#death phase

Microbial Physiology

The rate of bacterial cell decline in the death phase follows:

Loss of viability after stationary eventually outweighs division, producing decline phase where total colony forming units drop. Empirical measurements show semi-log plot of survivors versus time yields linear decay, indicating constant probability of death per unit time per surviving cell, independent of absolute numbers. This defines first order kinetics analogous to chemical decomposition rate minus kd N integrated ln N equals ln No minus kd t. Decimal reduction value D equals ln10 over kd, time required for tenfold drop, used in sterilization validation. Mechanistically stochastic oxidativ

Ref: Brock Biology of Microorganisms, 16th ed., Chapter 6: Death kinetics - First-order decline.

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Microbial Physiology

What is the primary reason for bacterial death in the death phase?

Transition to death phase reflects inability to maintain energy homeostasis and repair. Prolonged incubation exhausts fermentable carbon, electron acceptors, phosphate, amino acids, halting ATP generation via respiration and substrate level phosphorylation. Concomitantly toxic end products accumulate: organic acids acetate and lactate lower pH below 5, alcohols ethanol, ammonia, hydrogen sulfide inhibit cytochrome oxidases, and reactive oxygen species superoxide and H2O2 from autooxidation damage iron sulfur clusters. Oxidative lesions cause DNA strand breaks, protein carbonylation, membrane l

Ref: Brock Biology of Microorganisms, 16th ed., Chapter 6: Death phase - Toxic metabolites accumulation.

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Microbial Physiology

The rate of bacterial cell decline in the death phase follows:

Decline phase marks period when lethal environmental stresses exceed capacity to repair damage and maintain homeostasis, leading to net loss of viability. Population decay is often well described by exponential decay mathematically analogous to radioactive decay, reflecting stochastic individual death. First-order kinetics states instantaneous rate of viable cell loss is directly proportional to number of viable cells present at that instant expressed as dN/dt equals minus kd times N where kd is first-order death rate constant per time. Integration from time zero yields ln Nt equals ln N0 minu

Ref: Lodish et al., Molecular Cell Biology, 8th ed., Chapter 4: Death Phase and First-Order Kinetics Model.

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Microbial Physiology

In which phase do bacteria begin dying exponentially due to nutrient depletion?

Death or post-stationary decline phase follows stationary when lethal stresses exceed repair capacity. Utilizable substrates fully depleted, waste products such as fermentation acids, alcohols, reactive oxygen species and toxic secondary metabolites accumulate to inhibitory levels, extracellular pH shifts outside optimum disrupting proton motive force and increasing competition for maintenance energy. Proteases Lon and Clp degrade non-essential proteins recycling amino acids, nucleases degrade rRNA, membrane depolarization causes ion leakage. Viability loss typically follows exponential first-

Ref: Madigan et al., Brock Biology of Microorganisms, 16th ed., Chapter 4: Death Phase and Nutrient Depletion.

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