Table 1.

Summary of distribution of major properties for organisms belonging to the phylum Chlorobi.

	I. album	“Ca. T. aerophilum”a	C. thalassium	Chlorobiaceae
Genome size (Mb)	3.66	3.18	3.29	1.97–3.13
Photosynthetic apparatus	No	Yes	Yes	Yes
Relationship with O2	Oxic and anoxic	Oxic	Anoxic	Anoxic
Reverse TCA cycle	Incompleteb	Incomplete	Yes	Yes
PFOR and KFORc	Yes	Yes	Yes	Yes
RNF complex	Yes	No	No	Some
Type-1 NADH dehydrogenase	Two copies (14 and 11 SU)d	Two copies (12 and 11 SU)d	Two copies (14 and 11 SU)d	One copy (11 SU)d
Complex III	ACIIIe	Both ACIIIe and Cyt b-Rieske	Cyt b-Rieske	Cyt b-Rieske
Terminal oxidases	Cyt caa3, cbb3, bd(1), bd(2)f	Cyt caa3	Cyt bd(2)	Cyt cbb3 and/or bd(1)
Flagella genes	Yes	No	No	No
Chemotaxis genes	Yes	Partial	Partial	No
Sulfide oxidation to polysulfide	Yes	No	Yes	Yes
Sulfur oxidation to sulfite	No	No	Nog	Mostg
Nitrogen fixation	No	No	Yes	Yes

^aInferences made from metagenome and metatranscriptome data (Liu et al., 2012). Additional genes could be present in the organism.

^bI. album lacks ATP citrate lyase to have a complete reverse TCA cycle. It is possible that (ATP-independent) citrate lyase enables an unconventional reverse TCA cycle under certain growth conditions.

^cPFOR, pyruvate:ferredoxin oxidoreductase; KFOR, 2-oxoglutarate:ferredoxin oxidoreductase

^dSU, subunits.

^eACIII, alternative complex III.

^fTwo different cytochrome bd-quinol oxidases exist among Chlorobi. See Figures 6 and 8B for details.

^gMost organisms belonging to the Chlorobiaceae have genes involved in oxidation of sulfide to sulfate, with a few exceptions (see Gregersen et al., 2011).