Table 6
Occurrence of B12 biosynthetic pathways and B12-dependent enzymes in archaea
| Phylum | Total organisms | B12-utilizing organisms | B12 biosynthesis pathway | B12-dependent isomerase | B12-dependent methyltransferase | |||
| MCM/MeaA/ICM* | GM | RNR II | Other MTs | MtrA | ||||
| Nanoarchaeota | 1 | - | - | - | - | - | - | - |
| Crenarchaeota/Thermoproteales | 6 | 6 | 2 | - | - | 5 | 1 | - |
| Crenarchaeota/Desulfurococcales | 4 | 3 | - | 1 | - | 2 | 1 | - |
| Crenarchaeota/Sulfolobales | 4 | 4 | 4 | 4 | - | 4 | - | - |
| Euryarchaeota/Thermoplasmales | 4 | 4 | 4 | 4 | - | 4 | - | - |
| Euryarchaeota/Archaeoglobales | 1 | 1 | 1 | 1 | - | 1 | 1 | - |
| Euryarchaeota/Halobacteriales | 5 | 5 | 5 | 5 | 2 | 5 | - | - |
| Euryarchaeota/Methanosarcinales | 5 | 5 | 5 | - | - | 4 | 4 | 5 |
| Euryarchaeota/Thermococcales | 4 | 4 | - | 4 | - | 4 | - | - |
| Euryarchaeota/Methanococcales | 5 | 5 | 5 | - | - | - | 3 | 5 |
| Euryarchaeota/Methanopyrales | 1 | 1 | 1 | - | - | - | - | 1 |
| Euryarchaeota/Methanobacteriales | 3 | 3 | 3 | - | - | 1 | 3 | 3 |
| Euryarchaeota/Methanomicrobiales | 4 | 4 | 4 | - | - | 3 | 2 | 4 |
| Total | 47 | 45 | 34 | 19 | 2 | 33 | 15 | 18 |
*: MCM, methylmalonyl-CoA mutase; ICM, isobutyryl-CoA mutase; MeaA, a B12-dependent mutase with sequence similarity to MCM and ICM. There three subfamilies are quite similar and combined as one group in this study. GM, glutamate mutase; RNR II, B12-dependent ribonucleotide reductase; Other MTs, various B12-dependent methyltransferases such as Mta, Mtm, Mtb, Mtt, Mts, Mtv and Mtr systems.