Table 2. Discriminatory criteria to evaluate which alphaproteobacteria may be close to protomitochondria.

Taxa were selected from those that presented with cumulative scores of aerobic traits above 20, thus overlapping the distribution values of aerobic mitochondria (Fig. 2), both types of cardiolipin synthase (Fig. 3E) and a collinearity bloc of ribosomal proteins (RP) encoded in the mtDNA of Jakobida (15). “Yes” indicates that a taxon has passed the discriminatory criterion indicated in a given column. Taxa are listed at the genus level when other species of the same genus passed equivalent criteria. Rhodothalas. MAG indicates Rhodothalassiaceae bacterium KatS3mg119 (75), an early-branching Iodidimonadales.

Alphaproteobacteria taxon	Both Cls types	RP synteny*	NO INDELS†	SPT & KynU	≥3 anaerobic traits	Top hits MPPbeta	M16B-ISP synteny
Tistrella		Yes	Yes
Elioraea rosea	Yes	Yes
Nitrospirillum amazon.				Yes	Yes
Caenispirillum	Yes	Yes			Yes
Rhodospirillaceae SP28	Yes		Yes			Yes
80m_m2_115 new clade		Yes			Yes
Oceanibacterium			Yes	Yes		Yes
oxycline co234_bin8		Yes	Yes		Yes	Yes
Alpha J067‡	Yes				Yes
Rhodothalas. MAG§	Yes	Yes	Yes	Yes			Yes
Alpha J134‡	Yes		Yes			Yes	Yes
Iodidimonas muriae	Yes	Yes	Yes	Yes	Yes		Yes
Kordiimonas pumila		Yes		Yes	Yes
Odyssella sp.§	Yes			Yes	Yes
Camelimonas	Yes	Yes	Yes
Tepidicaulis marinus	Yes	Yes
Hansschlegelia quercus	Yes	Yes
Microvirga arabica	Yes		Yes
Methylocella	Yes		Yes
Aestuariivirga litoralis	Yes			Yes

*Major collinearity bloc of RP proteins and RNA polymerase shared with Jakobida mtDNA (15).

†No conserved INDELs in COX3 and ISP as in mitochondrial homologs (11).

‡MAG largely incomplete, even after reassembling (see Materials and Methods).

§Taxa with cumulative aerobic traits below the second quartile of mitochondria.