BOX 2-3Community Robustness: The Case of Sludge

The removal of phosphorus from wastewater by microbes by a process known as enhanced biological phosphorus removal (EBPR) depends upon the stability and robustness of the microbial community responsible for phosphorus accumulation (Levantesi et al. 2002; Garcia Martin et al. 2006). A single organism, Candidatus Accumulibacter phosphatis, supplies all the required biochemical functions to remove phosphorus in many systems. However, although A. phosphatis can be enriched to high numbers in laboratory scale bioreactors, the organisms remain recalcitrant to growth in pure culture, and this suggests a role for additional community members in their maintenance.

Although EBPR is generally stable and was first used in full-scale waste-water treatment facilities over thirty years ago, these facilities must continue to maintain backup chemical phosphorus-removal systems to respond to periodic crashes of the biological systems. The cause of crashes is not well understood, but they are hypothesized to result from particular biological and environmental perturbations that destabilize the phosphorus-accumulating microbial community. In laboratory-scale reactors that mimic the wastewater treatment plant cycling, small perturbations in pH and the type of carbon supplied can stimulate the growth of competitors of the phosphorus accumulators and result in less efficient or completely abolished phosphorus removal. In addition, homogeneity of the population of A. phosphatis may leave the community vulnerable to infection by bacteriophage. Greater understanding of the interactions sustaining the EBPR microbial community will lead to more reliable phosphorus-removal systems.

From: 2, A New Light on Biology

Cover of The New Science of Metagenomics
The New Science of Metagenomics: Revealing the Secrets of Our Microbial Planet.
National Research Council (US) Committee on Metagenomics: Challenges and Functional Applications.
Washington (DC): National Academies Press (US); 2007.
Copyright © 2007, National Academy of Sciences.

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