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 Desmodesmus. During operation, the algal community became a more diverse consortium
of Desmodesmus, Parachlorella, Characiopodium, and Bacillariophytina.
In the Prokaryotic community, there was an initial enrichment of the
PAO Candidatus Accumulibacter phosphatis (Accumulibacter)
Acc-SG2, and the dominant ammonia-oxidizing organism was Nitrosomonas
oligotropha; however, these populations decreased in relative
abundance, becoming dominated by Accumulibacter Acc-SG3 and Nitrosomonas ureae. Furthermore, functional guilds that
were not abundant initially became enriched including the putative Cyanobacterial PAOs Obscuribacterales and Leptolyngbya and the H2-oxidizing denitrifying
autotroph Sulfuritalea. After a month of operation,
the most-abundant prokaryote belonged to an uncharacterized clade
of Chlorobi classified as Chlorobiales;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.