Glycogen-accumulating organisms (GAOs) are common microorganism phenotypes observed in wastewater treatment processes. Through microscopy, traditional GAO phenotypes may be viewed as “grape-like” weakly Neisser-positive conglomerates.
Historically, it has been accepted that GAOs compete with Polyphosphate Accumulating Organisms (PAOs) for substrate in enhanced biological nutrient processes by storing glycogen under anaerobic conditions. Through advances in research, we are learning that the relationships between GAOs and PAOs may be far more complex than originally thought due to extensive genetic diversity within these phenotypes as well as other factors. As an example, the genus Ca Accumulibacter (57 currently recognized species in MIDAS database) is a PAO,
