the potential for polyphosphate metabolism in archaea and anaerobic polyphosphate formation in methanosarcina mazei inorganic polyphosphate polyp is ubiquitous across all forms of life but the study of its metabolism has been mainly confined to bacteria and yeasts few reports detail the presence and accumulation of polyp in archaea and little information is available on its functions and regulation here we report that homologs of bacterial polyp metabolism proteins are present across the major taxa in the archaea suggesting that archaeal populations may have a greater contribution to global phosphorus cycling than has previously been recognised we also demonstrate that polyp accumulation can be induced under strictly anaerobic conditions in response to changes in phosphate pi availability ie pi starvation followed by incubation in pi replete media overplus in cells of the methanogenic archaeon methanosarcina mazei pistarved m mazei cells increased transcript abundance of the alkaline phosphatase phoa gene and of the highaffinity phosphate transport pstscabphou operon no increase in polyphosphate kinase 1 ppk1 transcript abundance was observed subsequent incubation of pistarved m mazei cells under pi replete conditions led to a 237 increase in intracellular polyphosphate content and a57fold increase in ppk1 gene transcripts ppk1 expression in m mazei thus appears not to be under classical phosphate starvation control