Microbiology Lecture 8 Enzymes and Bacterial Growth

Environmental limits on cell growth

• temperature

• oxygen

• UV

• pH

• Salt concentration/Osmolarity

• Pressure

Growth rate graph parts

No growth: temperatures are to cold so process proceed to slow to sustain life and membrane loses fluidity

Increase growth: As temperature rises toward optimal range enzymes and reactions occur at increasing rate

Optimal growth: Temperature where enzymes and reactions occur at maximal rate

Dip to no growth: Temperature is too high and begins denaturing proteins and causes lysis

Microbe classification by temperature range

Psychrophile: grow below 20C

Mesophile: grow between 20-50C

Thermophile: grow between 50-80C

Extreme thermophile (Hyperthermophiles): grow between 65-113C

What does temperature range mean for classification

Range of temperature where proteins are active for growth (optimal temperature is within range)

Room temp and body temp

Room temp = 20C

Body temp = 37C

Examples of environments for microbes with different optimal temperatures

Psychrophile: fridge or freezer

Mesophile: Human body

Thermophile: Archaea in hot tubs

Hyperthermophile: Hot springs

What are all human pathogens classified as

Mesophiles

Result of rapid temperature changes

Heat shock response to protect chromosomes

What can trigger heat shock response

Not just heat but other environmental stressors

• salt

• cold

• dry

protein products of heat shock

chaperons that maintain protein structure

enzymes that change membrane lipid composition

what organisms have heat shock response

All organisms have response

Oxygen effect to aerobes vs anaerobes

Aerobes: Use oxygen as final electron acceptor to extract energy from nutrients

Anaerobes: Toxic because do not have enzymes to break down reactive oxygen species (ROS)

ROS examples

• singlet oxygen

• hydrogen peroxide

• superoxide

• hydroxyl radicals

Effect of ROS

Damage to DNA, RNA, proteins, and lipids by stripping electrons

Enzymes used for ROS

SOD: neutralizes O2 radical to H2O2

catalase: aerobes have to break down ROS

Oxygen dependency classifications and tube growth

Obligate Aerobe: Grow at highest concentration of O2

Obligate Aerobe: Grow farthest away from O2

Facultative: slight preference for oxygen but dispersed growth

Aerotolerant: can grow with or without O2 so evenly dispersed throughout tube

Microaerophile: Favor O2 but not completely so grow at sublayer

Enzymes that oxygen groups have

Obligate Aerobe: SOD and catalase

Obligate Anaerobe: Neither

Facultative: SOD and catalase

Aerotolerant: Only has SOD

Microaerophile: SOD and catalase