Bacterial Growth

What is bacterial growth?

Leads to the increase in the number of individuals making up a population or culture

What is generation time (doubling time)?

Time interval for formation of 2 cells from 1 cell (generation time)

How can turbidity be measured?

With a spectrophotometer and a growth curve

What are the 4 phases of bacteria population growth curve?

• Lag phase 

• Exponential phase

• Stationary phase (nutrients become limiting factor) 

• Death phase 

What happens in the lag phase?

• Growth is not immediate (adaptation to new habitat) 

• Varies considerably in length with the condition of bacteria and nature of medium 

• Number of cells does not increase 

What happens in exponential phase?

• Cells are actively dividing at their maximum growth rate 

• Number of bacteria doubles at regular intervals 

• Influenced by environmental conditions (temperature, compostition of culture medium) 

What happens in stationary phase?

• Happens when bacteria have exhausted the requirements for growth

• Growth slows as wastes accumulate or nutrients are depleted

• Rate of cell division = rate of cell death 

• No net increase or decrease in cell numbers 

What happens in death phase

• Cells die 

• Rate at which cells die > rate at which they divide 

What are the limiting factors in the environment

• Lack of food, water or nutrients

• Space

• Accumulation of metabolic waste (ammonia changes pH so its acidic) 

• Lack of oxygen

• Changes in pH 

• Temperature 

Oxygen Requirements

• Obligate aerobes - only aerobic growth

• Facultative anaerobes - both aerobic and anaerobic but greater growth at aerobic 

• Obligate anaerbes - only anaerobic growth 

• Aerotolerant anaerobes - only anaerobic growth but continues in presence of oxygen 

• Microaerophiles - only aerobic growth but in low conc

Temperature

• Psychrophiles grow best at 

• Mesophiles grow best at 

• Termophiles and hyperthemophiles grow best at 

Psychrophiles grow best at: 0-15C

Mesophiles grow best at: Moderator temperatures of 20-45C

Termophiles and hyperthemophiles grow best at: Above 50C

pH - what are:

• Acidophiles 

• Neutrophiles 

• Alkalinophiles 

Acidophiles: pH 3 (acid conditions)

Neutrophiles: pH 6 - 8 (near neutral) 

Alkalinophiles: pH 10.5 (alkaline substance