“Microbes – The Good, The Bad, and the Globally Powerful”

Important Groups of Microbes1. Bacteria2. Fungi3. Protozoa

Eukaryotes (“true nucleus”)

• Fungi -- single cells (e.g., yeasts); mycelia (e.g., mushrooms)

• Plants (algae)

• Animals (e.g., protozoans, rotifers, nematodes)

Prokaryotes (“before the nucleus”)

• Bacteria

– Eubacteria (true bacteria) – E. coli, Cyanobacteria

– Archaebacteria (old bacteria) – deep oceans, hot springs

Important Groups of Microbes

1. 1. BacteriaBacteria

* 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 % of dry weight

C 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 = Eubacteria and Archaebacteria

 2. Evolutionary Distance: Eubacteria

ArchaebacteriaPlantsAnimals

(a) Eubact -- Archae ------------------- Plant -------- Animal  

? - OR - ? (b) Eubact -------------- Archae ------- Plant --------Animal

Important Groups of Microbes

2.2.FungiFungi

* Thin strands called “hyphae”* Uncommon in aquatic environments* Common in terrestrial environments* Secrete enzymes to break down cellulose

* 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).

Soils - fungi = 1000-1500 m/mL

Water = no fungi

Gall on tree – fungal infection

Bread mold Hyphae strands & sporangia

Fungus fruiting bodies

Root fungus

“mycorrhizae”

Important Groups of Microbes

3.3.ProtozoaProtozoa

* Single-celled eukaryotes* Important predators on bacteria

Protozoan ciliate. Their primary food is bacteria and very small algae.

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

Organic matter

Bacteria

Heterotroph Organic matter Organic matter Bacteria, fungi, animals

1. Assimilative versus Dissimilative Processes All cells need ATP and a source of

Carbon

2. How do Microbes make a Living? “Production” versus “Respiration” 

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

H2 CHO CH4 HS-

CHO + + - -

CO2 + + - -

SO4 2- + + ? -

NO3- + + ? +

O2 + + + +

Ele

ctro

n (

e-)

Acc

epto

r [O

xida

nt]

Electron (e-) Donor [Reductant]

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 + SO4

2- + 2H+ 2CO2 + HS- +

2H2O

190

Methanogenesis

H2 CO2 4H2 + CO2 CH4 + 2H2O

8.3

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.

Legume roots with nodules that enclose the N-fixing bacteria

PeaClover

(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 % of primaryproduction consumed by

herbivores

Phytoplankton (open water) 60 - 90

Grasslands 12 - 45

Kelp beds 10

Salt marshes 7

Mangroves 5

Deciduous forests 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.