Phylum Planctomycetes

Phylum Planctomycetes

This very ancient group of bacteria has a number of unusual properties, including cell division by budding, the lack of any peptidoglycan in their cell walls and the presence of a degree of internal compartmentalisation. (Recall that membrane-bound compartments are regarded as a quintessentially eucaryotic feature.)

The recently discovered reaction known as anammox (anaerobic ammonium oxida-tion), whereby ammonium and nitrite are converted to nitrogen gas:

NH₄⁺+ NO₂^−= N₂+ 2H₂O

has been attributed to certain members of the Planctomycetes. It is thought that this reaction may be responsible for much of the nitrogen cycling in the world’s oceans. The bacteria concerned have only been identified by means of their rRNA gene sequences, and have as yet been assigned only provisional generic and specific names. They are anaerobic chemolithoautotrophs, however this is not typical of the Planctomycetes, most of which are aerobic chemoorganoheterotrophs.

Recent studies propose that the Planctomycetes should be placed much closer to the root of any proposed phylogenetic tree than had previously been proposed.

Representative genera: Planctomyces, Pirellula