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PIMO
is closely linked to the LTER project. The LTER
research addresses how changing inorganic nutrient
supply and the quality and quantity of organic
matter interact to affect estuarine trophic
structure. The Microbial Observatory uses LTER data
to place microbial communities into the larger
context of their physical and chemical environment.
In turn, the LTER research gains detailed knowledge
about the microbial communities underlying the
processes and control parameters which it
investigates. In
the salt marsh sediments, nitrogen and sulfur
cycles influence all of the salt marsh
biogeochemical cycles while sulfate reduction
dominates decomposition. Therefore, the Observatory
Project focuses on the microbes involved with the
nitrogen and sulfur cycle with special attention to
nitrification and sulfate reduction. This focus is
possible because these P.I.s bring a suite of tools
for culturing, molecular detection, and
identification of nitrifying and sulfate reducing
bacteria. The
Microbial Observatory carries out the following
activities: Investigates
the seasonal changes in the community structure
with culture methods, denaturing gradient gel
electrophoresis (DGGE), and environmental clone
library sequencing of 16S rRNA genes. Links
functional genes and microbial populations
responsible for specific processes with rRNA
hybridization techniques. Correlates
the presence and activity of various populations
with ecological measurements of major processes
in the salt marsh. Molecular
surveys using functional genes and rRNA
hybridization techniques are correlated with LTER
measures of sulfate reduction and the nitrogen
cycle. Carbon sources are identified with
techniques using the d13C
of phospholipid fatty acids specific to
bacteria. Salt
marshes provide one of the best examples of a site
where microbes build and shape an entire ecosystem.
Cyanobacteria are the pioneer organisms in salt
marshes; they initiate microbial mat communities on
mudflats that prevent erosion, trap sediment
particles, and elevate the surface of the
sediments. When higher plants colonize the site,
the microbes fix nitrogen, recycle organic matter
and nutrients, oxidize sulfides, and provide food
for higher trophic levels. Salt
marshes continue to be important models for basic
microbiological and biogeochemical research. These
systems are easily accessible. Their high process
rates, large and diverse populations of
functionally distinct microbes, and steep chemical
and microbial gradients allow scientists to
understand how microbial interactions and chemical
cycles work. For example, many of our insights into
the process and microbiology of sulfate reduction
in the marine environment have come from the study
of salt marshes. The
value of salt marshes in teaching and education is
well established. Microbiology textbooks emphasize
microbial mats. Students of the Microbial Diversity
Course at the MBL in Woods Hole, associated with
this Microbial Observatory, use the salt marsh as a
"Microbial Rainforest" for the isolation and
identification of a wide diversity of microbes.
This course has introduced more than 600 students
to the discipline of microbial ecology.
The
Plum Island Estuary Microbial Observatory (PIMO),
located at the Plum Island Estuary LTER site in
coastal Massachusetts, identifies prokaryotes in
salt marsh sediments and plankton and determines
their role in controlling major ecosystem
processes.Identifies
the microbes and microbial communities by means
of culture and sequencing techniques.
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