Pseudo vitamin B12 or 5-hydroxybenzimidazolyl-cobamide are the corrinoids found in methanogenic bacteria

Thirteen species of methanogenic bacteria were analyzed for corrinoids. Pseudo vitamin B₁₂ (Co--(7-adenyl)]-cobamide) was the predominant cobamide of methanococcales and Methanoplanus. All other methanogens contained factor III (Co--(5-hydroxybenzimidazolyl)]-cobamide). Vitamin B₁₂ (Co--(5,6-dimethylbenzimidazolyl)]-cobamide) was not detected in any of these archaebacteria. Their cobamide content was 100 to 1400 nmol per gram cell dry weight, indicating that abundant cobamides are essential for methanogens.