Methanobacteriaceae

Abstract: The methanogenic bacteria are unique among pro-karyotes because they produce a hydrocarbon, methane, as a major product of anaerobic metabolism. This physiological property was proposed in 1956 by H. A. Barker as the main taxonomic characteristic of a morphologically diverse group of bacteria which he termed the Methanobacteriaceae. The taxonomy of this physiological family has been obfuscated by the difficulty of obtaining members in pure culture. Consequently, various species were named on the basis of the types of substrates converted to methane by “purified” (i.e., enrichment) cultures containing a predominant morphological type suspected of methanogenesis. Only three species, Methanobacterium formicicum, Methano-coccus vannielii, and Methanosarcina barkeri, were isolated in axenic culture by the time of Barker’s review of these organisms (Barker, 1956).

Abstract: Five pure cultures of methanogenic bacteria were isolated from Minnesota peatlands by enrichment culture techniques. One strain, identified as a member of the family Methanobacteriaceae by antigenic fingerprinting, was acid tolerant and able to produce methane at pH 3.1. Growth could not be demonstrated at pH less than 5.3.

Abstract: Members of the order Methanobacteriales are distinguished from other methanogens by their limited range of catabolic substrates, their morphology, lipid composition, and rDNA sequence. The Methanobacteriales are generally hydrogenotrophic, using H2 to reduce CO2 to CH4. Some members of this order can use formate, CO, or secondary alcohols as electron donors for CO2 reduction. However, members of one genus within this order, Methanosphaera, use H2 to reduce methanol to methane. The predominant cell wall polymer of Methanobacteriales is pseudomurein, which distinguishes this order from the Methanomicrobiales. Lipids composing the cell membranes include caldarchaeol and myo-inositol. Cells usually stain Gram positive and are generally rod-shaped, often forming chains or long filaments up to 40 μm in length. The order Methanobacteriales is divided into two families, the Methanobacteriaceae and Methanothermaceae, on the basis of phylogenetic analysis of 16S rRNA gene sequences as well as phenotypic characteristics (Boone, 2001).