1. Lecture 18. Diversity of Microbial Life
Lecture 18. Diversity of Microbial Life.  What Do Microbes Need to Survive?  Energy and Metabolism.  Extremophiles, Photosynthesis, and Chemosynthesis.
EXAM1:
High: 88
Low: 55
Average: 72.2
reading: Chapter 6

2. Pervasiveness of Life Earth life extraordinarily successful
Natural selection & evolution
--> adaptability
Organisms found EVERYWHERE
glaciers & permafrost
hot springs
hydrothermal vents
desert rocks
clouds
deep sea sediments
soils
Snow algae on glacier
Sierra Nevada, CA

3. Five Things You Need to Have Life
Stable Environment
be able to adapt to changes
Liquid water
-20˚C to 121˚C
Energy Source
O2 and carbohydrates
oxidant (O2) and reductant (sugars)
Carbon Source
carbohydrates
sometimes different from an energy source
Nutrients
The Biogenic Elements: C, H, N, O, P, S
Trace Nutrients: Ca, Fe, Cu, Zn, vitamins…..
some organisms need more than others
when considering the
potential for life elsewhere:

4. Liquid Water If T below 0˚C, microbes can be found
growing between ice crystals or in the
pore spaces of ice.
Microbes can secrete compounds that can
inhibit ice crystal formation.
Soil still contains substantial thin films of
liquid water below 0˚C
… could be important for life on Mars.

5. Energy Sources Light Energy - photosynthesis phototroph
convert light energy into chemical energy (ATP)
Inorganic Compounds chemotroph, lithotroph
need an oxidant: O2, SO42- (sulfate), NO3- (nitrate), Fe3+
need a reductant: H2, H2S (sulfide), Fe2+, Mn2+
react oxidant and reductant, convert to ATP
Organic Compounds organotroph
need an oxidant
organic compounds as a reductant: glucose, cellulose

6. Carbon Source CO2 autotrophs organic carbon heterotrophs
Can combine words for energy and carbon sources:
Name
Energy Source
Carbon Source
Photoheterotroph
Light
Organic C
Photoautotroph
CO2
Chemoorganotroph
Organic (reductant) and inorganic chemicals (oxidant)
Chemoautotroph
Inorganic chemicals (reductant & oxidant)

7. Five Things You Need to Have Life
Also need Nutrients
The Biogenic Elements: C, H, N, O, P, S
Trace Nutrients: Ca, Fe, Cu, Zn, vitamins…..
some organisms need more than others

8. Microbial Life Runs Planet Earth
Microbial diversity is vast.
Number of species astronomical.
<99.9% of microbial species have
been cultured in the lab.
Whole new uncultured lineages.
Almost nothing known about them.
Microbes:
turn CO2 into organic matter
most photosynthesis on the
planet is done by prokaryotes
then turn organic matter back
into CO2
microbial metabolism is incredibly
diverse

9. Aerobic Metabolisms (Aerobes)
Animals “CH2O” O > CO H2O organotrophy
Manganese Mn O > MnO4 (manganese oxide) chemotrophy
Oxidizers
Iron Fe O > Fe2O3 (iron oxide) chemotrophy
Sulfide H2S O > H2SO4 (sulfuric acid) chemotrophy
Methane CH O > CO H2O chemotrophy
Hydrogen 2H O > 2H2O ???
Arsenic AsO3 (arsenite) + O > AsO4 (arsenate) chemotrophy

10. Anaerobic Metabolisms (Anaerobes)
Sulfate H2SO H > H2S H2O chemotrophy
Reducers
Methanogenesis CO H > CH H2O chemotrophy
Take home:
-a lot of chemical reactions in the environment are catalyzed
by microorganisms.
-microbes can carry out some “unusual” reactions to make energy
-energy generation results in constant oxidizing and reducing of
compounds: sulfur, iron, manganese, carbon…..
-called biogeochemical cycling.

11. The Importance of Oxygen
Oxygen is a potent source of energy (strongest oxidant available)
Anaerobic metabolisms don’t produce as much energy (ATP).
Oxygen is also toxic - it is reactive.
- causes damage to DNA
- causes damage to proteins
- causes damage to lipids
- cells must be able to repair this damage

12. Extremophiles
What is extreme for one organism is necessary for another.
Organisms are all highly adapted to their niches.

13. Temperature Temperature
One of the most important environmental factors that
affect growth and survival of organisms.
Too hot - proteins denature (think: fried egg - unfolded, coaggulated)
Too cold - membranes and proteins freeze
For every organism, there is a:
minimum T
optimal T (can be 4 or 105˚C)
maximum T
(remember water has to be liquid water)
typical range of growth T is 30-40˚C

14. Growth Temperature Psychrophile - grows optimally below 15˚C
80% of Earth’s biosphere is < 15˚C.
Mesophile - grows optimally between 15-45˚C
Thermophile - grows optimally between 45-80˚C
Hyperthermophiles - grows optimally above 80˚C
ice core
permanently
frozen seawater
McMurdo Sound
Antarctica

15. Temperature Gradients
72˚C

16. pH Another environmental factor that affects growth and survival.
pH is a logarithmic function so a
change of 1 pH unit is a 10x change
in [H+]
Each organism has a pH range and
a pH optimum.
Most have a pH range of 2-3
units.

17. pH, cont.
Most organisms grow optimally between pH They are neutrophiles.
Much fewer species can live outside of pH 5-9.
Organisms that grow best below pH 5 are acidophiles.
Organisms that grow best above pH 9 are alkaliphiles.
pH 10 soda lake Lake Hamara, Egypt
trona: Na2CO3 - habitat for halophilic, alkaliphilic archaea
Acidic hot spring in Yellowstone
National Park. Green: acidic eukaryotic algae

18. Water Activity Water activity is the availability of free water.
Water can be loosely bound up by ions, proteins, clay minerals - this
is NOT free water.
hydration shell of ions in solution
hydration shell of a protein
Binding of free water reduces water activity in the environment.

19. Water Activity, cont.
Water concentration (water activity) in salty environments is low.
Water diffuses from high concentration --> low.
Water diffuses from high water activity --> low.
So, in a salty environment, free water diffuses out of the cell.
Cells shrink and desiccate, proteins denature.
Organisms must adapt to balance the water activity inside the cell with
the water activity outside the cells.
Salt Evaporation Ponds,
San Francisco Bay
Reddish purple: Halophilic Euryarchaeota

20. Halophiles
Halophiles grow optimally at the water activity of seawater.
3% salt - halophile
1-6% salt - mild halophile
7-15% salt - moderate halophile
15-30% salt - extreme halophile
Not very many species have adapted to these environments.
Halotolerant organisms - grow best at low salt, but can tolerate
short periods of elevated salt.
Halogeometricum
Square cells!

21. Lecture 19. Proterozoic Earth, Rise in Oxygen, Microbial Paleontology
reading: Chapter 4