Melainabacteria

Melainabacteria, or Candidatus Melainabacteria, is a phylum of bacteria. The name Melainabacteria is derived from the title of the 'Greek nymph of dark waters' and is a new phylum related to Cyanobacteria. It has been difficult to study by traditional 16S rRNA analysis or whole-genome sequencing because it has not been possible to isolate or culture its members. Organisms belonging to this phylum have been found in the human gut and various aquatic habitats such as groundwater. By analyzing genomes of Melainabacteria, predictions are possible about the cell structure and metabolic abilities. The bacterial cell is similar to cyanobacteria in being surrounding by two membranes. It differs from cyanobacteria in its ability to move by flagella (like gram-negative flagella), though some members (e.g. Gastranaerophilales) lack flagella. Melainabacteria are not able to perform photosynthesis, but obtain energy by fermentation (obligatory fermentation). The genomes of Melainabacteria organisms isolated from ground water indicate that the organism has the capacity to fix nitrogen.Melainabacteria lack linked electron transport chains but have multiple methods to generate a membrane potential which can then produce ATP via ATP synthase. They are able to use Fe hydrogenases for H2 production that can be consumed by other microorganisms. Melainabacteria from the human gut also synthesize several B and K vitamins, which suggests that these bacteria are beneficial to their host because they are consumed along with plant fibers.