QUANTIFICATION OF GORDONA-AMARAE STRAINS IN FOAMING ACTIVATED-SLUDGE AND ANAEROBIC DIGESTER SYSTEMS WITH OLIGONUCLEOTIDE HYBRIDIZATION PROBES

Previous studies have shown the predominance of mycolic acid-containin g filamentous actinomycetes (mycolata) in foam layers in activated slu dge systems, Gordona (formerly Nocardia) amarae often is considered th e major representative of this group in activated sludge foam. In this study, small-subunit rRNA genes of four G. amarae strains were sequen ced, and the resulting sequences were compared to the sequence of G. a marae type strain SE-6, Comparative sequence analysis showed that the five strains used represent two lines of evolutionary descent; group 1 consists of strains NM23 and ASAC1, and group 2 contains strains SE-6 , SE-102, and ASF3. The following three oligonucleotide probes were de signed: a species-specific probe for G. amarae, a probe specific for g roup 1, and a probe targeting group 2, The probes were characterized b y dissociation temperature and specificity studies, and the species-sp ecific probe was evaluated for use in fluorescent in situ hybridizatio ns. By using the group-specific probes, it was possible to place addit ional G, amarae isolates in their respective groups, The probes were u sed along with previously designed probes in membrane hybridizations t o determine the abundance of G, amarae, group 1, group 2, bacterial, m ycolata, and Gordona rRNAs in samples obtained from foaming activated sludge systems in California, Illinois, and Wisconsin. The target grou ps were present in significantly greater concentrations in activated s ludge foam than in mixed liquor and persisted in anaerobic digesters. Hybridization results indicated that the presence of certain G. amarae strains may be regional or treatment plant specific and that previous ly uncharacterized G, amarae strains may be present in some systems.