The activated sludge system is a widely used wastewater treatment process, which relies on diverse bacterial communities to remove organic and inorganic nutrients. Excess proliferation of filamentous bacteria can cause operational problems which affect adversely the treatment process. Reliable control methods for filamentous bacteria, many of which are still uncultured, are not readily available. Although the major bacterial populations in activated sludge are well characterised, these studies did not extend to many Australian plants, where the expectation is that the raw influent and edaphic factors differ markedly from plants in other countries. Therefore, this study aimed to explore the filamentous bacterial communities in four Australian wastewater treatment plants of different plant configuration, using both culture-dependent, following cell micromanipulation, and culture independent methods, using Illumina ampicon sequencing of the community 16S rRNA genes.
Although a core microbiome was seen in all four treatment plants, population differences in the relative abundances and biodiversity of their filamentous bacteria were detected. Sequence data analysis predicted that each activated sludge sample contained approximately 10% filamentous bacteria, of which more than half belonged to the Chloroflexi. After micromanipulation, two filamentous bacteria were isolated from plants in Gold Coast in Queensland and Epping in Melbourne and grown on R2A agar. These were identified as a novel Acidovorax species and a Moraxella species respectively. The Acidovorax filaments, most closely related to Acidovorax temperans (98% similarity), appeared to fragment into elongated rods. The Moraxella sp. exhibited a morphology similar to the Eikelboom morphotype 1863 and is most closely related to Moraxella osloensis. Whole genome sequencing of these two filamentous bacteria are now being generated in the expectation that clues as to how they might be controlled will be revealed.