Microbial 'blueprint' may unlock mysteries of wastewater treatment
 UW-Madison environmental engineer and her graduate
student are among researchers on a multi-institutional team who have
mapped the metagenome of elusive phosphorous-eating organisms key to
thousands of wastewater treatment processes in the developed world.
A genomic blueprint of many organisms within the
bacterial species Accumulibacter phosphatis,
this metagenome will help researchers learn more about the underlying
microbiology of an environmentally friendly wastewater treatment process
known as enhanced biological phosphorous removal, or EBPR. Increased
biochemical understanding of the organism, which for decades scientists
have been unable to culture in the laboratory, may enable engineers
to optimize wastewater treatment systems.
The researchers published their findings in the Sept.
24 online early edition of the journal Nature Biotechnology.
Scientists’ current understanding of EBPR is
based only on empirical evidence, says Assistant Professor Katherine
McMahon, who is among the study’s co-authors. “From
an engineering perspective, we know how to make the bacteria remove
phosphorous from wastewater, but we don’t understand why or how
they do it,” she says.
On the surface, the organisms within the A.
phosphatis species look like average lake bacteria, yet their
physiology is bizarre, she says. Subjected to bi-phasic conditions in
a wastewater treatment plant, the organisms clean sewage by gorging
themselves on phosphorous, releasing it, gorging themselves on carbon,
extracting energy from it, and repeating the process over and over.
Using enriched sludge samples from laboratory-scale
bioreactors, seeded from wastewater treatment plants in Madison and
Brisbane, Australia, researchers at the Department of Energy Joint Genome
Institute in California spent a year and a half mapping the metagenome
of different Accumulibacter genera, species
and strains.
Among their findings, the researchers discovered
that A. phosphatis has a set of genes that
would enable it to live in fresh water. They learned the organism can
make a novel protein that helps it expel electrons—a finding that
may help them understand how A. phosphatis
captures energy from its food. They also uncovered clues, including
the organism’s ability to fix nitrogen and its dependence on cobalt,
that may point to ways researchers can culture A.
phosphatis in the lab.
Now the group is conducting follow-up experiments
using metaproteomics. A new technique not feasible without the metagenome
sequence, metaproteomics enables the researchers to study the protein
content of the entire sludge community. “We want to see, at the
level of protein expression, what happens if the organisms don’t
have enough food, for example,” says McMahon.
This lack of food can occur when storms overload
wastewater treatment plants, releasing phosphorous into the environment
and polluting lakes and rivers, she says.
In addition, the researchers are studying each gene
in the pathways responsible for phosphorous uptake and storage, as well
as how genes turn on or off based on an environmental stimulus like
oxygen or oxygen depletion. That knowledge is key,says McMahon, to designing
more efficient wastewater treatment processes. “Engineers have
control over the oxygen concentration or the amount of food the bacteria
are given, but we do not currently understand how these things impact
bacterial gene expression,” she says. “With understanding
on a biochemical level, engineers can optimize the process more rationally.”
Other co-authors of the research paper include scientists
from the Advanced Wastewater Management Group at the University of Queensland,
Australia.
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