial
	Bathy symbiont	Ruthia	Endoriftia	Thiodiazotropha	Solemya symbiont	Thiosymbion	Kentron
Autotrophy
CBB cycle (RuBisCO, phosphoribulokinase)	+	+	+	+	+	+
PPi-phosphofructokinase	+	+	+	+	+	+	+
rTCA (citrate cleavage)			+
Diazotrophy, nitrogenase				+		(+)
TCA cycle
Oxidative TCA			+	+	+	+	+
Kor and Frd (reductive TCA)			+	+		+	+
Glyoxylate shunt				+	+	+
Central metabolism
Pyruvate phosphate dikinase			+	+	+	+	+
PEP synthase			+	+	+	+
Pyruvate synthase (PFOR)			+	+	+	+	+
Pyruvate carboxylase				+		+
PEP carboxylase				+	+
PEP carboxykinase (GTP)				+		+	+
Malic enzyme	+	+	+	+	+	+	(+)
C5 reactions of p3HPB						+	+
Energy
Rnf transporter	+	+	+	+	+	+	+
V-type ATPase			+	+	+
Cyt c oxidase cbb3 type	+	+	+	+	+	+	+
Cyt c oxidase aa3 type	+	+		+	+	+
Storage compounds
Glycogen			+	+	+	+	+
Polyhydroxyalkanoates				+	+	+	+
Polyphosphate synthesis				+	+	+	+

^aSymbols: +, present; (+), not in all genomes. Abbreviations: Bathy, Bathymodiolus; CBB, Calvin-Benson-Bassham cycle; Cyt c, cytochrome c; Frd, fumarate reductase; Kor, 2-oxoglutarate:ferredoxin oxidoreductase; PEP, phosphoenolpyruvate; PP_i, pyrophosphate; rTCA, reverse TCA cycle.