Formation of stable foam by the cells and culture supernatant of Gordonia (Nocardia) amarae

Gordonia amarae is the cause of foaming activated sludge. In this study, th e mechanism of foam formation by G. amarae SC1 was investigated. A liquid c ulture of SCI cells generated a stable foam when shaken reciprocally. This foam formation was dependent on the presence of both bacterial cells and cu lture supernatant. A high-molecular-weight fraction (Mw>10000) of the super natant was capable of emulsifying n-hexadecane in addition to exhibiting fo aming activity, indicating that it contains a surface-active substance(s). The bacterial cells showed a high affinity to hexadecane. This hydrophobic cell surface property might be involved in the attachment of cells to air b ubbles to generate a stable foam. The results demonstrated the participatio n of cells and the extracellular biosurfactant in the formation and stabili zation of foam in G. amarae SCI culture.