Community Assembly and Ecology of Activated Sludge under Photosynthetic Feast–Famine Conditions

Here, we demonstrate that photosynthetic oxygen production under light–dark and feast–famine cycles with no mechanical aeration and negligible oxygen diffusion is able to maintain phosphorus cycling activity associated with the enrichment of polyphosphate accumulating organisms (PAOs). We investigate the ecology of this novel system by conducting a time series analysis of prokaryotic and eukaryotic biodiversity using the V3–V4 and V4 regions of the 16S and 18S rRNA gene sequences, respectively. In the Eukaryotic community, the initial dominant alga observed was <i>Desmodesmus</i>. During operation, the algal community became a more diverse consortium of <i>Desmodesmus</i>, <i>Parachlorella</i>, <i>Characiopodium</i>, and <i>Bacillariophytina</i>. In the Prokaryotic community, there was an initial enrichment of the PAO <i>Candidatus</i> Accumulibacter phosphatis (Accumulibacter) Acc-SG2, and the dominant ammonia-oxidizing organism was <i>Nitrosomonas oligotropha</i>; however, these populations decreased in relative abundance, becoming dominated by Accumulibacter Acc-SG3 and <i>Nitrosomonas ureae</i>. Furthermore, functional guilds that were not abundant initially became enriched including the putative <i>Cyanobacterial</i> PAOs <i>Obscuribacterales</i> and <i>Leptolyngbya</i> and the H<sub>2</sub>-oxidizing denitrifying autotroph <i>Sulfuritalea</i>. After a month of operation, the most-abundant prokaryote belonged to an uncharacterized clade of <i>Chlorobi</i> classified as <i>Chlorobiales</i>;SJA-28 Clade III, the first reported enrichment of this lineage. This experiment represents the first investigation into the ecological interactions and community assembly during photosynthetic feast–famine conditions. Our findings suggest that photosynthesis may provide sufficient oxygen to drive polyphosphate cycling.