Environmental Influences on Growth

What is a “normal” environment?

Environment where most species grow: sea level, 20-40°C, neutral pH, 0.9% salt, ample nutrients

What are extremophiles?

Microbes that grow in non-”normal” environments

Stress response?

Measures that provide temporary protection from environmental stress

Suffix “-philic”, what is a thermophilic organism?

Organisms that like higher temperatures and has optimal growth/enzyme & protein function at them

Suffix  “-tolerant”

Organisms that can survive at higher temperatures, but its optimal growth/enzyme & protein function at more moderate (lower) temperatures

Hyperthermophile*

growth > 80°C

Thermophile*

growth 50°C- 80°C

Mesophile

growth 15°C-45°C

Psychrophile*

growth < 15°/20°

Alkliphile*

growth > pH 9

Neutralophile

growth pH 5- pH 8

Acidophile*

growth < pH 3

Halophile*

growth in high salt, >2 M NaCl

Strict aerobe

growth only in O₂

Facultative microbe

growth with or without O₂

Mircoaerophile

growth only in small amounts of O₂

Strict anaerobe

growth only without O₂

Barophile/Piezophile*

growth at high pressure, greater than 380 atm

Barotolerant

growth between 10 and 500 atm

What are the three cardinal temperatures?

the optima, the minimum, and the maximum (very for each organisms)

What happens at the cardinal minimum temperature?

Membrane gelling, transport processes too slow to support growth

What happens at the cardinal maximum temperature?

Protein denaturation, membrane damage, lysis

What is the relationship between growth rate and temperature?

The growth rate roughly doubles for every 10°C rise in temperature

What is special about thermophilic proteins?

Thermophilic proteins have a higher number of ionic interaction (smaller and more rigid/tightly packed than mesophilic counterparts

What is special about thermophilic membrane lipids?

Have more saturated fatty acids

Archaeal organisms have either lipids or tetraether lipids (monolayer)

What specific features do hyperthermophiles have?

Solutes that stabilize proteins

Have high internal salt concentrations & some have histone-like proteins (stabilize DNA)

Molecular chaperones/heat shock (stress) proteins purpose?

Assist in the folding of newly synthesized proteins and refolding denatured proteins

DnaK-DnaJ purpose? Energy?

Bind to hydrophobic regions of newly made proteins/denatured proteins to fold them.

Dependent on ATP hydrolysis

GroEL-GroES complex purpose? Energy?

If a protein is partially folded (DnaK-DnaJ couldn’t do it) GroEL-GroES complex encapsulates it and folds it

Dependent on ATP hydrolysis

Barophiles/piezophiles

Organisms adapted to grow at very high pressures

Barotolerant

Organisms that grow well over the range of 1-50 MPa, but their growth falls off afterwards

Water availability depends on?

Moisture/dryness of the environment and the concentrations of dissolved solutes (sugar/salts)

Water activity, (aw)? Formula?

A mesaure of how much water is available and free to use for organisms

solution vapor pressure (Vs) /the vapor pressure of water (Vw), with Aw being 0-1

Osmolarity?

The total concentration of dissolved particles (solutes) in a solution?

How are osmolarity and water activity related?

Inversely; the more solute you have in the medium the less “available” water, so the higher the osmolarity

Osmotic stress

when the solute concentration outside the cell is different from inside, causing water to move

How does water move?

from a region of higher water concentration (lower solute/salt concentration) to a region of lower water concentration (higher solute/salt concentration)

Aquaporins

membrane channels that allow water ro cross the membrane. These are a fast response to osmotic stresses (both hypertonic and hypotonic)

What do cells do under hypertonic stress conditions to prevent water loss?

They synthesize/import compatible solutes

Four types of solutes cells can synthesize/import:

Amino acid-type, carbohydrate type, alcohol type, other (dimethylsulfoniopropinate)

How can cells respond to hypotonic stress conditions?

solutes can be leaked from the cell by pressure-sensetive or mechanosensitive channels

What do halophilic archaea do?

Love salt

maintain an internal monovalent salt concentration (NaCl, KCl, LiCl) that equals their external environment.

Obligate acidophiles?

their membranes are destroyed at neutral pH. The cytoplasmic membrane must be stable

What’s special about Alkaliphiles proton motive force?

Some have sodium motive force rather than proton motive force

pH formula? One unit change in pH is how much of an H+ change?

pH= log (1/[H+])

One unit change in pH corresponds to a 10x change in [H+]

Terminal electron acceptor in aerobic respiration vs. in anaerobic respiration?

Aerobic: oxygen (this is favored)

Anaerobic: alternative, like nitrate

Does fermentation use anaerobic respiration?

No, because ATP is generated on a substrate level not by the respiratory chain

(Obligate) Aerobes? How do they detoxify O₂?

Organism that can grow in the presence of full oxygen tension (air 21% O₂)

SOD and Catalase

Aerotolerant anaerobes? How do they detoxify O₂?

can tolerate small amounts of oxygen, but do not use it as an electron acceptor use fermentation)

SOD (+/- Catalase)

Facultative aerobes (anaerobes)? How do they detoxify O₂?

Can generate ATP through aerobic respiration when oxygen is present, but can also switch and grow anaerobically (or through fermentation) is not enough oxygen/right nutrients

SOD and Catalase

Microaerophiles? How do they detoxify O₂?

A type of aerobe, but can only tolerate lower levels of O₂

_{Decreased SOD and Catalase}

(Obligate) Anaerobes? How do they detoxify O₂?

Organisms that cannot tolerate O₂ and are inhibited/killed by its presence

None

Electron/Redox Tower?

Ranks molecules by how much energy they can release when they gain or lose electrons

Bigger drop = more energy released (O₂ has the biggest drop)

What must you do to the liquid media to grow aerobes?

liquid media requires forced aeration or vigorous shaking since oxygen is sparingly soluble in water (As temperature of water ↑, concentration/solubility of O₂ in solution ↓)

What must you do to the media to grow anaerobes?

Exclude O₂ but strictiness depends on the organism

What are the three Reactive Oxygen Species (ROS)? Their toxicity?

Superoxide anion: •O₂^-, toxic

Hydrogen peroxide: H₂O₂, least toxic

Hydroxyl radical: •OH, very toxic and very reactive

Equations for breaking down superoxide?

Superoxide dismutase: 2O₂ + 2H⁺ → H₂O₂ + O₂

Superoxide reductase: O₂ + 2H⁺ → H₂O₂

Equation for turning peroxide into something worse?

Fenton reaction: H₂O₂ + Fe²⁺ → OH^- + •OH

Equations for breaking down peroxide before it becomes hydroxyl radical?

Peroxidase: H₂O₂ + NADH/H⁺ → 2 H₂O + NAD⁺

Catalase: 2H₂O₂  →  2 H₂O + O₂