The significance and future potential of using Microbes for assessing ecosystem health: The Great Lakes example

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The significance and future potential of using
Microbes for assessing ecosystem health The
Great Lakes example
Lightmicroscopy of Chlamydomonas sp.
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• Historically, chemistry and general limnology
  have been the major focus of research in the
  Great Lakes, with little emphasis given to their
  biota and their ecology. (Vollenweider quote)
• becoming increasingly apparent that it is
  essential to undertake such ecosystemic,
  integrated and holistic assessments of the food
  web structure and its various components from
  bacteria to fish.

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Phytoplankton bloom around Shetland Isles
Courtesy of Earth Observatory
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focus on the abundance, role and significance of
the Great Lakes microbes and their potential role
in assessing health of large ecosystems.
Planktonic terminology microplankton, 20-200
microns dia. nanoplankton, 2-20
microns picoplankton, 0.2-2 microns
Thalassionema (or Thalassiothrix?) Courtesy of
Bigelow Lab.
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Phytoplankton analyses have been carried out
since the end of the last century (1900)
Fisheries and Oceans Canada embarked on
extensive lakewide surveys since 1969. Size
fractionation techniques, pioneered by author
enabled classification by size. Epifluorescence
microscopy
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Above UV light, individual bacteria and
flagellates visible by DAPI-induced blue
fluorescence. Below blue light , Yellow and
smaller red fluorescing picoplankton cells
visible. Only the autofluorescence of the natural
photosynthetic pigments can be seen. The large,
very bright cell is a dinoflagellate, about 20µm).
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Extensive studies on Great Lakes in late summer
1988 and 1989. Average bacterial abundance
0.7 to 2.2 million per ml. In contaminated
waters 0.7 to 1.2 million per ml. At end of
municipal waste disposal pipe 3.4 million per
ml. Positive relationship found between trophic
status and microbial biomass
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Autotrophic picoplankton (APP), heterotrophic
nanoflagellate (HNF) and bacterial cell numbers
were low in the oligotrophic areas, North
Channel, Georgian Bay and main Lake Huron and
considerably higher in the meso-eutrophic to
eutrophic lakes Michigan, Erie and Ontario. HNF
of unknown importance, abundance 400 to 3000
cells per ml.
Choanoflagellates Courtesy of Bigelow Lab.
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Population dynamics are poorly researched at time
of writing. Ciliates are, however considered the
top predators in the microbial loop
Two hypotrich ciliates Euplotes (left) and
Stylonychia (right)
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Feeding of ciliates has great impact on food web
structure. They provide a link to the larger
crustacean zooplankton, transferring the
microbial production to higher trophic levels. An
earlier survey found abundance to be between 2
and 10 cells per ml, with 28 cells per ml in
contaminated areas. So, what is the impact of
nutrient enrichment and other stresses?
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Bioassays were carried out in the lab, after
developing rapid collection and concentration
techniques. Metals were tested and the level
considered safe for the biota caused
overwhelming inhibition of carbon assimilation.
Research also included monitoring the
components of the food web at various levels to
evaluate impact on structure and function and to
test the usefulness of microbes as early warning
systems
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Great Lakes Areas of Concern 43 areas that
needed immediate attention were identified and
measures implemented for their decontamination. Da
ta collected as part of this program compared
picoplankton in contaminated and relatively clean
areas. ANOVA tests showed that APP were
significantly lower in comtaminated areas but
there was no SSD where the bacteria and HNF were
concerned. This indicates APP sensitivity to
stress
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Microbial community appears to have potential as
an early warning and rapid bioassessment tool.
Application also in sediment assays. Assay of
contaminated sediment from Toledo Harbour
suggested that the toxicty resulting in a
reduction of picoplankton might have been caused
by dissolved forms of zinc and manganese
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Cytology. Picoplankton being discovered and
named. Use of transmission electron microscopy
proves two principal groups, eukaryotes and
prokaryotes. TEM is invaluable for
identification of both healthy and unhealthy
cells thus providing a measure of health status.
TEM can be used where cells are too small for
epiflourescence microscopy.
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Freshwater Autotrophic Picoplankton Review C.
Callieri and J.G. Stockner Journal of Limnology
2002
Courtesy of Liverpool University, UK
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Picoplankton Autotrophic Heterotrophic Prokar
yote Eukaryote Also size classification Micro
20 - 200 µm Nano 2 - 64
µm Ultranano lt2 µm Ultra
lt5 µm Pico 0.2 - 2
µm Femto 0.02 - 0.2 µm
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1911 Lohmann called small plankton
nanoplankton. 1955 Rodhe described µ-algae
in Swedish Lakes. Algae in this size range also
known as LRGT (little round green things). 1956
Experiment showed much
photosynthesis
achieved by organisms lt64µm 1970s and
1980s Epifluorescence microscopy Flow
citometry Electron microscopy Immunofluorescence
techniques Chromatographic techniques
Photo by Peter Parks. Courtesy of Image Quest.
