TABLE 1.

Rex regulons in 11 species of clostridia^a

Operon and metabolism	Presence of gene in Clostridium species:											Functional role
	C. acetobutylicum ATCC 824	C. beijerinckii NCIMB 8052	C. botulinum ATCC 3502	C. butyricum 5521	C. kluyveri DSM 555	C. novyi NT	C. perfringens ATCC 13124	C. tetani E88	C. cellulovorans 743B	C. carboxidivorans P7	C. ljungdahlii DSM 13528
Fermentation
ldh	+*	−	+	−	−	−	+	−	0	0	0	l-Lactate dehydrogenase
pflBA	−	+*	−	−	−	−	−	0	+	0	0	Pyruvate formate-lyase
adhA	0	+*	+	+	−	+	−	+	−	+	+	Alcohol dehydrogenase [Fe]
adhE2	+*	−	+	+	−	0	+	+	+	+	−	Alcohol/acetaldehyde dehydrogenase
thlA	+*	+	+	+	−	+	+	+	−	−	0	Acetyl-CoA acetyltransferase
crt-bcd-etfBA-hbd	+*	+	+	+	+	+	+	+	+	−	0	Butyryl-CoA synthesis enzymes
ctfAB	−	−	−	0	0	+*	0	0	0	0	0	CoA-transferase
ptb-buk	+*	+	−	+	0	0	+	+	−	+	0	Phosphotransbutyrylase, butyrate kinase
butA	0	+*	+	+	0	−	0	0	0	−	−	2,3-Butanediol dehydrogenase
hydB	0	+*	−	−	0	+	−	+	0	−	−	Fe-hydrogenase
fld-Cbei_4318	−	+*	−	+	−	−	−	−	0	0	−	Flavodoxin, pyruvate flavodoxin/ferredoxin oxidoreductase
TCA cycle
frdA	0	0	0	0	0	0	0	+*	0	0	0	Fumarate reductase flavoprotein subunit
maeB	0	−	+*	+	0	0	0	0	0	−	−	Malic enzyme
NAD biosynthesis
nadABC	+*	−	−	−	−	−	−	0	−	−	−	NAD biosynthesis enzymes
Nitrate and sulfite reduction
narAB	0	0	0	+	0	0	+	0	0	+*	+	Nitrate reductase
narK	0	0	0	0	0	0	−	0	0	+*	+	Nitrate/nitrite transporter
asrABC	+*	−	−	−	0	−	−	−	−	+	+	Sulfite reductase
asrT	+*	−	−	0	0	0	−	−	−	+	0	Predicted sulfite/sulfate transporter
Wood-Ljungdahl pathway
codH-cooC-fhs-fchA-folD-metF-lpdA-cooC-acsDCEB	0	0	0	0	0	0	0	0	0	+*	+*	Wood-Ljungdahl pathway enzymes
Other
grdIH	0	0	0	0	0	0	0	0	0	+*	+	Betaine/glycine reductase
noxE	0	−	+	−	0	+	+*	+	0	0	0	NADH oxidase
bcd2-fldA-bcd-etfBA	0	0	0	0	0	0	0	0	0	0	+*	Acyl-CoA dehydrogenase, acyl-CoA transferase, flavoprotein

^aThe genes preceded by a conserved Rex-binding site are indicated by +, and the predicted Rex-binding sites verified by targeted experiments are marked by bold type and an asterisk. Genes without a candidate Rex-binding site are indicated by −. The absence of an orthologous gene(s) in the analyzed genomes is indicated by 0.