An interesting set of microorganisms is the group (or supergroup) of anaerobic methanotrophic archaea (ANME), which are described in the glossary of the book Echoes of Life  as follows:
These microorganisms participate in the anaerobic oxidation of methane and incorporate carbon from the methane. At least three phylogenetically distinct groups of ANME have been identified; these appear to be related to several genera of methanogens. ANME are often found living in close association with sulfate-reducing bacteria, sometimes in consortia where methane is oxidized and sulfate reduced.The first discovered “ANME species” was ANME 1—a name that doesn't show much resemblance to the typical binomial nomenclature used within the Linnaean system of taxonomy. With phylogenetics, the concept of a microbe species is loosing sharpness. ANME 1 was discovered and named by microbiologist Ed DeLong and his colleagues at the Monterey Bay Aquarium Research Institute in California, where they studied ribosomal RNA sequences of methanogens found in marine environments and sediments.
Keywords: microbes, taxonomy, phylogenetics
 Susan M. Gaines, Geoffrey Eglington, and Jürgen Rullkötter: Echoes of Life • What Fossil Molecules Reveal about Earth History. Oxford University Press, New York, 2009; see, for example, pages 201-204 and glossary.