Genome-Resolved Metatranscriptomics Provide Insights on Immigration Influence in Structuring Microbial Community Assembly of a Full-Scale Aerobic Granular Sludge Plant

Understanding the relative influence of immigration and
species
sorting in wastewater treatment systems is essential, as bacteria
in influent wastewater can significantly impact treatment system functionality.
This study investigated the contribution of immigration to the community
assembly of different-sized microbial aggregates in a full-scale aerobic
granular sludge (AGS) system using genome-resolved metatranscriptomics.
Our novel analysis revealed that negative-net-growth-rate populations,
which persist due to immigration, can exhibit substantial activity
and potentially contribute to the AGS system’s functionality.
The results also highlighted that sulfate-reducing and fermenting
bacteria, along with some nitrifiers and glycogen-accumulating organisms
(GAOs), were more active in the influent wastewater, serving as a
continuous source of both beneficial and competing immigrants to the
AGS system. Granular sludge (size >0.2 mm) demonstrated a robust
capacity
to resist immigration effects from competing immigrants, whereas flocculent
sludge (size <0.2 mm) was more susceptible. Importantly, flocculent
sludge harbored functional microbial groups such as active nitrifiers
and fermentative polyphosphate-accumulating organisms (PAOs) belonging
to Ca. Phosphoribacter, while granular
sludge enriched for active conventional PAOs such as Ca. Accumulibacter. These findings provide valuable
insights for engineers to design and operate AGS systems by optimizing
microbial aggregate sizes and emphasizing the importance of influent
microbial characterization in the design of wastewater treatment plants
to enhance the functionality and activity of AGS systems.