Lecture Notes: Bacterial Growth Phases and Chemostats

Bacterial Growth Phases

Exponential to Stationary Phase Transition

• Late Log Phase:
  • Occurs before the stationary phase.
  • Possible endospore formation.
  • Transformation process may occur for survival.

Stationary Phase

• Equal numbers of cells are dividing and dying.
• Results in no net change in cell numbers.
• Known as Cryptic Growth:
  • Subpopulations may adapt by cannibalizing resources from dying cells.
  • Molecular changes to DNA occur as an adaptation to nutrient depletion and toxic waste accumulation.

Decline Phase

• Cells begin to die, sometimes accompanied by cell lysis.
• This phase is exponential, but with a gentler slope than the exponential growth phase.

Prolonged Decline

• Also referred to as prolonged death.
• Cells undergo genetic changes to survive the stationary phase.
• Characterized by continued cycles of adaptation and death.

Continuous Culture Devices (Chemostats)

• Used to maintain cell populations in exponential growth for extended periods.
• Open System:
  • Continuous supply of fresh medium at a controlled rate.
  • Sterile air or other gases provided based on microbial needs.
  • Removal of excess waste and effluent to prevent toxic accumulation.

Applications

• Study of microbial physiology, ecology, and evolution.
• Important for maintaining cultures in a controlled exponential growth phase.