Andrew E. Cook

Granule formation mechanisms within an aerobic wastewater system for phosphorus removal

ABSTRACT Granular sludge is a novel alternative for the treatment of wastewater and offers numerous operational and economic advantages over conventional floccular-sludge systems. The majority of research on granular sludge has focused on optimization of engineering aspects relating to reactor operation with little emphasis on the fundamental microbiology. In this study, we hypothesize two novel mechanisms for granule formation as observed in three laboratory scale sequencing batch reactors operating for biological phosphorus removal and treating two different types of wastewater. During the initial stages of granulation, two distinct granule types (white and yellow) were distinguished within the mixed microbial population. White granules appeared as compact, smooth, dense aggregates dominated by 97.5% “Candidatus Accumulibacter phosphatis,” and yellow granules appeared as loose, rough, irregular aggregates with a mixed microbial population of 12.3% “Candidatus Accumulibacter phosphatis” and 57.9% “Candidatus Competibacter phosphatis,” among other bacteria. Microscopy showed white granules as homogeneous microbial aggregates and yellow granules as segregated, microcolony-like aggregates, with phylogenetic analysis suggesting that the granule types are likely not a result of strain-associated differences. The microbial community composition and arrangement suggest different formation mechanisms occur for each granule type. White granules are hypothesized to form by outgrowth from a single microcolony into a granule dominated by one bacterial type, while yellow granules are hypothesized to form via multiple microcolony aggregation into a microcolony-segregated granule with a mixed microbial population. Further understanding and application of these mechanisms and the associated microbial ecology may provide conceptual information benefiting start-up procedures for full-scale granular-sludge reactors.

Evidence of compositional differences between the extracellular and intracellular DNA of a granular sludge biofilm

Aims:  Extracellular polymeric substances (EPS) are an important component of microbial biofilms, and it is becoming increasingly apparent that extracellular DNA (eDNA) has a functional role in EPS. This study characterizes the eDNA extracted from the novel activated sludge biofilm process of aerobic granules.

Nocardia rhamnosiphila sp. nov., isolated from soil.

In this study two actinomycete strains were isolated in Cape Town (South Africa), one from a compost heap (strain 202GMO(T)) and the other from within the fynbos-rich area surrounded by the horseracing track at Kenilworth Racecourse (strain C2). Based on 16S rRNA gene sequence BLAST analysis, the strains were identified as members of the genus Nocardia. Phylogenetic analysis showed that the strains clustered together and are most closely related to Nocardia flavorosea NRRL B-16176(T), Nocardia testacea JCM 12235(T), Nocardia sienata IFM 10088(T) and Nocardia carnea DSM 43397(T). This association was also supported by gyrB based phylogenetic analysis. The results of DNA-DNA hybridization and physiological tests allowed genotypic and phenotypic differentiation of both strains 202GMO(T) and C2 from related species. However, their high DNA relatedness showed that they belong to the same species. Strain 202GMO(T) was selected as the type strain to represent this novel species, for which the name Nocardia rhamnosiphila is proposed (=DSM 45147(T)=NRRL B-24637(T)).