Anammoxosomes of Anaerobic Ammonium-oxidizing Planctomycetes

Abstract

Anammoxosomes are unique metabolically significant compartments ofplanctomycetes performing the anammox process. These bacteria carryout Anaerobic Ammonium Oxidation, a chemolithotrophic and autotrophicmetabolism. They comprise Candidatus genera Brocadia , Kuenenia andScalindua , mostly from wastewater treatment bioreactors or marineanaerobic habitats and none of which are yet in pure culture. Likecells of other planctomycetes, anammox species possess a sharedplanctomycete cell plan involving a single-membrane-bounded pirellulosomecompartment containing a nucleoid as well as paryphoplasm surroundingthe outer rim of the cell. Within the pirellulosome they possessanother compartment, the anammoxosome, unique to anammox planctomycetes.The anammoxosome harbours an enzyme, hydrazine oxidoreductase, importantfor models of anammox. The anammoxosome is wrapped in an envelopepossessing cyclobutane-containing ladderane lipids which may conferimpermeability to anammoxosome membranes. The ladderanes occur inboth ether-linked and ester-linked forms. This envelope may havespecialized functions, for example, protection from toxic intermediatesof anammox metabolism and proton gradient formation for bioenergetics.The anammoxosome is important for models of anaerobic ammonium oxidation.It has other unusual features related to cell biology, since withinthe anammoxosome tubules occur which may form distinct arrangementssuggesting a cytoskeletal function, and the nucleoid is often incontact with the anammoxosome envelope.