'Morphological shifts' in filamentous bacteria isolated from activated sludge processes

This study aimed at isolating filamentous bacteria from full-scale activated sludge processes and studying them in pure culture. Three cultures were isolated using conventional microbiological techniques. The isolates were positively identified as Gordonia amarae, Thiothrix nivea and Type 1863/Acinetobacter spp., using fluorescent in situ hybridization (FISH) with 16S rRNA-targeted oligonucleotide probes. However, a 'morphological shift' from filamentous to single-cell form was observed in pure culture. The application of fluorescent in situ hybridization (FISH) showed filamentous bacteria to be much more diverse in their ability to adapt to their changing enviroments. Pure culture studies of filamentous bacteria form the basis for application in full-scale activated sludge plants. It therefore remains important that the taxonomic status of filamentous bacteria be determined.