Methanobrevibacter filiformis sp. nov., a filamentous methanogen from termite hindguts

A morphologically distinct, filamentous methanogen was isolated from hindguts of the subterranean termite, Reticulitermes flavipes (Kollar) (Rhinotermitidae), wherein it was part of the microbiota colonizing the hindgut wall. Individual filaments of strain RFM-3 were 0.23-0.28 micrometers in diameter and usually > 50 micrometers in length and aggregated into flocs that were often greater than or equal to 0.1 mm in diameter. Optimal growth of strain RFM-3 was obtained at pH 7.0-7.2 and 30 degrees C with a yeast-extract-supplemented, dithiothreitol-reduced medium in which cells produced stoichiometric amounts of methane from H2 + CO2. The morphology and gram-positive staining reaction of strain RFM-3, as well as its resistance to cell lysis by various chemical agents and its restriction to H2 + CO2 as an energy source, suggested that it was a member of the Methanobacteriaceae. The nucleotide sequence of the SSU-rRNA-encoding gene of strain RFM-3 confirmed this affiliation and also supported its recognition as a new species of Methanobrevibacter, for which the epithet filiformis is herewith proposed. Although M. filiformis was one of the dominant methanogens in R. flavipes collected from Woods Hole (Mass., USA), cells of similar morphology were not consistently observed in R. flavipes collected from different geographical locations.