Microbial Growth: Key Concepts, Extremophiles, and Growth Phases

Microbial growth

Increase in number of microbial cells through replication

Maximum microbial growth potential

Microbes can replicate in <20 minutes; some in <10 minutes

Population potential

>10^12 cells in 24 hours from one microbe

Intrinsic constraints

Genome size, metabolism, physiology

Extrinsic constraints

Environmental factors (temperature, pH, salinity, nutrients, etc.)

Optimal temperature

20-40°C

Optimal pH

6.5-7.5

Optimal salinity

0.5-1.0%

Water activity (Aw)

Availability of water for growth

Extremophiles

Microbes that grow in extreme environments

Thermophiles

50-80°C

Hyperthermophiles

>80°C

Psychrophiles

<15°C

Acidophiles

pH <3

Alkaliphiles

pH >9

Halophiles

High salt

Piezophiles

High pressure environments

Generation time (g)

Time for one division

Growth rate (k)

Generations per unit time

g vs k

Inversely proportional

Exponential growth

Nt = 2^n

Exponential growth meaning

Maximum growth under conditions

Feast

Nutrient-rich growth

Famine

Nutrient-poor conditions

E. coli generation times

Glucose - 20 min, Intestine - 80 min, Glycerol - 120 min, 10°C - 600 min

Binary fission

Cell division into two identical cells

Lag phase

Preparation, no division

Log phase

Rapid exponential growth

Stationary phase

Growth = death

Death phase

Death > growth