An examination of the mechanisms for stable foam formation in activated sludge systems.
Screening pure cultures of 65 mycolic acid producing bacteria (Mycolata) isolated mainly from activated sludge with a laboratory based foaming test revealed that not all foamed under the conditions used. However, for most, the data were generally consistent with the flotation theory as an explanation for foaming. Thus a stable foam required three components, air bubbles, surfactants and hydrophobic cells. With non-hydrophobic cells, an unstable foam was generated, and in the absence of surfactants, cells formed a greasy surface scum. Addition of surfactant converted a scumming population into one forming a stable foam. The ability to generate a foam depended on a threshold cell number, which varied between individual isolates and reduced markedly in the presence of surfactant. Consequently, the concept of a universal threshold applicable to all foaming Mycolata is not supported by these data. The role of surfactants in foaming is poorly understood, but evidence is presented for the first time that surfactin synthesised by Bacillus subtilis may be important.
Biotechnology Research Centre, La Trobe University, PO Box 199, Bendigo, Victoria 3552, Australia. s.petrovski@latrobe.edu.au
Steve
S
Petrovski
Zoe A
ZA
Dyson
Eben S
ES
Quill
Simon J
SJ
McIlroy
Daniel
D
Tillett
Robert J
RJ
Seviour
D039903:Actinobacteria / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D017404:In Situ Hybridization, Fluorescence; D008969:Molecular Sequence Data; D009171:Mycolic Acids / Q000378:metabolism*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012722:Sewage / Q000382:microbiology*; D013045:Species Specificity; D013501:Surface-Active Agents / Q000737:chemistry / Q000378:metabolism*
D009171:Mycolic Acids; D012336:RNA, Ribosomal, 16S; D012722:Sewage; D013501:Surface-Active Agents