Toward a Universal Switch for Microbial Granulation: Photogranule Insights to Advance Granular Wastewater Treatment
- 1Department of Civil and Environmental Engineering, University of Massachusetts, Amherst, Massachusetts 01003, United States
- 2Department of Biology, University of Colorado, Colorado Springs, Colorado 80918, United States
- 3Department of Microbiology, University of Massachusetts, Amherst, Massachusetts 01003, United States
Abstract
Microbial granulationthe assembly of self-immobilized, spheroidal aggregatesis a transformative approach for high-density, energy-efficient wastewater treatment. By concentrating biomass and enhancing resilience to influent fluctuations, granular systems significantly reduce infrastructure footprints. Current granular technologies primarily leverage upflow continuous reactors or sequencing-batch reactors, where specific external selection pressures are imposed to drive granulation. However, granulation remains neither spontaneous nor reliably predictable, and its fundamental biological drivers are poorly understood. Recent advances in photogranules challenge selection-pressure models. Photogranules form from activated-sludge inocula in hydrostatic and hydrodynamic batches and even in CSTRs where classical selection conditions are weak or absent. Moreover, the recurring emergence of compact spheroidal granules across diverse natural and laboratory systems suggests shared, intrinsic biological drivers rather than purely engineered causes. In this Perspective, we propose that the bacterial second messenger c-di-GMP functions as a conserved, Goldilocks-like molecular switch that integrates diverse environmental cues into a coordinated granulation program. We synthesize transcriptomic, biochemical, and genetic evidence and advance three hypotheses linking c-di-GMP signaling and community physiology to granulation. If validated, targeted modulation of c-di-GMPby genetic or chemical meanscould enable predictable, resilient granulation across a wider range of systems, including the continuous horizontal-flow basins that dominate wastewater infrastructure.
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BibTeX
@article{park2026toward,
title = {{Toward a Universal Switch for Microbial Granulation: Photogranule Insights to Advance Granular Wastewater Treatment}},
author = {Chul Park and Douglas D. Risser and Yasu S. Morita and Klaus Nüsslein and Joseph G. Gikonyo},
journal = {Environmental Science \& Technology},
year = {2026},
month = oct,
doi = {10.1021/acs.est.6c05495},
url = {https://doi.org/10.1021/acs.est.6c05495},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Toward a Universal Switch for Microbial Granulation: Photogranule Insights to Advance Granular Wastewater Treatment
AU - Chul Park
AU - Douglas D. Risser
AU - Yasu S. Morita
AU - Klaus Nüsslein
AU - Joseph G. Gikonyo
PY - 2026
DA - 2026/10/20
JO - Environmental Science & Technology
DO - 10.1021/acs.est.6c05495
UR - https://doi.org/10.1021/acs.est.6c05495
AB - Microbial granulationthe assembly of self-immobilized, spheroidal aggregatesis a transformative approach for high-density, energy-efficient wastewater treatment. By concentrating biomass and enhancing resilience to influent fluctuations, granular systems significantly reduce infrastructure footprints. Current granular technologies primarily leverage upflow continuous reactors or sequencing-batch reactors, where specific external selection pressures are imposed to drive granulation. However, granulation remains neither spontaneous nor reliably predictable, and its fundamental biological drivers are poorly understood. Recent advances in photogranules challenge selection-pressure models. Photogranules form from activated-sludge inocula in hydrostatic and hydrodynamic batches and even in CSTRs where classical selection conditions are weak or absent. Moreover, the recurring emergence of compact spheroidal granules across diverse natural and laboratory systems suggests shared, intrinsic biological drivers rather than purely engineered causes. In this Perspective, we propose that the bacterial second messenger c-di-GMP functions as a conserved, Goldilocks-like molecular switch that integrates diverse environmental cues into a coordinated granulation program. We synthesize transcriptomic, biochemical, and genetic evidence and advance three hypotheses linking c-di-GMP signaling and community physiology to granulation. If validated, targeted modulation of c-di-GMPby genetic or chemical meanscould enable predictable, resilient granulation across a wider range of systems, including the continuous horizontal-flow basins that dominate wastewater infrastructure.
SN - 0013-936X
SN - 1520-5851
ER -