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“Microbes – The Good, The Bad, and the Globally Powerful”
Important Groups of Microbes
1. Bacteria
2. Fungi
3. Protozoa
Prokaryotes (“before the nucleus”)
• Bacteria
– Eubacteria (true bacteria) – E. coli, Cyanobacteria
– Archaebacteria (old bacteria) – deep oceans, hot springs
Eukaryotes (“true nucleus”)
• Fungi -- single cells (e.g., yeasts); mycelia (e.g.,
mushrooms)
• Plants (algae)
• Animals (e.g., protozoans, rotifers, nematodes)
Important Groups of Microbes
1. Bacteria
* Found everywhere
* Resting stages
* Short generation times
* Locomotion
•
Soils
– bacteria = 109 per mL
(fungi = 1000-1500 m per mL)
• Water (ocean, lakes, streams)
– bacteria =
106
per mL
(no fungi)
Elemental
composition of
bacteria =
Element
C
% of dry
weight
55
O
20
N
10
H
8
P
3
S
1
Bacteria on the head of a pin (~5 μm long)
Cholera - intestine thin section
Campylobacter - (food poisoning) rotary motor @ 6,000 rpm
Proteus - 20 μm
Microbial “mat” on the surface of a salt
marsh – an ecological community
Evolution of Bacteria
1. Two Main Groups
=
2. Evolutionary Distance:
Eubacteria and
Archaebacteria
Eubacteria
Archaebacteria
Plants
Animals
(a) Eubact -- Archae ------------------- Plant -------- Animal
?
- OR -
?
(b) Eubact -------------- Archae ------- Plant --------Animal
Important Groups of Microbes
2.Fungi
*
*
*
*
Thin strands called “hyphae”
Uncommon in aquatic environments
Common in terrestrial environments
Secrete enzymes to break down cellulose
Soils - fungi =
1000-1500 m/mL
Water = no fungi
* Fungal hyphae (~15
µm). A network of
hyphae = a mycelium.
* Picture of “fairy ring”
of mushrooms. Ring
moves outward as easily
digestible organic matter
is used up.
* One mycelium covered
1290 acres and was
thousands of years old
(100s of tons).
Gall on tree –
fungal infection
Bread mold
Hyphae strands & sporangia
Fungus fruiting bodies
Root fungus
“mycorrhizae”
Important Groups of Microbes
3.Protozoa
* Single-celled eukaryotes
* Important predators on bacteria
Protozoan ciliate. Their primary food is
bacteria and very small algae.
1. Assimilative versus Dissimilative Processes
All cells need ATP and a source of Carbon
2. How do Microbes make a Living?
“Production” versus “Respiration”
Classification
Energy source for
generating ATP
Source of carbon
for the cell
Example of
organisms
Photoautotroph
Light
CO2
Bacteria,
plants
Chemoautotroph
Inorganic
compounds
CO2
Bacteria
Photoheterotroph
Light
CO2
Bacteria
Organic matter
Heterotroph
Organic matter
Organic matter
Bacteria,
fungi, animals
Respiration
requires a reduced
organic compound
as an
electron donor
and an oxidized
molecule as an
electron
acceptor
(Freeman 2002).
Taken together, this is a
“Reduction-Oxidation”
or “Redox” reaction.
Diversity of Dissimilatory Reactions used by Bacteria
Electron (e-) Acceptor [Oxidant]
Electron (e-) Donor [Reductant]
H2
CHO
CH4
HS-
CHO
+
+
-
-
CO2
+
+
-
-
SO4 2-
+
+
?
-
NO3-
+
+
?
+
O2
+
+
+
+
Reaction name
Reductant Oxidant
Reaction
Stoichiometry
Energy
Yield
(kcal/mol)
Aerobic
Respiration
CHO
O2
C6H12O6 + 6O2 
6CO2 + 6H2O
686
Nitrate Reduction
CHO
NO3-
CHO + NO3- + H+ 
CO2 + N2 + H2O
649
Sulfate
Reduction
CHO
SO42-
2CHO + SO42- + 2H+
 2CO2 + HS- +
2H2O
190
H2
CO2
4H2 + CO2  CH4 +
2H2O
8.3
Methanogenesis
V. What are the Important Impacts of Microbes on Ecosystems?
(1) Generate Oxygen in the Atmosphere
(Blue-green algae = Cyanobacteria).
(2) Recycle Nutrients Stored in Organic Matter to an Inorganic Form.
(3) Fix nitrogen from the Atmosphere into a Useable Form.
(4) Allow Herbivores to Consume Poor Quality Food.
(5) Give Plant Roots Access to Nutrients in the Soil.
(2) Recycle Nutrients Stored in Organic Matter to an Inorganic Form.
* Decomposition releases mineral nutrients like Nitrogen and Phosphorus
* Fungi are the most important decomposers of structural plant compounds
* Decomposition can occur with or without oxygen
* Decomposition generates important by-products such as CO2 and CH4
(3) Fix nitrogen from the Atmosphere into a Useable Form.
* N-fixation removes N2 from the atmosphere
* N-fixation converts N2 into a useable nitrogen form (NH3)
* Plants and bacteria form a "symbiotic" relationship:
- Plants provide carbon compounds for the bacteria
- Bacteria provide nitrogen for the plant
Cyanobacteria (blue green algae) and “heterocysts” where the
nitrogen fixation occurs. Oxygen poisons N-fixation.
Clover
Pea
Legume roots with nodules that enclose the N-fixing bacteria
(4) Allow Herbivores to Consume Poor Quality Food.
* Animals lack digestive enzymes for cellulose and lignin
* Plants often have "anti-grazing" defenses
* Land plant material is poor in nutrients compared to animal
tissue
* This results in lower consumption of primary productivity
by herbivores on land than by herbivores in aquatic systems
Plant Community
Phytoplankton (open water)
Grasslands
Kelp beds
Salt marshes
Mangroves
Deciduous forests
% of primary
production consumed by
herbivores
60 - 90
12 - 45
10
7
5
1.5 - 5
(5) Give Plant Roots Access to Nutrients in the Soil.
* Plants create zones of nutrient depletion around their roots
* Plants form associations with fungi -- "ecto" or "endo"
* The plant provides the fungus with organic matter
(photosynthate)
* The fungi provide the plant with nutrients from
decomposition
Root fungus – “endotrophic”
Summary
Be able to answer these questions:
• What is the diversity of microbes?
• How do the different kinds of microbes function in gaining
energy?
• What impacts do microbes have on ecosystems and our globe?
Take-home points:
1. Microbes can do anything they want, wherever they
want, and
2. Without microbes, humans wouldn't be alive.