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Study Methods Preservation of
samples Fixing Counting Size fractionation Time
element Genetic differentiation Calculations
A member of the Bacillariophyceae
Courtesy of Clemson University
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For Elise and Lord Kelvin Calculation of primary
productivity at each depth
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Species composition and diversity Still working
on it! So far, three genera of single-cell
picocyanobacteria, more colonial and very little
knowledge of any crossovers. Most common
eukaryotic APP is Chlorella (LRGT). Due to the
size classification this can include many that
could be nanoplankton
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Ecology Found in a variety of freshwater
systems, including ultra-oligotrophic lakes like
Lake Baikal, high altitude, polar and subpolar
lakes, and shallow eutrophic lakes or ponds.
There is a pronounced difference in APP species
composition along trophic gradients and
seasonally within a lake. Single-cell
picocyanobacteria are very abundant in oligo- to
mesotrophic lakes, while colonial forms occur
mostly in meso- to eutrophic lakes or ponds.
Merismopedia tenuissima, a colonial
cyanobacteria. Courtesy of Maryland Dept. of
Natural Resources
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Eukaryotic APP generally an order of magnitude
less than picocyanobacteria. In temperate
regions, tend to show peak abundance in spring or
early summer during isothermal conditions of 5-10
C. Eukaryotic cells dominate APP in acidic
dystrophic and eutrophic lakes. Apparently,
picoeukaryotes progressively replace
picoprokaryotes in lakes with increasing nutrient
concentrations and decreasing pH and they tend to
be more abundant in the epilimnion in August and
September, during periods of nutrient limitation.
Depth profile of chlorophyll Courtesy of URI.
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In Lago Maggiore the pico size fraction account
for 35 of total plankton carbon annually. In
many other water bodies the importance of pico
fraction has been highlighted by indirect
estimates. Thus, an UV-B inhibition of pico-
plankton activities would likely affect the whole
organic carbon cycle of the lake.
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Paucity of data on seasonality of freshwater APP
primary productivity .. relative contribution
of APP to total phytoplankton production rarely
based on frequent samplings but average of the
summer or occasional samplings. Highest
percentages of APP productivity have been
measured in Lake Baikal, where 80 of 14C uptake
was in the lt3 µm size fraction. In lakes of
western Canada, the relative contribution of
picoplankton to total photosynthesis ranged from
29 to 53, in Lake Constance, Germany, relative
contribution was 5-65.
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Processes of cell growth and cell division
dependent on light and temperature in some cases,
but on an endogenous circadian clock in others.
Cell division reaching a maximum in the
afternoon triggering an increase in the cell
number, which then proceeds in the dark. APP
loss comes from grazing, viral lysis, parasitism,
aggregation and sedimentation. Heterotrophic
nanoflagellates and small ciliates are the most
important APP grazers. APP plays an important
part in the microbial loop and is at the base of
the carbon biomass food web.
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Concluding Remarks Reliance on application of new
molecular methods to study genetic
diversity. Questions of how the APP will respond
to changing climate, both UV-B radiation and
temperature change. Lakes may be warmer and more
strongly stratified with a severely nutrient
depleted euphotic zone. What effect on the APP
and the food chain? APP are the most ancient
survivors of primordial seas and the primary
carbon producer in aquatic ecosystems. Capable
of adapting to extreme environments, they are
distinct in many ways from all other algal
groups
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Example of environmental effects on LRGT
The green alga Phacotus lenticularis - the type
species of the chlamydophycean algal family
Phacotaceae - is an unicellular flagellate of
13-17 µm in diameter.
In a calcium poor medium
In a calcium rich medium
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From Jerry Evans website and mostly collected in
Bell County, Texas. http//www.vvm.com/jevans/
Botrycoccus
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Pandorina
Pleodorina
Protozoans
Actinophrys
Arcella
Closterium
Centropyxis
Mystery ciliated protozoan
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References Liverpool University
www.pcweb.liv.ac.uk/BAMBERI/Ugcourses/F901.htm Ima
ge Quest http//www.imagequest3d.com Maryland
Dept of Natural Resources http//www.dnr.state.md
.us/index.asp URI, University of Rhode Island
http//www.gso.uri.edu/criticalscales/about/kinds/
phyto/phytotxt.html Clemson University
http//people.clemson.edu/sadvs/index.html Begelo
w Laboratory http//www.bigelow.org/inves.html