Activated sludge for waste water remediation represents one of the most successful biotechnologies developed and contributes significantly to public health.  The communities are highly diverse, comprised of thousands of different species and must function together to achieve nutrient removal.  From an ecological perspective these communities represent sites of intense competition for resources essential for growth of the organisms present.  Improvements in waste water treatment systems include the removal of nitrogen and phosphorous, in addition to carbon, as well as the conversion of the loose, floccular biomass (suspended biofilms) into more dense, granules which settle faster than the flocs.  Despite more than 100 years of operation, there remains a great deal that is unknown about how these communities interact and such information could be used to manipulate the sludge community to more reproducibly control community structure (granulation) and function (nutrient removal). 

Here, we have investigated the role of N-acylated homoserine lactone based quorum sensing in mediating community behaviours over extended reactor operation.  We have quantitatively measured AHL concentrations using LC-MS/MS, quantitatively described the community composition by metacommunity sequencing, and combined the results with reactor performance data as well as data from isolates collected at various times.  The results show that AHLs are present and active in the reactor systems, although the concentrations are significantly below concentrations necessary to active laboratory based, single species systems.  We have also demonstrated clear correlations between signal production, granulation, nitrogen removal and community composition.  Add back experiments indicate that AHLs may be useful to drive granule formation.  We have further demonstrated a role for quorum quenching at the community level, which presumably plays an important role in the competition of the community members for resources.