The phylogeny, ecology and ecophysiology of the glycogen accumulating organism (GAO) Defluviicoccus in wastewater treatment plants

•This comprehensive review examines critically.•what is known about the ecophysiology of the glycogen accumulating organism Defluviicoccus.•which factors affect its relative abundance in EBPR wastewater treatment plants.•its interactions with other functionally important members of plant communities.•problems arising from incomplete phylogenetic identification of its populations.•which areas of research are needed to address current gaps in our knowledge.