Bug of the Month: Filament Type 0581, an Uncommonly Observed Bacterium

One of the most challenging filament types to diagnose is Eickelboom filament type 0581. It’s a curved or coiled shaped filament located inside the flocs with 0.5-0.8 µm diameter, no visible septa (cross-walls), and Gram negative staining characteristics. Based upon personal experience as well as discussions with colleagues, type 0581 appears to be one of the least common filament types observed in activated sludge processes. Type 0581 is recognized as an organic acid filament type, however due to its rarity, there are likely other factors involved with its growth. From a taxonomic perspective, type 0581 filament types are most generally believed