TABLE 1.
Number of genomes that encode MerA or MerB protein homologs and their distribution at the Phylum level in the database constructed in 2012 (Boyd and Barkay, 2012) and here in 2020.
| Number of genomes encoding MerA homologs | Number of genomes encoding MerB homologs* | |||
| Phylum/Class | 2020 | 2012 | 2020 | 2012 |
| Archaea | 271 | 24 | 11 | − |
| Candidatus Bathyarchaeota | 1 | − | − | − |
| Candidatus Diapherotrites | 1 | − | − | − |
| Candidatus Geoarchaeota | 4 | − | − | − |
| Candidatus Geothermarchaeota | 2 | − | − | − |
| Candidatus Heimdallarchaeota | 1 | − | 3 | − |
| Candidatus Micrarchaeota | 22 | − | − | − |
| Candidatus Odinarchaeota | 1 | − | − | − |
| Candidatus Parvarchaeota | 10 | − | − | − |
| Crenarchaeota | 139 | 15 | − | − |
| Euryarchaeota | 65 | 9 | 8 | − |
| Nanoarchaeota | 1 | − | − | − |
| Thaumarchaeota | 10 | − | − | − |
| unclassified | 14 | − | − | − |
| Bacteria | 6274 | 253 | 1778 | 40 |
| Acidobacteria | 7 | − | − | − |
| Actinobacteria | 958 | 36 | 468 | 13 |
| Aquificae | 7 | 3 | − | − |
| Armatimonadetes | 1 | − | − | − |
| Bacteroidetes | 131 | 5 | 3 | 4 |
| Balneolaeota | 4 | − | − | − |
| Candidate division GAL15 | 1 | − | − | − |
| Candidate division NC10 | − | − | 1 | − |
| Candidate division Zixibacteria | − | − | 1 | − |
| Candidatus Atribacteria | 1 | − | − | − |
| Candidatus Azambacteria | 1 | − | − | − |
| Candidatus Bipolaricaulota | 1 | − | − | − |
| Candidatus Blackburnbacteria | 1 | − | − | − |
| Candidatus Daviesbacteria | 7 | − | − | − |
| Candidatus Giovannonibacteria | 10 | − | − | − |
| Candidatus Gottesmanbacteria | 1 | − | − | − |
| Candidatus Kaiserbacteria | 1 | − | − | − |
| Candidatus Kryptonia | 1 | − | − | − |
| Candidatus Microgenomates | 2 | − | − | − |
| Candidatus Pacebacteria | 1 | − | − | − |
| Candidatus Parcubacteria | 2 | − | − | − |
| Candidatus Peregrinibacteria | 5 | − | − | − |
| Candidatus Roizmanbacteria | 2 | − | − | − |
| Candidatus Rokubacteria | 2 | − | 1 | − |
| Candidatus Sumerlaeota | 1 | − | − | − |
| Chlamydiae | 1 | − | 1 | − |
| Chloroflexi | 32 | 1 | 7 | − |
| Cyanobacteria | 1 | − | − | − |
| Deferribacteres | 2 | − | − | − |
| Deinococcus-Thermus | 14 | 2 | 2 | − |
| Firmicutes | 960 | 42 | 797 | 5 |
| Fusobacteria | − | − | 1 | − |
| Gemmatimonadetes | − | − | 1 | − |
| Ignavibacteriae | 15 | − | − | − |
| Nitrospirae | 18 | 1 | 6 | − |
| Planctomycetes | 1 | − | − | − |
| Proteobacteria | 4050 | 161 | 478 | 18 |
| Alphaproteobacteria | 668 | 25 | 84 | 3 |
| Betaproteobacteria | 412 | 24 | 72 | 2 |
| Gammaproteobacteria | 2869 | 104 | 298 | 13 |
| Deltaproteobacteria | 37 | 8 | 10 | − |
| Epsilonproteobacteria | 1 | − | − | − |
| Zetaproteobacteria | 27 | − | 4 | − |
| Acidithiobacillia | 25 | − | 6 | − |
| Hydrogenophilalia | 2 | − | 1 | − |
| Oligoflexia | 6 | − | 2 | − |
| Candidatus Muproteobacteria | 1 | − | − | − |
| Unclassified | 2 | − | 1 | − |
| Rhodothermaeota | 1 | − | − | − |
| Spirochaetes | 3 | − | 5 | − |
| Synergistetes | − | − | 3 | − |
| Tenericutes | 11 | 1 | − | − |
| Verrucomicrobia | 7 | 1 | − | − |
| unclassified | 10 | − | 3 | − |
| Plasmid:Bacteria | 29 | − | 6 | − |
| Alphaproteobacteria | 1 | − | 1 | − |
| Betaproteobacteria | 1 | − | − | |
| Gammaproteobacteria | 25 | − | 4 | − |
| Unclassified Proteobacteria | 2 | − | 1 | − |
| Ynclassified | − | 3 | − | 3 |
*In 2012 surveys, MerB was only noted when linked to a MerA that were identified by homology searches of the IMG database. In 2020, independent searches for MerB were performed. In the case of Proteobacteria and plasmids, taxonomic assignment at the class level is also shown.